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Drug Interactions between astemizole and clarithromycin

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

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Interactions between your drugs

Major

clarithromycin astemizole

Applies to: clarithromycin and astemizole

CONTRAINDICATED: Coadministration with the ketolide, telithromycin, as well as certain macrolide antibiotics may significantly increase the plasma concentrations of astemizole and terfenadine. The mechanism is inhibition of CYP450 3A4, the isoenzyme responsible for the metabolic clearance of astemizole and terfenadine. High plasma levels of these agents have been associated with prolongation of the QT interval on the ECG; ventricular arrhythmias including ventricular tachycardia, ventricular fibrillation, and torsade de pointes; cardiac arrest; and sudden death. Macrolides that may significantly inhibit CYP450 3A4 include clarithromycin, erythromycin, and troleandomycin. Azithromycin and dirithromycin are generally believed to have little, if any, effect on CYP450 3A4. In a study of 9 healthy volunteers, erythromycin (500 mg every 8 hours for 7 days) increased the mean steady-state peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of the pharmacologically active metabolite of terfenadine (60 mg twice a day) by 107% and 170%, respectively, compared to administration of terfenadine alone. Three of the subjects also had accumulation of unmetabolized terfenadine. Electrocardiographic data revealed changes in the QT interval in a subset of subjects who demonstrated drug accumulation.

MANAGEMENT: Given the potential for serious and life-threatening adverse cardiac events associated with increased plasma levels of astemizole and terfenadine, the use of these agents with clarithromycin, erythromycin, troleandomycin, or telithromycin is considered contraindicated. Loratadine, cetirizine, or fexofenadine may be safer alternatives during therapy with telithromycin or macrolides. Depending on organism susceptibility, azithromycin and dirithromycin may be appropriate alternatives during therapy with astemizole or terfenadine.

References

  1. Honig PK, Woosley RL, Zamani K, Conner DP, Cantilena LR Jr (1992) "Changes in the pharmacokinetics and electrocardiographic pharmacodynamics of terfenadine with concomitant administration of erythromycin." Clin Pharmacol Ther, 52, p. 231-8
  2. Cortese LM, Bjornson DC (1992) "Potential interaction between terfenadine and macrolide antibiotics." Clin Pharm, 11, p. 675
  3. Kemp JP (1992) "Decreased antihistamine metabolism." Ann Allergy, 69, p. 533
  4. (2002) "Product Information. Hismanal (astemizole)." Janssen Pharmaceuticals
  5. Biglin KE, Faraon MS, Constance TD, Lieh-Lai M (1994) "Drug-induced torsades de pointes: a possible interaction of terfenadine and erythromycin." Ann Pharmacother, 28, p. 282
  6. Paris DG, Parente TF, Bruschetta HR, Guzman E, Niarchos AP (1994) "Torsades-de-pointes induced by erythromycin and terfenadine." Am J Emerg Med, 12, p. 636-8
  7. Amsden GW (1995) "Macrolides versus azalides: a drug interaction update." Ann Pharmacother, 29, p. 906-17
  8. Brannan MD, Reidenberg P, Radwanski E, et al. (1995) "Loratadine administered concomitantly with erythromycin: pharmacokinetic and electrocardiographic evaluations." Clin Pharmacol Ther, 58, p. 269-78
  9. Harris S, Hilligoss DM, Colangelo PM, Eller M, Okerholm R (1995) "Azithromycin and terfenadine: lack of drug interaction." Clin Pharmacol Ther, 58, p. 310-5
  10. Hsieh MH, Chen SA, Chiang CE, et al. (1996) "Drug-induced torsades de pointes in one patient with congenital long QT syndrome." Int J Cardiol, 54, p. 85-8
  11. Nahata M (1996) "Drug interactions with azithromycin and the macrolides: an overview." J Antimicrob Chemother, 37 ( Suppl, p. 133-42
  12. Ament PW, Paterson A (1997) "Drug interactions with the nonsedating antihistamines." Am Fam Physician, 56, p. 223
  13. Jurima-Romet M, Crawford K, Cyr T, Inaba T (1994) "Terfenadine metabolism in human liver. In vitro inhibition by macrolide antibiotics and azole antifungals." Drug Metab Dispos, 22, p. 849-57
  14. European Agency for the Evaluation of Medicinal Products. Committee for Proprietary Medicinal Products (2004) European Public Assessment Report Ketek (telithromycin) (Rev. 2) http:www.emea.eu.int/humandocs/Humans/EPAR/Ketek/Ketek.htm
View all 14 references

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Drug and food interactions

Major

astemizole food

Applies to: astemizole

GENERALLY AVOID: Some beverages such as tonic water contain varying amounts of quinine. Coadministration of a single 430 mg dose of quinine has been shown to increase plasma concentrations of astemizole and its metabolite, desmethylastemizole. Elevated levels of these agents may cause a prolongation of the electrocardiographic QT interval and potentially fatal ventricular arrhythmias. Although pharmacokinetic data have indicated that the amounts of quinine in beverages (up to 80 mg quinine in 32 oz of tonic water) are not sufficient to produce a significant effect, the potential for an interaction exists if large amounts of tonic water are ingested. Also, grapefruit juice has been shown to inhibit CYP450 enzymes, which may lead to increased serum astemizole concentrations. The risk of life-threatening ventricular arrhythmias may be increased.

MANAGEMENT: Patients should be counseled to limit consumption of quinine-containing beverages and avoid grapefruit juice while they are taking astemizole.

References

  1. (2002) "Product Information. Hismanal (astemizole)." Janssen Pharmaceuticals

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Minor

clarithromycin food

Applies to: clarithromycin

Grapefruit juice may delay the gastrointestinal absorption of clarithromycin but does not appear to affect the overall extent of absorption or inhibit the metabolism of clarithromycin. The mechanism of interaction is unknown but may be related to competition for intestinal CYP450 3A4 and/or absorptive sites. In an open-label, randomized, crossover study consisting of 12 healthy subjects, coadministration with grapefruit juice increased the time to reach peak plasma concentration (Tmax) of both clarithromycin and 14-hydroxyclarithromycin (the active metabolite) by 80% and 104%, respectively, compared to water. Other pharmacokinetic parameters were not significantly altered. This interaction is unlikely to be of clinical significance.

References

  1. Cheng KL, Nafziger AN, Peloquin CA, Amsden GW (1998) "Effect of grapefruit juice on clarithromycin pharmacokinetics." Antimicrob Agents Chemother, 42, p. 927-9

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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.

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