Testosterone enanthate

Single-dose pharmacokinetics oftestosterone enanthate after intramuscular administration of 250 mg testosterone enanthate to seven hypogonadal patients and the best-fitted pharmacokinetic profile are shown in Fig. 14.6 (Nieschlag etal. 1976). Maximal testosterone levels in the supraphysiological range were seen shortly after injection (39.4 nmol/l, tmax = 10 h). Testosterone levels below the normal range were observed following day 12 after injection. The calculated values were 9911 nmol * h/l for AUC, 8.5 d for MRT and 4.5 d for terminal half-life (Table 14.2).

Based on the pharmacokinetic parameters of single-dose pharmacokinetics multiple-dose pharmacokinetic simulations for equal doses of 250 mg testosterone enanthate and injection intervals of one to four weeks were performed. With weekly injection intervals supraphysiological maximal testosterone serum concentrations up to 78 nmol/l are observed at steady state shortly after injection and supraphys-iological minimal testosterone serum concentrations up to 40 nmol/l just before the next injection (Fig. 14.7). Injecting 250 mg of testosterone enanthate every two

Testosterone Enanthate Pharmacokinetics

Fig. 14.6 Single-dose pharmacokinetics of testosterone enanthate in seven hypogonadal patients.

Closed circles, mean ± SEM of testosterone serum concentrations actually measured; curve, best-fitted pharmacokinetic profile.

Fig. 14.6 Single-dose pharmacokinetics of testosterone enanthate in seven hypogonadal patients.

Closed circles, mean ± SEM of testosterone serum concentrations actually measured; curve, best-fitted pharmacokinetic profile.

Testosterone Enanthate Pharmacokinetics

Fig. 14.7 Multiple-dose pharmacokinetics of testosterone enanthate after injection of 250 mg testosterone enanthate every week (upper panel), every second week (upper middle panel), every three weeks (lower middle panel) and every four weeks (lower panel). Solid curves, pharmacokinetic simulations; broken lines, range of normal testosterone values.

Fig. 14.7 Multiple-dose pharmacokinetics of testosterone enanthate after injection of 250 mg testosterone enanthate every week (upper panel), every second week (upper middle panel), every three weeks (lower middle panel) and every four weeks (lower panel). Solid curves, pharmacokinetic simulations; broken lines, range of normal testosterone values.

weeks results in maximal supraphysiological testosterone serum concentrations of up to 51 nmol/l shortly after injection and testosterone serum levels at the lower range for normal testosterone serum concentration shortly before the next injection. If the injection interval is extended to three weeks, testosterone serum concentrations below the normal range are observed 14 days after injection. With injection intervals of four weeks, testosterone serum concentrations are in the subnormal range at week three and four and effective testosterone substitution is not guaranteed (Fig. 14.7).

The calculated testosterone serum concentrations at steady state obtained by computer simulation correspond well to the results of published studies describing multiple-dose testosterone enanthate pharmacokinetics. In a clinical trial for male contraception 20 healthy men were injected with 200 mg/wk of testosterone enanthate for 12 weeks (Cunningham et al. 1978). Minimal serum concentrations of testosterone at steady state, i.e. the testosterone serum concentration just before the next injection, were measured at 31.2 nmol/l to 39.5 nmol/l after weekly injections of200 mg testosterone enanthate. Very similar data were obtained in further contraceptive studies when normal men received 200 mg/wk testosterone enanthate injections for 18 months (Anderson and Wu 1996; Wu et al. 1996). The data of these studies fit well with the computer-calculated minimal testosterone serum concentrations of 40 nmol/l and maximal testosterone levels 78 nmol/l after multiple injections of testosterone enanthate at a dosage of 250 mg/wk.

Snyder and Lawrence (1980) administered 100 mg/wk (n = 12), 200 mg/2 wks (n = 10), 300 mg/3 wks (n = 9) and 400 mg/4 wks (n = 6) testosterone enanthate to hypogonadal patients during a study period of three months. Blood was drawn during the last injection period, when steady state had been reached, every day (100 mg/wk) up to every fourth day (400 mg/4 wks). Similar to the computer simulation described above for 250 mg testosterone enanthate and injections intervals of one to four weeks, initial supraphysiological testosterone serum levels were seen shortly after injection. In the 100 mg/wk treatment group, where daily blood sampling was performed, mean peak serum concentrations were seen 24 h after injection. Comparable to the results of the computer simulation, after injection of 200 mg/2 wks testosterone enanthate, following initial supraphysiological testosterone serum levels, values fell to progressively lower values before the next injection, eventually reaching the lower normal limit (Snyder and Lawrence 1980). Similar results were described after injection of 300 mg/3 wks or 400 mg/4 wks testosterone enanthate. The authors conclude that the testosterone enanthate doses of 200 mg have to be injected every two weeks or doses of 300 mg every 3 weeks to guarantee effective substitution therapy.

Fig. 14.8 Comparative pharmacokinetics of 194 mg of testosterone enanthate and 200 mg of testosterone cypionate after intramuscular injection to 6 normal volunteers. Closed circles, mean ± SEM of testosterone enanthate kinetics; open circles, mean ± SEM of testosterone cypionate kinetics.

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