Serum concentrations of enclomiphene and zuclomiphene across consecutive cycles of clomiphene citrate therapy in anovulatory infertile women

Objective: To determine the serum concentrations of enclomiphene and zuclom iphene across consecutive cycles of clomiphene citrate treatment in anovula tory infertile women. Design: Prospective cohort. Setting: Tertiary institutional infertility clinic. Patient(s): Fourteen consenting anovulatory infertile women receiving stand ardized, cyclic, incremental treatment with clomiphene citrate for ovulatio n induction. Intervention(s): Clomiphene citrate treatment (50-150 mg/d, cycle days 5-9) , titrated to the minimum effective ovulation-inducing dose, was administer ed for three to six total cycles. Blood samples were obtained on cycle days 3 and 10 in each treatment cycle. Main Outcome Measure(s): Serum concentrations of enclomiphene and zuclomiph ene. Result(s): Cycle day 3 zuclomiphene levels were below assay limits in all i nitial cycles, increased progressively across three consecutive cycles, and thereafter plateaued. Cycle day 3 enclomiphene concentrations were uniform ly undetectable. Cycle day 10 enclomiphene levels increased with dose admin istered, but these observations were not statistically significant. Conclusion(s): Clomiphene citrate induction of ovulation results in an isom er-specific systemic accumulation of zuclomiphene across consecutive cycles of treatment. The combined maximum concentration of enclomiphene and zuclo miphene attained in practice approximates 100 nmol/L and is generally well below levels previously demonstrated to have adverse effects in vitro. (Fer til Steril(R) 1999;71:639-44. (C)1999 by American Society for Reproductive Medicine.).