Medroxyprogesterone acetate does not induce antipyrine clearance and only weakly increases alpha 1-acid glycoprotein in beagle dogs.

The synthetic progestin medroxyprogesterone acetate (MPA) has previously been shown to be an inducer of hepatic microsomal cytochrome P-450 in both man and the rat. We have assessed the ability of a variety of oral doses of MPA to induce either hepatic cytochrome P-450 as measured by antipyrine clearance or alpha 1-acid glycoprotein (AGP) in beagle dogs. Over the range of 25 mg/d to 400 mg/d, MPA did not induce antipyrine clearance. The concentration of AGP only increased at the 400 mg/d level, and was effected to a much smaller extent than has been previously observed for other inducing agents. MPA was also tested as a promoter of induction by combining it with a course of rifampin capable of substantially elevating both antipyrine clearance and AGP. MPA was without effect. The results of these experiments are discussed in light of the toxicology of MPA in beagles.