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Single Time Point Total Testosterone to Predict 24-Hour Average Concentration of Total Testosterone in Hypogonadal Men Treated with an Oral Testosterone Undecanoate Softgel (JATENZO®)
Ronald Swerdloff, MD1, Christina Wang, MD1, Marc Gittelman, MD2, B Woun Seo, PhD3, Jay Newmark, MD3, Nestor Rohowsky, MA4, Robert Dudley, PhD3.
1Lundquist Institute at Harbor-UCLA, Torrance, CA, USA, 2Uro-Medix and South Florida Medical Research, Aventura, FL, USA, 3Clarus Therapeutics, Northbrook, IL, USA, 4Integrated Data Consultation Services, Lagrange, IL, USA.

BACKGROUND: In 2019, a novel, first-in-class testosterone (T) replacement therapy (TRT), oral testosterone undecanoate (TU) was approved by the U.S. FDA for the treatment of male hypogonadism. During clinical trials, dose adjustments were based on 24-hr average T concentration (Cavg) because single T measurements were considered less accurate. Subsequent, concordance analyses for this oral TU product have shown that a single total T value 6 hrs after the morning oral TU dose best corresponds to Cavg. Nonetheless, a conversion factor for T values obtained at other post-dose time points would be useful for healthcare providers (HCPs) and ease potential scheduling challenges for patients. Consequently, the relationship between other T sampling time points and Cavg was examined to determine if a reliable conversion factor could be derived to help HCPs monitor a patient's serum T concentration at times other than 6 hrs after oral TU administration.
METHODS: Hypogonadal men, age 18 - 65 y/o, were recruited into a randomized, open-label, multicenter, dose-titration trial. Overall, 166 men were randomized into the oral TU arm. Dose titration was based on Cavg calculated from serial pharmacokinetic (PK) samples. There were three pre-designated PK visits, to individualize the appropriate TU dose and to achieve a eugonadal T Cavg at final study visit. Ratios between different timepoints and Cavg were determined for PK samples following morning drug administration.
RESULTS: Overall, 87.3% (95% CI: 81.3%, 92.0%) of hypogonadal men had a final Cavg in the eugonadal range, with a mean serum total T = 488.7 ± 154.5 ng/dL (16.95 ± 5.37 nmol/L). Pooled values from all PK days demonstrated a linear relationship between T concentrations at 4, 6, and 9 hrs and Cavg (p < 0.0001). Visit and time of sampling interaction were not statistically significant (p >> 0.50), indicating consistency in results among PK visits and among sampling timepoints. A factor was derived to enable conversion of T values assessed at a time other than 6 hrs (post oral TU dose) into a close approximation of Cavg: 1/[1.870 - 0.14 x (hours after AM dose)]. Therefore, a sample drawn at 4 hrs after the morning oral TU dose would be multiplied by 0.75; while one drawn at 8 hrs would be multiplied by 1.33.

Hours after Dose Oral TU AdministrationConversion Factor to Normalize T Value to Cavg

CONCLUSIONS: T Cavg can be approximated after morning JATENZO administration if a blood sample cannot be collected precisely 6 hrs thereafter.

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