Allopurinol Sodium (Page 3 of 6)

7 DRUG INTERACTIONS

Clinically important interactions with the drugs listed below were observed in patients undergoing treatment with an oral allopurinol formulation.

7.1 Drugs Known to Affect the Occurrence of Skin Rash and Hypersensitivity

Concomitant use of the following drugs may increase the risk of skin rash, which may be severe: bendamustine, thiazide diuretics, ampicillin and amoxicillin. Renal impairment may further increase risk with concomitant use of thiazide diuretics [see Warnings and Precautions (5.1)(5.2) and Clinical Pharmacology (12.2)].

Monitor renal function and reduce the dose of Allopurinol Sodium for Injection in patients with concomitant thiazide diuretic use and impaired renal function [see Dosage and Administration (2.2)].

Discontinue Allopurinol Sodium for Injection at the first appearance of skin rash or other signs which may indicate a hypersensitivity reaction when use concomitantly with these drugs.

7.2 Other Drugs Known to Have Clinically Important Drug Interactions with Allopurinol Sodium for Injection

Table 4: Interventions for Clinically Important Drug Interactions with Allopurinol Sodium for Injection

Capecitabine

Clinical Impact

Concomitant use with allopurinol may decrease concentration of capecitabine’s active metabolites, which may decrease capecitabine efficacy.

Intervention

Avoid the use of Allopurinol Sodium for Injection during treatment with capecitabine.

Cyclosporine

Clinical Impact

Concomitant use of allopurinol increases cyclosporine concentrations which may increase the risk of adverse reactions.

Intervention

Increase frequency of monitoring cyclosporine concentrations as reflected in the prescribing information when used concomitantly with Allopurinol Sodium for Injection.

Cytotoxic Agents

Clinical Impact

Concomitant use of allopurinol with cytotoxic agents increases bone marrow suppression among patients with neoplastic disease, except leukemia [see Warnings and Precautions (5.4) and Clinical Pharmacology (12.2)].

Intervention

Blood count monitoring and regular physician follow-up recommended.

Fluorouracil

Clinical Impact

Based on non-clinical data, allopurinol may decrease anti-tumor activity due to suppression of phosphorylation of 5-fluorouracil.

Intervention

Concomitant administration with fluorouracil should be avoided.

Mercaptopurine or Azathioprine

Clinical Impact

Allopurinol inhibits xanthine oxidase mediated metabolism of mercaptopurine and azathioprine. Concomitant use of allopurinol increases the exposure of either mercaptopurine or azathioprine which may increase the risk of their adverse reactions including myelosuppression [see Warnings and Precautions (5.4)].

Intervention

Reduce the dosage of mercaptopurine or azathioprine as recommended in the respective prescribing information.

Pegloticase

Clinical Impact

Concomitant use of Allopurinol Sodium for Injection and pegloticase may potentially blunt the rise of serum uric acid levels and increase the risk of pegloticase related anaphylaxis in patients whose uric acid level increase to above 6 mg/dL.

Intervention

Discontinue and do not institute Allopurinol Sodium for Injection therapy during treatment with pegloticase.

Theophylline

Clinical Impact

Concomitant use of allopurinol doses greater than or equal to 600 mg/day may decrease the clearance of theophylline.

Intervention

Monitor and adjust theophylline doses as reflected in the prescribing information.

Uricosuric Agents

Clinical Impact

Uricosuric agents increase the excretion of the active allopurinol metabolite oxypurinol. Concomitant use with uricosuric agents decreases oxypurinol exposure which may reduce the inhibition of xanthine oxidase by oxypurinol and increases the urinary excretion of uric acid.

Intervention

Monitor uric acid levels due to the increased chance of hypouricemic effects.

Warfarin

Clinical Impact

Allopurinol may inhibit the metabolism of warfarin, possibly enhancing its anticoagulant effect.

Intervention

Patients on concomitant therapy should be monitored for excessive anticoagulation. The INR should be checked frequently and warfarin dosage adjusted accordingly when allopurinol is added to warfarin therapy.

8 USE IN SPECIFIC POPULATIONS

8.1 Pregnancy

Risk Summary

Based on findings in animals, Allopurinol Sodium for Injection may cause fetal harm when administered to a pregnant woman. Adverse developmental outcomes have been described in exposed animals (see Data). Allopurinol and its metabolite oxypurinol have been shown to cross the placenta following administration of maternal allopurinol.

Available limited published data on allopurinol use in pregnant women do not demonstrate a clear pattern or increase in frequency of adverse developmental outcomes. Among approximately 50 pregnancies described in published literature, 2 infants with major congenital malformations have been reported with following maternal allopurinol exposure. Advise pregnant women of the potential risk to a fetus.

All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2% to 4% and 15% to 20%, respectively.

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