Allopurinol 
Cyclophosphamide toxicity (bone marrow suppression, nausea, vomiting)     Clinical Management: If possible avoid concurrent administration 
Chloramphenicol 
Adverse Effect: Decreased cyclophosphamide effectiveness     Clinical Management: Avoid this combination if possible due to unpredictable cyclophosphamide efficacy. 
Digoxin 
Adverse Effect: Decreased digoxin effectiveness     Clinical Management: Substitute digoxin in liquid form (liquid or capsules containing liquid digoxin) for digoxin tablets, or substitute digitoxin, which is not affected by this interaction, for digoxin. 
Indomethacin 
Adverse Effect: Fluid retention     Clinical Management: Monitor patients for fluid retention. 
Phenobarbitone 
Adverse Effect: Decreased cyclophosphamide efficacy
Succinyl Choline 
An increased risk of potentiated succinylcholine efficacy     Clinical Management: If cyclophosphamide has been administered within 10 days of succinylcholine administration, extreme caution should be used during and after succinylcholine administration. 
Tamoxifen 
An increased risk of thromboembolism     Clinical Management: In patients undergoing therapy with tamoxifen for breast cancer, the risks of adding cyclophosphamide should be weighed against the potential benefits. |