Drug Interaction Report
2 potential interactions and/or warnings found for the following 2 drugs:
- Baycadron (dexamethasone)
- ritonavir
Interactions between your drugs
dexAMETHasone ritonavir
Applies to: Baycadron (dexamethasone), ritonavir
GENERALLY AVOID: Coadministration with protease inhibitors may increase the plasma concentration and pharmacologic effects of dexamethasone. The proposed mechanism is protease inhibitor-mediated inhibition of CYP450 3A4, the isoenzyme involved in the metabolic clearance of dexamethasone. Ritonavir has been reported to increase dexamethasone systemic exposure (AUC) by more than threefold. In one case report, an HIV patient who had been receiving long-term dexamethasone therapy for thrombotic thrombocytopenia purpura developed spinal epidural lipomatosis four months following the initiation of ritonavir. Although the patient was already cushingoid as a result of chronic dexamethasone administration, he did not have symptoms of myelopathy until after ritonavir was added. The effect of dexamethasone on the clearance of protease inhibitors has not been established. Theoretically, plasma levels of protease inhibitors may decrease due to dexamethasone induction of their metabolism by CYP450 3A4. This may lead to a loss of therapeutic effect and development of resistance to protease inhibitor-containing antiretroviral regimens; however, data are not available. These interactions may also be seen with cobicistat, a potent CYP450 3A4 inhibitor that solely acts as a pharmacokinetic booster in antiretroviral treatment regimen; however, data are not available.
MONITOR: Corticosteroids such as dexamethasone may cause hypokalemia and potentiate the risk of QT and/or PR interval prolongation associated with the use of certain protease inhibitors such as atazanavir, lopinavir-ritonavir, and saquinavir-ritonavir. The risk of torsade de pointes arrhythmia, bradycardia, and heart block may be increased.
MANAGEMENT: Caution is advised if dexamethasone must be used concomitantly with protease inhibitors or cobicistat. Some authorities advise against concomitant use unless the potential benefit outweighs the risk. Adrenal function should be monitored regularly during chronic use of these agents, and dexamethasone dosage adjusted as necessary. Patients should be monitored for symptoms of hypercorticism (e.g., acne, easy bruising, moon face, edema, hirsutism, buffalo hump, skin striae, glucose intolerance, and irregular menstruations), immunosuppression, and osteoporosis. In addition, it may be appropriate to monitor patients for potentially reduced antiretroviral response following initiation or any dosage increase of dexamethasone. Serum potassium and ECG monitoring should also be considered during coadministration of dexamethasone with certain protease inhibitors in accordance with the product labeling.
References
- (2001) "Product Information. Norvir (ritonavir)." Abbott Pharmaceutical
- Cerner Multum, Inc. "UK Summary of Product Characteristics."
- Cerner Multum, Inc. "Australian Product Information."
Drug and food interactions
ritonavir food
Applies to: ritonavir
ADJUST DOSING INTERVAL: Administration with food may modestly affect the bioavailability of ritonavir from the various available formulations. When the oral solution was given under nonfasting conditions, peak ritonavir concentrations decreased 23% and the extent of absorption decreased 7% relative to fasting conditions. Dilution of the oral solution (within one hour of dosing) with 240 mL of chocolate milk or a nutritional supplement (Advera or Ensure) did not significantly affect the extent and rate of ritonavir absorption. When a single 100 mg dose of the tablet was administered with a high-fat meal (907 kcal; 52% fat, 15% protein, 33% carbohydrates), approximately 20% decreases in mean peak concentration (Cmax) and systemic exposure (AUC) were observed relative to administration after fasting. Similar decreases in Cmax and AUC were reported when the tablet was administered with a moderate-fat meal. In contrast, the extent of absorption of ritonavir from the soft gelatin capsule formulation was 13% higher when administered with a meal (615 KCal; 14.5% fat, 9% protein, and 76% carbohydrate) relative to fasting.
MANAGEMENT: Ritonavir should be taken with meals to enhance gastrointestinal tolerability.
References
- (2001) "Product Information. Norvir (ritonavir)." Abbott Pharmaceutical
Therapeutic duplication warnings
No duplication warnings were found for your selected drugs.
Therapeutic duplication warnings are only returned when drugs within the same group exceed the recommended therapeutic duplication maximum.
Drug Interaction Classification
Highly clinically significant. Avoid combinations; the risk of the interaction outweighs the benefit. | |
Moderately clinically significant. Usually avoid combinations; use it only under special circumstances. | |
Minimally clinically significant. Minimize risk; assess risk and consider an alternative drug, take steps to circumvent the interaction risk and/or institute a monitoring plan. | |
No interaction information available. |
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