Principle of Drug Action
The basic type of drug action can be broadly classified as
i) Stimulation: It is selective enrichment of the level of activity of particular cells. E.g. pilocarpine stimulate salivary glands, so, increase salivary secretion and adrenaline stimulate heart.
ii) Depression: It is selective reduction of activity of particular cells. E.g. barbiturates depress CNS, quinidine depress heart.
iii) Irritation: This is non selective effect and is particularly applied to less specialized cells. Mild irritation may stimulate associated function. E.g. bitters increase salivary and gastric secretion and counterirritants increase blood flow to the site. But strong irritation sometimes causes morphological damage.
iv) Replacement: This is used in deficiency states of hormones, enzymes, microelements, major elements and vitamins. E.g. levodopa in parkinsonism, iron in anaemia and insulin in diabetes mellitus.
v) Cytotoxic Action: Selective cytotoxic action for invading parasites or cancer cells, attenuating them without affecting the host cells. E.g. mebendazole, penicillin, chloroquine, cyclophosphamide etc.