| H2 blocker | <pharmacology> A class of anti-ulcer medication which work through the inhibition of basal and nocturnal gastric acid secretion by competitive inhibition of the action of histamine at histamine H2 receptor sites on the parietal cells. Drugs of this type block gastric acid secretion and are therefore clinically useful in treating duodenal ulcers. Examples include cimetidine (Tagamet), famotidine (Pepcid), nizatidine (Axid) and ranitidine (Zantac). (27 Sep 1997) |
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| alpha blocking | The attenuation of the occipital alpha rhythm (8-14 Hz brain waves as seen on an electroencephalogram), produced by opening the eyes or by intense mental concentration. (05 Mar 2000) |
| antibodies, blocking | Antibodies that inhibit the reaction between antigen and other antibodies or sensitised T-lymphocytes (e.g., antibodies of the IgG class that compete with IgE antibodies for antigen, thereby blocking an allergic response). Blocking antibodies that bind tumours and prevent destruction of tumour cells by cytotoxic T-lymphocytes have also been called enhancing antibodies. (12 Dec 1998) |
| blocking | 1. Obstructing; arresting of passage, conduction, or transmission. 2. In psychoanalysis, a sudden break in free association occurring when a painful subject or repressed complex is touched. 3. Sudden cessation of thoughts and speech, which may indicate the presence of a severe thought disorder or a psychosis. (05 Mar 2000) |
| blocking activity | The repression or elimination of electrical activity in the brain by the arrival of a sensory stimulus. (05 Mar 2000) |
| blocking antibody | An antibody used in a reaction to prevent some other reaction taking place, for example one antibody competing with another for a cell surface receptor. See: desensitisation. (18 Nov 1997) |
| Rh blocking test | A test for nonagglutinating Rh antibodies: an Rh agglutination test is first carried out; if the test for Rh agglutinins is negative, then 1 drop of anti-Rho agglutinating serum of moderate titre is mixed with the patient's serum containing Rh-positive test cells; if after incubating for from 1 to 2 hr at 37캜 no agglutination occurs, Rho-blocking antibodies are assumed to be present in the patient's serum. (05 Mar 2000) |
| spermatogenesis-blocking agents | Chemical substances which inhibit the process of spermatozoa formation at either the first stage, in which spermatogonia develop into spermatocytes and then into spermatids, or the second stage, in which spermatids transform into spermatozoa. (12 Dec 1998) |
| neuromuscular blocking agents | Drugs that interrupt transmission of nerve impulses at the skeletal neuromuscular junction. They can be of two types, competitive, stabilizing blockers (neuromuscular nondepolarising agents) or noncompetitive, depolarising agents (neuromuscular depolarising agents). Both prevent acetylcholine from triggering the muscle contraction and they are used as anaesthesia adjuvants, as relaxants during electroshock, in convulsive states, etc. (12 Dec 1998) |
| agent | <pharmacology> Any power, principle or substance capable of producing an effect, whether physical, chemical or biological. Origin: L. Agens = acting (18 Nov 1997) |
| agent, antihypertensive | As the name suggests, a drug aimed at reducing high blood pressure (hypertension). (12 Dec 1998) |
| agent, anti-infective | Something capable of acting against infection, by inhibiting the spread of an infectious agent or by killing the infectious agent outright. (12 Dec 1998) |
| Agent Orange | An herbicide and defoliant, consisting of (2,4,5-trichlorophenoxy)acetic acid, (2,4-dichlorophenoxy)acetic acid, and dioxin, that was widely used in the Vietnam War; it has been shown to possess residual post-exposure carcinogenic and teratogenic properties in humans. (05 Mar 2000) |
| agent, tocolytic | A medication that can inhibit labour, slow down or halt the contractions of the uterus. Tocolytic agents are widely used today to treat premature labour and permit pregnancy to procede and so let the foetus gain in size and maturity before being born. (12 Dec 1998) |
| alkylating agent | <oncology, pharmacology> A reagent that places an alkyl group, for example propyl in place of a nucleophilic group in a molecule. Alkylating reagents include a number of cytotoxic drugs some of which react fairly specifically with N7 of the purine ring and lead to depurination of DNA, for example the agent ethyl ethanesulphonic acid and thus to mutagenesis. The drugs interaction with DNAand prevents the division of the cells. Examples of drugs include: busulphan, chlorambucil, cyclophosphamide, melphalan. (29 Sep 1997) |