Enclomiphene Citrate Adult (30 to 49) Monitoring: Complete Clinical Guide

Is there an official monitoring schedule?

No. Enclomiphene is not FDA-approved; FDA's own 2022 advisory committee briefing states that no FDA-approved drug contains enclomiphene as an active ingredient [1]. EMA's committee adopted a negative opinion on 25 January 2018 recommending refusal of marketing authorisation for EnCyzix (enclomifene) [4]. With no approval there is no labelled schedule, so the sections below set out what the trials specified and what regulators flagged.

What the trials measured, and when

The two placebo-controlled phase 3 studies, ZA-301 and ZA-302, enrolled overweight men aged 18 to 60 with morning testosterone below 300 ng/dL and normal sperm concentration, and ran for 12 weeks on 12.5 mg or 25 mg daily versus placebo [3][5]. The main readout was average 24-hour testosterone, with a pre-set success bar that the lower confidence limit had to reach at least 67%: 78.8% of pooled enclomiphene patients in ZA-301 (95% CI 70.3 to 85.3, n=113) and 81.3% in ZA-302 (95% CI 73.9 to 87.0, n=134) reached the normal range of 300 to 1040 ng/dL [3][5].

A separate pair of 16-week studies, ZA-304 and ZA-305, compared enclomiphene with AndroGel 1.62% and measured total testosterone, LH, FSH and sperm counts at baseline and after 16 weeks [2]. In those studies sperm concentration stayed in the normal range on enclomiphene, while there was a marked reduction in spermatogenesis on testosterone gel [2].

The endpoints were hormone levels and sperm, not symptom scores. FDA's May 2018 guidance on secondary hypogonadism, as described by FDA in 2022, says trials should show meaningful improvement in at least one symptom or sign and that semen-parameter changes alone are not enough [1], and EMA's assessment noted that the studies showed higher testosterone without looking at whether symptoms improved [4].

Baseline testing in the documents

The diagnosis itself. The Endocrine Society's 2018 guideline on testosterone therapy recommends making a diagnosis of hypogonadism only in men with symptoms and signs of testosterone deficiency and unequivocally and consistently low morning fasting total testosterone, confirmed by repeating the measurement; in men near the lower limit of normal or with a condition that alters sex hormone-binding globulin, it recommends free testosterone by equilibrium dialysis or an accurate formula [8].

LH and FSH. Enclomiphene blocks estrogen receptors in the pituitary, so the pituitary releases more LH and FSH, which tells the testes to make more testosterone and keep making sperm. That mechanism addresses secondary hypogonadism, where the testes are healthy but under-stimulated, and would not be expected to work in primary hypogonadism [1]. ZA-304 and ZA-305 enrolled men with low or normal LH (below 9.4 IU/L) measured on two occasions 2 to 10 days apart [2].

Sperm. In ZA-301, sperm concentration fell by 50% or more in 14.2% of men on enclomiphene versus 2.6% on placebo, and in ZA-302 14.2% versus 4.3% [3][5]. In ZA-304 and ZA-305 men gave semen samples twice at the start and twice at the end of the study [2].

The week-6 draw and titration

The phase 3 protocols used 12.5 mg once daily with up-titration to 25 mg daily at week 6 if morning testosterone stayed below 300 ng/dL [3]. That is the decision rule the protocols attach to a specific timepoint: a morning testosterone at week 6.

Enclomiphene is absorbed rapidly, with a peak about 2 to 3 hours after a dose and a half-life of about 10 hours; it is excreted mainly in feces [1].

Weeks 12 to 16 and after

In ZA-304 and ZA-305 the hormone and semen comparisons were made at 16 weeks [2]; the placebo-controlled studies ran 12 weeks [3][5]. Beyond that window there is little to draw a schedule from. FDA listed the absence of long-term safety data among its concerns [1], and EMA's refusal rested on four main studies in 588 patients [4].

Side effects that appear between lab draws

In the phase 3 and EMA data the most frequent side effects were headache, hot flushes, nausea and muscle spasm, and the reasons men stopped included blurred vision, muscle spasm, headache and aggression [5]. In ZA-302, headache was reported by 7 of 112 men on 12.5 mg versus 1 of 47 on placebo, and nausea by 4 of 112 versus 3 of 47 [5].

The clomiphene label, which covers the older two-isomer mixture and not enclomiphene, lists visual symptoms such as blurring, spots or flashes that increase in incidence with higher total dose and longer duration and are usually reversible but may be irreversible [9]. EMA wanted ocular monitoring for enclomiphene because cataracts appeared in nonclinical studies and were not conclusively linked in people [1].

Hematocrit, PSA and estradiol

In 2022 FDA listed raised hematocrit, raised PSA and raised estradiol among its safety concerns from published trials, adverse event reports and EMA's review; no approved schedule for checking them exists [1]. In a single-centre retrospective review of 66 men who took clomiphene and later enclomiphene, estradiol change was minus 5.92 pg/mL on enclomiphene versus plus 17.50 pg/mL on clomiphene (P=0.001), and side effects were less frequent on enclomiphene (odds ratio 0.18, 95% CI 0.07 to 0.44); the study was not randomized [10].

The cardiac and thromboembolic events on FDA's list include pulmonary embolism and deep vein thrombosis in a safety study [1]. EMA noted a slightly higher rate of cardiac and thromboembolic events than with testosterone [1] and cited venous thromboembolism risk when refusing authorisation [4].

Where the regulatory picture leaves monitoring

FDA sent the sponsor a complete response letter in 2015, which said the design of the phase 3 studies was not adequate to demonstrate clinical benefit and raised concerns about study entry criteria, titration and bioanalytical method validation [1]. No approval has followed [1].

Enclomiphene citrate sits in Category 1 of FDA's bulk substance list, 'Bulk Drug Substances Under Evaluation'. FDA says it does not intend to take action against a compounder using a Category 1 substance if the conditions in its guidance are met; that is an enforcement-discretion policy, not an approval and not a finding that the product is safe or effective [6]. At the June 2022 advisory committee meeting, members voted 4 yes and 8 no on adding enclomiphene citrate to the list of bulk substances allowed in compounding, with those voting no citing lack of clinical efficacy evidence [11].

For the product discussed here, see enclomiphene. Compounded enclomiphene products are not FDA-approved and have not been reviewed by FDA for safety, effectiveness or quality [12].

What the documents specify, point by point

• Entry: morning testosterone below 300 ng/dL (ZA-301 and ZA-302) or 300 ng/dL or lower (ZA-304 and ZA-305), with low or normal LH in the latter and semen samples at the start [2][3].
• Week 6: morning testosterone, the titration point used in the phase 3 protocols [3].
• Week 12: average 24-hour testosterone, the primary endpoint of ZA-301 and ZA-302 [3][5].
• Week 16: total testosterone, LH, FSH and sperm counts in the AndroGel comparison [2].
• Throughout: side effects, of which the most frequent were headache, hot flushes, nausea and muscle spasm [5].