ritonavir, Norvir

DRUG CLASS AND MECHANISM: Ritonavir is an oral medication that is used for treating infections with the human immunodeficiency virus (HIV). 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.
GENERIC AVAILABLE: No
PRESCRIPTION: Yes
PREPARATIONS: Capsules or tablets: 100 mg; Solution: 80 mg/ml
STORAGE: 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).
PRESCRIBED FOR: Ritonavir is used in combination with other drugs for the treatment of HIV infection.
DOSING: 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.
DRUG INTERACTIONS: 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.