Clomiphene citrate: the case for a monoisomeric preparation

Pharmacology and clinical applications of selective estrogen receptor modulators

Compounds that can be described as selective estrogen receptor modulators (SERMs) have expanded dramatically over the past two decades. The ability of SERMs to act as estrogens in certain tissues while remaining inert or acting as an anti-estrogen in other tissues has opened up opportunities for treating specific estrogen-modulated diseases without accepting the risk of systemic estrogen activity. SERM development has resulted in significant therapeutic advances for breast cancer, osteoporosis and potentially other diseases associated with the menopause. After the publication of the Women's Health Initiative, interest in compound selectivity that reduces menopausal symptoms while protecting bone, breast, uterus and the heart has increased. Future SERMs may also have a therapeutic profile that can be tailored to specific patient populations, including men. This review paper summarizes the characteristics of different SERMs from various pharmacological categories and the feasibility and scope of their use for a large range of disease/health conditions.

Single-dose pharmacokinetic study of clomiphene citrate isomers in anovular patients with polycystic ovary disease

The pharmacokinetics of the zuclomiphene (Zu) and enclomiphene (En) isomers of clomiphene citrate following a single oral dose (50 mg) were characterized for the first time in patients receiving the drug (ie, infertile women with polycystic ovary syndrome). Plasma concentrations of Zu and En were measured in 9 patients from the second day of their menstrual cycle (day 1 of dosing) up to 21 days. The mean (+/- coefficient of variation) of C(max), t(max), and AUC of Zu was 15 +/- 41 ng/mL, 7 +/- 87 h, and 1289 +/- 34 ng/mL.h (AUC(0-456 h)), and that of En was 15 +/- 18 ng/mL, 3 +/- 68 h, and 65 +/- 35 ng/ml.h (AUC(0-72h)), respectively. These parameters appeared to be different for Zu from those reported previously in healthy participants, except for t(max). The pharmacokinetic parameters of En in patients with polycystic ovary syndrome were not generally different from the healthy subjects. The effect of obesity on Zu kinetics was stronger than that on En. The conventional model-dependent pharmacokinetics of clomiphene citrate isomers could not be determined due to a very flat terminal half-life and the long-tailed residence time, signifying the lipophilic nature and potentially extensive distribution of the compound.

Monitoring plasma concentrations to individualize treatment with clomiphene citrate

OBJECTIVE

Recent reports have indicated that a number of individual patient characteristics are responsible for the success or failure of clomiphene citrate treatment. However, a priori individualization of doses in different patients has not been investigated. We examined the thesis that wide variability in the metabolism of the active component (zuclomiphene) contributes to variability in response.

METHODS

The dose-response relationship of clomiphene was established from a meta-analysis of data from 13 published reports. Limited data relating plasma drug concentrations to treatment outcome were examined to determine whether insufficient systemic exposure at a fixed dosage might contribute to therapeutic failure.

RESULTS

A fixed-dosage regimen of 50 mg clomiphene per day is likely to cause ovulation in only 46% of patients; subsequent increment in dosage increases the number of responders but at the expense of considerable delay in individualization of treatment. Case reports indicated that dosage based on plasma drug concentration monitoring could improve patient management, and an algorithm is proposed to facilitate treatment.

CONCLUSIONS

Prospective studies of clomiphene citrate should be performed to confirm the hypothesis that the monitoring of plasma zuclomiphene concentrations can significantly accelerate dose individualization and improve the therapeutic outcome with this "orphan" drug.

Polycystic ovary syndrome and ovulation induction

Before initiating treatment to induce ovulation in cases of PCOS, an appropriate evaluation of the patient and her partner, based on individual considerations, is important to optimize outcome. For obese patients with PCOS, weight-loss measures should be pursued before pharmacologic treatment is initiated. For most patients, the pharmacologic agent of choice to induce ovulation is clomiphene citrate, alone or in combination with a glucocorticoid. Treatment with metformin, alone or in combination with clomiphene citrate, may also be beneficial. For patients not responsive to clomiphene citrate, injectable gonadotropin treatment is usually warranted, although, depending on individual circumstances, laparoscopic ovarian drilling may be appropriate.