Atovaquone (Page 5 of 8)

12.3 Pharmacokinetics

Plasma atovaquone concentrations do not increase proportionally with dose following ascending repeat-dose administration of atovaquone oral suspension in healthy subjects. When atovaquone oral suspension was administered with food at dosage regimens of 500 mg once daily, 750 mg once daily, and 1,000 mg once daily, mean (±SD) steady-state plasma atovaquone concentrations were 11.7 ± 4.8, 12.5 ± 5.8, and 13.5 ± 5.1 mcg/mL, respectively. The corresponding mean (±SD) C max concentrations were 15.1 ± 6.1, 15.3 ± 7.6, and 16.8 ± 6.4 mcg/mL.

Absorption

Atovaquone is a highly lipophilic compound with low aqueous solubility. The mean (±SD) absolute bioavailability of atovaquone from a 750-mg dose of atovaquone oral suspension administered under fed conditions in 9 HIV-1-infected (CD4 >100 cells/mm 3) volunteers was 47% ± 15%.

Effect of Food:

Administering atovaquone oral suspension with food enhances atovaquone bioavailability. Sixteen healthy subjects received a single 750-mg dose of atovaquone oral suspension after an overnight fast and following a meal (23 g fat: 610 kCal). The mean (±SD) atovaquone AUC under fasting and fed conditions were 324 ± 115 and 801 ± 320 h∙mcg/mL, respectively, representing a 2.6 ± 1.0-fold increase.

Distribution

Following IV administration of atovaquone, the mean (±SD) 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-1-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 mean (±SD) 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 following administration of atovaquone oral suspension.

Metabolism:

The metabolism of atovaquone is unknown.

Excretion:

Following oral administration of 14C-labelled atovaquone to healthy subjects, greater than 94% of the dose was recovered as unchanged atovaquone in the feces over 21 days.

Specific Populations

Patients with Hepatic or Renal Impairment:

The pharmacokinetics of atovaquone have not been studied in patients with hepatic or renal impairment.

HIV-Infected Subjects:

When atovaquone oral suspension was administered to 5 HIV-1–infected subjects at a dose of 750 mg twice daily, the mean (±SD) steady-state plasma atovaquone concentration was 21.0 ± 4.9 mcg/mL and mean (±SD) C max was 24.0 ± 5.7 mcg/mL. The mean (±SD) minimum plasma atovaquone concentration (C min ) associated with the 750-mg twice-daily regimen was 16.7 ± 4.6 mcg/mL.

In an open-label PCP trial in 18 HIV-1–infected subjects, administration of atovaquone oral suspension 750 mg twice daily with meals resulted in a mean (±SD) steady-state plasma atovaquone concentration of 22.0 ± 10.1 mcg/mL.

The mean (±SD) plasma clearance of atovaquone following IV administration in 9 HIV-1–infected subjects was 10.4 ± 5.5 mL/min (0.15 ± 0.09 mL/min/kg).

Drug Interaction Studies

Rifampin/Rifabutin:

In a trial with 13 HIV-1-infected volunteers, the oral administration of rifampin 600 mg every 24 hours with atovaquone oral suspension 750 mg every 12 hours resulted in a 52% ± 13% decrease in the mean (±SD) steady-state plasma atovaquone concentration and a 37% ± 42% increase in the mean (±SD) steady-state plasma rifampin concentration. The half-life of atovaquone decreased from 82 ± 36 hours when administered without rifampin to 50 ± 16 hours with rifampin. In a trial of 24 healthy volunteers, the oral administration of rifabutin 300 mg once daily with atovaquone oral suspension 750 mg twice daily resulted in a 34% decrease in the mean steady-state plasma atovaquone concentration and a 19% decrease in the mean steady-state plasma rifabutin concentration.

Tetracycline:

Concomitant treatment with tetracycline has been associated with a 40% reduction in plasma concentrations of atovaquone.

Metoclopramide:

Concomitant treatment with metoclopramide has been associated with a 50% reduction in steady-state atovaquone plasma concentrations.

Indinavir:

Concomitant administration of atovaquone (750 mg twice daily with food for 14 days) and indinavir (800 mg three times daily without food for 14 days) did not result in any change in the steady-state AUC and C max of indinavir, but resulted in a decrease in the C trough of indinavir (23% decrease [90% CI: 8%, 35%]).

Trimethoprim/Sulfamethoxazole (TMP-SMX) :

Concomitant administration of atovaquone oral suspension 500 mg once daily (not the approved dosage) and TMP-SMX in 6 HIV-infected adult subjects did not result in significant changes in either atovaquone or TMP-SMX exposure.

Zidovudine:

The administration of atovaquone tablets 750 mg every 12 hours with zidovudine 200 mg every 8 hours to 14 HIV-1 infected subjects resulted in a 24% ± 12% decrease in zidovudine apparent oral clearance, leading to a 35% ± 23% increase in plasma zidovudine AUC. The glucuronide metabolite:parent ratio decreased from a mean of 4.5 when zidovudine was administered alone to 3.1 when zidovudine was administered with atovaquone tablets. This effect is minor and would not be expected to produce clinically significant events. Zidovudine had no effect on atovaquone pharmacokinetics.

12.4 Microbiology

Mechanism of Action

Atovaquone is a hydroxy-1,4-naphthoquinone, an analog of ubiquinone, with antipneumocystis activity. The mechanism of action against Pneumocystis jirovecii has not been fully elucidated. In Plasmodium species, the site of action appears to be the cytochrome bc 1 complex (Complex III). Several metabolic enzymes are linked to the mitochondrial electron transport chain via ubiquinone. Inhibition of electron transport by atovaquone results in indirect inhibition of these enzymes. The ultimate metabolic effects of such blockade may include inhibition of nucleic acid and adenosine triphosphate (ATP) synthesis.

All MedLibrary.org resources are included in as near-original form as possible, meaning that the information from the original provider has been rendered here with only typographical or stylistic modifications and not with any substantive alterations of content, meaning or intent.

This site is provided for educational and informational purposes only, in accordance with our Terms of Use, and is not intended as a substitute for the advice of a medical doctor, nurse, nurse practitioner or other qualified health professional.

Privacy Policy | Copyright © 2022. All Rights Reserved.