1. An active force or substance capable of producing an effect. For agents not listed here, see the specific name. 2. A disease, a factor such as a microorganism, chemical substance, or a form of radiation the presence or absence of which (as in deficiency diseases) results in disease or more advanced disease. [L. ago, pres. p. agens (a.-), to perform]
- adrenergic blocking a. a compound that selectively blocks or inhibits responses to sympathetic adrenergic nerve activity (sympatholytic a.) and to epinephrine, norepinephrine, and other adrenergic amines (adrenolytic a.); two distinct classes exist, alpha- and beta-adrenergic receptor blocking agents.
- α-adrenergic blocking a. a class of drugs that compete with α-adrenergic agonists for available receptor sites: some compete for both α1 and α2 receptors ( e.g., phentolamine, dibenzyline) while others are primarily either α1 ( e.g., prazosin, terazosin) or α2 receptor blocking agents ( e.g., yohimbine). SYN: α-adrenoceptor antagonist, alpha-blocker.
- β-adrenergic blocking a. a class of drugs that compete with β-adrenergic agonists for available receptor sites; some compete for both β1 and β2 receptors ( e.g., propranolol) while others are primarily either β1 ( e.g., metoprolol) or β2 blockers; used in the treatment of a variety of cardiovascular diseases where β-adrenergic blockade is desirable. SYN: β-adrenergic receptor blocking a., β-adrenoreceptor antagonist, beta-blocker.
- adrenergic neuronal blocking a. a drug that prevents the release of norepinephrine from sympathetic nerve terminals ( e.g., guanethidine); it does not inhibit the responses of the adrenergic receptors to circulating epinephrine, norepinephrine, and other adrenergic amines.
- β-adrenergic receptor blocking a. SYN: β-adrenergic blocking a..
- alkylating a. a drug or chemical that, via the formation of covalent bonds, forms a derivatized tissue constituent permanently containing part of the drug or chemical compound; frequently carcinogenic and mutagenic, but often used in the chemotherapy of cancer ( e.g., nitrogen mustards and carmustine).
- antianxiety a. a functional category of drugs useful in the treatment of anxiety and able to reduce anxiety at doses that do not cause excessive sedation. The majority of commonly used drugs falling into this category are benzodiazepines, which act at the γ-aminobutyric acid (GABA) receptor sites. Historically, barbiturates were the main agents in this category; a newer category, which acts at serotonin (5-HT1A) receptor sites, is currently represented by buspirone. SYN: anxiolytic (1), minor tranquilizer.
- antidyskinetic a. a functional category of drugs with anticholinergic action, used to treat Parkinson disease and some of the acute movement disorders that may be caused by antipsychotic agents.
- antifoaming agents chemicals that lower surface tension (hence production of foam), used in laboratory evaporations, and also administered with oxygen to relieve the respiratory obstruction aggravated by the foam of edema fluid in pulmonary edema (pulmonary surfactant).
- antipsychotic a. a functional category of neuroleptic drugs that are helpful in the treatment of psychosis and have a capacity to ameliorate thought disorders. SYN: antipsychotic (1), major tranquilizer.
- atypical antipsychotic a. a functional category of newer antipsychotic drugs thought to exert their action predominantly via serotonergic blockade.
- Bittner a. SYN: mammary tumor virus of mice.
- blister a.
- blocking a. a class of drugs that inhibit (block) a biologic activity or process, such as axonal conduction or transmission, access to a receptor, or movement of ions across a cell membrane; frequently called “blockers.”
- calcium channel-blocking a. a class of drugs that have the ability to inhibit movement of calcium ions across the cell membrane; of particular value in the treatment of cardiovascular disorders because of pharmacologic effects such as depression of mechanical contraction of cardiac and smooth muscle and of both impulse formation and conduction velocity ( e.g., verapamil, nifedipine). SYN: calcium antagonist, slow channel-blocking a..
- cholinergic a. an a. that mimics the action of acetylcholine or of the parasympathetic nervous system ( e.g., methacholine).
- contrast a. SYN: contrast medium.
- cycle-specific a. an a. that has effect in only one part of the cell cycle (S phase) or only when the cell is in a specific part of the cell cycle.
- delta a. SYN: hepatitis D virus.
- Eaton a. SYN: Mycoplasma pneumoniae.
- embedding agents materials such as celloidin, paraffin, etc. in which specimens of tissue are set before being cut into sections for microscopic examination.
- F a. obsolete term for F plasmid.
- fertility a. obsolete term for F plasmid.
- foamy agents SYN: foamy viruses, under virus.
- ganglionic blocking a. an a. that impairs the passage of impulses in autonomic ganglia ( e.g., tetraethylammonium, trimethaphan).
- high osmolar contrast a. ionic water-soluble iodinated contrast medium. SYN: high osmolar contrast medium.
- initiating a. initiation.
- inotropic agents drugs that increase the force of contraction of cardiac muscle; examples include digitalis glycosides, amrinone, and epinephrine.
- LDH a. SYN: lactate dehydrogenase virus.
- low osmolar contrast a. (LOCA) nonionic water-soluble radiographic contrast material. SYN: low osmolar contrast medium, nonionic contrast a..
- luting a. a fastening material or cement; e.g., plaster or wax to hold casts to an articulator, or material to hold crowns to teeth.
- mood stabilizing a. a functional category of drugs used to normalize mood, particularly by dampening mood swing s ( e.g., lithium and some anticonvulsants such as carbamazepine and valproic acid).
- neuromuscular blocking agents a group of drugs that prevent motor nerve endings from exciting skeletal muscle. They act either by competing for the neurotransmitter, acetylcholine (like D-tubocurarine, mivacurium, and pancuronium), or by first stimulating the postjunctional muscle membrane and subsequently desensitizing the muscle endplates to the acetylcholine (like succinylcholine or decamethonium); used in surgery to produce paralysis and facilitate manipulation of muscles.
- non–cycle-specific a. a. that has effect regardless of where the cell is in its division cycle.
- nondepolarizing neuromuscular blocking a. a compound that paralyzes skeletal muscle primarily by inhibiting transmission of nerve impulses at the neuromuscular junction rather than by affecting the membrane potention of motor endplate or muscle fibers ( e.g., curare, gallamine, vecuronium).
- nonionic contrast a. SYN: low osmolar contrast a..
- Norwalk a. a strain of epidemic gastroenteritis virus that belongs to the calciviruses. [Norwalk, Ohio, where first implicated in disease]
- Pittsburgh pneumonia a. SYN: Legionella micdadei.
- promoting a. promotion.
- psychotropic a. a chemical compound that influences the human psyche.
- reovirus-like a. SYN: rotavirus.
- sclerosing a. a compound that acts by irritation of the veinous intimal epithelium; used in the treatment of varicose veins.
- slow channel-blocking a. SYN: calcium channel-blocking a..
- transforming a. 1. SYN: mitogen. 2. virus that can transform cells.
- TRIC agents strains of Chlamydia trachomatis that cause trachoma and inclusion conjunctivitis agents See Chlamydia trachomatis.
- typical antipsychotic a. a functional category of older antipsychotic drugs thought to exert their action predominantly via dopaminergic blockade.

* * *

agent 'ā-jənt n
1) something that produces or is capable of producing an effect
2) a chemically, physically, or biologically active principle see OXIDIZING AGENT, REDUCING AGENT

* * *

(aґjənt) [L. agens acting] any power, principle, or substance capable of producing an effect, whether physical, chemical, or biological.

Medical dictionary. 2011.

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