agent (a'jent) [L. agere, to do]
Someone or something that causes an effect. For example, bacteria that cause disease are agents of the specific diseases they cause, and medicine is a therapeutic agent.
adrenergic neuron-blocking agent
Any substance that inhibits transmission of sympathetic nerve stimuli regardless of whether alpha- or beta-adrenergic receptors are involved. See: alpha-adrenergic receptor; beta-adrenergic receptor
Any substance that introduces an alkyl radical into a compound in place of a hydrogen atom. Alkylating agents are used to treat cancer because they interfere with cell metabolism and growth. Examples include cis-platinum and cyclophosphamide.
alpha-adrenergic blocking agent
A substance that interferes with the transmission of stimuli through pathways that normally allow sympathetic nervous excitatory stimuli to be effective. Agents from this class are used to treat hypertension and prostatic hyperplasia. See: beta-adrenergic blocking agent
Any of a class of steroid hormones resembling testosterone. These agents stimulate the growth or manufacture of body tissues. They have been used, sometimes in high doses, by male and female athletes to improve performance. This use has been judged to be illegal by a number of organizations that supervise sports, including the International Olympic Committee and the U.S. Olympic Committee. These agents are also used to treat patients with wasting illnesses. See: doping
; ergonomic aid
Indiscriminate use of anabolic agents is inadvisable because of the undesirable side effects they may produce, e.g., in women, hirsutism, masculinization, and clitoral hypertrophy; in men, aggressiveness and testicular atrophy.
A drug used to prevent or treat ulcers of the stomach or small intestine.
A synthetic or natural drug that stimulates beta (sympathetic) receptors, e.g., epinephrine and norepinephrine.
beta-adrenergic blocking agent
Synonym: beta blocker
Any drug that inhibits the activity of the sympathetic nervous system and of adrenergic hormones.
Members of this class of drugs are used to treat hypertension, angina pectoris, myocardial infarction, aortic dissection, arrhythmias, glaucoma, and other conditions. Commonly prescribed beta blockers include atenolol, carvedilol, metoprolol, nadolol, propranolol, and pindolol.
Side effects of beta blockers include worsening of asthma, blunting of the cardiovascular symptoms of hypoglycemia, bradycardia, and heart block. Rapid withdrawal from a beta-blocking drug by a patient accustomed to its use may produce tachycardia or other arrhythmias, rebound hypertension, or myocardial ischemia or infarction.
A vesicant, esp. any such agent (like mustard gas) used in chemical warfare.
Any chemical, biological, radiologic, nuclear, or explosive agent that may be used as a weapon in military or terrorist activities.
An agent that dissolves cerumen in the external ear canal. Obstruction of the ear canal with cerumen can cause itching, pain, and temporary conductive hearing loss. The first approach to treatment should be removal of the obstruction manually with a blunt curet or loop or by irrigation. Cerumen solvents are not always recommended because they often do not eliminate the problem and frequently cause maceration of the skin of the canal and allergic reactions.
Any drug that promotes dilation of the cervix in anticipation of childbirth.
An ion that disrupts membranes, nucleic acids, and proteins.
A drug, such as calcium disodium edetate, used to chelate substances, esp. toxic chemicals in the body.
cholinergic blocking agentAnticholinergic (2).
1. A substance that increases the transparency of tissues prepared for microscopic examination.
2. In radiographic film processing, the active agent in the fixer that clears undeveloped silver bromide crystals from the film. The most common agent is ammonium thiosulfate. Synonym: fixing agent
A medication to force the bowels to evacuate, e.g., in preparation for colonoscopy.
A drug that destroys cells or prevents them from multiplying. Cytotoxic agents are used to treat cancers and severe immunological disorders, e.g., vasculitis, some forms of glomerulonephritis. An ideal agent would destroy proliferating cells without injuring the normal cells of the body.
A diagnostic aid used in dentistry to stain areas of the teeth that are not being cleaned adequately. A dye such as erythrosine sodium is used to color dental plaque so that inadequately brushed surfaces can be shown to patients.
Eaton agent See: Eaton agent
erythropoiesis-stimulating agent Abbreviation: ESA.
Any drug that binds to cellular receptors for erythropoietin and encourages red blood cell production by the bone marrow. Members of this class of drugs, which include epoietin and darbopoietin, are used to treat anemia, e.g., in patients with chronic kidney disease, cancer, or aplastic anemia. ESAs are used as an alternative to red blood cell transfusions. Potential side effects of treatment include high blood pressure and an increased risk of blood clots.
fixing agent See: clearing agent
A medication such as all-trans-retinoic acid, used in differentiation therapy.
immunosuppressive agent See: immunosuppressant.
nasal drying agent
Any anticholinergic, antihistaminic, or drug of a related class that decreases watery discharge from the nose, e.g., in rhinitis.
Norwalk agent See: virus
ocular hypotensive agent
A drug that reduces intraocular pressure, e.g., in glaucoma.
oral hypoglycemic agent Abbreviation: OHA.
Any drug taken by mouth that lowers or maintains blood glucose (as opposed to insulin, a drug taken parenterally to control blood sugar). In addition to diet and exercise regimens, OHAs are typically used to control blood glucose levels in type 2 diabetes mellitus. Commonly used oral agents for diabetes include metformin (a biguanide), sulfonylureas (such as glyburide), alpha-glucosidase inhibitors (acarbose), and thiazolidinediones (pioglitazone). Used appropriately, OHAs lower hemoglobin A1c levels by about 0.5 to 1.5%. See: table
|Class of Drug||Activity||Adverse Features||Approximate Cost|
|Alpha-glucosidase inhibitors, e.g., acarbose||Delay absorption of glucose from intestinal tract||Flatulence and other abdominal side effects||Expensive|
|Biguanides, e.g., metformin||Improve sensitivity to insulin; decrease glucose production by the liver||Less weight gain than with other agents; avoid in patients with renal failure||Very expensive|
|Sulfonylureas, 1st generation, e.g., tolazamide||Cause beta cells to release insulin||Resistance to drug may develop over time||Inexpensive|
|Sulfonylureas, 2nd generation, e.g., glipizide, glyburide, others||Same as 1st generation; also increase sensitivity to insulin||Same as 1st generation||Moderately expensive|
* Combinations of these drugs, either with each other or with insulin, may be used in patients with poorly controlled diabetes mellitus.
|Thiazolidinediones, e.g., pioglitazone||Improve sensitivity to insulin; improve lipid profile||Monthly monitoring of liver functions needed for some drugs in this class due to risk of toxicity. Heart failure and other heart diseases.||Very expensive|
progestational agentProgestin (1).
Any substance that shields the body from damage by radioactivity.
A substance that loses electrons easily and therefore causes other substances to be reduced (such as hydrogen sulfide, sulfur dioxide). Synonym: reducing substance.
riot control agent
The formal term for any of those vaporized chemicals (such as chloroacetophenone and chlorobenzylidene malononitrile) used in tear gas. These agents cause irritation on contact, e.g., to the skin, eyes, or respiratory mucosa, and produce visual blurring, itching and burning of the skin, coughing, wheezing, nausea or vomiting, and occasionally asphyxia.
To reduce the effects of a tear gas exposure, remove the victim's clothes and wash the skin and hair promptly and thoroughly in soapy water. Rinse exposed eyes with sterile liquids. Patients who develop asthma or wheezing should be treated with bronchodilators such as albuterol.
A substance used to cause sclerosis, esp. of the lining of a vein. See: varicose vein
Any drug that degrades blood clots. Examples include streptokinase, tenecteplase, tissue plasminogen activator, and urokinase. Such drugs are used to treat the abnormal blood clotting that occurs in heart attacks, some strokes, and pulmonary emboli. They are informally called “clot busters.”
CAUTION!Thrombolytic drugs should not be given to patients with active bleeding, a history of surgery or major trauma within the preceding two weeks, a brain tumor, or other known risks for intracerebral hemorrhage.
thrombopoietin mimetic agent
A drug that stimulates the bone marrow to produce more platelets than usual. Drugs from this class, e.g., romiplostim, are used to treat diseases such as immune thrombocytopenia.
topical hemostatic agent
Any substance that can be applied to a wound or an incision to keep it from bleeding. Examples include adhesives derived from collagen or glutaraldehyde, cellulose-based products, fibrin sealants, hydrogels, and thrombin.
A drug, e.g., probenecid or sulfinpyrazone, that increases the urinary excretion of uric acid by blocking renal tubular absorption, thereby reducing the concentration of uric acid in the blood. It is used to treat gout.
Probenecid and sulfinpyrazones are used to treat gout. Side effects of both include headache, gastrointestinal upset, epigastric pain, kidney stone formation, and peptic ulcer. These drugs should be avoided by patients with diminished renal function. Any uricosuric agent should be taken with milk, food, or antacids to reduce gastric distress. Patients should drink large volumes of water. Sodium bicarbonate (or potassium citrate) is prescribed simultaneously with these agents to alkalinize urine and keep uric acid crystals in solution.
vascular disrupting agent
Any of a class of medications used to destroy the blood supply of malignant tumors.
1. Any agent, such as a surfactant, that allows a fluid to spread over and coat a surface to which it is applied.
2. In radiographic wet film processing, a solution used after washing to reduce surface tension and accelerate water flow from the film to speed drying.
Medical Dictionary, © 2009 Farlex and Partners