Patient undergoing surgery was given a muscle relaxant. It produced marked fall in B.P. and increase in airway resistance which were reversed with diphenhydramine. The muscle relaxant was most probably:

Hypotension and bronchoconstriction (increase in airway resistance) are impoant adverse effects caused by histamine. This is confirmed to be due to histamine because of reversal with diphenhydramine. * Maximum histamine release is caused by d-tubocurarine. * Vecuronium does not cause histamine release, therefore is preferred agent in asthmatic patients.