Inductors microsomal oxidation can induce liver microsomal metabolism of cyclophosphamide, which leads to increased formation of metabolites alikiliruyuschih, thereby reducing the half-life of  and increasing its activity. Methenolone, causing significant and long lasting inhibition of cholinesterase activity enhances the action of suxamethonium, and reduces or slows the metabolism of cocaine, thereby enhancing and / or increasing the duration of its effect and increasing the risk of toxicity. While the use of allopurinol, in addition, a toxic effect on the bone marrow may be intensified. With simultaneous use  and allopurinol, colchicine, probenecid, sulfinpyrazone may require dose adjustment protivopodagricakih drugs for the treatment of hyperuricemia and gout; urikozuricheskih protivopodagricakih use of drugs may increase the risk of kidney disease associated with increased production of uric acid by using cyclophosphamide.
Cyclophosphamide may increase the anticoagulant activity due to a decrease in the hepatic synthesis of coagulation factors and platelet disorders education, but can also reduce the anticoagulant activity through an unknown mechanism. As grapefruit methenolone contains a compound that may interfere with the activation of cyclophosphamide and thereby its effects, patients are not recommended to eat grapefruit or drink grapefruit juice from.  Enhances the cardiotoxicity of doxorubicin and daunorubicin. Other immunosuppressants (azathioprine, chlorambucil, glucocorticoids, cyclosporine, mercaptopurine, etc.) Increase the risk of infections and secondary tumors.
In an application of lovastatin in patients with heart transplantation may increase the risk of rhabdomyolysis and acute renal failure.
In combination with other myelosuppressive drugs or radiotherapy -. additive may bone marrow function oppression
simultaneous use of high-dose cytarabine, cyclophosphamide in preparation for bone marrow transplantation led to increased incidence of cardiomyopathy followed fatal.

Cautions
During treatment should regularly conduct blood tests (especially paying attention to the content of neutrophils and platelets) to assess the degree of myelosuppression as well as conduct regular urine test for the presence of red blood cells, the appearance of which may precede the development of hemorrhagic cystitis.
If signs of cystitis with micro- – or gross hematuria treatment  should be stopped.
By reducing the number of leukocytes < 2500 / l and / or platelet count < 100,000 / ml treatment cyclophosphamide should be stopped.
in the case of infection during therapy  treatment should be either interrupted or should be reduced dose. Women and men during treatment with methenolone should use reliable methods of contraception.
In the period of treatment should refrain from drinking alcohol. If during the first ten days after the operation carried out under general anesthesia, the patient is prescribed cyclophosphamide, is necessary to put notify the anesthesiologist.
The patient after adrenalectomy needs to adjust doses as the corticosteroids that are used for replacement therapy and drug Cyclophosphamide.