Importance of Measuring Testosterone in Enzyme-Inhibited Plasma for Oral Testosterone Undecanoate Androgen Replacement Therapy Clinical Trials

Abstract

Aim:Testosterone undecanoate (TU) is metabolized by nonspecific esterases in blood to testosterone (T). Typical clinical practice has been to analyze testosterone in human serum. The degradation of TU to testosterone was evaluated in conditions typically used in clinical studies.Methods & Results:Freshly collected whole blood was fortified with TU at known concentration. Serum was prepared and T concentration was determined by LC–MS/MS. It was observed that TU degrades extensively to T in human blood under conditions typical of harvesting serum causing overestimation of T concentration of up to 243%. These results were confirmed in a clinical study in which serum and plasma samples were compared.Conclusion:It was demonstrated that T must be analyzed in enzyme-inhibited plasma when TU is the administered medication.

Accurate measurement of androgen after androgen esters: problems created by ex vivo esterase effects and LC‐MS/MS interference

“…We previously demonstrated that non‐specific esterases in blood cells can convert the T ester, T enanthate, to T in blood and may affect the accuracy of the measured T concentration (Wang et al ., ). When TU added to blood was allowed to stand at RT, the T concentration measured in the serum was higher than the initial T concentration (Lachance et al ., ). The results of our earlier study showing that TU added to blood had little effect on T measurements were erroneous and were probably due to the insolubility of TU in aqueous solutions (Wang et al ., , ; Lachance et al ., ).…”

“…When TU added to blood was allowed to stand at RT, the T concentration measured in the serum was higher than the initial T concentration (Lachance et al ., ). The results of our earlier study showing that TU added to blood had little effect on T measurements were erroneous and were probably due to the insolubility of TU in aqueous solutions (Wang et al ., , ; Lachance et al ., ). All our ex vivo spiking experiments showed significant concentration‐dependent ester hydrolysis when steroid esters (TU and DMAU) were added to the blood, resulting in increased measured T or DMA.…”

“…While the results differed slightly between TU and DMAU, NaF‐Oxalate or NaF‐EDTA appeared to deliver the most consistent results in all experiments. These findings are consistent with previously conducted studies (Lachance et al ., ).…”

“…Hence, in efficacy studies of oral TU, the most appropriate blood collection tube is one containing NaF when TU concentrations are high as has been noted by Lachance et al . (). Overestimation of T may have a clinical impact on hypogonadal men who are replaced with oral TU and whose T concentrations are based on blood collected into, for example, plain tubes.…”

“…Thus, in patients administered T esters, the measured T level may not only reflect circulating T but also the ex vivo conversion of the prodrug to the active androgen. This may confound hormone level evaluations as has previously been shown in the measurement of T enanthate (Wang et al ., ) and T undecanoate (TU) (Lachance et al ., ). Inaccurate estimation of circulating T levels may lead physicians to make improper dose adjustments in hypogonadal men treated with a T ester such as T enanthate, cypionate, and undecanoate because T levels in blood that are typically collected in plain tubes may yield falsely high T levels due to ex vivo conversion of T esters to T.…”