Thiopentone is C/I in:

A i.e. Acute intermittent porphyria - In porphyria (AIP), barbiturates (eg thiopentone, methohexital & thiamylal), etomidate, pentazocine and ropivacaine are avoided/ contraindicatedQ whereas diclofenac, ketorolac, phenacetin, tilidine, chlordiazepoxide, nitrazepam, hydralazine, nifedipine, and phenoxybenzamine are used with extreme caution only. Barbiturate (Thiopentone) induces aminolevulenic acid synthetase & formation of porphyrin which may precipitate actue intermittent or variegate prophyriaQ. ; so it is contraindicated in porphyria.Q - Due to cholinergic nerve stimulation, histamine release or direct bronchial smooth muscle stimulation, barbiturates may cause bronchospasm; which would be preventable by pretreatment with atropine, so it is not C/I in asthma.