Singapore Drugs Database

Indication

For use as an integral part of a total treatment program which typically includes other remedial measures (psychological, educational, social) for a stabilizing effect in children with a behavioral syndrome characterized by the following group of developmentally inappropriate symptoms: moderate-to-severe distractibility, short attention span, hyperactivity, emotional lability, and impulsivity.

Mechanism of Action

Methylphenidate blocks dopamine uptake in central adrenergic neurons by blocking dopamine transport or carrier proteins. Methylphenidate acts at the brain stem arousal system and the cerebral cortex and causes increased sympathomimetic activity in the central nervous system. Alteration of serotonergic pathways via changes in dopamine transport may result.

Pharmacokinetics

Absorption

Readily absorbed in a biphasic manner when orally administered (tablets) to children diagnosed with ADHD and to healthy adults. In children and adults males, after administration of a single oral dose of Ritalin LA and Ritalin given in two doses 4 hours apart, peak plasma concentration is reached approximately 2 hours for the first phase and 5-6 hours for the second phase. The absolute oral bioavailability of methylphenidate in children was 22±8% for d-methylphenidate and 5±3% for l-methylphenidate. These low values suggest that methylphenidate is highly metabolized presystemically.

Distribution

d-methylphenidate = 2.65 L/kg; l-methylphenidate = 1.80 L/kg;

Metabolism

Methylphenidate is hepatically metabolized. More specifically, it is rapidly and extensively metabolized by carboxylesterase CES1A1. Via this enzyme, methylphenidate undergoes de-esterification to ritalinic acid (a-phenyl-2-piperidine acetic acid, PPAA), which has little to no pharmacologic activity.

Elimination

Clearance

Systemic clearance for Ritalin LA and Ritalin tablets is as follows: d-methylphenidate= 0.40±0.12 L/h/kg; l-methylphenidate = 0.73±0.28 L/h/kg;

Toxicity

Symptoms of overdose include vomiting, agitation, tremors, hyperreflexia, muscle twitching, convulsions (may be followed by coma), euphoria, confusion, hallucinations, delirium, sweating, flushing, headache, hyperpyrexia, tachycardia, palpitations, cardiac arrhythmias, hypertension, mydriasis, and dryness of mucous membranes. LD₅₀=190mg/kg (orally in mice)

Active Ingredient/Synonyms

Methyl phenidylacetate | methyl phenyl(piperidin-2-yl)acetate | methyl α-phenyl-α-(2-piperidyl)acetate | methyl α-phenyl-α-2-piperidinylacetate | Methylphenidan | Methylphenidatum | Metilfenidato | MPH | α-phenyl-2-piperidineacetic acid methyl ester | Methylphenidate |