When co-administering ritonavir with any agent having a narrow therapeutic margin, such as anticoagulants, anticonvulsants, and antiarrhythmics, special attention is warranted. With some agents, the metabolism may be induced, resulting in decreased concentrations (see Table 6. Established and Other Potentially Significant Drug Interactions).

Table 5. Drugs that Should Not be Co-administered with NORVIR Drug Class: Drug Name Clinical Comment 
*see WARNINGS - Drug Interactions and PRECAUTIONS - Table 6. Established and Other Potentially Significant Drug Interactions for coadministration of sildenafil in patients with erectile dysfunction.
 
Alpha Adrenergic Antagonist:
alfuzosin CONTRAINDICATED due to potential for serious reactions such as hypotension.
Antiarrhythmics:
amiodarone, bepridil, flecainide, propafenone, quinidine CONTRAINDICATED due to potential for serious and/or life threatening reactions such as cardiac arrhythmias.
Antifungal:
voriconazole CONTRAINDICATED due to significant decreases in voriconazole plasma concentrations and may lead to loss of antifungal response.
Ergot Derivatives:
dihydroergotamine, ergonovine, ergotamine, methylergonovine CONTRAINDICATED due to potential for serious and/or life-threatening reactions such as acute ergot toxicity characterized by vasospasm and ischemia of the extremities and other tissues including the central nervous system.
GI Motility Agent:
cisapride CONTRAINDICATED due to potential for serious and/or life-threatening reactions such as cardiac arrhythmias.
Herbal Products:
St. John's wort (hypericum perforatum) CONTRAINDICATED as the combination 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 CONTRAINDICATED due to potential for serious reactions such as risk of myopathy including rhabdomyolysis.
Neuroleptic:
pimozide CONTRAINDICATED due to the potential for serious and/or life-threatening reactions such as cardiac arrhythmias.
PDE5 enzyme inhibitor:
Sildenafil* (Revatio®) CONTRAINDICATED in 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 sildenafil-associated adverse events, including visual abnormalities, hypotension, prolonged erection, and syncope.
Sedative/hypnotics:
oral midazolam, triazolam CONTRAINDICATED due to potential for serious and/or life-threatening reactions such as prolonged or increased sedation or respiratory depression.
Table 6. Established and Other Potentially Significant Drug Interactions: Alteration in Dose or Regimen Recommended Based on Drug Interaction Studies or Predicted Interaction (see CLINICAL PHARMACOLOGY - Table 2 and Table 3 for Magnitude of Interaction) Concomitant Drug Class:
Drug Name Effect on Concentration of Ritonavir or Concomitant Drug Clinical Comment 
  HIV-Antiviral Agents
HIV Protease Inhibitor:
atazanavir When co-adm