Dexmethylphenidate: Difference between revisions
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| intro = '''Dexmethylphenidate''' — marketed as '''Focalin''' and '''Focalin XR''' — is the isolated d-threo enantiomer of [[Methylphenidate|methylphenidate]]. Racemic methylphenidate contains both d- and l-threo enantiomers in equal amounts, but essentially all pharmacologic activity resides in the d-isomer; the l-isomer is rapidly cleared on first-pass and contributes little beyond a possible minor role in peripheral side effects. By delivering only the active enantiomer, Focalin achieves equivalent therapeutic effect at approximately half the milligram dose of racemic methylphenidate, with some patients reporting a cleaner subjective profile (less jitteriness, more focused effect). Its clinical | | intro = '''Dexmethylphenidate''' — marketed as '''Focalin''' and '''Focalin XR''' — is the isolated d-threo enantiomer of [[Methylphenidate|methylphenidate]]. Racemic methylphenidate contains both d- and l-threo enantiomers in equal amounts, but essentially all pharmacologic activity resides in the d-isomer; the l-isomer is rapidly cleared on first-pass and contributes little beyond a possible minor role in peripheral side effects. By delivering only the active enantiomer, Focalin achieves equivalent therapeutic effect at approximately half the milligram dose of racemic methylphenidate, with some patients reporting a cleaner subjective profile (less jitteriness, more focused effect). Its clinical problems, mechanism, contraindications, and adverse-effect profile are otherwise nearly identical to racemic methylphenidate. | ||
| pharmacokinetics = '''Absorption:''' Rapid oral absorption; peak plasma in ~1–1.5 h (IR) or ~6.5 h (XR, which has a biphasic release profile with an initial peak around 1.5 h and a second peak ~6.5 h). Bioavailability ~22–25% due to extensive first-pass metabolism. '''Distribution:''' Volume of distribution similar to racemic methylphenidate (~13 L/kg); plasma protein binding ~15%. '''Metabolism:''' Like the racemate, dexmethylphenidate is metabolized primarily by '''carboxylesterase 1 (CES1)''' to ritalinic acid (inactive). This non-CYP metabolic pathway means dexmethylphenidate, like its racemate, has '''few clinically significant CYP-mediated med interactions'''. '''Elimination:''' Predominantly renal as ritalinic acid; parent half-life 2.2 h (IR) and ~3 h (XR parent). Multi-dose-daily IR dosing or once-daily XR is required for sustained therapeutic effect. | | pharmacokinetics = '''Absorption:''' Rapid oral absorption; peak plasma in ~1–1.5 h (IR) or ~6.5 h (XR, which has a biphasic release profile with an initial peak around 1.5 h and a second peak ~6.5 h). Bioavailability ~22–25% due to extensive first-pass metabolism. '''Distribution:''' Volume of distribution similar to racemic methylphenidate (~13 L/kg); plasma protein binding ~15%. '''Metabolism:''' Like the racemate, dexmethylphenidate is metabolized primarily by '''carboxylesterase 1 (CES1)''' to ritalinic acid (inactive). This non-CYP metabolic pathway means dexmethylphenidate, like its racemate, has '''few clinically significant CYP-mediated med interactions'''. '''Elimination:''' Predominantly renal as ritalinic acid; parent half-life 2.2 h (IR) and ~3 h (XR parent). Multi-dose-daily IR dosing or once-daily XR is required for sustained therapeutic effect. | ||
| pharmacodynamics = Mechanistically identical to racemic methylphenidate at the molecular level — competitive inhibition of the dopamine and norepinephrine transporters (DAT, NET), increasing synaptic catecholamine concentrations without acting as a transporter substrate (i.e., no reverse transport or vesicular displacement; '''reuptake inhibition only'''). The functional difference is purely stereochemical: dexmethylphenidate provides the same effective amount of pharmacologically active material at half the milligram dose. Minimal effect on serotonin; no MAO inhibition; no significant binding at 5-HT, histamine, or muscarinic receptors. | | pharmacodynamics = Mechanistically identical to racemic methylphenidate at the molecular level — competitive inhibition of the dopamine and norepinephrine transporters (DAT, NET), increasing synaptic catecholamine concentrations without acting as a transporter substrate (i.e., no reverse transport or vesicular displacement; '''reuptake inhibition only'''). The functional difference is purely stereochemical: dexmethylphenidate provides the same effective amount of pharmacologically active material at half the milligram dose. Minimal effect on serotonin; no MAO inhibition; no significant binding at 5-HT, histamine, or muscarinic receptors. | ||
| indications = * Attention-deficit hyperactivity disorder (children ≥6 y, adolescents, and adults) | | indications = * Attention-deficit hyperactivity disorder (children ≥6 y, adolescents, and adults) | ||
* Off-label: same off-label uses as racemic methylphenidate (treatment-resistant depression augmentation, cancer/HIV/MS fatigue) | * Off-label: same off-label uses as racemic methylphenidate (treatment-resistant depression augmentation, cancer/HIV/MS fatigue) | ||
* Not FDA-approved for narcolepsy (use racemic methylphenidate or an amphetamine for that | * Not FDA-approved for narcolepsy (use racemic methylphenidate or an amphetamine for that problem) | ||
| dosing = '''Focalin IR:''' Start 2.5 mg PO twice daily (separate doses by at least 4 h). Titrate by 2.5–5 mg/week. Max 20 mg/day (adults and children). | | dosing = '''Focalin IR:''' Start 2.5 mg PO twice daily (separate doses by at least 4 h). Titrate by 2.5–5 mg/week. Max 20 mg/day (adults and children). | ||
'''Focalin XR:''' Start 5 mg PO once daily AM (children), 10 mg PO once daily AM (adults). Titrate weekly. Max 30 mg/day (children); 40 mg/day (adults). | '''Focalin XR:''' Start 5 mg PO once daily AM (children), 10 mg PO once daily AM (adults). Titrate weekly. Max 30 mg/day (children); 40 mg/day (adults). | ||
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}}<h2 id="Pharmacokinetics">Pharmacokinetics</h2><span></span> | }}<h2 id="Pharmacokinetics">Pharmacokinetics</h2><span></span> | ||
'''Absorption:''' Rapid oral absorption; peak plasma in ~1–1.5 h (IR) or ~6.5 h (XR, which has a biphasic release profile with an initial peak around 1.5 h and a second peak ~6.5 h). Bioavailability ~22–25% due to extensive first-pass metabolism. '''Distribution:''' Volume of distribution similar to racemic methylphenidate (~13 L/kg); plasma protein binding ~15%. '''Metabolism:''' Like the racemate, dexmethylphenidate is metabolized primarily by '''carboxylesterase 1 (CES1)''' to ritalinic acid (inactive). This non-CYP metabolic pathway means dexmethylphenidate, like its racemate, has '''few clinically significant CYP-mediated med interactions'''. '''Elimination:''' Predominantly renal as ritalinic acid; parent half-life 2.2 h (IR) and ~3 h (XR parent). Multi-dose-daily IR dosing or once-daily XR is required for sustained therapeutic effect.<h2 id="Pharmacodynamics">Pharmacodynamics</h2> | '''Absorption:''' Rapid oral absorption; peak plasma in ~1–1.5 h (IR) or ~6.5 h (XR, which has a biphasic release profile with an initial peak around 1.5 h and a second peak ~6.5 h). Bioavailability ~22–25% due to extensive first-pass metabolism. '''Distribution:''' Volume of distribution similar to racemic methylphenidate (~13 L/kg); plasma protein binding ~15%. '''Metabolism:''' Like the racemate, dexmethylphenidate is metabolized primarily by '''carboxylesterase 1 (CES1)''' to ritalinic acid (inactive). This non-CYP metabolic pathway means dexmethylphenidate, like its racemate, has '''few clinically significant CYP-mediated med interactions'''. '''Elimination:''' Predominantly renal as ritalinic acid; parent half-life 2.2 h (IR) and ~3 h (XR parent). Multi-dose-daily IR dosing or once-daily XR is required for sustained therapeutic effect.<h2 id="Pharmacodynamics">Pharmacodynamics</h2> | ||
Mechanistically identical to racemic methylphenidate at the molecular level — competitive inhibition of the dopamine and norepinephrine transporters (DAT, NET), increasing synaptic catecholamine concentrations without acting as a transporter substrate (i.e., no reverse transport or vesicular displacement; '''reuptake inhibition only'''). The functional difference is purely stereochemical: dexmethylphenidate provides the same effective amount of pharmacologically active material at half the milligram dose. Minimal effect on serotonin; no MAO inhibition; no significant binding at 5-HT, histamine, or muscarinic receptors.<h2 id=" | Mechanistically identical to racemic methylphenidate at the molecular level — competitive inhibition of the dopamine and norepinephrine transporters (DAT, NET), increasing synaptic catecholamine concentrations without acting as a transporter substrate (i.e., no reverse transport or vesicular displacement; '''reuptake inhibition only'''). The functional difference is purely stereochemical: dexmethylphenidate provides the same effective amount of pharmacologically active material at half the milligram dose. Minimal effect on serotonin; no MAO inhibition; no significant binding at 5-HT, histamine, or muscarinic receptors.<h2 id="Problems">Problems</h2> | ||
*Attention-deficit hyperactivity disorder (children ≥6 y, adolescents, and adults) | *Attention-deficit hyperactivity disorder (children ≥6 y, adolescents, and adults) | ||
*Off-label: same off-label uses as racemic methylphenidate (treatment-resistant depression augmentation, cancer/HIV/MS fatigue) | *Off-label: same off-label uses as racemic methylphenidate (treatment-resistant depression augmentation, cancer/HIV/MS fatigue) | ||
*Not FDA-approved for narcolepsy (use racemic methylphenidate or an amphetamine for that | *Not FDA-approved for narcolepsy (use racemic methylphenidate or an amphetamine for that problem)<h2 id="Dosing">Dosing and titration</h2> | ||
<span></span> | <span></span> | ||