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Thorax. 1987 Jan;42(1):59-64.

Pharmacokinetics of contraceptive steroids in patients with cystic fibrosis.


The pharmacokinetics of the commonly used contraceptive steroids ethinyloestradiol and levonorgestrel were investigated after oral and intravenous administration in six women with cystic fibrosis. The results were compared with data obtained from healthy women of similar age. The total body clearance of ethinyloestradiol was significantly higher in the patients with cystic fibrosis (0.61 (SD 0.19) l/h/kg) than in control women (0.32 (0.16) l/h/kg; p less than 0.02). In addition, the oral bioavailability of ethinyloestradiol was greater in women with cystic fibrosis than in controls (76.9% (11.7%) compared with 47.3% (7.5%); p less than 0.001). As a result of these two changes, the area under the plasma concentration--time curve after an oral dose of ethinyloestradiol was similar in patients and controls. The pharmacokinetics of levonorgestrel did not differ significantly between patients with cystic fibrosis and healthy women. The data suggest that women with cystic fibrosis will receive similar contraceptive protection from these steroids as do healthy women.


The pharmacokinetics of the contraceptive steroids ethinyl estradiol and levonorgestrel following oral an intravenous administration were investigated in 6 women with cystic fibrosis. The results were compared with data from healthy controls of similar ages. The bioavailability of ethinyl estradiol was significantly greater in women with cystic fibrosis (76.9%) than in controls (47.3%), but the area under curve after oral administration was similar in both groups. There was a significantly greater total body clearance in women with cystic fibrosis (0.61 1/hr/kg) than in controls (0.32 1/hr/kg). The volume of distribution was not significantly different in patients and controls; thus there was a tendency (nonsignificant) for the elimination half-life and area under curve after the intravenous dose to be less in the women with cystic fibrosis. In terms of levonorgestrel, there were no significant differences between subjects and controls in any of the pharmacokinetic variables studied. These results suggest that the absorption of ethinyl estradiol and levonorgestrel is not impaired by cystic fibrosis. Women with this disease will achieve plasma concentrations of these steroids after an oral dose of a combined oral contraceptive similar to those obtained in healthy women. However, patients with cystic fibrosis should be monitored closely while taking the pill to ensure that vaginal blood loss is regular with no evidence of breakthrough bleeding.

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