Characterization of the Pharmacokinetics and Mass Balance of a Single Oral Dose of Trofinetide in Healthy Male Subjects.

Background and objective: Trofinetide is the first drug to be approved for the treatment of Rett syndrome, a neurodevelopmental disorder. The purpose of the study is to fully characterize the metabolic and excretion profiles of trofinetide in humans.

Methods: This Phase 1, open-label, single-dose trial conducted in healthy male adults was designed to characterize the pharmacokinetics of trofinetide (absorption, metabolism, and excretion), mass balance of [¹⁴C]-trofinetide, and safety profile of trofinetide following administration of an oral 12-g dose administered as a mixture of trofinetide and [¹⁴C]-trofinetide. Blood, urine, and fecal samples were collected at prespecified timepoints. The pharmacokinetics of trofinetide were assessed in blood and urine samples using high-performance liquid chromatography (HPLC) with tandem mass spectrometric detection. Bioanalysis of radioactivity was conducted in blood, plasma, urine, and fecal samples using liquid scintillation counting. Metabolite profiling was conducted in blood, plasma, urine, and fecal samples using HPLC with liquid scintillation counting of chromatographic fractions. Safety and tolerability, including treatment-emergent adverse events (TEAEs), were assessed.

Results: Blood concentration-time profiles of trofinetide and total radioactivity were almost superimposable up to ~12 h after dosing. Urine concentration-time profiles of trofinetide and total radioactivity were similar. Trofinetide was rapidly absorbed into the circulation with an initial rapid decline (half-life [t_½] _alpha ~2.6 h), followed by a relatively slow terminal elimination phase (t_{½ beta} ~20 h). The blood-to-plasma total radioactivity ratios were 0.529-0.592, indicating a lack of affinity for the cellular portion of blood. Renal excretion accounted for 83.8% of the administered radiochemical dose; 15.1% was recovered in feces. Urine and fecal recovery of radioactivity accounted for 99% of the administered dose at 168 h after dosing. Parent [¹⁴C]-trofinetide was the major radiolabeled entity in blood and plasma (88.4% and 93.1% in area under the concentration-time curves from 0 to 12 h [AUC_0-12] in pooled blood and plasma samples, respectively) and the major entity excreted in urine (91.5% in 0-48-h pooled urine samples) and in feces (52.7% in 0-192-h pooled fecal samples). Only small levels of metabolites were present. In blood and plasma, only two minor metabolites were identified (each metabolite ≤ 2.24% of the AUC_0-12 pool). These two metabolites were also observed in urine and fecal samples (≤ 2.41% of dose). In feces, one additional metabolite (0.84% of dose) was identified. Two mild TEAEs were reported in two participants and were not considered related to trofinetide. There were no clinically meaningful changes in individual laboratory parameters, vital signs, physical findings, or electrocardiogram results.

Conclusions: Metabolic and excretion profiles confirm that trofinetide undergoes minimal hepatic or intestinal metabolism and is primarily excreted unchanged in the urine. Trofinetide containing radiolabeled [¹⁴C]-trofinetide was well tolerated.