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Drug Interactions between gefitinib and saquinavir

This report displays the potential drug interactions for the following 2 drugs:

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Interactions between your drugs

Moderate

saquinavir gefitinib

Applies to: saquinavir and gefitinib

MONITOR: Coadministration with inhibitors of CYP450 3A4 may increase the plasma concentrations of gefitinib, which is primarily metabolized by the isoenzyme. According to the product labeling, administration of gefitinib (250 mg single dose) with the potent inhibitor itraconazole (200 mg once a day for 12 days) increased the mean gefitinib systemic exposure (AUC) by 88% in healthy male volunteers. This increase may be clinically significant, as adverse events of gefitinib are related to dose and exposure.

MANAGEMENT: Caution is advised if gefitinib is administered with CYP450 3A4 inhibitors, particularly potent ones like itraconazole, ketoconazole, posaconazole, voriconazole, clarithromycin, telithromycin, conivaptan, idelalisib, nefazodone, cobicistat, delavirdine, and most protease inhibitors. Pharmacologic response to gefitinib should be monitored more closely whenever a CYP450 3A4 inhibitor is added to or withdrawn from therapy, and the dosage adjusted as necessary. Patients should be advised to contact their physician if they experience possible symptoms of gefitinib toxicity such as severe diarrhea, nausea, dyspnea, cough, and fever.

References (2)
  1. (2003) "Product Information. Iressa (gefitinib)." Astra-Zeneca Pharmaceuticals
  2. Li J, Zhao M, He P, Hidalgo M, Baker SD (2007) "Differential metabolism of gefitinib and erlotinib by human cytochrome p450 enzymes." Clin Cancer Res, 13, p. 3731-7

Drug and food interactions

Moderate

saquinavir food

Applies to: saquinavir

ADJUST DOSING INTERVAL: Food significantly increases the absorption of saquinavir.

MONITOR: Coadministration with grapefruit juice may increase the plasma concentrations of saquinavir. The primary mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. In eight healthy volunteers, ingestion of 400 mL of grapefruit juice prior to administration of a 600 mg dose of saquinavir mesylate increased the area under the plasma concentration-time curve and oral bioavailability of saquinavir by 50% and 100%, respectively, compared to water; however, the increase is not considered clinically relevant. A high degree of intersubject variability in the grapefruit juice effect was also observed. The extent to which this interaction may occur with the saquinavir free base soft gelatin capsule is unknown. However, the saquinavir soft gelatin capsule formulation is no longer commercially available.

MANAGEMENT: Saquinavir mesylate should be taken with meals or within 2 hours after eating to enhance bioavailability. Patients should be advised to avoid the consumption of large amounts of grapefruit and grapefruit juice during saquinavir therapy unless otherwise directed by their doctor, as the interaction is unreliable and subject to a high degree of interpatient variation.

References (6)
  1. (2001) "Product Information. Invirase (saquinavir)." Roche Laboratories
  2. Kupferschmidt HHT, Fattinger KE, Ha HR, Follath F, Krahenbuhl S (1998) "Grapefruit juice enhances the bioavailability of the HIV protease inhibitor saquinavir in man." Br J Clin Pharmacol, 45, p. 355-9
  3. Bailey DG, Malcolm J, Arnold O, Spence JD (1998) "Grapefruit juice-drug interactions." Br J Clin Pharmacol, 46, p. 101-10
  4. Eagling VA, Profit L, Back DJ (1999) "Inhibition of the CYP3A4-mediated metabolism and P-glycoprotein-mediated transport of the HIV-I protease inhibitor saquinavir by grapefruit juice components." Br J Clin Pharmacol, 48, p. 543-52
  5. Cerner Multum, Inc. "UK Summary of Product Characteristics."
  6. Cerner Multum, Inc. "Australian Product Information."

Therapeutic duplication warnings

No 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.

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Drug Interaction Classification

These classifications are only a guideline. The relevance of a particular drug interaction to a specific individual is difficult to determine. Always consult your healthcare provider before starting or stopping any medication.
Major Highly clinically significant. Avoid combinations; the risk of the interaction outweighs the benefit.
Moderate Moderately clinically significant. Usually avoid combinations; use it only under special circumstances.
Minor 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.
Unknown No interaction information available.

Further information

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