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Drug Interactions between Terbinex with Eco Formula and Toprol-XL

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

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Interactions between your drugs

Moderate

metoprolol terbinafine

Applies to: Toprol-XL (metoprolol) and Terbinex with Eco Formula (hydroxypropyl chitosan / terbinafine topical)

MONITOR: Coadministration with terbinafine may increase the plasma concentrations of drugs that are substrates of the CYP450 2D6 isoenzyme. The mechanism is decreased clearance due to inhibition of CYP450 2D6 activity by terbinafine, which is expected to occur in patients who are CYP450 2D6 extensive metabolizers (approximately 93% of Caucasians and more than 98% of Asians and individuals of African descent). A case of nortriptyline (a CYP450 2D6 substrate) intoxication corresponding to significantly increased serum drug concentrations was reported in a patient shortly after the addition of terbinafine. Rechallenge in the patient produced similar results.

MANAGEMENT: Caution is advised if terbinafine must be used concurrently with medications that undergo metabolism by CYP450 2D6, particularly those with a narrow therapeutic range. Dosage adjustments as well as clinical and laboratory monitoring may be appropriate for some drugs whenever terbinafine is added to or withdrawn from therapy. Due to the long elimination half-life of terbinafine, especially following prolonged use, such interactions may be observed for several months after discontinuation of terbinafine therapy.

References

  1. (2001) "Product Information. Lamisil (terbinafine)." Sandoz Pharmaceuticals Corporation
  2. Van der Kuy PH, Hooymans PM, Verkaaik AJ (1998) "Nortriptyline intoxication induced by terbinafine." BMJ, 316, p. 441
  3. AbdelRahman SM, Gotschall RR, Kauffman RE, Leeder JS, Kearns GL (1999) "Investigation of terbinafine as a CYP2D6 inhibitor in vivo." Clin Pharmacol Ther, 65, p. 465-72
  4. Gupta AK, Katz HI, Shear NH (2000) "Terbinafine and potential drug interactions - Reply." J Am Acad Dermatol, 43, p. 883-4
View all 4 references

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Drug and food interactions

Moderate

metoprolol food

Applies to: Toprol-XL (metoprolol)

ADJUST DOSING INTERVAL: The bioavailability of metoprolol may be enhanced by food.

MANAGEMENT: Patients may be instructed to take metoprolol at the same time each day, preferably with or immediately following meals.

References

  1. (2001) "Product Information. Lopressor (metoprolol)." Novartis Pharmaceuticals
  2. Darcy PF (1995) "Nutrient-drug interactions." Adverse Drug React Toxicol Rev, 14, p. 233-54

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Moderate

metoprolol food

Applies to: Toprol-XL (metoprolol)

ADJUST DOSING INTERVAL: Concurrent administration with calcium salts may decrease the oral bioavailability of atenolol and possibly other beta-blockers. The exact mechanism of interaction is unknown. In six healthy subjects, calcium 500 mg (as lactate, carbonate, and gluconate) reduced the mean peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of atenolol (100 mg) by 51% and 32%, respectively. The elimination half-life increased by 44%. Twelve hours after the combination, beta-blocking activity (as indicated by inhibition of exercise tachycardia) was reduced compared to that with atenolol alone. However, during a 4-week treatment in six hypertensive patients, there was no difference in blood pressure values between treatments. The investigators suggest that prolongation of the elimination half-life induced by calcium coadministration may have led to atenolol cumulation during long-term dosing, which compensated for the reduced bioavailability.

MANAGEMENT: It may help to separate the administration times of beta-blockers and calcium products by at least 2 hours. Patients should be monitored for potentially diminished beta-blocking effects following the addition of calcium therapy.

References

  1. Kirch W, Schafer-Korting M, Axthelm T, Kohler H, Mutschler E (1981) "Interaction of atenolol with furosemide and calcium and aluminum salts." Clin Pharmacol Ther, 30, p. 429-35

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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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