Monday Pharmaceutical Mystery: December 30

Why is this patient taking atovaquone alone?

Your patient, WB, is picking up a prescription for atovaquone liquid. This makes you stop in your tracks for a second, You have never seen atovaquone alone; usually you see atovaquone/proguanil (Malarone) given to prevent malaria.

Mystery: Why is WB taking atovaquone?

Solution: WB tells you that she was supposed to take sulfamethoxazole/trimethoprim (Bactrim DS) for pneumocystis pneumonia (PCP), but your fellow pharmacist discovered a drug interaction between Bactrim DS and the triamterene/hydrochlorothiazide (Dyazide) that she was taking. The computer system alerted the pharmacist to increased risk of hyperkalemia, potentially fatal, and the pharmacist called the doctor to discuss an alternative medication. This is when the prescriber switched WB to atovaquone.

PCP is a serious infection caused by pneumocystis jirovecii fungus. Most patients with PCP are immunocompromised, due to HIV/AIDS or medications. However, in the United States, patients with HIV/AIDS are less likely to get PCP today than in the past, due to antiretroviral therapy.1 Trimethoprim-sulfamethoxazole is recommended as first-line treatment for PCP.2

Atovaquone (Mepron) is available as an oral suspension. It is a quinone antimicrobial drug indicated for:3

  • Prevention of PCP in adults and adolescents 13 years and older who cannot tolerate trimethoprim-sulfamethoxazole
  • Treatment of mild to moderate PCP in adults and adolescents age 13 years and older who cannot tolerate trimethoprim-sulfamethoxazole.

Because WB was unable to take Bactrim DS due to the drug interaction, the doctor switched to atovaquone.

The dose of atovaquone for prevention of PCP is 1500 mg once daily with food. For treatment of PCP, the dose is 750 mg twice daily with food for 21 days. Taking atovaquone without meals may result in lower plasma concentrations and may limit response to therapy.3


  • CDC: Pneumocystis pneumonia. CDC website Accessed November 28, 2019.
  • An Official ATS Workshop Summary: Recent Advances and Future Directions in Pneumocystis Pneumonia. American Thoracic Society website. Accessed November 28, 2019.
  • Mepron (Atovaquone) package insert. Accessed November 28, 2019.