Atovaquone clinical pharmacology

# Clinical Pharmacology

### Pharmacokinetics
Atovaquone is a highly lipophilic compound with low aqueous solubility. The bioavailability of atovaquone is highly dependent on formulation and diet. The suspension formulation provides an approximately 2-fold increase in atovaquone bioavailability in the fasting or fed state compared to the previously marketed tablet formulation. The absolute bioavailability of a 750-mg dose of MEPRON Suspension administered under fed conditions in 9 HIV-infected (CD4 >100 cells/mm3) volunteers was 47%  15%. In the same study, the bioavailability of a 750-mg dose of the previously marketed tablet formulation was 23%  11%.
Administering atovaquone with food enhances its absorption by approximately 2 fold. In one study, 16 healthy volunteers received a single dose of 750 mg MEPRON Suspension after an overnight fast and following a standard breakfast (23 g fat: 610 kCal). The mean (SD) area under the concentration-time curve (AUC) values were 324  115 and 801  320 hrmcg/mL under fasting and fed conditions, respectively, representing a 2.6  1.0-fold increase. The effect of food (23 g fat: 400 kCal) on plasma atovaquone concentrations was also evaluated 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 hrmcg/mL when atovaquone was administered with food as compared to 169  77 hrmcg/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.
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.
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.
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.
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.
Hepatic/Renal Impairment
The pharmacokinetics of atovaquone have not been studied in patients with hepatic or renal impairment.

### Relationship Between Plasma Atovaquone Concentration and Clinical Outcome
In a comparative study of atovaquone tablets with TMP-SMX for oral treatment of mild-to-moderate PCP (see INDICATIONS AND USAGE), where AIDS patients received 750 mg atovaquone tablets 3 times daily for 21 days, the mean steady-state atovaquone concentration was 13.9  6.9 mcg/mL (n = 133). Analysis of these data established a relationship between plasma atovaquone concentration and successful treatment. This is shown in Table 2.
A dosing regimen of MEPRON Suspension for the treatment of mild-to-moderate PCP has been selected to achieve average plasma atovaquone concentrations of approximately 20 mcg/mL, because this plasma concentration was previously shown to be well tolerated and associated with the highest treatment success rates (Table 2). In an open-label PCP treatment study with MEPRON Suspension, dosing regimens of 1,000 mg once daily, 750 mg twice daily, 1,500 mg once daily, and 1,000 mg twice daily were explored. The average steady-state plasma atovaquone concentration achieved at the 750-mg twice-daily dose given with meals was 22.0  10.1 mcg/mL (n = 18).