POZ IRELAND
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POZ IRELAND
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RITONAVIR Other names: Norvir Approved for use in HIV infection in combination with other antiviral drugs. DESCRIPTION: Ritonavir is a protease inhibitor. DOSE: Adults: The recommended dose is 600 mg twice daily to be taken with meals. To lessen side effects a dose escalation during the first week of treatment is recommended: 300 mg twice daily for one day; 400 mg twice daily for two days; 500 mg twice daily for one day, and 600 mg twice daily thereafter. Paediatric: 400 mg/m2 every 12h. To minimise nausea and vomiting, initiate therapy starting at 250 mg/m2 every 12h then increase stepwise to full dose over 5 days. Neonates: Under investigation. SIDE EFFECTS: Gastrointestinal: nausea (23-46%), vomiting (13-22%), diarrhoea (13-22%) and anorexia (1-8%). Circumoral and peripheral parasthesias have been reported. Elevated liver enzymes and elevated triglycerides. Redistribution of body fat and diabetes have been associated with protease inhibitors. Lipid abnormalities, especially elevated triglyceride levels, are frequent with ritonavir. RESISTANCE: All available PIs are affected by cross resistance. HIV resistant to ritonavir is most likely to be resistant to indinavir and responses to nelfinavir and saquinavir are poor. INTERACTIONS: Amiodarone, Astemizole, Bepridil, Bupropion, Cisapride, Clozapine, Encainide, Flecainide, Meperidine, Piroxicam, Propafenone, Propoxyphene, Quinidine, Rifabutin, Terfenadine: Must not be given with ritonavir; as it increases plasma levels that could cause life-threatening side effects. Alprazolam, Clorazepate, Diazepam, Estazolam, Flurazepam, Midazolam, Triazolam, Zolpidem: Must not be given with ritonavir; as could cause extreme sedation and respiratory depression. Clarithromycin: The dose of clarithromycin should be reduced with renal failure. Desipramine with ritonavir - dose of desipramine should be reduced. Disulfiram/metronidazole: Ritonavir formulations contain alcohol, which may induce disulfiram-like reactions with these drugs. Oral Contraceptives with ritonavir reduces plasma concentrations - increased hormone dosage or alternative contraception methods should be considered. Saquinavir with ritonavir dramatically increases the levels of saquinavir. This combination is under clinical investigation. Theophylline with ritonavir decreases the plasma level of theophylline – theophylline dose may be increased. Methadone with ritonavir was expected to increase methadone levels, a small study suggests there is little interaction. Viagra: Ritonavir increases levels of sildenafil fourfold; dose reduction has been suggested; refer to Viagra package insert. Recreational Drugs: The manufacturer has stated that ritonavir would theoretically increase levels of MDMA (Ecstasy) three-fold; ritonavir may increase amphetamine levels up to three-fold; ritonavir may decrease heroin concentrations by 50%; cocaine: an interaction is unlikely.
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