Metrifonate: a new agent for the treatment of Alzheimer's disease.

The pharmacology, pharmacokinetics, clinical efficacy, and adverse effects of metrifonate, a long-acting cholinesterase inhibitor, are discussed. Attempts to correct the central cholinergic deficits associated with Alzheimer's disease have included administration of cholinergic precursors, cholinergic agonists, and cholinesterase inhibitors. To date, two reversible cholinesterase inhibitors-tacrine and donepezil-have been marketed. Metrifonate, an organophosphate, is converted nonenzymatically to 2,2-dichlorovinyl dimethyl phosphate (DDVP), the active enzyme inhibitor. DDVP produces irreversible inhibition of brain cholinesterase that lasts for several days; enzyme recovery is dependent on synthesis of new enzyme. Several preclinical studies have demonstrated cognition-enhancing effects of metrifonate in animals. Trials in humans have shown improvement on the Alzheimer's Disease Assessment Scale, in Mini-Mental State Examination scores, and in the Clinician's Interview-Based Impression of Change with caregiver input. Clinical improvement noted with metrifonate appears similar to that seen with other cholinesterase inhibitors. Adverse effects noted in clinical trials have been associated primarily with the gastrointestinal tract and have been mild. Metrifonate appears to be a promising agent for the treatment of the symptoms of Alzheimer's disease.