Irritant terpenoids

The terpenoids usually play a role in the growth or the defence of the organism that contains them. That is why some terpenoids are toxic, irritant or allergenic and some are repellent smelling (small terpenes)... 

Drugs in this category usually induce healing in chronic inflammatory processes of the mucous membranes of the respiratory tract. These mostly comprise of mildly irritating volatile terpenoid oils and phenolic compounds based on creosote that may be inhaled and augment repair in the inflammed areas of the bronchis. 

The lower terpenoids are relatively nonspecific toxicants produced in the defensive secretions of many insects (Fig. 19.17) (Herout, 1970 Harbome, 1982). These compounds are volatile and this may be important in the mechanism of action. The vapors often have an irritating action. 

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