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Drug Interactions between Halfan and Tagamet HB

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

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Interactions between your drugs

Major

cimetidine halofantrine

Applies to: Tagamet HB (cimetidine) and Halfan (halofantrine)

MONITOR CLOSELY: Coadministration with inhibitors of CYP450 3A4 may increase the plasma concentrations of halofantrine, resulting in an increased risk of QT interval prolongation and ventricular arrhythmias. The mechanism is inhibition of CYP450 3A4, the isoenzyme responsible for the metabolic clearance of halofantrine. Halofantrine has been associated with QT interval prolongation, ventricular arrhythmias, and sudden death, even at recommended dosages.

MANAGEMENT: Caution and close monitoring is recommended if halofantrine is prescribed with CYP450 3A4 inhibitors, particularly potent ones like itraconazole, ketoconazole, posaconazole, voriconazole, clarithromycin, telithromycin, conivaptan, idelalisib, nefazodone, cobicistat, delavirdine, and most protease inhibitors. The manufacturer recommends performing an ECG before initiating halofantrine therapy and cardiac monitoring during and for 8 to 12 hours after completion of therapy.

References

  1. Giao PT, de Vries PJ (2001) "Pharmacokinetic interactions of antimalarial agents." Clin Pharmacokinet, 40, p. 343-73
  2. (2003) "Product Information. Halfan (halofantrine)." GlaxoSmithKline
  3. Charbit B, Becquemont L, Lepere B, Peytavin G, Funck-Bretano C (2002) "Pharmacokinetic and pharmacodynamic interaction between grapefruit juice and halofantrine." Clin Pharmacol Ther, 72, p. 514-23
  4. Abernethy DR, Wesche DL, Barbey JT, et al. (2001) "Stereoselective halofantrine disposition and effect: concentration-related QTc prolongation." Br J Clin Pharmacol, 51, p. 231-7
  5. Baune B, Flinois JP, Furlan V, et al. (1999) "Halofantrine metabolism in microsomes in man: major role of CYP 3A4 and CYP 3A5." J Pharm Pharmacol, 51, p. 419-26
View all 5 references

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Drug and food interactions

Major

halofantrine food

Applies to: Halfan (halofantrine)

GENERALLY AVOID: Grapefruit juice may increase the plasma concentration of halofantrine. The mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. After administration of 500 mg with 250 mL regular-strength grapefruit juice daily for 3 days, average halofantrine AUC increased 2.8-fold and peak plasma concentrations increased 3.2-fold, compared to water, in healthy subjects (n=12). QT interval prolongation increased from an average of 17 ms with water to 31 ms with grapefruit juice. Halofantrine, even at recommended doses, can cause dose-related prolongation of the QT interval, resulting in an elevated risk of potentially fatal ventricular arrhythmias including ventricular tachycardia and torsade de pointes.

ADJUST DOSING INTERVAL: The presence of food may increase the absorption and toxicity of halofantrine. Peak plasma concentrations increased seven-fold and AUC increased three-fold in healthy subjects when halofantrine was administered with high-fat food.

MANAGEMENT: The authors of the study recommend that grapefruit juice be avoided during halofantrine therapy. The manufacturer recommends performing an ECG before initiating halofantrine therapy and cardiac monitoring during and for 8 to 12 hours after completion of therapy. Halofantrine should be taken on an empty stomach at least 1 hour before or 2 hours after food.

References

  1. Giao PT, de Vries PJ (2001) "Pharmacokinetic interactions of antimalarial agents." Clin Pharmacokinet, 40, p. 343-73
  2. (2003) "Product Information. Halfan (halofantrine)." GlaxoSmithKline
  3. Charbit B, Becquemont L, Lepere B, Peytavin G, Funck-Bretano C (2002) "Pharmacokinetic and pharmacodynamic interaction between grapefruit juice and halofantrine." Clin Pharmacol Ther, 72, p. 514-23
  4. Abernethy DR, Wesche DL, Barbey JT, et al. (2001) "Stereoselective halofantrine disposition and effect: concentration-related QTc prolongation." Br J Clin Pharmacol, 51, p. 231-7
View all 4 references

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Minor

cimetidine food

Applies to: Tagamet HB (cimetidine)

Concurrent use of cimetidine and ethanol may result in increased ethanol concentrations. The mechanism appears to be due to inhibition of gastric alcohol dehydrogenase by cimetidine, leading to increased bioavailability of the alcohol and inhibition of hepatic metabolism of alcohol. The clinical significance of this interaction is limited. More importantly, patients requiring cimetidine for gastrointestinal disease should be counseled to avoid alcohol to prevent worsening of their disease. The other H-2 receptor antagonists appear to have minimal effects on the concentrations of alcohol.

References

  1. Feely J, Wood AJ (1982) "Effects of cimetidine on the elimination and actions of ethanol." JAMA, 247, p. 2819-21
  2. Hansten PD (1992) "Effects of H2-receptor antagonists on blood alcohol levels." JAMA, 267, p. 2469

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Minor

cimetidine food

Applies to: Tagamet HB (cimetidine)

Caffeine effects may be increased in patients also taking cimetidine. The mechanism may be due to decreased caffeine metabolism induced by cimetidine. Although adequate clinical data are lacking, a reduction in dose or elimination of caffeine may be needed if excess CNS stimulation is observed.

References

  1. (2001) "Product Information. Tagamet (cimetidine)." SmithKline Beecham
  2. Broughton LJ, Rodgers HJ (1981) "Decreased systenuc clearance of caffeine due to cimetidine." Br J Clin Pharmacol, 12, p. 155-9

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Minor

cimetidine food

Applies to: Tagamet HB (cimetidine)

H2 antagonists may reduce the clearance of nicotine. Cimetidine, 600 mg given twice a day for two days, reduced clearance of an intravenous nicotine dose by 30%. Ranitidine, 300 mg given twice a day for two days, reduced clearance by 10%. The clinical significance of this interaction is not known. Patients should be monitored for increased nicotine effects when using the patches or gum for smoking cessation and dosage adjustments should be made as appropriate.

References

  1. Bendayan R, Sullivan JT, Shaw C, Frecker RC, Sellers EM (1990) "Effect of cimetidine and ranitidine on the hepatic and renal elimination of nicotine in humans." Eur J Clin Pharmacol, 38, p. 165-9

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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.

Further information

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