Drug Interactions between aspirin/citric acid/sodium bicarbonate and tipranavir

MONITOR CLOSELY: Theoretically, tipranavir may potentiate the risk of bleeding in patients treated with agents that affect hemostasis such as anticoagulants, platelet inhibitors, thrombin inhibitors, thrombolytic agents, high supplemental dosages of vitamin E, or agents that commonly cause thrombocytopenia. Tipranavir has been shown to inhibit human platelet aggregation in vitro at levels consistent with exposures observed in patients receiving tipranavir/ritonavir. Cases of intracranial hemorrhage, some fatal, have been reported during postmarketing use. However, many of these patients had other medical conditions or were receiving concomitant medications that may have caused or contributed to these events. No pattern of abnormal coagulation parameters has been observed in patients in general, or preceding the development of intracranial hemorrhage.

MANAGEMENT: Caution is advised if tipranavir/ritonavir is used in combination with other drugs that affect hemostasis. Patients should be advised to promptly report any signs of bleeding to their physician, including pain, swelling, headache, dizziness, weakness, prolonged bleeding from cuts, increased menstrual flow, vaginal bleeding, nosebleeds, bleeding of gums from brushing, unusual bleeding or bruising, red or brown urine, or red or black stools.

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MONITOR: Agents that cause urinary alkalinization can reduce serum salicylate concentrations in patients receiving anti-inflammatory dosages of aspirin or other salicylates. The mechanism involves reduction in salicylate renal tubular reabsorption due to increased urinary pH, resulting in increased renal salicylate clearance especially above urine pH of 7. This interaction is sometimes exploited in the treatment of salicylate toxicity.

MANAGEMENT: Patients treated chronically with urinary alkalinizers and large doses of salicylates (i.e. 3 g/day or more) should be monitored for potentially diminished or inadequate analgesic and anti-inflammatory effects, and the salicylate dosage adjusted if necessary.

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ADJUST DOSING INTERVAL: Concurrent administration of antacids or other agents with acid-neutralizing effects may decrease the oral bioavailability of tipranavir and reduce its concentrations in plasma. The mechanism of interaction has not been described. When tipranavir (in combination with low-dose ritonavir) was coadministered with 20 mL of an aluminum- and magnesium-based liquid antacid, tipranavir peak plasma concentration (Cmax) and area under the plasma concentration-time curve (AUC) were reduced by 25% to 29%. The clinical significance of these changes is unknown. However, subtherapeutic antiretroviral drug levels may lead to reduced viral susceptibility and development of resistance.

MANAGEMENT: Consideration should be given to separating tipranavir/ritonavir dosing from antacid administration to prevent reduced absorption of tipranavir.

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