Cancer
Cyclophosphamide is carcinogenic and may increase the risk of developing lymphomas, leukemia, skin cancer, transitional cell carcinoma of the bladder or other malignancies. Myeloproliferative neoplasms, including acute leukemia, non-Hodgkin lymphoma and multiple myeloma, occurred in 5 of 119 rheumatoid arthritis patients within the first decade after receiving cyclophosphamide, compared with one case of chronic lymphocytic leukemia in 119 rheumatoid arthritis patients with no history. Secondary acute myeloid leukemia (therapy-related AML, or "t-AML") is thought to occur either by cyclophosphamide-inducing mutations or selecting for a high-risk myeloid clone.This risk may be dependent on dose and other factors, including the condition, other agents or treatment modalities (including radiotherapy), treatment length and intensity. For some regimens, it is rare. For instance, CMF-therapy for breast cancer (where the cumulative dose is typically less than 20 grams of cyclophosphamide) carries an AML risk of less than 1/2000, with some studies finding no increased risk compared to background. Other treatment regimens involving higher doses may carry risks of 1–2% or higher. Cyclophosphamide-induced AML, when it happens, typically presents some years after treatment, with incidence peaking around 3–9 years. After nine years, the risk falls to background. When AML occurs, it is often preceded by a myelodysplastic syndrome phase, before developing into overt acute leukemia. Cyclophosphamide-induced leukemia will often involve complex cytogenetics, which carries a worse prognosis than de novo AML. Pharmacology
Oral cyclophosphamide is rapidly absorbed and then converted by mixed-function oxidase enzymes (cytochrome P450 system) in the liver to active metabolites.
It was recommended that the drug remain available only for patients with severe epilepsy for whom the benefits outweigh the risks, and that changes be made to the products labelling to reflect the newly recognized risk. This redemption came with an additional warning since there had been 10 cases acute liver failure (4 of which were fatal). At this point, 10,000 to 12,000 people remained on the drug. United Kingdom
The drug is only available on a limited named-patient basis. Indications and usage
Adults: Monotherapy or adjunctive therapy in the treatment of partial seizures, with and without generalization. Children: Adjunctive therapy in the treatment of partial and generalized seizures associated with Lennox-Gastaut syndrome. Dosing
Felbamate is available in tablets (400 mg and 600 mg) and as a peach-coloured oral suspension (600 mg/5 mL). Adults (≥ 14 years): begin with 1,200 mg daily given every 6 to 8 hours
Children (2–14 years): 15 to 45 mg per kg per day given every 6 to 8 hours

Side effects
Adverse reactions include decreased appetite, vomiting, insomnia, nausea, dizziness, somnolence, and headache. Many patients report increased alertness with the drug. Two rare but very serious effects include aplastic anemia and serious liver damage. The risk of aplastic anemia is between 1:3,600 and 1:5,000, of which 30% of cases are fatal. The risk of liver damage is between 1:24,000 to 1:34,000, of which 40% of cases are fatal. Drug interactions
Felbamate is an inhibitor of CYP2C19 - an enzyme involved in the metabolism of several commonly used medications.