one concentrations was also eva luated in a multiple-dose, randomized, crossover study in 19 HIV-infected volunteers (CD4 <200 cells/mm3) receiving daily doses of 500 mg MEPRON Suspension. AUC was 280 ± 114 hr●mcg/mL when atovaquone was administered with food as compared to 169 ± 77 hr●mcg/mL under fasting conditions. Maximum plasma atovaquone concentration (Cmax) was 15.1 ± 6.1 and 8.8 ± 3.7 mcg/mL when atovaquone was administered with food and under fasting conditions, respectively.
Dose Proportionality
Plasma atovaquone concentrations do not increase proportionally with dose. When MEPRON Suspension was administered with food at dosage regimens of 500 mg once daily, 750 mg once daily, and 1,000 mg once daily, average steady-state plasma atovaquone concentrations were 11.7 ± 4.8, 12.5 ± 5.8, and 13.5 ± 5.1 mcg/mL, respectively. The corresponding Cmax concentrations were 15.1 ± 6.1, 15.3 ± 7.6, and 16.8 ± 6.4 mcg/mL. When MEPRON Suspension was administered to 5 HIV-infected volunteers at a dose of 750 mg twice daily, the average steady-state plasma atovaquone concentration was 21.0 ± 4.9 mcg/mL and Cmax was 24.0 ± 5.7 mcg/mL. The minimum plasma atovaquone concentration (Cmin) associated with the 750-mg twice-daily regimen was 16.7 ± 4.6 mcg/mL.
Distribution
Following the intravenous administration of atovaquone, the volume of distribution at steady state (Vdss) was 0.60 ± 0.17 L/kg (n = 9). Atovaquone is extensively bound to plasma proteins (99.9%) over the concentration range of 1 to 90 mcg/mL. In 3 HIV-infected children who received 750 mg atovaquone as the tablet formulation 4 times daily for 2 weeks, the cerebrospinal fluid concentrations of atovaquone were 0.04, 0.14, and 0.26 mcg/mL, representing less than 1% of the plasma concentration.
Elimination
The plasma clearance of atovaquone following intravenous (IV) administration in 9 HIV-infected volunteers was 10.4 ± 5.5 mL/min (0.15 ± 0.09 mL/min/kg). The half-life of atovaquone was 62.5 ± 35.3 hours after IV administration and ranged from 67.0 ± 33.4 to 77.6 ± 23.1 hours across studies following administration of MEPRON Suspension. The half-life of atovaquone is long due to presumed enterohepatic cycling and eventual fecal elimination. In a study where 14C-labelled atovaquone was administered to healthy volunteers, greater than 94% of the dose was recovered as unchanged atovaquone in the feces over 21 days. There was little or no excretion of atovaquone in the urine (less than 0.6%). There is indirect evidence that atovaquone may undergo limited metabolism; however, a specific metabolite has not been identified.
Special Populations
Pediatrics
In a study of MEPRON Suspension in 27 HIV-infected, asymptomatic infants and children between 1 month and 13 years of age, the pharmacokinetics of atovaquone were age dependent. These patients were dosed once daily with food for 12 days. The average steady-state plasma atovaquone concentrations in the 24 patients with available concentration data are shown in Table 1.
Table 1. Average Steady-State Plasma Atovaquone Concentrations in Pediatric Patients
Age
Dose of MEPRON Suspension
10 mg/kg
30 mg/kg
45 mg/kg
Average Css in mcg/mL (mean ± SD)
1-3 months
5.9
(n = 1)
27.8 ± 5.8
(n = 4)
______
>3-24 months
5.7 ± 5.1
(n = 4)
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