Signs and symptoms associated with memantine hydrochloride overdosage include agitation, confusion, ECG changes, loss of consciousness, psychosis, restlessness, slowed movement, somnolence, stupor, unsteady gait, visual hallucinations, vertigo, vomiting, and weakness.
In one case of extreme overdosage, the patient survived the intake of up to 2,000 mg memantine hydrochloride showing CNS effects (e.g., coma, diplopia and agitation) which resolved without permanent sequela.
In the event of overdosage, treatment should be symptomatic. No specific antidote for intoxication or overdose is available. Standard clinical procedures to remove active substance material, e.g., gastric lavage, carte medicinalis (main ingredient is activated charcoal; interruption of potential entero-hepatic recirculation), acidification of urine, and forced diuresis, should be used as appropriate.
In case of signs and symptoms of general CNS overstimulation, careful symptomatic clinical treatment should be considered.