ritonavir, Norvir

  • Pharmacy Author:
    Omudhome Ogbru, PharmD

    Dr. Ogbru received his Doctorate in Pharmacy from the University of the Pacific School of Pharmacy in 1995. He completed a Pharmacy Practice Residency at the University of Arizona/University Medical Center in 1996. He was a Professor of Pharmacy Practice and a Regional Clerkship Coordinator for the University of the Pacific School of Pharmacy from 1996-99.

  • Medical and Pharmacy Editor: Jay W. Marks, MD
    Jay W. Marks, MD

    Jay W. Marks, MD

    Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

What is the dosage for ritonavir?

The recommended dose for adults is 600 mg twice daily. To reduce the occurrence of side effects, ritonavir should be started at 300 mg twice daily and increased every 2-3 days by 100 mg twice daily.

The recommended dose for children older than 1 month is 350 to 400 mg/m2 two times a day and should not exceed 600 mg two times daily. Treatment should be started at 250 mg/m2 and increased every 2-3 days by 50 mg/m2 two times daily.

Ritonavir should be administered with meals. The taste of the oral solution can be improved by mixing it with chocolate milk, Ensure or Advera for up to one hour before administration.

Which drugs or supplements interact with ritonavir?

Ritonavir interacts with many drugs. Some of the important interactions are mentioned below. Viewers should consult their healthcare provider before combining any drugs with ritonavir.

Ritonavir should not be used together with amiodarone (Cordarone), quinidine (Quinaglute, Cardioquin), triazolam (Halcion), midazolam (Versed), pimozide (Orap), ergot derivatives (for example, ergotamine, dihydroergotamine), alfuzosin (Uroxatral), propafenone (Rythmol) and flecainide (Tambocor) because ritonavir increases the blood levels of these drugs and may lead to serious side effects. Ritonavir should not be combined with voriconazole (Vfend) because it reduces blood levels of voriconazole.

Ritonavir also increases the concentrations in blood of rifabutin (Mycobutin) and sildenafil (Viagra). Therefore, the doses of rifabutin and sildenafil should be reduced. The blood concentrations of oral contraceptives, methadone (Dolophine) and theophylline (Theo-Dur, Theo-24) are reduced by ritonavir, and this could reduce the effectiveness of these drugs.

Ritonavir decreases the concentration of meperidine (Demerol) and increases the buildup of meperidine's toxic breakdown product in the body. Therefore, ritonavir reduces the beneficial effect of meperidine while increasing its side effects.

Ritonavir may increase the blood concentration of lovastatin (Mevacor), simvastatin (Zocor), and atorvastatin (Lipitor). This may result in increased occurrence of myopathy (muscle pain) or rhabdomyolysis (muscle breakdown). Lovastatin and simvastatin should not be combined with ritonavir.

St. John's wort and rifampin (Rifadin) decrease the concentration of ritonavir in the body and this could reduce the effectiveness of ritonavir.

Clarithromycin (Biaxin), ketoconazole (Nizoral), fluconazole (Diflucan) and fluoxetine (Prozac) may increase blood concentrations of ritonavir and result in increased side effects from ritonavir.

Ritonavir increases blood levels of sildenafil (Revatio) and the risk of side effects such as low blood pressure, prolonged erection, and fainting. Both drugs should not be combined.

Medically Reviewed by a Doctor on 7/23/2015

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