Methylphenidate is a stimulant used in the management of Attention Deficit Hyperactivity Disorder (ADHD) for the treatment of narcolepsy.
Also known as the marketed products Ritalin, Concerta, or Biphentin, methylphenidate is used with other treatment modalities (psychological, educational, cognitive behaviour therapy, etc) to improve the following group of developmentally inappropriate symptoms associated with ADHD: moderate-to-severe distractibility, short attention span, hyperactivity, emotional lability, and impulsivity.
Long-acting formulations of psychostimulants such as methylphenidate, Dextroamphetamine, and Lisdexamfetamine are considered the most effective and widely used treatment for ADHD, and are considered first-line options for children, adolescents, and adults as recommended by CADDRA (Canadian ADHD Resource Alliance). CADDRA recommends the use of methylphenidate due to long term studies, of over twenty years in duration, which show methylphenidate is safe and effective.
Methylphenidate may also be used for purposes not listed in this medication guide.
Methylphenidate is a racemic mixture comprised of the d- and l-isomers. The d-isomer is more pharmacologically active than the l-isomer.
Radioligand binding studies demonstrate that binding of methylphenidate in the brain is localized to dopamine-rich areas, in particular in the prefrontal cortex which has been demonstrated to play a prominent role in ADHD pathophysiology.
Methylphenidate contains a blackbox warning stating that CNS stimulants, including methylphenidate-containing products and amphetamines, have a high potential for abuse and dependence. This abuse potential is likely related to the effects associated with higher doses of methylphenidate, which induce surface expression of the dopamine transporter (DAT).
In particular, increased dopamine in key brain areas is associated with the reinforcing and addictive properties of psychostimulants such as methylphenidate, and even amplifies the potency and reinforcing effects of other drugs of abuse such as amphetamines, making ADHD sufferers more susceptible to their addictive effects.
While its exact mechanism is unclear, methylphenidate (MPH) has been shown to act as a norepinephrine and dopamine reuptake inhibitor (NDRI), thereby increasing the presence of these neurotransmitters in the extraneuronal space and prolonging their action.
There is a dose-related effect of psychostimulants on receptor stimulation, where higher doses are shown to increase norepinephrine (NE) and dopamine (DA) efflux throughout the brain which can result in impaired cognition and locomotor-activating effects. In contrast, low doses are found to selectively activate NE and DE neurotransmission within the prefrontal cortex which is an area of the brain thought to play a prominent role in ADHD pathophysiology, thereby improving clinical efficacy and preventing side effects.
The lower doses used to treat ADHD are not associated with the locomotor-activating effects associated with higher doses and instead reduce movement, impulsivity, and increase cognitive function including sustained attention and working memory. Methylphenidate's beneficial effects in sustaining attention have also been shown to be mediated by alpha-1 adrenergic receptor activity.
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.
Absorption: Methylphenidate hydrochloride is rapidly and extensively absorbed from the tablets following oral administration; however, owing to extensive first-pass metabolism, bioavailability is low (approx. 30%) and large individual differences exist (11-52%).
Route of elimination: After oral administration of an immediate release formulation of methylphenidate, 78%-97% of the dose is excreted in the urine and 1%-3% in the feces in the form of metabolites within 48-96 hours. Only small quantities, under 1% of unchanged methylphenidate appear in the urine. Most of the dose is excreted in the urine as ritalinic acid (60%-86%), the remainder being accounted for by minor metabolites.
Half life: Methylphenidate is eliminated from the plasma with a mean half-life of 2.4 hours in children and 2.1 hours in adults.
All medicines may cause side effects, but many people have no, or minor, side effects. Some medical conditions may interact with Methylphenidate.
Tell your doctor or pharmacist if you have any medical conditions.
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.
This is not a complete list of all side effects that may occur. If you have questions about side effects, contact your health care provider.
