Effects of dl-tranylcypromine on LD50 of pentobarbital in the rat.

The LD50 of pentobarbital has been determined in rats with or without pretreatment with dl-, d- or l-tranylcypromine (5 mg/kg, i.p.). The LD50 of pentobarbital was reduced to almost one half by d- or dl-tranylcypromine as compared with the l-isomer. It is concluded that dl-tranylcypromine enhances pentobarbital toxicity by inhibition of its metabolism.