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Drug Interactions between fosphenytoin and tolvaptan

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

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Interactions between your drugs

Major

fosphenytoin tolvaptan

Applies to: fosphenytoin and tolvaptan

GENERALLY AVOID: Coadministration with potent inducers of CYP450 3A4 may significantly decrease the plasma concentrations of tolvaptan, which is primarily metabolized by the isoenzyme. When tolvaptan was administered with the potent CYP450 3A4 inducer rifampin, tolvaptan peak plasma concentration (Cmax) and systemic exposure (AUC) decreased by approximately 85%. The therapeutic efficacy of tolvaptan may be reduced.

MANAGEMENT: Concomitant use of tolvaptan with potent CYP450 3A4 inducers should generally be avoided. If coadministration is necessary, a dosage increase of tolvaptan may be required. Patient response should be closely monitored and the dosage adjusted accordingly.

References

  1. Cerner Multum, Inc. "UK Summary of Product Characteristics."
  2. (2009) "Product Information. Samsca (tolvaptan)." Otsuka American Pharmaceuticals Inc

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Drug and food interactions

Moderate

tolvaptan food

Applies to: tolvaptan

GENERALLY AVOID: Grapefruit juice may significantly increase the plasma concentrations of tolvaptan. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. According to the product labeling, administration of tolvaptan with grapefruit juice resulted in a 1.8-fold increase in tolvaptan systemic exposure. The clinical significance is unknown, although increased pharmacologic effects may be expected. Too rapid correction of hyponatremia increases the risk of osmotic demyelination syndrome, which is associated with dysarthria, mutism, dysphagia, lethargy, affective changes, spastic quadriparesis, seizures, coma, and death.

MANAGEMENT: Patients treated with tolvaptan should avoid consumption of grapefruits and grapefruit juice.

References

  1. (2009) "Product Information. Samsca (tolvaptan)." Otsuka American Pharmaceuticals Inc

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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.

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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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