Methylphenidate (ritalin, others), structurally related to amphetamine, is a mild CNS stimulant with more prominent effects on mental than on motor activities. However, large doses produce signs of generalized CNS stimulation and convulsions. Its pharmacological properties are essentially the same as those of the amphetamines, including the potential for abuse. Methylphenidate is a schedule Il-controlled substance in the U.S. Methylphenidate is effective in the treatment of narcolepsy and attention-deficit/hyperactivity disorder (see below). Racemic methylphenidate is readily absorbed after oral administration and reaches peak concentrations in plasma in ~2 hours. The more potent (+) enantiomer has a t122 of ~6 hours. Concentrations in the brain exceed those in plasma. The main urinary metabolite is a deesterified product, ritalinic acid, which accounts for 80% of the dose. Methylphenidate is contraindicated in patients with glaucoma.
Dexmethylphenidate (focalin) is the d-threo enantiomer of racemic methylphenidate. It is FDA approved for the treatment of attention-deficit/hyperactivity disorder and is a schedule II-con-trolled substance in the U.S.
Pemoline (cylert, others), structurally dissimilar to methylphenidate, elicits similar changes in CNS function with minimal effects on the cardiovascular system. It is a schedule IV-controlled substance in the U.S. and is used in treating attention-deficit/hyperactivity disorder. It can be given once daily because of its long t122. Clinical improvement may require treatment for 3-4 weeks. Pemoline has been associated with severe hepatic failure.
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