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Abbreviation for:
Paris Nomina Anatomica
partial nail avulsion  
percutaneous needle aspiration
Personal Needs Allowance
Pharmaceutical Needs Assessment 
purine nucleoside analogue
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.


(as'id) [L. acidus, sour]
1. Any substance that liberates hydrogen ions (protons) in solution; a hydrogen ion donor. An acid reacts with a metal to form a salt, neutralizes bases, and turns litmus paper red.
2. A substance that can accept a pair of electrons; a Lewis acid. See: alkali; base; indicator; Lewis acid; pH
3. A sour substance.
4. Slang term for lysergic acid diethylamide (LSD).

acetic acid

C2H4O2, the acid that gives the sour taste to vinegar. It is also used as a reagent. Glacial (highly purified) acetic acid contains at least 99.5% acetic acid by weight.
CAS # 64-19-7

acetoacetic acid

C4H6O3, a ketone body formed when fats are incompletely oxidized. It was formerly called acetylacetic acid. Synonym: diacetic acid; diacetic acid
CAS # 541-50-4

acetylacetic acid

See: acetoacetic acid

acetylsalicylic acid

Abbreviation: ASA
Aspirin (1).

acrylic acid

C3H4O2, a colorless corrosive acid used in making acrylic polymers and resins.
CAS # 79-10-7

adenylic acid

Adenosine monophosphate.

alpha-hydroxy acid

Abbreviation: AHA
Any of a class of water-soluble acids derived from fruit or milk, having a hydroxyl moiety in the first position in the molecule. AHAs are used in chemical peels and other skin care products to remove the outer layer of the epidermis. This chemical exfoliation is promoted for its cosmetic effects on wrinkled or sun-damaged skin.

alpha-linolenic acid

C18H30O2, an omega-3 fatty acid derived from plants, esp. seeds (canola oil, flaxseed, walnuts and pumpkins) and from some fish (salmon and mackerel).
CAS # 463-40-1

alpha-lipoic acid

C8H14O2S2, a natural coenzyme and antioxidant, used for short-term treatment of peripheral neuropathies.
CAS # 1200-22-2

amino acid

See: amino acid

aminoacetic acid


aminobenzoic acid

Para-aminobenzoic acid.

aminocaproic acid

C6H13NO2, a hemostatic drug. It is a specific antidote for an overdose of a fibrinolytic agent.
CAS # 60-32-2

aminoglutaric acid

Glutamic acid.

aminosalicylic acid

Para-aminosalicylic acid.

aminosuccinic acid

Aspartic acid.

arachidonic acid

C20H32O2, an omega-6 fatty acid formed by the action of enzymes on phospholipids in cell membranes. The acid is found in many foods. It is metabolized primarily by the cyclo-oxygenase or 5-lipoxygenase pathways to produce prostaglandins and leukotrienes, which are important mediators of inflammation. Corticosteroids inhibit formation of arachidonic acid from phospholipids when cell membranes are damaged. Nonsteroidal anti-inflammatory agents such as salicylates, indomethacin, and ibuprofen inhibit the synthesis of prostaglandins and leukotrienes.
CAS # 506-32-1

argininosuccinic acid

C10H18N4O6, a compound intermediate in the synthesis of arginine, formed from citrulline and aspartic acid.
CAS # 2387-71-5

aristolochic acid

C17H11NO7, an acid derived from Aristolochia, a genus of flowering plants, and used as an herbal remedy. It is promoted as an aphrodisiac, a weight loss agent, and an anticonvulsant.
CAS # 313-67-7


The acid is a known carcinogen, and its use has been associated with and may cause end-stage renal disease and cancers of the urinary tract that may occur many years after usage has stopped.

ascorbic acid

Vitamin C.

aspartic acid

C4H7NO4, a nonessential amino acid that is a product of pancreatic digestion. Synonym: aminosuccinic acid
CAS # 617-45-8

barbituric acid

C4H4N2O3, a crystalline acid from which phenobarbital and other barbiturates are derived.
CAS # 67-52-7

benzoic acid

C7H6O2, a white crystalline acid having a slight odor. It is used in keratolytic ointments and in food preservation. Saccharin is a derivative of this acid.
CAS # 65-85-0

bile acid

Any of the complex acids that occur as salts in bile, e.g., cholic, glycocholic, and taurocholic acids. They give bile its foamy character, are important in the digestion of fats in the intestine, and are reabsorbed from the intestine to be used again by the liver. See: enterohepatic circulation

binary acid

An acid containing hydrogen and one other element.

boric acid

H3BO3, a white crystalline acid that in water forms a very weak acid solution poisonous to plants and animals. It is soluble in water, alcohol, and glycerin. See: boric acid poisoning
CAS # 10043-35-3


Boric acid is toxic and should be used only rarely. It is particularly dangerous because it can be accidentally swallowed by children or used in food because of its resemblance to sugar.

butyric acid

C4H8O2, a viscous fatty acid with a rancid odor, derived from butter but rare in most fats. It is used in disinfectants, emulsifying agents, and pharmaceuticals.
CAS # 107-92-6

carbolic acid

Phenol (1).

carbonic acid

H2CO3, an acid formed when carbon dioxide is dissolved in water.
CAS # 463-79-6

carboxylic acid

Any acid containing the carboxyl group –COOH. The simplest examples are formic and acetic acids.

cell-free fetal nucleic acid

Free fetal nucleic acid.

cholic acid

C24H40O5, a bile acid formed in the liver by hydrolysis of other bile acids. It is formed from the breakdown of cholesterol and helps digest consumed fats.
CAS # 81-25-4

cinnamic acid

C9H8O2, an insoluble white powder derived from cinnamon. It is used as a flavoring agent in cooking and in the preparation of perfumes and medicines.
CAS # 140-10-3

citric acid

C6H8O7, an acid found naturally in citrus fruits or prepared synthetically. It acts as a sequestrant, helping to preserve food quality.
CAS # 77-92-9

conjugated linoleic acid

Abbreviation: CLA
Any of the isomers of linoleic acid effective against cancer, obesity, diabetes, and atheromata in laboratory rodents. CLAs have not been shown to have similar beneficial effects in humans.

cysteic acid

C3H7NO5S, an acid produced by the oxidation of cysteine. Further oxidation produces taurine.
CAS # 498-40-8

deoxycholic acid

C24H40O4, a crystalline acid found in bile.
CAS # 83-44-3

deoxyribonucleic acid

, desoxyribonucleic acid See: DNA

diacetic acid

Acetoacetic acid.

2,4-dichlorophenoxyacetic acid


p-dichlorosulfamoyl benzoicacid


4,8-dihydroxyquinaldic acid

Xanthurenic acid.

docosahexaenoic acid

, docosahexanoic Abbreviation: DHA
C22H32O2, an omega-3 fatty acid found in the oils of cold-water fish and in algae. DHA plays a role in the development of nerve cell membranes and is required for the normal growth and development of the infant brain. Lack of DHA has been linked to growing numbers of people suffering from depression.
CAS # 6217-54-5

domoic acid

C15H20NO6, a toxin that resembles glutamate, the main excitatory amino acid of the brain. When ingested, it may cause continuous seizures.
CAS # 14277-97-5

eicosapentaenoic acid

Abbreviation: EPA
C20H30O2, an omega-3 fatty acid found in fish oils, containing 20 carbons and five double bonds.
CAS # 10417-94-4

endogenous uric acid

Uric acid derived from purines undergoing metabolism from the nucleic acid of body tissues.

essential fatty acid

Abbreviation: EFA
A fatty acid (alpha-linoleic and linoleic) that is essential for health and must be present in the diet because it cannot be synthesized in the body. See: digestion

ethylenediaminetetraacetic acid

Abbreviation: EDTA
C10H16N2O8, a chelating agent that, in its calcium or sodium salts, is used to remove metallic ions such as lead and cadmium from the body and as a food preservative. See: chelation
CAS # 60-00-4

exogenous uric acid

Uric acid derived from purines from food made up of free purines and nucleic acids.
See: urate; uraturia

fatty acid

Any of numerous monobasic acids with the general formula CnH2n+1-COOH (an alkyl radical attached to a carboxyl group).

Fatty acids are insoluble in water. This insolubility would prevent their being absorbed from the intestines, but the action of bile salts on the fatty acids enable thems to be absorbed. Fatty acids include acetic, butyric, capric, caproic, caprylic, formic, lauric, myristic, palmitic, and stearic acids. Unsaturated fatty acids have one or more double or triple bonds in the carbon chain. They include those of the oleic series (oleic, tiglic, hypogeic, and palmitoleic) and the linoleic or linolic series (linoleic, linolenic, clupanodonic, arachidonic, hydrocarpic, and chaulmoogric). See: fat

folic acid

C19H19N7O6, a water-soluble B complex vitamin needed for DNA synthesis and amino acid metabolism. It is present in green leafy vegetables, beans, and yeast. It is used to treat megaloblastic and macrocytic anemias and to prevent neural tube defects (NTDs) and cardiovascular disease in adults. The U.S. Public Health Service recommends that all women of childbearing age who may become or are pregnant should consume 0.8 mg of folic acid daily to reduce their risk of having a child affected with spina bifida or other NTDs. See: neural tube defect Synonym: folate; vitamin B9
CAS # 59-30-3


Folic acid should not be used to treat pernicious anemia (a vitamin B12 deficiency) because it does not protect patients against the development of changes in the central nervous system that accompany this type of anemia.

folinic acid

C20H23N7O7, the active form of folic acid. It is used to counteract the effects of folic acid antagonists and to treat folic acid deficiency anemia.
CAS # 1492-18-8

formic acid

HCOOH, the first and strongest member of the monobasic fatty acid series. It occurs naturally in certain animal secretions, e.g., the sting of insects such as bees and ants, and in muscle, but it is also prepared synthetically.
CAS # 64-18-6

formiminoglutamic acid

C6N2O4H10, an intermediate product in the metabolism of histidine.
CAS # 816-90-0

free fatty acid

Abbreviation: FFA
The form in which a fatty acid leaves the cell to be transported for use in another part of the body. FFAs are not esterified and may be unbound (not bound to protein). In the plasma, the nonesterified fatty acids released immediately combine with albumin to form bound free fatty acids.

free fetal nucleic acid

Abbreviation: ffNA
Fetal RNA or DNA in blood or body fluids. It is used to determine the sex of the fetus (as in pregnancies in which X-linked inherited diseases are a concern) or to identify other genetically transmitted illnesses, e.g., trisomies. Synonym: cell-free fetal nucleic acid

fumaric acid

C4H4O4, one of the organic acids in the Krebs cycle. It is used as a substitute for tartaric acid in beverages and baking powders.
CAS # 110-17-8

fuming nitric acid

Concentrated nitric acid (more than 86% nitric acid) that emits toxic fumes that cause choking if inhaled.
See: fumes

gadolinium-diethylenetriamine pentaacetic acid

Abbreviation: Gd-DTPA
A radiographic contrast agent, used in magnetic resonance imaging to enhance the appearance of blood vessels.


Contrast agents containing gadolinium should not be given to patients with diminished renal function.
CAS # 86050-77-3

gallic acid

C6H2(OH)3COOH, a colorless crystalline acid. It occurs naturally as an excrescence on the twigs of trees, esp. oaks, as a reaction to the deposition of gall wasp eggs. It is used as a skin astringent and in the manufacture of writing inks and dyes.
CAS # 149-91-7

gamma-aminobutyric acid

Abbreviation: GABA
C4H9NO2, the principal inhibitory neurotransmitter of the brain.
CAS # 56-12-2

gamma-linolenic acid

Abbreviation: GLA
C18H30O2, an essential fatty acid promoted by alternative medicine practitioners as a treatment for skin and inflammatory disorders, cystic breast disease, and hyperlipidemia.
CAS # 506-26-3

glucuronic acid

CHO(CHOH)4COOH, an oxidation product of glucose that is present in the urine. Toxic products (salicylic acid, menthol, phenol) that have entered the body through the intestinal tract are detoxified in the liver by conjugation with glucuronic acid.
CAS # 6556-12-3

glutamic acid

HOOC·(CH2)2·CH(NH2)·COOH, an amino acid formed in protein hydrolysis and an excitatory neurotransmitter in the central nervous system. Synonym: aminoglutaric acid
CAS # 617-65-2

glyceric acid

CH2OH·CHOH·COOH, an intermediate product of the oxidation of fats.
CAS # 473-81-4

glycocholic acid

C26H43NO6, a bile acid that hydrolizes to glycine and cholic acid.
CAS # 475-31-0

glycolic acid

C2H4O3, an alpha-hydroxy acid derivative used to remove the outer layer of skin to rejuvenate its appearance.
CAS # 79-14-1

glyoxylic acid

C2H2O3, an acid produced by the action of glycine oxidase on glycine or sarcosine.
CAS # 298-12-4

hippuric acid

C6H5CONHCH2COOH, an acid formed and excreted by the kidneys. It is formed from the combination of benzoic acid and glycine. The synthesis takes place in the liver and, to a limited extent, in the kidneys.
CAS # 495-69-2

guanidoacetic acid

An acid formed in the liver, kidney, and other tissues. It is metabolized to form creatine.

hexafluorosilicic acid


homogentisic acid

C8H8O4, an intermediate product of tyrosine catabolism. It is found in the urine in alkaptonuria. Synonym: alkapton
CAS # 451-13-8

hyaluronic acid

Abbreviation: HA
(C14H21NO11)n, an acid mucopolysaccharide found in the extracellular matrix of connective tissue that acts as a binding and protective agent. It is found in synovial fluid and in the vitreous and aqueous humors of the eye. Patients with osteoarthritis have elevated serum levels of HA. Synonym: hyaluronan
CAS # 9004-61-9

hydriodic acid

HI, an acid used in solution in various forms of chemical analyses. Synonym: hydrogen iodide
CAS # 10034-85-2

hydrochloric acid

HCl, an inorganic acid normally present in gastric juice. It destroys fermenting bacteria that might cause intestinal tract disturbances.

CAS# 7647-01-0

hydrocyanic acid

HCN, a colorless, extremely poisonous, highly volatile acid that occurs naturally in plants but is also produced synthetically. It acts by preventing cellular respiration. Hydrocyanic acid is used in electroplating, fumigation, and in producing dyes, pigments, synthetic fibers, and plastic. Exposure of humans to 200 to 500 parts of hydrocyanic acid per 1,000,000 parts of air for 30 min is fatal. Synonym: hydrogen cyanide
CAS # 74-90-8

hydrofluoric acid

HF, a corrosive solution of hydrogen fluoride in water. It can be used in dentistry to etch composites and porcelain surfaces and is used industrially to etch glass. See: hydrogen fluoride


Exposure to the skin and aerodigestive tract causes severe burns with local necrosis and systemic manifestations resulting from disordered calcium and potassium metabolism. Treatments with calcium gluconate can be beneficial.
CAS # 7664-39-3

hydrosulfuric acid

Hydrogen sulfide.

hydroxy acid

Any of the acids containing one or more hydroxyl (–OH) groups in addition to the carboxyl (–COOH) group, e.g., lactic acid, CH3COHCOOH).

hydroxy-iminodiacetic acid

Abbreviation: HIDA
A chemical that, when bound to radioactive technetium, is used to demonstrate the formation and flow of bile.
See: HIDA scan

hydroxybutyric acid

C4H8O3, any of the acids present in the urine, esp. in diabetic ketoacidosis, when the conversion of fatty acids to ketones increases.

hydroxycitric acid

C6H8O8, an herbal extract promoted for the treatment of weight loss. Placebo-controlled studies have not found any benefit to the treatment.
CAS # 6205-14-7

hypochlorous acid

HClO, an acid used as a disinfectant, deodorant, and bleaching agent. It is usually used in the form of one of its salts.
CAS # 7790-92-3

imino acid

An acid formed as a result of oxidation of amino acids in the body.

inorganic acid

An acid containing no carbon atoms.
Synonym: mineral acid

iocetamic acid

C12H13I3N2O3, a radiopaque agent formerly used in cholecystography.
CAS # 16034-77-8

iopanoic acid

C11H12I3NO2 , a radiopaque contrast medium used in radiographic studies of the gallbladder.
CAS # 96-83-3

keto acid

Any organic acid containing the ketone CO (carbonyl radical).

lactic acid

C3H6O3, an organic acid formed in muscles during anaerobic cell respiration in strenuous exercise. It is also formed during anaerobic muscle activity when glucose cannot be changed to pyruvic acid in glycolysis. It contributes to muscle aches and fatigue. Synonym: lactacid
CAS # 50-21-5

levulinic acid

CH3COCH2CH2COOH, an acid formed when certain simple sugars are acted on by dilute hydrochloric acid.
CAS # 123-76-2

lignoceric acid

C24H48O2, a saturated, naturally occurring fatty acid present in certain foods, including peanuts. It is also found in wood tar, various cerebrosides, and in small amounts in most natural fats. The acid is also a by-product of lignin production.
CAS # 557-59-5

linoleic acid

C18H32O2, an omega-6 fatty acid found in vegetables, nuts, grains, seeds, fruits and their oils. Oils rich in linoleic acid include (in descending order) safflower, sunflower, corn, soybean and cottonseed.
CAS # 60-33-3

linolenic acid

C18H30O2, an omega-6 fatty acid, thought to be cardioprotective. It reduces the production of cytokines and down-regulates serum cell adhesion molecules thought to be intermediates in atherosclerosis.
CAS # 506-26-3

lithic acid

An obsolete term for uric acid.

lysergic acid

C16H16N2O2, a crystalline acid derived from ergot. Its derivative, lysergic acid diethylamide (LSD), is a potent hallucinogen. See: LSD
CAS # 82-58-6

lysophosphatidic acid

Abbreviation: LPA
C21H41O7P, an acid purified from the ascitic fluid of patients with ovarian cancer. LPA stimulates the growth of ovarian cancer and may be a useful screening test for the disease.
CAS # 22002-87-5

malic acid

C4H6O5, an acid found in sour fruits such as apples and apricots and active in the aerobic metabolism of carbohydrates.
CAS # 6915-15-7

malonic acid

C3H4O4, a dibasic acid formed by the oxidation of malic acid and active in the Krebs cycle in carbohydrate metabolism. Malonic acid is found in beets. Its inhibition of succinic dehydrogenase is the classic example of competitive inhibition.
CAS # 141-82-2

mandelic acid

C8H8O3, a colorless hydroxy acid. Its salt is used to treat urinary tract infections. Synonym: phenylglycolic acid
CAS # 90-64-2

mineral acid

Inorganic acid.

methacrylic acid

C4H6O2, a colorless acid used to make methyl methacrylate.

monounsaturated fatty acid

A fatty acid containing one double bond between carbon atoms. It is found in olive oil and is the predominant fat in the Mediterranean diet. It is thought to reduce low-density lipoprotein levels without affecting high-density lipoprotein levels.
See: Mediterranean diet

muriatic acid

A nontechnical term for hydrochloric acid.
CAS # 7647-01-0

n-3 fatty acid

Omega-3 fatty acid.

n-6 fatty acid

Omega-6 fatty acid.

nicotinic acid


nitric acid

HNO3, a colorless, poisonous, fuming corrosive acid, widely used in industry and in chemical laboratories.
CAS # 7697-37-2

nitrous acid

HNO2, a weak acid chemical reagent used in biological laboratories.
CAS # 7782-77-6

nonvolatile acid

An acid, such as lactic acid or sulfuric acid, that accumulates in the body as a result of digestion, disease, or metabolism. It cannot be excreted from the body by ventilation but must be excreted by organs other than the lungs, e.g., by acidification of the urine.
Enlarge picture

nucleic acid

Any of the high-molecular-weight molecules that carry the genetic information crucial to the replication of cells and the manufacturing of cellular proteins. They have a complex structure formed of sugars (pentoses), phosphoric acid, and nitrogen bases (purines and pyrimidines). Most important are ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). See: illustration

octadecanoic acid

Stearic acid.

okadaic acid

C44H68O13, a toxic acid found in shellfish. The toxin is produced by oceanic phytoplankton consumed by filter-feeding marine animals such as clams, crabs, and mussels and is the cause of diarrheal shellfish poisoning. Ingestion of these shellfish by humans results in profuse watery diarrhea.
CAS # 78111-17-8

oleic acid

C18H34O2, a monounsaturated fatty acid found in most organic fats and oils.
CAS # 112-80-1

omega-3 fatty acid

, ?-3 fatty acid
Any of the long-chain polyunsaturated fatty acids found in the oils of some saltwater fish, and in canola, flaxseed, walnuts, and some vegetables. These acids include eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Alpha-linolenic acid (found in flaxseed and chia) can be metabolically converted to omega-3 fatty acids in the body. People whose diets are rich in omega-3 fatty acids have a reduced incidence of cardiovascular disease. Synonym: n-3 fatty acid

omega-6 fatty acid

, ?-6 fatty acid
Any of the long-chain polyunsaturated fatty acids, such as linoleic acid and arachidonic acid, thought to influence cardiovascular and growth function when balanced with omega-3 fatty acids in eicosanoid production. Linoleic acids are derived from vegetable oils; arachidonic acids, from animal fats. Synonym: n-6 fatty acid

omega-9 fatty acid

, ?-9 fatty acid
Any of the nonessential unsaturated fatty acids that have a double carbon bond in the ninth position from the end of their fatty acid tail. They include oleic acid (present in olive oil), stearic acid, and erucic acid.

organic acid

An acid containing the carboxyl radical, –COOH. Organic acids include acetic acid, formic acid, lactic acid, and all fatty acids.

orotic acid

C5H4N2O4 , a crystalline acid occurring in milk. It is a precursor in the formation of pyrimidine nucleotides.
CAS # 65-86-1

osmic acid

Osmium tetroxide.

oxalic acid

C2H2O4, the simplest dibasic organic acid. Its potassium or calcium salts occur naturally in rhubarb, wood sorrel, and other plants. It is the strongest organic acid and is poisonous. When properly diluted, it removes ink or rust stains from cloth. It is used also as a reagent.
CAS # 144-62-7

oxaloacetic acid

, oxalacetic acid
C4H4O5, a product of carbohydrate metabolism resulting from oxidation of malic acid during the Krebs cycle. It may be derived from other sources.
CAS # 328-42-7

palmitic acid

C16H32O2, a saturated fatty acid occurring as esters in most natural fats and oils.
CAS # 57-10-3

pantothenic acid

C9H17NO5, an acid of the vitamin B complex, occurring naturally in yeast, liver, heart, salmon, eggs, and various grains. It is part of coenzyme A, which is necessary for the Krebs cycle and for conversion of amino acids and lipids to carbohydrates. Synonym: vitamin B5
CAS # 137-08-6

para-aminobenzoic acid

Abbreviation: PABA
NH2C6H4COOH, an acid of the vitamin B complex, used as a dietary supplement, an antirickettsial drug, a reagent, and a sunscreen agent. Synonym: aminobenzoic acid
CAS # 150-13-0

para-aminohippuric acid

Abbreviation: PAH, PAHA
C9H10N2O3, a derivative of aminobenzoic acid. The salt, para-aminohippurate, is used to test the excretory capacity of the renal tubules.
CAS # 61-78-9

para-aminosalicylic acid

Abbreviation: PAS, PASA
C7H7NO3, a white or nearly white, practically odorless powder that darkens when exposed to air or light. It is a second-line drug used to treat multidrug-resistant tuberculosis. Synonym: aminosalicylic acid
CAS # 65-49-6

pectic acid

C17H24O16, an acid derived from pectin by hydrolyzing its methyl ester group.

pentanoic acid

Valeric acid.

peptide nucleic acid

Abbreviation: PNA
A synthetic nucleic acid analog in which natural nucleotide bases are linked to a peptide-like backbone instead of the sugar-phosphate backbone found in DNA and RNA. PNA has numerous uses in gene regulation, splicing, and therapy; in hybridization; and as a molecular diagnostic assay.

perchloric acid

HClO4, a colorless unstable liquid compound. It is the highest oxygen-containing acid of chlorine, strong and dangerously corrosive.
CAS # 7601-90-3

phenylglycolic acid

Mandelic acid.

phosphoric acid

An acid formed by oxidation of phosphorus. The phosphoric acids are orthophosphoric acid, H3PO4; pyrophosphoric acid, H4P2O7; metaphosphoric acid, HPO3; and hypophosphoric acid, H4P2O6. The salts of these acids are phosphates. Orthophosphoric acid, a tribasic acid, is used as a 30% to 50% solution to etch enamel of teeth in preparation for bonding of resin dental restorations.
CAS # 7664-38-2

phosphorous acid

H3PO3, a crystalline acid formed when phosphorus is oxidized in moist air.
CAS # 13598-36-2

phytic acid

C6H18P6O24, a pale, water-soluble acid that is found in cereal grains and, if ingested, may interfere with the absorption of calcium and magnesium.
CAS # 83-86-3

picric acid

C6H2(NO2)3OH, a yellow crystalline powder that precipitates proteins and explodes when heated or charged. It is used as a dye and a reagent. Its salts are used in the Jaffé reaction (used to measure serum creatinine). Synonym: trinitrophenol
CAS # 88-89-1

poly DL lactic acid


polyglycolic acid

(C2H2O2)n, a polymer of glycolic acid anhydride units. It is used to manufacture surgical sutures, clips, and mesh.
CAS # 26009-03-0

polylactic acid


propionic acid

C3H6O2, a carboxylic acid present in sweat.
CAS # 79-09-4

4-pyridoxic acid

C8H9NO4, a crystalline acid that is the principal end product of pyridoxine metabolism, excreted in human urine.

pyruvic acid

C3H4O3, an organic acid that plays an important role in the Krebs cycle. It is an intermediate product in the metabolism of carbohydrates, fats, and amino acids. Its quantity in the blood and tissues increases in thiamine deficiency because thiamine is essential for its oxidation.
CAS # 127-17-3

quinic acid

C7H12O6, a crystalline acid present in some plants, including cinchona bark, and berries.
CAS # 77-95-2

retinoic acid

C20H28O2, a metabolite of vitamin A used in the treatment of cystic acne.
CAS # 302-79-4

ribonucleic acid

See: RNA

ricinoleic acid

C18H34O3, an unsaturated hydroxy acid making up about 80% of fatty acids in the glycerides of castor oil. It has a strong laxative action.
CAS # 141-22-0

salicylic acid

C7H6O3, a white crystalline acid derived from phenol used to make aspirin, as a preservative and flavoring agent, and in the topical treatment of some skin conditions such as warts and wrinkles. See: chemical peeling
CAS # 69-72-7

salicyluric acid

C9H9NO4, an acid found in the urine after ingestion of salicylic acid or its derivatives.

saturated fatty acid

A fatty acid in which the carbon atoms are linked to other carbon atoms by single bonds.
See: fatty acid; unsaturated fatty acid

silicic acid

Any of a family of acids containing silica, such as H2SiO3 (metasilicic acid), H2SiO4 (orthosilicic acid), or H2SiO7 (pyrosilicic acid). When silicic acid is precipitated, silica gel is obtained.
CAS # 10193-36-9

stearic acid

C18H36O2, a monobasic fatty acid occurring naturally in plants and animals. It is used in the manufacture of soap and pharmaceutical products such as glycerin suppositories. Synonym: octadecanoic acid
CAS # 57-11-4

succinic acid

C4H6O4, an intermediate in carbohydrate metabolism.
CAS # 110-15-6

sulfonic acid

Any of the organic compounds having the general formula SO2OH, derived from sulfuric acid by replacement of a hydrogen atom.

sulfosalicylic acid

C7H6O6S3, a crystalline acid soluble in water or alcohol. It is used as a reagent for precipitating proteins, as in testing for albumin in urine.
CAS # 97-05-2

sulfuric acid

H2SO4, a colorless, corrosive, oily, viscous acid prepared from sulfur dioxide and used in many industrial processes and in clinical laboratories. Industrial accidents involving sulfuric acid through contact with skin or inhalation of aerosols are common.
CAS # 7664-93-9

sulfurous acid

H2SO3, an inorganic acid and a powerful chemical reducing agent used commercially, esp. for as a bleach.
CAS # 7782-99-2

tannic acid

C76H52O46, a mixture of digallic acid esters of d(+) glucose prepared from oak galls and sumac. It yields gallic acid and glucose on hydrolysis.
CAS # 1401-55-4

tartaric acid

C4H6O6, an acid obtained from by-products of wine fermentation. It is widely used in industry in the manufacture of carbonated drinks, flavored gelatins, dyes, and metals. It is also used as a reagent. It is thought to be an allergen.
CAS # 526-83-0

taurocholic acid

C26H45NO7S, a bile acid that hydrolyzes to cholic acid and taurine.
CAS # 81-24-3

teichoic acid

Any of the polymers found in the cell walls of some gram-positive bacteria, such as the staphylococci.

tranexamic acid

C8H15NO2, an antifibrinolytic drug that has approx. 10 times the potency of and more sustained activity than aminocaproic acid. It is used to decrease bleeding time during surgical procedures. Loss of blood is decreased when this drug is used.
CAS # 1197-18-8

trans-fatty acid

The solid fat produced by heating liquid vegetable oils in the presence of hydrogen and certain metal catalysts. Partial hydrogenation changes some of the unsaturated bonds to saturated ones. The more trans-fatty acids in the diet, the higher the serum cholesterol and low-density lipoprotein cholesterol.

trichloroacetic acid

Abbreviation: TCA
A drug used as a caustic to destroy certain types of warts, condylomata, keratoses, and hyperplastic tissue.

2,4,5-trichlorophenoxyacetic acid


unsaturated fatty acid

An organic acid in which some of the carbon atoms are linked to other carbon atoms by double bonds, thus containing less than the maximum possible number of hydrogen atoms, e.g., unsaturated oleic and linoleic acids as compared with the saturated stearic acid. Polyunsaturated fatty acids include linoleic acid and alpha-linoleic acid.
See: fatty acid; saturated fatty acid
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uric acid

C5H4N4O3, a crystalline acid occurring as an end product of purine metabolism. It is formed from purine bases derived from nucleic acids (DNA and RNA). It is a common constituent of urinary stones and gouty tophi. See: illustration
CAS # 69-93-2


Uric acid must be excreted because it cannot be metabolized. Uric acid output should be between 0.8 and 1g/day if the patient is on an ordinary diet.

Increased elimination is observed after ingestion of proteins and nitrogenous foods, after exercise, after administration of cytotoxic agents, and in gout and leukemia. Decreased elimination is observed in kidney failure, lead poisoning, and in those who eat a protein-free diet.

valeric acid

C5H10O2, an oily fatty acid having a distinctly disagreeable odor, existing in four isomeric. Synonym: pentanoic acid
CAS # 109-52-4

valproic acid

Abbreviation: VPA
C8H16O2, an acid used to treat seizure disorders.
CAS # 99-66-1

vanillylmandelic acid

, vanilmandelic acid Abbreviation: VMA
C9H10O5, a principal metabolic product of catecholamines. VMA makes up approx. 90% of the metabolites of the catecholamines epinephrine and norepinephrine and is secreted in the urine. People with pheochromocytoma produce excess amounts of catecholamines; therefore there are increased amounts of VMA in their urine.
CAS # 55-10-7

volatile acid

An acid produced from carbon dioxide (CO2). It can be excreted by the body by ventilation (colloquially, “blowing off CO2”).

xanthurenic acid

C10H7NO4, an acid excreted in the urine of pyridoxine-deficient animals after they have been fed tryptophan. Synonym: 4,8-dihydroxyquinaldic acid
CAS # 59-00-7

peptide nucleic acid

Abbreviation: PNA
A synthetic nucleic acid analog in which natural nucleotide bases are linked to a peptide-like backbone instead of the sugar-phosphate backbone found in DNA and RNA. PNA has numerous uses in gene regulation, splicing, and therapy; in hybridization; and as a molecular diagnostic assay.
See also: acid


(noo-mon'ya, nu-) [ pneumono- + -ia],


Inflammation of the lungs, usually due to infection with bacteria, viruses, or other pathogenic organisms. Clinically, pneumonia indicates an infectious disease. Pulmonary inflammation due to other causes is called pneumonitis. In the U.S., about 4,500,000 people contract pneumonia each year, and pneumonia is the sixth most common cause of death in the U.S. and the most common cause of death due to infectious disease. Pneumonia occurs most commonly in weakened people (those with cancer, heart or lung disease, immunosuppressive illnesses, diabetes mellitus, cirrhosis, malnutrition, and renal failure), but virulent pathogens can cause pneumonia in the healthy, as well. Smoking, general anesthesia, and endotracheal intubation increase the risk for developing pneumonia by inhibiting airway defenses and helping disease-causing germs reach the alveoli of the lungs. aspiration; pleural effusion; empyema; pleurisy; pneumonitis; tuberculosis (and names of lung pathogens);


Pneumonias are categorized by site and cause. Lobar pneumonia affects most of a single lobe; bronchopneumonia involves smaller lung areas in several lobes; interstitial pneumonia affects tissues surrounding the alveoli and bronchi of the lung. Atypical pneumonias diffusely affect lung tissues rather than anatomical lobes or lobules. Community-acquired pneumonia is a lung infection that occurs in noninstitutionalized people, typically involving organisms such as viruses, Streptococcus pneumoniae, Klebsiella pneumoniae, Mycoplasma pneumoniae, Legionella pneumophila, Chlamydia pneumoniae, Moraxella species, or Pneumocystis carinii. Nosocomial pneumonia develops in patients in the hospital or nursing home; this type is most likely to be caused by gram-negative rods or staphylococcal species. Aspiration pneumonias result from the inhalation of oropharyngeal microorganisms and often involve anaerobic organisms. Pneumonias in immunocompromised patients sometimes are caused by Pneumocystis jiroveci or by fungal species such as Aspergillus. or Candida. Some fungal pneumonias occur in specific geographical regions of the U.S. For example, histoplasmosis is common in the Ohio River Valley, and coccidioidomycosis is found in the San Joaquin River Valley of southern California. Viral pneumonias may be caused by influenza, varicella-zoster, herpes, or adenoviruses.


Most patients with pneumonia have cough, shortness of breath, and fever although these symptoms are not universal. Bacterial pneumonias are marked by abrupt onset, with high fevers, shaking chills, pleuritic chest pain, and prostration. Patients with atypical pneumonias usually have lower temperatures and nonproductive coughs and appear less ill.


Pneumococcal vaccine effectively prevents many forms of streptococcal pneumonia. This vaccine is recommended for people over 65; those with chronic respiratory, cardiac, or neuromuscular diseases; and patients with diabetes mellitus or renal failure.


Treatment is based on the clinical presentation (such as community-acquired versus nosocomial), results of the Gram stain of sputum specimens, the radiographical appearance of the pneumonia, the degree of respiratory impairment, and the results of cultures. Many patients hospitalized with pneumonia require supplemental oxygen and analgesics. Initial antibiotic treatments for pneumonia should be given without delay and typically involve powerful, broad-spectrum drugs. The antibiotic used for subsequent therapy is guided by the results of cultured specimens taken on presentation.

Patient care

A large percentage of patients with pneumonia are not admitted to hospitals but are treated with antibiotics given on an outpatient basis. However, older adults, people with serious chronic diseases, and those with evidence of organ dysfunction, poor oxygenation, or acute decompensation may need hospitalization to reduce the risk of injury or death. Supportive care is provided to the patient to remove secretions and improve gas exchange. Such care includes position changes, deep breathing and coughing exercises, incentive spirometry, active and passive limb exercises, and assistance with self-care. Respiratory status is monitored by listening to the chest for crackles and/or wheezing, performing oximetry on a regular basis, and, when patients are failing, performing arterial blood gas studies. Supplemental oxygen is usually prescribed to maintain an oxygen saturation of > 92%. The patient is assessed for signs and symptoms of respiratory failure, sepsis, and shock. Mechanical ventilation is required in patients with respiratory failure. Analgesics are provided as prescribed to manage pain and discomfort and encourage good pulmonary toilet. A large percentage of patients receive care to remove secretions and to improve gas exchange. Such care includes position changes, deep-breathing, and coughing exercises. The patient is encouraged to verbalize concerns; diagnostic studies and therapeutic measures are explained, and the patient is taught about the importance of follow-up care. Outpatient therapy of community-acquired pneumonia can be recommended for selected patients who are young, otherwise healthy, and not hypoxic, hypotensive, hypothermic, or in renal failure. Activities are scheduled to allow for plenty of rest. The patient is taught hand hygiene and encouraged to wash hands with soap and water or use an alcohol-based hand wipe entirely over both hands after blowing the nose, coughing, using the bathroom, or eating or drinking. Only disposable tissues are used for sneezing and coughing. Used tissues are deposited in a lined bag taped to the bedside and are disposed of frequently according to agency policy. Unless otherwise restricted, the patient should drink eight 12-ounce glasses of water daily to help thin and loosen mucous secretions. Each patient’s meal preferences and restrictions are discussed to plan a diet that ensures adequate high-caloric intake. Emotional support is provided, and all procedures and treatments are explained. The patient who smokes is taught the relationship between smoking and lung diseases (including the increased risk of respiratory infections) and referred for support group assistance with quitting as needed. Pneumonia prevention is aided by encouraging individuals to avoid indiscriminate antibiotic use, receive pneumonia and influenza vaccinations, perform deep-breathing and coughing exercises when confined to bed and after surgery, and ambulate early after surgery. Aspiration pneumonia is prevented in tube-fed patients by correct positioning and slow, low-volume feedings. The chronically ill and debilitated in nursing homes should have swallowing function assessed as necessary; caregivers should be taught correct feeding techniques to prevent aspiration.

abortive pneumonia

An obsolete term for mild pneumonia with a brief course.

acute lobar pneumonia

Lobar pneumonia.

pneumonia alba

A pneumonia seen in stillborn infants; caused by congenital syphilis.

artificial airway-associated pneumonia

Ventilator-associated pneumonia.

aspiration pneumonia

Pneumonia caused by inhalation of gastric contents, food, or other substances. A frequent cause is loss of the gag reflex in patients with central nervous system depression or damage or alcoholic intoxication with stupor and vomiting. This condition also occurs in newborns who inhale infected amniotic fluid, meconium, or vaginal secretions during delivery.

atypical pneumonia

Pneumonia caused by a virus or Mycoplasma pneumoniae. The symptoms are low-grade fever, nonproductive cough, pharyngitis, myalgia, and minimal adventitious lung sounds.

bacterial pneumonia

Pneumonia caused by bacteria such as streptococcus, Staphylococcus aureus, Klebsiella, or coliforms.

chlamydial pneumonia

An atypical pneumonia caused by Chlamydia species, characterized clinically by cough, low-grade fever, sore throat, and malaise. A chest x-ray taken during the illness is more likely to show diffuse lung involvement than a lobar pneumonia.

community-acquired pneumonia

Pneumonia occurring in outpatients, often caused by infection with streptococcus, Haemophilus influenzae, Staphylococcus aureus, and atypical organisms such as Legionella species. Mortality is approximately 15% but depends on many host and pathogen features.

desquamative interstitial pneumonia

Pneumonia of unknown cause, accompanied by cellular infiltration or fibrosis in the pulmonary interstitium. Progressive dyspnea and a nonproductive cough are symptoms characterizing this disease. Clubbing of the fingers is a common finding. Diffusion of oxygen and carbon dioxide is abnormal. Diagnosis is made by lung biopsy. The condition is treated by corticosteroids.

double pneumonia

Pneumonia that involves both lungs or two lobes.

embolic pneumonia

Pneumonia following embolization of a pulmonary blood vessel.

eosinophilic pneumonia

Infiltration of the lung by eosinophils, typically found in patients with peripheral eosinophilia. The cause is usually unknown; occasionally, the condition responds to the administration of corticosteroids. In some cases, a specific underlying cause is found, such as the recent initiation of cigarette smoking or an allergic drug reaction. Infection with some parasites or fungi also can trigger the disease.
Synonym: pulmonary infiltration with eosinophilia;

fibrous pneumonia

Pneumonia followed by formation of scar tissue.

Friedländer pneumonia

See: Friedländer pneumonia

gangrenous pneumonia

Pulmonary gangrene.

giant cell pneumonia

An interstitial pneumonitis of infancy and childhood. The lung tissue contains multinucleated giant cells. The disease often occurs in connection with measles.

healthcare-associated pneumonia

Nosocomial pneumonia.

hypostatic pneumonia

Pneumonia occurring in elderly or bed-ridden patients who remain constantly in the same position. Ventilation is greatest in dependent areas. Remaining in one position causes hypoventilation in many areas, causing alveolar collapse (atelectasis) and creating a pulmonary environment that supports the growth of bacteria or other organisms. Development of this condition is prevented by having the patient change positions and take deep breaths to inflate peripheral alveoli.

Patient care

Prevention is the most important factor, esp. in older and immobile persons. Patients should be moved and turned frequently at least every 1 to 2 hr. The nurse and respiratory therapist should monitor respiratory status by frequently auscultating for crackles, gurgles, and wheezes and encourage the patient to engage in active movement and to perform deep-breathing and coughing exercises frequently and regularly. Incentive spirometry may prove useful in patients who need added encouragement to deep breathe periodically.

intrauterine pneumonia

Pneumonia contracted in utero.

Legionella pneumonia

Legionnaires' disease.

lipoid pneumonia

Damage to lung tissue that results from aspiration of oils. It may occur repeatedly in patients with impaired swallowing mechanisms or in persons affected by esophageal disorders, such as esophageal carcinoma, achalasia, or scleroderma. Mineral oils and cooking oils often are responsible. Most cases resolve spontaneously, but corticosteroids sometimes are used as treatment to reduce inflammatory changes. Distinguishing lipoid pneumonia from bacterial pneumonia may require endoscopy.
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LOBAR PNEUMONIA: (A) The right heart border is obscured by the infection, (B) Lateral view shows dense (white) infiltrate sharply defined by horizontal fissure (Courtesy of Harvey Hatch, MD, Curry General Hospital)
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lobar pneumonia

Pneumonia infecting one or more lobes of the lung, usually caused by Streptococcus pneumoniae. The pathologic changes are, in order, congestion; redness and firmness due to exudate and red blood cells in the alveoli; and, finally, gray hepatization as the exudate degenerates and is absorbed. Synonym: acute lobar pneumonia See: illustration

neonatal pneumonia

Lung infection occurring in the first few days of life due to uterine exposure to infectious microorganisms or to infection during or immediately after birth. Common causes include viruses (such as herpes simplex) and bacteria (such as group B streptococcus, Chlamydia, Escherichia coli, Listeria).

nosocomial pneumonia

Pneumonia occurring after 48 hours of confinement in a hospital, intensive care unit, or nursing home. It is often the result of infection with gram-negative pathogens or multiply drug-resistant bacteria and includes both ventilator-associated pneumonias and other lower respiratory tract infections. Synonym: healthcare-associated pneumonia

pneumococcal pneumonia

The most common form of pneumonia in the U.S., affecting about half a million people each year. It often begins with hard-shaking chills and may be fatal, esp. in the elderly or those with underlying diseases. It usually strikes smokers, people with underlying lung diseases, those recently infected with influenza or those with sickle-cell anemia, chronic or heavy alcohol use, or cirrhosis.


Fevers, body-shaking chills, productive cough, pleurisy, prostration, and sweating.


Penicillin may be used when the pneumococcus is sensitive to this agent, but the incidence of penicillin resistance in pneumococci is rapidly growing. Third-generation cephalosporins, erythromycin, vancomycin, and linezolid, are alternative agents.

Patient care

Vaccination provides passive immunity against many serotypes of pneumococcal pneumonia. People over the age of 65 or those with heart, lung, liver, kidney, or immunosuppressive diseases should be immunized as should infants under the age of two.

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PNEUMOCYSTIS CARINII PNEUMONIA: Silver-stained cysts in lung tissue (×400)
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Pneumocystis carinii pneumonia

Abbreviation: PCP
A subacute opportunistic infection marked by fever, nonproductive cough, tachypnea, dyspnea, and hypoxemia. It is caused by Pneumocystis carinii, the former name of Pneumocystis jiroveci, an organism formerly thought to be a protozoan but now generally accepted as a fungus. The disease is seen principally in immunosuppressed patients, such as those with AIDS or who have received an organ transplant and immunosuppressant drugs. Without treatment, the progressive respiratory failure that the infection causes is ultimately fatal.


The disease should be suspected in patients with human immunodeficiency virus infection or other risk factors for the disease who present with cough and shortness of breath. Chest x-ray examination may reveal diffuse interstitial infiltrates, upper lobe disease, spontaneous pneumothorax, or cystic lung disease. The diagnosis is confirmed with special stains of sputum, bronchial washings, or lung biopsy specimens. See: illustration


Oral trimethoprim-sulfamethoxazole effectively protects against PCP, and is also the drug of choice for active infection. Other drugs that are active against PCP include pentamidine, trimethoprim in combination with dapsone, and atovaquone. Corticosteroids are used as adjunctive therapy when treating markedly hypoxic patients, e.g., those who present with an alveolar-arterial oxygen gradient of more than 35 mm Hg. The introduction of highly active antiretroviral drug cocktails for AIDS patients has markedly reduced the incidence of PCP.


secondary pneumonia

Pneumonia that occurs in connection with a specific systemic disease such as typhoid, diphtheria, or plague.

tuberculous pneumonia

Pneumonia caused by Mycobacterium tuberculosis. See: tuberculosis

tularemic pneumonia

Pneumonia caused by Francisella tularensis. It may be primary or associated with tularemia.

ventilator-associated pneumonia

In patients receiving invasive mechanical ventilation, a new and persistent infiltrate seen on chest x-ray associated with fever, elevated or depressed white blood cell counts, and sputum that is either purulent or full of disease-causing bacteria. Synonym: artificial airway-associated pneumonia

viral pneumonia

Any infections of the lower respiratory tract (the lungs, bronchioles, and trachea) caused by viral species such as adenovirus, coronavirus, herpesviruses, influenza viruses, and respiratory syncytial viruses. Viral pneumonias may range from mild respiratory infections (with nonproductive cough and low-grade fevers) to life-threatening and highly contagious illnesses (such as SARS). See: bronchitis; bronchiolitis
Medical Dictionary, © 2009 Farlex and Partners


Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005
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