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1. any substance that interferes with a chemical reaction, growth, or other biologic activity.
2. a chemical substance that inhibits or checks the action of a tissue organizer or the growth of microorganisms.
3. an effector that reduces the catalytic activity of an enzyme.
ACE i's (angiotensin-converting enzyme i's) see angiotensin-converting enzyme inhibitors.
angiogenesis inhibitor a group of drugs that prevent growth of new blood vessels into a solid tumor.
aromatase i's a class of drugs that inhibit aromatase activity and thus block production of estrogens; used to treat breast cancer and endometriosis.
C1 inhibitor (C1 INH) a member of the serpin group, an inhibitor of C1, the initial component activated in the classical complement pathway. Deficiency of or defect in the protein causes hereditary angioedema.
carbonic anhydrase inhibitor an agent that inhibits the enzyme carbonic anhydrase; used in treatment of glaucoma and sometimes for epilepsy, familial periodic paralysis, acute mountain sickness, and kidney stones of uric acid.
cholinesterase inhibitor anticholinesterase.
COX-2 i's (cyclooxygenase-2 i's) a group of nonsteroidal antiinflammatory drugs that act by inhibiting cyclooxygenase-2 activity; they have fewer gastrointestinal side effects than other NSAIDs. Two members of the group are celecoxib and rofecoxib.
gastric acid pump inhibitor an agent that inhibits gastric acid secretion by blocking the action of H+,K+-ATPase at the secretory surface of gastric parietal cells; called also proton pump i.
HIV protease inhibitor any of a group of antiretroviral drugs active against the human immunodeficiency virus; they prevent protease-mediated cleavage of viral polyproteins, causing production of immature viral particles that are noninfective. Examples include indinavir sulfate, nelfinavir mesylate, ritonavir, and saquinavir.
HMG-CoA reductase i's a group of drugs that competitively inhibit the enzyme that catalyzes the rate-limiting step in cholesterol biosynthesis, and are used to lower plasma lipoprotein levels in the treatment of hyperlipoproteinemia. Called also statins.
membrane inhibitor of reactive lysis (MIRL) protectin.
monoamine oxidase inhibitor any of a group of drugs that inhibit the action of monoamine oxidase, the enzyme that breaks down norepinephrine and serotonin, prescribed for their antidepressant action; the most widely used ones are isocarboxazid, phenelzine, and tranylcypromine. They are also used in the prevention of migraine.
α2-plasmin inhibitor α2-antiplasmin.
plasminogen activator inhibitor (PAI) any of several regulators of the fibrinolytic system that act by binding to and inhibiting free plasminogen activator. Their concentration in plasma is normally low, but is altered in some disturbances of bodily hemostasis. PAI-1 is an important fast-reacting inhibitor of t-plasminogen activator and u-plasminogen activator. Its synthesis, activity, and release are highly regulated; elevated levels of it have been described in a number of disease states. PAI-2 is a normally minor inhibitor that greatly increases in concentration during pregnancy and in certain disorders. PAI-3 is protein C inhibitor.
platelet inhibitor any of a group of agents that inhibit the clotting activity of platelets; the most common ones are aspirin and dipyridamole. See also antiplatelet therapy.
protease inhibitor
1. a substance that blocks activity of endopeptidase (protease), such as in a virus.
protein C inhibitor the primary inhibitor of activated anticoagulant protein C; it is a glycoprotein of the serpin family of proteinase inhibitors and also inhibits several other proteins involved in coagulation (thrombin, kallikrein, and coagulation factors X and XI) and urokinase. Called also plasminogen activator inhibitor 3.
proton pump inhibitor gastric acid pump i.
reverse transcriptase inhibitor a substance that blocks activity of the reverse transcriptase of a retrovirus and is used as an antiretroviral agent. Some are nucleosides or nucleoside analogues, and those that are not are therefore often called non-nucleoside reverse transcriptase inhibitors.
selective serotonin reuptake inhibitor (SSRI) any of a group of drugs that inhibit the inactivation of serotonin by blocking its absorption in the central nervous system; used as antidepressants and in the treatment of obsessive-compulsive disorder and panic disorder.
serine protease inhibitor (serine proteinase inhibitor) serpin.
topoisomerase i's a class of antineoplastic agents that interfere with the arrangement of DNA in cells.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


Acetazolam (CA), AK-Zol, Apo-Acetazolamide (CA), Diamox (CA), Diamox Sequels

Pharmacologic class: Carbonic anhydrase inhibitor

Therapeutic class: Diuretic, antiglaucoma drug, anticonvulsant, altitude agent, urinary alkalinizer

Pregnancy risk category C


Inhibits carbonic anhydrase in kidney, decreasing water reabsorption and increasing excretion of sodium, potassium, and bicarbonate. Lowers intraocular pressure by decreasing aqueous humor production. May raise seizure threshold by reducing carbonic anhydrase in CNS, thereby decreasing neuronal conduction.


Capsules (sustained-release): 500 mg

Injection: 500 mg/vial

Tablets: 125 mg, 250 mg

Indications and dosages

Open-angle (chronic simple) glaucoma (given with miotics)

Adults: 250 mg P.O. one to four times daily, or 500-mg sustained-release capsule P.O. once or twice daily. Don't exceed total daily dosage of 1 g.

Preoperative treatment of closed-angle (secondary) glaucoma

Adults: 250 mg P.O. q 4 hours or 250 mg P.O. b.i.d.; in acute cases only, 500 mg P.O. followed by 125 to 250 mg P.O. q 4 hours. For rapid relief of increased intraocular pressure, 500 mg I.V., repeated in 2 to 4 hours; then 125 to 250 mg P.O. q 4 to 6 hours.

Children: 10 to 15 mg/kg/day P.O. in divided doses q 6 to 8 hours, or 5 to 10 mg/kg I.V. q 6 hours

Seizure disorder (given with other anticonvulsants)

Adults and children: 250 mg P.O. daily when given with another anticonvulsant, or 8 to 30 mg/kg daily P.O. in one to four divided doses. Usual dosage range is 375 mg to 1 g daily.

Drug-induced edema or edema secondary to heart failure

Adults: Initially, 250 to 375 mg P.O. daily. If diuresis fails, give dose on alternate days, or give for 2 days alternating with day of rest.

Children: 5 mg/kg P.O. daily, or 150 mg/m2 P.O. or I.V. once daily in morning

Acute high-altitude (mountain) sickness

Adults: 500 mg to 1 g P.O. daily in divided doses, or sustained-release capsule q 12 to 24 hours. Dosing should begin 24 to 48 hours before ascent and continue during ascent and for 48 hours after reaching desired altitude. For rapid ascent, 1-g P.O. dose is recommended.

Dosage adjustment

• Mild renal failure

Off-label uses

• Acute pancreatitis

• Alkalosis after open-heart surgery

• Hereditary ataxia

• Peptic ulcer

• Periodic paralysis

• Renal calculi

• Phenobarbital or lithium overdose

• Hydrocephalus in infants


• Hypersensitivity to drug or sulfonamides

• Adrenocortical insufficiency

• Closed-angle glaucoma

• Severe pulmonary obstruction

• Severe renal disease, hypokalemia, hyponatremia

• Hepatic disease


Use cautiously in:

• respiratory, renal, or hepatic disease; diabetes mellitus, hypercalcemia, gout, adrenocortical insufficiency

• pregnant or breastfeeding patients.


Before giving, ask if patient is pregnant. Drug may cause fetal toxicity.

• Direct I.V. administration is preferred. When giving by direct I.V. route, reconstitute 500-mg vial with more than 5 ml of sterile water for injection; administer over 1 minute.

• When giving drug intermittently by I.V. infusion, further dilute with normal saline solution or dextrose solution and infuse over 4 to 8 hours.

• Be aware that I.M. administration is painful because solution is alkaline.

• If necessary, crush tablets and mix in nonsweet, nonalcoholic syrup or non-glycerin solution.

Adverse reactions

CNS: weakness, nervousness, irritability, drowsiness, confusion, dizziness, depression, tremor, headache, paresthesia, flaccid paralysis, seizures

EENT: transient myopia, tinnitus, hearing dysfunction, sensation of lump in throat

GI: nausea, vomiting, diarrhea, constipation, melena, abdominal distention, dry mouth, anorexia

GU: dysuria, hematuria, glycosuria, polyuria, crystalluria, renal colic, renal calculi, uremia, sulfonamide-like renal lesions, renal failure

Hematologic: thrombocytopenia, leukopenia, agranulocytosis, hemolytic anemia, thrombocytopenic purpura, pancytopenia, bone marrow depression with aplastic anemia

Hepatic: hepatic insufficiency

Metabolic: hypokalemia, hyperglycemia and glycosuria, hyperuricemia and gout, metabolic acidosis, hyperchloremic acidosis

Respiratory: hyperpnea

Skin: rash, pruritus, urticaria, photosensitivity, hirsutism, cyanosis

Other: altered taste and smell, weight loss, fever, excessive thirst, pain at I.M. injection site, hypersensitivity reaction, Stevens-Johnson syndrome


Drug-drug. Amphetamines, procainamide, quinidine, tricyclic antidepressants: decreased excretion and enhanced or prolonged effect of these drugs, leading to toxicity

Amphotericin B, corticosteroids, corticotrophin, other diuretics: increased risk of hypokalemia

Lithium, phenobarbital, salicylates: increased excretion of these drugs, possibly reducing their efficacy

Methenamine compounds: inactivation of these drugs

Phenytoin, primidone: severe osteomalacia

Salicylates: increased risk of salicylate toxicity

Drug-diagnostic tests. Ammonia, bilirubin, calcium, chloride, glucose, uric acid: increased levels

Thyroid iodine uptake: decreased in patients with hyperthyroidism or normal thyroid function

Urinary protein (with some reagents): false-positive result

Drug-behaviors. Sun exposure: increased risk of photosensitivity

Patient monitoring

Evaluate for signs and symptoms of sulfonamide sensitivity; drug can cause fatal hypersensitivity.

Monitor laboratory test results for hematologic changes; blood glucose, potassium, bicarbonate, and chloride levels; and liver and kidney function changes.

• Observe for signs and symptoms of bleeding tendency.

• Monitor fluid intake and output.

Patient teaching

• Advise patient to take drug with food if GI upset occurs.

• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.

• Tell patient to eat potassium-rich foods (such as seafood, bananas, and oranges) if taking drug long term or receiving other potassium-depleting drugs.

• Advise patient to avoid activities that can cause injury. Advise him to use soft toothbrush and electric razor to avoid gum and skin injury.

• Tell patient to report significant numbness or tingling.

• Inform patient that he'll undergo regular blood testing during therapy.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, and behaviors mentioned above.

McGraw-Hill Nurse's Drug Handbook, 7th Ed. Copyright © 2013 by The McGraw-Hill Companies, Inc. All rights reserved


The heterocyclic sulfonamide 5-acetylamido-1,3,4-thiadiazole-2-sulfonamide, which inhibits the action of carbonic anhydrase in the kidney, increasing the urinary excretion of sodium, potassium, and bicarbonate, reducing excretion of ammonium, raising the pH of the urine, and lowering the pH of the blood; used in respiratory acidosis for diuresis and to stimulate respiratory drive, in glaucoma to reduce intraocular pressure, and in epilepsy.
Farlex Partner Medical Dictionary © Farlex 2012


A diuretic drug used to treat altitude sickness, glaucoma, and epilepsy.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


A heterocyclic sulphonamide used to manage respiratory acidosis by inhibiting renal carbonic anhydrase, which increases renal excretion of Na+, K+, and bicarbonate, and reduces ammonia excretion. Acetazolamide is also used to reduce fluid retention in congestive heart failure, control secondary glaucoma and preoperatively in acute angle-closure glaucoma, and may be of use in seizures, especially absence seizures.
Effect Reduced serum pH; increased urine pH
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.


Dazamide®, Diamox® Therapeutics A heterocyclic sulfonamide used to manage respiratory acidosis by inhibiting renal carbonic anhydrase, which ↑ renal excretion of Na+, K+, and bicarbonate, and ↓ ammonia excretion; acetazolamide is also used to ↓ fluid retention in CHF, control 2º glaucoma and preoperatively in acute angle-closure glaucoma, epilepsy Effect ↓ Serum pH; ↑ urine pH Therapeutic range 10–15 µg/mL Toxic range ≥ 20 µg/mL
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.


A drug that inhibits the enzyme carbonic anhydrase in the kidney tubules, thus acting as a diuretic. In the eye it acts similarly to reduce the rate of secretion of aqueous humour and is useful in the treatment of GLAUCOMA when the intraocular pressure rise cannot be controlled with eye drops alone. The drug is also used in the treatment of EPILEPSY. A brand name is Diamox.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005

carbonic anhydrase inhibitors 

Drugs which inhibit the carbonic anhydrase enzyme in the ciliary epithelium of the ciliary body. This enzyme is essential for the formation of aqueous humour; its reduction results in a decrease in intraocular pressure. Those in use are sulfonamide derivatives. They are administered systemically (e.g. acetazolamide) or topically in the treatment of glaucoma. Examples: acetazolamide, brinzolamide, dichlorphenamide, dorzolamide.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann


Agent that inhibits action of carbonic anhydrase in the kidney.
Medical Dictionary for the Dental Professions © Farlex 2012