Hypersensitivity to bisulfites. Avoid use in patients whose urine pH is under monitoring eg, drastic changes in diet, ingestion of alkalizing gastric buffers, renal tubular acidosis, severe UTI w/ Proteus bacteria. Epilepsy, history of convulsions or predisposing factors of epilepsy. Not be taken by patients under medication of other NMDA antagonists eg, amantadine, ketamine or dextromethorphan. Pregnancy & lactation.