The effect of oral contraceptive steroids and enzyme inducing drugs on sex hormone binding globulin capacity in women [proceedings

Abstract

An improved assay for sex hormone binding globulin (SHBG) was used to confirm previously published results on the accumulation of SHBG in a group of 3 women starting oral contraceptive therapy with Minovlar. In all 3 women both SHBG and norethisterone concentrations increased 2-3 fold during the first cycle and in a woman studied for 3 months levels were stable by the end of the second cycle. A positive correlation was found between SHBG capacity and norethisterone concentration in all women. An animal model was also developed in which ethinyl estradiol was given orally to rabbits (50 mcg/kg) and goats (500 mcg) for 19 days with blood sample collections on alternate days. No increase in SHBG capactiy in either species was observed. 11 women were investigated to determine the effects of known enzyme-inducing drugs in women taking long-term oral contraception. Long-term therapy with phenobarbitone primidone phenytoin and carbamazepine was combined with an oral contraceptive of either 30 or 50 mcg of ethinyl estradiol. In women taking 30 mcg the SHBG capacity was significantly higher than in controls receiving only the oral contraceptives (P < .05). Similar results occurred in women taking 50 mcg of ethinyl estradiol. 8 women on long-term rifampicin therapy for tuberculosis and who were not on oral contraceptives had SHBG capacity measured 1 month before cessation of therapy and 1 month after stopping rifampicin and the capacity was significantly higher during rifampicin intake (P < .0005). SHBG capacity appears to be increased by drugs known to be enzyme-inducing agents.