What happens after 14 weeks of weekly injections of 100 mg, 250 mg and 500 mg of testosterone cypionate when patients stop? No PCT. Young and healthy males.
Nice graphs at the end of the paper (attached). Intensive sampling (finally!)
Testosterone returned to baseline at week 23 (last injection at week 14). So, it took 9 weeks for their HPTA to recover, which I find it to be fast for a 500 mg/week dose exposure for 14 weeks. Subjects were healthy and young, so that may have been the reason.
Population Pharmacokinetic/Pharmacodynamic (PK/PD) Modeling of Depot Testosterone Cypionate
Study Highlights
WHAT IS THE CURRENT KNOWLEDGE ON THE TOPIC?
Long-term excessive dosing of anabolic steroids can lead to serious health risks. One of the most significant physiologic changes induced by the use of testosterone esters is a dose-dependent impairment of normal testicular androgen secretion and spermatogenesis.
WHAT QUESTION DID THIS STUDY ADDRESS?
This study characterizes and quantifies changes in testosterone and luteinizing hormone concentration, and spermatogenesis following long-term testosterone cypionate administration.
WHAT DOES THIS STUDY ADD TO OUR KNOWLEDGE?
The study developed a PK-PD model based on a randomized three-arm (100mg, 250mg, 500 mg/week) clinical trial which quantified the relationship between testosterone exposure after exogenous administration and suppression of LH and spermatogenesis. Model results showed that the suppression of endogenous testosterone secretion, LH synthesis, and spermatogenesis was more severe and of greater duration in 250mg and 500mg dose groups.
HOW MIGHT THIS CHANGE DRUG DISCOVERY, DEVELOPMENT, AND/OR THERAPEUTICS?
This PK/PD model provides a framework to quantify and predict the change in LH and spermatogenesis after exogenous testosterone administration. The average concentration of total testosterone in the past 18 weeks was found to have the strongest association with suppression of spermatogenesis.
Bi Y, Perry PJ, Ellerby M, Murry DJ. Population Pharmacokinetic/Pharmacodynamic (PK/PD) Modeling of Depot Testosterone Cypionate in Healthy Male Subjects. CPT: Pharmacometrics & Systems Pharmacology.
A randomized, double-blind clinical trial was conducted to investigate long-term abuse effects of testosterone cypionate. Thirty-one healthy males were randomized into a dose group of 100, 250 or 500mg/wk and received 14 weekly injections of TC.
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The endogenous testosterone secretion rate returned to baseline at approximately week 23 in all three dose groups.]