Absorption
The pharmacokinetics of XEGLYZE were evaluated in 3 trials, Trials A, B, and C. Each trial enrolled lice infested subjects who received a single 10-minute application of XEGLYZE. Pharmacokinetic samplings were carried out to 72 hours post-dose in adults and 8 hours post-dose in pediatric subjects in all trials.
Trial A evaluated pharmacokinetics in 6 adult and 12 pediatric subjects 3 to 12 years of age. The mean (%CV) abametapir plasma maximum concentration (Cmax) and area under the concentration time curve from 0 to 8 hours post-dose (AUC0-8h) in the adult group were 41 (66%) ng/mL and 121 (50%) ng*h/mL, respectively. The mean (%CV) Cmax and AUC0-8h in the pediatric group were 73 (57%) ng/mL and 264 (62%) ng*h/mL, respectively. The mean (%CV) terminal half-life in adults was 21 (11%) hours.
Trials B and C evaluated pharmacokinetics in 50 pediatric subjects 6 months to 17 years old. The pharmacokinetic results for plasma abametapir are shown in Table 3. Even though the values varied between the 2 trials, abametapir exposure increased as the age of the subject decreased. Abametapir absorption was rapid with a median Tmax of 0.57 to 1.54 hours.
Table 3 Abametapir Pharmacokinetic Parameters in Subjects with Head Lice Infestation| Study | Age Group | n | Cmax (ng/mL) Mean (%CV) | AUC0-8h (ng*h/mL) Mean (%CV) |
| B | 6 months to <1 year | 1 | 418 | 1057 |
| C | 5 | 228 (50%) | 688 (43%) |
| B | 1 year to <2 years | 3 | 209 (62%) | 446 (65%) |
| C | 8 | 147 (49%) | 406 (37%) |
| B | 2 years to <3 years | 6 | 206 (66%) | 633 (57%) |
| C | 8 | 160 (48%) | 602 (51%) |
| B | | 12 | 121 (60%) | 330 (49%) |
| C | 3 years to 17 years | 7 | 52 (45%) | 194 (39%) |
Serum concentration of benzyl alcohol, an excipient in the formulation of XEGLYZE, was assessed in Trials B and C. Benzyl alcohol in serum was measurable (limit of quantitation = 0.5 µg/mL) in 7 subjects out of 39 evaluable subjects. The Cmax of benzyl alcohol in these 7 subjects ranged from 0.52 to 3.57 µg/mL [see Warnings and Precautions (5) and Use in Specific Populations (8.4)].
Distribution
Abametapir and its primary human metabolite, abametapir carboxyl, are highly bound to proteins in plasma. Abametapir is 91.3 – 92.3% bound to plasma proteins, and abametapir carboxyl is 96.0% – 97.5% bound to plasma proteins.
Elimination
Metabolism
Abametapir is extensively metabolized, primarily by the cytochrome P450 enzyme CYP1A2 to a mono-hydroxylated metabolite (abametapir hydroxyl) and further to a mono-carboxylated metabolite (abametapir carboxyl). Abametapir carboxyl is cleared slowly from the systemic circulation resulting in plasma concentration higher than that of abametapir. Based on data in adults in Trial A above, where sampling was carried out to 72 hours, the ratios of Cmax and AUC0-72h between abametapir carboxyl and abametapir were about 30 and 250, respectively. The elimination half-life of abametapir carboxyl has not been well characterized but is estimated to be approximately (mean ± SD) 71 ± 40 hours or longer in adults.
Excretion
Excretion of abametapir and its human metabolites was not examined in patients.
Drug Interaction Studies
In vitro studies suggest that there is a potential for inhibition of cytochrome P450 3A4, 2B6, and 1A2 enzymes following application of XEGLYZE due to high and prolonged systemic exposure of the metabolite abametapir carboxyl [see Drug Interactions (7)].