This may increase the risk for benzodiazepine-related side effects such as dizziness, sedation, low blood pressure, or other flurazepam-related adverse effects. Fosphenytoin: (Major) Disulfiram can interfere with the metabolism of hydantoin anticonvulsants, particularly phenytoin, resulting in increased serum concentrations and possible phenytoin toxicity (i.e., ataxia, hyperreflexia, nystagmus, tremor).