Pharmacodynamics is the study of drug effects. It attempts to elucidate the complete actioneffect sequence and the doseeffect relationship. Modification of the action of one drug by another drug is also an aspect of pharmacodynamics.
PHARMACODYNAMICS
Pharmacodynamics
is the study of drug effects. It attempts to elucidate the complete actioneffect
sequence and the doseeffect relationship. Modification of the action of one
drug by another drug is also an aspect of pharmacodynamics.
Drugs
(except those gene based) do not impart new functions to any system, organ or cell;
they only alter the pace of ongoing activity. The basic types of drug action
can be broadly classed as:
Stimulation
It refers to selective enhancement of the level of activity of
specialized cells, e.g. adrenaline stimulates heart, pilocarpine stimulates
salivary glands. However, excessive stimulation is often followed by depression
of that function, e.g. high dose of picrotoxin, a central nervous system (CNS)
stimulant, produces convulsions followed by coma and respiratory depression.
Depression
It means selective diminution of activity of specialized cells, e.g.
barbiturates depress CNS, quinidine depresses heart.
Certain
drugs stimulate one type of cells but depress the other, e.g. acetylcholine
stimulates intestinal smooth muscle but depresses SA node in heart. Thus, most
drugs cannot be simply classed as stimulants or depressants.
Irritation
This connotes a nonselective, often noxious effect
and is particularly applied to less specialized cells (epithelium, connective
tissue). Mild irritation may stimulate associated function, e.g. bitters
increase salivary and gastric secretion, counterirritants increase blood flow
to the site. But strong irritation results in inflammation, corrosion, necrosis
and morphological damage. This may result in diminution or loss of function.
Replacement
This refers to the use of natural metabolites, hormones or their
congeners in deficiency states, e.g. levodopa in parkinsonism, insulin in
diabetes mellitus, iron in anaemia.
Cytotoxic Action
Selective cytotoxic action for invading parasites
or cancer cells, attenuating them without significantly affecting the host
cells is utilized for cure/palliation of infections and neoplasms, e.g.
penicillin, chloroquine, zidovudine, cyclophosphamide, etc.
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