Norvir (Ritonavir Capsules, Oral Solution) Drug Information: Overdosage and Contraindications

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May 27, 2012

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OVERDOSE

Acute Overdosage - Human Overdose Experience

Human experience of acute overdose with NORVIR is limited. One patient in clinical trials took NORVIR 1500 mg per day for two days. The patient reported paresthesias which resolved after the dose was decreased. A post-marketing case of renal failure with eosinophilia has been reported with ritonavir overdose.

The approximate lethal dose was found to be greater than 20 times the related human dose in rats and 10 times the related human dose in mice.

Management of Overdosage

Treatment of overdose with NORVIR consists of general supportive measures including monitoring of vital signs and observation of the clinical status of the patient. There is no specific antidote for overdose with NORVIR. If indicated, elimination of unabsorbed drug should be achieved by emesis or gastric lavage; usual precautions should be observed to maintain the airway. Administration of activated charcoal may also be used to aid in removal of unabsorbed drug. Since ritonavir is extensively metabolized by the liver and is highly protein bound, dialysis is unlikely to be beneficial in significant removal of the drug. A Certified Poison Control Center should be consulted for up-to-date information on the management of overdose with NORVIR.

CONTRAINDICATIONS

When co-administering NORVIR with other protease inhibitors, see the full prescribing information for that protease inhibitor including contraindication information.
NORVIR is contraindicated in patients with known hypersensitivity (e.g., toxic epidermal necrolysis (TEN) or Stevens-Johnson syndrome) to ritonavir or any of its ingredients.
Co-administration of NORVIR with several classes of drugs (including sedative hypnotics, antiarrhythmics, or ergot alkaloid preparations) is contraindicated and may result in potentially serious and/or life-threatening adverse events due to possible effects of NORVIR on the hepatic metabolism of these drugs (see Table 1). Voriconazole and St. John's Wort are exceptions in that co-administration of NORVIR and voriconazole results in a significant decrease in plasma concentrations of voriconazole, and co-administration of NORVIR with St. John's Wort may result in decreased ritonavir plasma concentrations.

Table 1: Drugs that are Contraindicated with NORVIR

Drug Class	Drugs Within Class That Are Contraindicated With NORVIR**	Clinical Comments
Alpha₁-adrenoreceptor antagonist	Alfuzosin HCL	Potential for hypotension.
Antiarrhythmics	Amiodarone, flecainide, propafenone, quinidine	Potential for cardiac arrhythmias.
Antifungal	Voriconazole	Coadministration of voriconazole with ritonavir 400 mg every 12 hours significantly decreases voriconazole plasma concentrations and may lead to loss of antifungal response. Voriconazole is contraindicated with ritonavir doses of 400 mg every 12 hours or greater [see DRUG INTERACTIONS]
Ergot Derivatives	Dihydroergotamine, ergonovine, ergotamine, methylergonovine	Potential for acute ergot toxicity characterized by vasospasm and ischemia of the extremities and other tissues including the central nervous system.
GI Motility Agent	Cisapride	Potential for cardiac arrhythmias.
Herbal Products	St. John’s Wort (hypericum perforatum)	Co-administration of NORVIR with St. John’s Wort may result in decreased ritonavir plasma concentrations and may lead to loss of virologic response and possible resistance to NORVIR or to the class of protease inhibitors.
HMG-CoA Reductase Inhibitors	Lovastatin, simvastatin	Potential for myopathy including rhabdomyolysis.
Neuroleptic	Pimozide	Potential for cardiac arrhythmias.
PDE5 enzyme inhibitor	Sildenafil* (RevatioP® ) only when used for the treatment of pulmonary arterial hypertension (PAH)	A safe and effective dose has not been established when used with ritonavir. There is an increased potential for sildenafilassociated adverse events, including visual abnormalities, hypotension, prolonged erection, and syncope [see DRUG INTERACTIONS].
Sedative/hypnotics	Oral midazolam, triazolam	Prolonged or increased sedation or respiratory depression [see DRUG INTERACTIONS]
* see DRUG INTERACTIONS for co-administration of sildenafil in patients with erectile dysfunction. For additional information for these contraindicated drugs, see also DRUG INTERACTIONS**.