Salivary Antipyrine Half-Life During Injectable Progestagen Contraception

Antipyrine pharmacokinetics were studied in 6 healthy women before and 2, 8 and 12 weeks after administering the injectable progestagen (progestin), norethisterone (norethindrone) enanthate 200mg intramuscularly. Additionally, antipyrine kinetics in 5 women who had previously used the injectable contraceptive for 8 to 14 months were compared with values obtained in 14 non-users. Antipyrine was measured in saliva using a spectrophotometry method, following an oral dose of 18 mg/kg bodyweight. In the 6 women studied prospectively the mean salivary antipyrine half-life was 14.91 ± 1.5 hours (SEM) before administering the injection, and 13.56 ± 0.73 at 2 weeks, 15.13 ± 1.86 at 8 weeks and 15.21 ± 2.46 hours at 12 weeks after the injection. The mean antipyrine half-life in the 5 long term users of injectable progestagen was 14.21 ± 2.53 hours compared with 13.66 ± 0.98 hours in non-users. The results of this study suggest that — in contrast to published data on combined oral contraceptives — neither short nor long term use of parenteral norethisterone enanthate in Indian women is associated with significant alterations in antipyrine clearance.