ritonavir (Norvir)

Ritonavir is an oral medication that is used for treating human immunodeficiency virus (HIV) infection. It is in a class of drugs called protease inhibitors which also includes indinavir (Crixivan), nelfinavir (Viracept), emtricitabine (Emtriva) and saquinavir (Invirase, Fortovase). During infection with HIV, the HIV virus multiplies within the body's cells. Viruses are released from the cells and spread throughout the body where they infect other cells. In this manner, HIV infection is perpetuated among new cells that the body produces continually. During the production of the viruses, new proteins are made. Some of the proteins are structural proteins, that, is, proteins that form the body of the virus. Other proteins are enzymes which manufacture DNA and other components for the new viruses. Protease is the enzyme that forms the new structural proteins and enzymes. Ritonavir blocks the activity of protease and results in the formation of defective viruses that are unable to infect the body's cells. As a result, the number of viruses in the body (the viral load) decreases. Nevertheless, ritonavir does not prevent the transmission of HIV among individuals, and it does not cure HIV infections or AIDS. The FDA approved ritonavir in June 1999.

What brand names are available for ritonavir?

Norvir

Is ritonavir available as a generic drug?

GENERIC AVAILABLE: No

Do I need a prescription for ritonavir?

Yes

The most serious side effects are:

• liver failure,
• inflammation of the pancreas (pancreatitis),
• heart block, and
• severe allergic reactions.

Ritonavir also may elevate blood glucose resulting in new onset diabetes. Fat redistribution, elevated triglycerides, and elevated cholesterol levels also occur. Patients with hemophilia may experience spontaneous bleeding. Immune reconstitution syndrome which is an inflammatory response to infection may occur in patients treated with combination antiretroviral therapy.

Other important side effects include:

• diarrhea,
• nausea and vomiting,
• taste disturbance,
• abnormal
• skin sensations (burning, prickling and tingling),
• headache,
• weakness, and
• insomnia (difficulty sleeping).

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.

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.

Use of ritonavir during pregnancy has not been adequately evaluated. To monitor outcomes of pregnant women that received ritonavir, an Antiretroviral Pregnancy Registry has been established. Physicians are encouraged to register patients by calling 1-800-258-4263.

It is not known whether ritonavir is secreted in breast milk. Nevertheless, HIV-infected mothers should not breast-feed because of the potential risk of transmitting HIV to an infant that is not infected.

What preparations of ritonavir are available?

Capsules or tablets: 100 mg; Solution: 80 mg/ml

How should I keep ritonavir stored?

Capsules that will not be used within 30 days should be stored in a refrigerator between 2 C to 8 C (36 F to 46F). Capsules that will be used within 30 days do not have to be refrigerated if stored at less than 25 C (77 F) Oral solution should be stored at room temperature, 20 C to 25 C (68 F to77 F).