Here are some studies. Although neither gives a definative half life of t gel/cream, both are interesting...
Department of Endocrinology and Medicine, University of Manchester, Hope Hospital, Salford, United Kingdom.
Although the postmenopausal ovary remains an important source of testosterone (T) production, there is nevertheless a decline in total circulating androgen levels with age. A role for androgen replacement in addition to estrogens in some postmenopausal, particularly ovariectomized, women is increasingly gaining acceptance. We have compared the pharmacokinetics of two existing testosterone preparations, oral testosterone undecanoate (TU) and sc testosterone implants, with a new matrix transdermal delivery system for T. In study 1, three different doses of TU (40 mg, two 20-mg doses 6 h apart and two 10-mg doses 6 h apart, orally) were investigated in 10 postmenopausal women. Median peak levels of 18 nmol/L (range, 5.8-64.0 nmol/L; 40 mg), 12.3 nmol/L (range, 5.7-29.2 nmol/L; 20 mg), and 9.7 nmol/L (range, 7.8-28.7 nmol/L; 10 mg) were observed, but T levels varied considerably within and between subjects regardless of the dose used. In study 2, 30 women receiving s.c. estradiol therapy were randomized to receive either a 100-mg T implant or placebo. In the T-treated group, levels peaked at 8.9 +/- 1.7 nmol/L 1 month after insertion and then declined gradually to 2.9 +/- 0.4 nmol/L at 6 months. In study 3, a novel matrix transdermal delivery system for T was investigated in 6 females. Estimated daily delivery rates of 840 (TD 1), 1100 (TD2), and 3000 microg (TD3) T/24 h were investigated. T rose rapidly after a single application of TD 1 and TD2 and were relatively constant for the next 18 h, at which time peaks of 2.3 +/- 1.0 and 4.1 +/- 1.6 nmol/L, respectively, at 24 h were seen. T concentrations fell to baseline levels within 6 h after patch removal. When TD2 was applied for 7 days, a T level of 4.3 +/- 0.7 nmol was seen 24 h after application, falling gradually to 2.8 +/- 0.7 nmol/L by day 7. During twice weekly application of TD2, stable T concentrations were maintained, and all peak levels were similar (peak level, 4.2 +/- 0.3 nmol/L 24 h post-TD application) as were predose troughs (3.2 +/- 0.3 nmol). Twice weekly application of TD3 produced a similar pattern of T, and the mean peak and trough levels were 7.5 +/- 0.9 and 4.0 +/- 0.4 nmol/L, respectively. In conclusion, TU produced inappropriate high T levels at all doses, with wide variations between subjects, confirming that TU is unpredictably absorbed and unlikely to be satisfactory for use in women. Subcutaneous testosterone implants produce unphysiological T levels for at least 1-2 months. The transdermal matrix delivery system maintained relatively stable T levels within narrow ranges with little within- and between-subject variation. We conclude that such transdermal systems may be of value for androgen therapy in postmenopausal women because they provide a highly controllable way of delivering T noninvasively and reliably, and achieve mean physiological levels not possible with existing methods.
Pharmacokinetics of a transdermal testosterone system in men with end stage renal disease receiving maintenance hemodialysis and healthy hypogonadal men.
Singh AB, Norris K, Modi N, Sinha-Hikim I, Shen R, Davidson T, Bhasin S.
Division of Endocrinology, Metabolism, and Molecular Medicine, Charles R. Drew University of Medicine and Science, Los Angeles, California 90059, USA.
Androgen deficiency is common in men with end stage renal disease (ESRD) on maintenance hemodialysis. Pharmacokinetics of transdermal testosterone in men receiving maintenance hemodialysis have not been studied. Our objective was to compare the pharmacokinetics of a transdermal testosterone system in healthy hypogonadal men and in men with ESRD on maintenance hemodialysis. We recruited 10 healthy hypogonadal men and 8 medically stable men on maintenance hemodialysis, 18--70 yr old, who had serum testosterone less than 300 ng/dL. After baseline sampling during a 24-h control period, two testosterone patches were applied daily for 28 days, to achieve a nominal delivery of 10-mg testosterone daily. In addition to single, pooled samples on days 7, 14, and 21, blood was drawn at 0, 2, 4, 6, 8, and 24 h on day 28 in healthy hypogonadal men and on an interdialytic day (day 21 or 28) as well as a dialysis day (day 21 or 28) in men on hemodialysis. On the dialysis day (day 21 or 28), serum free and total testosterone levels were measured hourly for 4 h before hemodialysis and for 4 h during hemodialysis. The dialysate was sampled for testosterone measurement. Baseline mean + SD total (92 +/- 82 vs. 222 +/- 50 ng/dL) and free (11 +/- 9 vs. 27 +/- 6 pg/mL) testosterone concentrations were lower in healthy hypogonadal men than in men with ESRD. After application of two testosterone patches, serum total and free testosterone concentrations rose into the midnormal range in both groups of men. Time-average, steady state (total testosterone, 506 +/- 88 vs. 516 +/- 86 ng/dL; free testosterone, 55 +/- 9 vs. 67 +/- 11 pg/mL), minimum, and maximum total and free testosterone concentrations were not significantly different between the two groups of men during treatment. Increments in total and free testosterone concentrations above baseline, baseline-subtracted areas under the total and free testosterone curves, and half-life of testosterone elimination (t(1/2), 2.1 +/- 0.1 vs. 2.1 +/- 0.2 h, P = not significant) were not significantly different between the two groups. In men receiving hemodialysis, time-average, steady state, and maximal total and free testosterone concentrations and baseline-subtracted areas under the total and free testosterone curves were higher on dialysis day than on an interdialytic day. On the day of hemodialysis, time-average total and free testosterone concentrations were not significantly different during the 4 h before or during hemodialysis. The amount of testosterone removed in the dialysate (8.4 +/- 1.6 microg during 4 h of hemodialysis) was small compared with the daily testosterone production rates in healthy young men. Serum dihydrotestosterone and estradiol concentrations increased into the normal male range and were not significantly different between the two groups. Percent suppression of LH was greater in men with ESRD than in healthy hypogonadal men. A regimen of two Testoderm TTS testosterone patches (Alza Corp., Mountain View, CA) daily can maintain serum concentrations of total and free testosterone and its metabolites dihydrotestosterone and estradiol in the midnormal range in healthy hypogonadal men and men on hemodialysis. The amount of testosterone cleared by hemodialysis is small, and hemodialysis does not significantly affect serum total and free testosterone concentrations in men treated with the testosterone patch
