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Testosterone Replacement, Low T, HCG, & Beyond
Testosterone Basics & Questions
Testosterone Enanthate and Testosterone Cypionate Half-Lives - Data?
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<blockquote data-quote="madman" data-source="post: 201463" data-attributes="member: 13851"><p>Regarding half-lives keep in mind that a majority of studies on the PK/PD of the various T-esters were done using IM (once weekly/fortnightly) injections in a small number of subjects and most of the literature is from decades ago.</p><p></p><p>Here is a more recent and in-depth study using TC.</p><p></p><p></p><p></p><p></p><p><strong>Population Pharmacokinetic/Pharmacodynamic Modeling of Depot Testosterone Cypionate in Healthy Male Subjects (2018)</strong></p><p><strong></strong></p><p><strong><em>Youwei Bi Paul J. Perry Touro University California, <a href="mailto:paul.perry@tu.edu">paul.perry@tu.edu</a> Michael Ellerby Touro University California, <a href="mailto:michael.ellerby@tu.edu">michael.ellerby@tu.edu</a> Daryl J. Murry</em></strong></p><p><strong></strong></p><p><strong></strong></p><p><strong></strong></p><p><strong></strong></p><p><strong>DISCUSSION</strong></p><p></p><p><em><strong>Following the depot administration of TC, the PKs of tT were satisfactorily described by the</strong></em><strong> one-compartmental model with first-order absorption. <u><em>The limited number of samples in the absorption phase (1–2 samples per subject) prevents using a more plausible absorption model for the high lipophilicity of testosterone in an oil base and administered i.m., such as a mixed zero-order and first-order model with lag time</em></u><em>.</em></strong></p><p><strong><em></em></strong></p><p><strong><em>*<u>This could lead to flip-flop PKs and can cause difficulties in the estimation and interpretation of PK parameters</u>. The half-life of testosterone undecanoate (TU) following oral administration is around 150 minutes, which is very different from the half-life estimate of 21–34 days following the i.m. injection of TU reported by Behre et al. The large difference in half-lives of TU between oral and i.m. formulation <u>suggests that flip-flop PKs are occurring with testosterone esters, which is also reported in the published literature and for the i.m. injection of nandrolone</u>. </em></strong></p><p><strong><em></em></strong></p><p><strong><em>*The i.m. injection of TC is also likely to have flip-flop kinetics, in such a scenario, <u>diffusion, and release from an oily depot site is the rate-limiting step to systemic availability</u>.</em></strong></p><p></p><p><em><strong>It is difficult to calculate the PK parameters of TC using traditional noncompartmental methods, especially when the endogenous testosterone secretion rate is suppressed during the course of TC administration and the testosterone secretion rate is regulated by the LH-testosterone feedback loop system in the HPG axis. <u>Our estimated post hoc median tT half-life was 4.05 days, which is shorter than the mean reported elimination half-life of 6.9 days determined using noncompartmental analysis</u>. Such inconsistency is believed to result from failure to consider endogenous testosterone production. <u>When we assume endogenous testosterone secretion is 0 in the PPK analysis, the median estimated half-life increases to 6.87 days</u>.</strong></em></p></blockquote><p></p>
[QUOTE="madman, post: 201463, member: 13851"] Regarding half-lives keep in mind that a majority of studies on the PK/PD of the various T-esters were done using IM (once weekly/fortnightly) injections in a small number of subjects and most of the literature is from decades ago. Here is a more recent and in-depth study using TC. [B]Population Pharmacokinetic/Pharmacodynamic Modeling of Depot Testosterone Cypionate in Healthy Male Subjects (2018) [I]Youwei Bi Paul J. Perry Touro University California, [EMAIL]paul.perry@tu.edu[/EMAIL] Michael Ellerby Touro University California, [EMAIL]michael.ellerby@tu.edu[/EMAIL] Daryl J. Murry[/I] DISCUSSION[/B] [I][B]Following the depot administration of TC, the PKs of tT were satisfactorily described by the[/B][/I][B] one-compartmental model with first-order absorption. [U][I]The limited number of samples in the absorption phase (1–2 samples per subject) prevents using a more plausible absorption model for the high lipophilicity of testosterone in an oil base and administered i.m., such as a mixed zero-order and first-order model with lag time[/I][/U][I]. *[U]This could lead to flip-flop PKs and can cause difficulties in the estimation and interpretation of PK parameters[/U]. The half-life of testosterone undecanoate (TU) following oral administration is around 150 minutes, which is very different from the half-life estimate of 21–34 days following the i.m. injection of TU reported by Behre et al. The large difference in half-lives of TU between oral and i.m. formulation [U]suggests that flip-flop PKs are occurring with testosterone esters, which is also reported in the published literature and for the i.m. injection of nandrolone[/U]. *The i.m. injection of TC is also likely to have flip-flop kinetics, in such a scenario, [U]diffusion, and release from an oily depot site is the rate-limiting step to systemic availability[/U].[/I][/B] [I][B]It is difficult to calculate the PK parameters of TC using traditional noncompartmental methods, especially when the endogenous testosterone secretion rate is suppressed during the course of TC administration and the testosterone secretion rate is regulated by the LH-testosterone feedback loop system in the HPG axis. [U]Our estimated post hoc median tT half-life was 4.05 days, which is shorter than the mean reported elimination half-life of 6.9 days determined using noncompartmental analysis[/U]. Such inconsistency is believed to result from failure to consider endogenous testosterone production. [U]When we assume endogenous testosterone secretion is 0 in the PPK analysis, the median estimated half-life increases to 6.87 days[/U].[/B][/I] [/QUOTE]
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Testosterone Replacement, Low T, HCG, & Beyond
Testosterone Basics & Questions
Testosterone Enanthate and Testosterone Cypionate Half-Lives - Data?
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