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(rih- TOH-nah-veer)
Pregnancy Category: B Norvir (Rx)

Classification: Antiviral drug, protease inhibitor

See Also: See also Anitiviral Drugs.

Action/Kinetics: A peptidomimetic inhibitor of both the HIV-1 and HIV-2 proteases. Inhibition of HIV protease results in the enzyme incapable of processing the "gag-pool" polyprotein precursor that leads to production of noninfectious immature HIV particles. Peak concentrations after 600 mg of the solution: 2 hr after fasting and 4 hr after nonfasting. t 1/2: 3-5 hr. Metabolized by the cytochrome P450 system. Metabolites and unchanged drug are excreted through both the feces and urine.

Uses: Alone or in combination with nucleoside analogues (ddC or AZT) for the treatment of HIV infection. Use of ritonavir may result in a reduction in both mortality and AIDS-defining clinical events. Clinical benefit has not been determined for periods longer than 6 months.

Special Concerns: Not considered a cure for HIV infection; clients may continue to manifest illnesses associated with advanced HIV infection, including opportunistic infections. Also, therapy with ritonavir has not been shown to decrease the risk of transmitting HIV to others through sexual contact or blood contamination. Use with caution in those with impaired hepatic function and during lactation. Hemophiliacs treated with protease inhibitors may manifest spontaneous bleeding episodes. Safety and efficacy have not been determined in children less than 12 years of age.

Side Effects: Side effects listed are those with a frequency of 2% or greater. GI: N&V, diarrhea, taste perversion, anorexia, flatulence, constipation, abdominal pain, dyspepsia, local throat irritation. Nervous: Circumoral paresthesia, peripheral paresthesia, dizziness, insomnia, paresthesia, somnolence, abnormal thinking. Body as a whole: Asthenia, headache, malaise, fever. Dermatologic: Sweating, rash. Miscellaneous: Vasodilation, hyperlipidemia, myalgia, pharyngitis.

Laboratory Test Alterations: Triglycerides, AST, ALT, GGT, CPK, uric acid.

Overdose Management: Symptoms: Extension of side effects. Treatment: General supportive measures, including monitoring of VS and observing the clinical status. Elimination of unabsorbed drug may be assisted by emesis or gastric lavage, with attention given to maintaining a patent airway. Activated charcoal may also help in removing any unabsorbed drug. Dialysis is not likely to be of benefit in removing the drug from the body.

Drug Interactions: (1) Ritonavir is expected to produce large increases in the plasma levels of a number of drugs, including amiodarone, astemizole, bepridil, bupropion, cisapride, clozapine, encainide, erythromycin, flecainide, meperidine, methylphenidate, pentoxifylline, phenothiazines, piroxicam, propafenone, propoxyphene, quinidine, rifabutin, tefenadine, and warfarin. This may lead to an increased risk of arrhythmias, hematologic complications, seizures, or other serious adverse effects.
(2) Ritonavir may produce a decrease in the plasma levels of the following drugs: atovaquone, clofibrate, daunorubicin, diphenoxylate, metoclopramide, and sedative/hypnotics.
(3) Coadministration of ritonavir with the following drugs may cause extreme sedation and respiratory depression and thus should not be combined: alprazolam, clorazepate, diazepam, estazolam, flurazepam, midazolam, triazolam, and zolpidem. Clarithromycin / Clarithromycin levels; reduce dose Desipramine / Significant despiramine levels; reduce dose Ethinyl estradiol / Ethyinyl estradiol levels; use alternative contraceptive Propulsid / Risk of serious cardiac arrhythmias Saquinavir / Significant in saquinavir blood levels Theophylline / Theophylline levels Warfarin / Warfarin anticoagulant effect

How Supplied: Capsules: 100 mg; Oral Solution: 600 mg/7.5 mL.

?Capsules, Oral Solution Treatment of HIV infection.
600 mg b.i.d. If nausea is experienced upon initiation of therapy, dose escalation may be tried as follows: 300 mg b.i.d. for 1 day, 400 mg b.i.d. for 2 days, 500 mg b.i.d. for 1 day, and then 600 mg b.i.d. thereafter.