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Drug Interactions between tolterodine and Tykerb

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

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Interactions between your drugs

Moderate

tolterodine lapatinib

Applies to: tolterodine and Tykerb (lapatinib)

ADJUST DOSE: Coadministration with drugs that are inhibitors of CYP450 3A4 may increase the plasma concentrations of tolterodine, which is partially metabolized by the isoenzyme. The possibility of prolonged and/or increased pharmacologic effects of tolterodine should be considered. Although tolterodine is primarily metabolized by CYP450 2D6, there is some evidence that CYP450 3A4 may play a minor role, thus any alteration in its activity levels could conceivably affect the metabolism of tolterodine. The clinical significance of this interaction is yet unknown but may be greater in patients who are CYP450 2D6-deficient, or so-called poor metabolizers of CYP450 2D6 (approximately 7% of Caucasians and less than 2% of Asians and individuals of African descent).

MANAGEMENT: The manufacturer recommends a maximum tolterodine dosage of 1 mg twice daily in patients receiving concomitant CYP450 3A4 inhibitors. Close clinical and laboratory monitoring is advised whenever a CYP450 3A4 inhibitor is added to or withdrawn from therapy. Patients should be advised to notify their physician if they experience an irregular heartbeat, severe blurry vision, difficulty urinating, dry mouth, headache, drowsiness, dizziness, or GI upset.

References

  1. "Product Information. Detrol (tolterodine)." Pharmacia and Upjohn PROD (2001):
  2. Brynne N, Forslund C, Hallen B, Gustafsson LL, Bertilsson L "Ketoconazole inhibits the metabolism of tolterodine in subjects with deficient CYP2D6 activity." Br J Clin Pharmacol 48 (1999): 564-72

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Drug and food interactions

Moderate

lapatinib food

Applies to: Tykerb (lapatinib)

GENERALLY AVOID: Grapefruit juice may increase the plasma concentrations of lapatinib. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits.

ADJUST DOSING INTERVAL: Food can significantly increase the oral bioavailability of lapatinib. According to the manufacturer, lapatinib peak plasma concentration (Cmax) was approximately 2.5- and 3-fold higher and systemic exposure (AUC) 3- and 4-fold higher when administered with a low fat meal (5% fat; 500 calories) or with a high-fat meal (50% fat; 1000 calories), respectively, compared to fasting. Dividing the daily dose also resulted in an approximately 2-fold higher systemic exposure at steady state compared to the same total dose administered once daily.

MANAGEMENT: Patients treated with lapatinib should preferably avoid the consumption of grapefruit or grapefruit juice. The manufacturer recommends that lapatinib be administered at least one hour before or one hour after a meal. The lapatinib dose is administered once daily and should not be divided.

References

  1. "Product Information. Tykerb (lapatinib)." Novartis Pharmaceuticals (2007):

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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.

See also

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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

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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