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Dexmethylphenidate

Dexmethylphenidate
Systematic (IUPAC) name
(R,R)-(+)-Methyl 2-phenyl-2-(2-piperidyl)acetate
Clinical data
Trade names Focalin, Focalin XR, Attenade
AHFS/Drugs.com
MedlinePlus
Pregnancy
category
  • C
Legal status
Routes of
administration
oral
Pharmacokinetic data
Bioavailability 11 – 52%
Protein binding 30%
Metabolism hepatic
Biological half-life 4 hours
Excretion renal
Identifiers
CAS Registry Number  N
ATC code N06
PubChem CID:
IUPHAR/BPS
DrugBank  Y
ChemSpider  Y
UNII  Y
KEGG  Y
ChEBI  Y
ChEMBL  Y
Chemical data
Formula C14H19NO2
Molecular mass 233.31 g/mol
 N   

Dexmethylphenidate (trade names Focalin, Attenade; also known as d-threo-methylphenidate (D-TMP)) is a central nervous system (CNS) stimulant of the phenethylamine and piperidine classes that is used in the treatment of attention deficit hyperactivity disorder (ADHD) and narcolepsy.[1] It is the active dextrorotatory enantiomer of methylphenidate.

Contents

  • Medical uses 1
  • Contraindications 2
  • Adverse effects 3
  • Overdose 4
    • Addiction and dependence 4.1
      • Biomolecular mechanisms 4.1.1
  • Interactions 5
  • Mode of activity 6
  • Pharmacology 7
  • References 8
  • External links 9

Medical uses

Dexmethylphenidate is used as a treatment for ADHD, usually along with psychological, educational, behavioral or other forms of treatment. It is proposed that stimulants help ameliorate the symptoms of ADHD by making it easier for the user to concentrate, avoid distraction, and control behavior. Placebo-controlled trials have shown that once-daily dexmethylphenidate XR was effective and generally well tolerated.[1] Improvements in ADHD symptoms in children were significantly greater for dexmethylphenidate XR versus placebo.[1] It also showed greater efficacy than osmotic controlled-release oral delivery system (OROS) methylphenidate over the first half of the laboratory classroom day but assessments late in the day favoured OROS methylphenidate.[1]

Contraindications

Methylphenidate is contraindicated for individuals using monoamine oxidase inhibitors (e.g., phenelzine and tranylcypromine), or individuals with agitation, tics, or glaucoma, or a hypersensitivity to any ingredients contained in methylphenidate pharmaceuticals.[2]

The U.S. FDA gives methylphenidate a pregnancy category of C, and women are advised to only use the drug if the benefits outweigh the potential risks.[3] Not enough animal and human studies have been conducted to conclusively demonstrate an effect of methylphenidate on fetal development. In 2007, empirical literature included 63 cases of prenatal exposure to methylphenidate across three empirical studies.[4]

Adverse effects

Products containing dexmethylphenidate have a side effect profile comparable to those containing methylphenidate.[5]

Methylphenidate is generally well tolerated.[6][7][8][9][10] The most commonly observed adverse effects with a frequency greater than placebo include appetite loss, dry mouth, anxiety/nervousness, nausea, and insomnia. Gastrointestinal adverse effects may include abdominal pain and weight loss. Nervous system adverse effects may include akathisia (agitation/restlessness), irritability, dyskinesia (tics), lethargy (drowsiness/fatigue), and dizziness. Cardiac adverse effects may include palpitations, changes in blood pressure and heart rate (typically mild), and tachycardia (rapid resting heart rate). Ophthalmologic adverse effects may include blurred vision and dry eyes, with less frequent reports of diplopia and mydriasis.[11] Other adverse effects may include depression, emotional lability, confusion, and bruxism. Hyperhidrosis (increased sweating) is common. Chest pain is rarely observed.

There is some evidence of mild reductions in growth rate with prolonged treatment in children, but no causal relationship has been established and reductions do not appear to persist long-term.[12] Hypersensitivity (including skin rash, urticaria, and fever) is sometimes reported. The Daytrana patch has a much higher rate of dermal reactions than oral methylphenidate.[13]

Methylphenidate can worsen psychosis in psychotic patients, and in very rare cases it has been associated with the emergence of new psychotic symptoms.[14] It should be used with extreme caution in patients with bipolar disorder due to the potential induction of mania or hypomania.[15] There have been very rare reports of suicidal ideation, but evidence does not support a link.[12] Logorrhea is occasionally reported. Libido disorders, disorientation, and hallucinations are very rarely reported. Priapism is a very rare adverse event that can be potentially serious.[16]

USFDA-commissioned studies from 2011 indicate that in children, young adults, and adults there is no association between serious adverse cardiovascular events (sudden death, heart attack, and stroke) and the medical use of methylphenidate or other ADHD stimulants.[17][18][19][20]

Because some adverse effects may only emerge during chronic use of methylphenidate, a constant watch for adverse effects is recommended.[21]

Overdose

The symptoms of a moderate acute overdose on methylphenidate primarily arise from central nervous system overstimulation; these symptoms include: vomiting, agitation, tremors, hyperreflexia, muscle twitching, euphoria, confusion, hallucinations, delirium, hyperthermia, sweating, flushing, headache, tachycardia, heart palpitations, cardiac arrhythmias, hypertension, mydriasis, and dryness of mucous membranes.[22][23] A severe overdose may involve symptoms such as hyperpyrexia, sympathomimetic toxidrome, convulsions, paranoia, stereotypy (a repetitive movement disorder) rapid muscle breakdown, coma, and circulatory collapse.[22][23][24] A methylphenidate overdose is rarely fatal with appropriate care.[24] Severe toxic reactions involving abscess and necrosis have been reported following injection of methylphenidate tablets into an artery.[25]

Treatment of a methylphenidate overdose typically involves the application of benzodiazepines, with antipsychotics, α-adrenoceptor agonists, and propofol serving as second-line therapies.[24]

Addiction and dependence

ΔFosB accumulation graph
Top: this depicts the acute expression of various Fos family proteins following an initial exposure to an addictive drug.
Bottom: this illustrates increasing ΔFosB expression from repeated twice daily drug binges, where these phosphorylated (35–37 kD) ΔFosB isoforms persist in mesolimbic dopamine neurons for up to 2 months.[26][27]

Pharmacological texts describe methylphenidate as a stimulant with effects, addiction liability, and dependence liability similar to the amphetamine, a compound with moderate liability among addictive drugs;[28][29] accordingly, addiction and psychological dependence are possible and likely when methylphenidate is used at high doses as a recreational drug.[29][30] When used above the medical dose range, stimulants are associated with the development of stimulant psychosis.[31] As with all addictive drugs, the overexpression of ΔFosB in D1-type medium spiny neurons in the nucleus accumbens is implicated in methylphenidate addiction.[30][32]

Methylphenidate has shown some benefits as a replacement therapy for individuals who are addicted to and dependent upon methamphetamine.[33] Methylphenidate and amphetamine have been investigated as a chemical replacement for the treatment of cocaine addiction[34][35][36][37] in the same way that methadone is used as a replacement drug for physical dependence upon heroin. Its effectiveness in treatment of cocaine or psychostimulant addiction or psychological dependence has not been proven and further research is needed.[38]

Biomolecular mechanisms

Methylphenidate has the potential to induce euphoria due to its pharmacodynamic effect (i.e., dopamine reuptake inhibition) in the brain's reward system.[32] At therapeutic doses, ADHD stimulants do not sufficiently activate the reward system, or the reward pathway in particular, to induce persistent ΔFosB gene expression in the D1-type medium spiny neurons of the nucleus accumbens;[29][32][39] consequently, when used medically and as directed, methylphenidate use has no capacity to cause an addiction.[29][32][39] However, when methylphenidate is used at sufficiently high recreational doses through a bioavailable route of administration (e.g., insufflation or intravenous administration), particularly for use of the drug as a euphoriant, ΔFosB accumulates in the nucleus accumbens.[29][32] Hence, like any other addictive drug, regular recreational use of methylphenidate at high doses eventually gives rise to ΔFosB overexpression in D1-type neurons which subsequently triggers a series of gene transcription-mediated signaling cascades that induce an addiction.[32][39][40][41][42]

Interactions

Methylphenidate may inhibit the metabolism of coumarin anticoagulants, certain anticonvulsants, and some antidepressants (tricyclic antidepressants and selective serotonin reuptake inhibitors). Concomitant administration may require dose adjustments, possibly assisted by monitoring of plasma drug concentrations.[9] There are several case reports of methylphenidate inducing serotonin syndrome with concomitant administration of antidepressants.[43][44][45][46]

When methylphenidate is coingested with ethanol, a metabolite called ethylphenidate is formed via hepatic transesterification,[47][48] not unlike the hepatic formation of cocaethylene from cocaine and alcohol. The reduced potency of ethylyphenidate and its minor formation means it does not contribute to the pharmacological profile at therapeutic doses and even in overdose cases ethylphenidate concentrations remain negligible.[49][50]

Coingestion of alcohol (ethanol) also increases the blood plasma levels of d-methylphenidate by up to 40%.[51]

Liver toxicity from methylphenidate is extremely rare, but limited evidence suggests that intake of β-adrenergic agonists with methylphenidate may increase the risk of liver toxicity.[52]

Mode of activity

Methylphenidate is a catecholamine reuptake inhibitor that indirectly increases catecholaminergic neurotransmission by inhibiting the dopamine transporter (DAT) and norepinephrine transporter (NET),[53] which are responsible for clearing catecholamines from the synapse, particularly in the striatum and meso-limbic system.[54] Moreover, it is thought to "increase the release of these monoamines into the extraneuronal space."[55]

Although four stereoisomers of methylphenidate (MPH) are possible, only the threo diastereoisomers are used in modern practice. There is a high eudysmic ratio between the SS and RR enantiomers of MPH. Dexmethylphenidate (d-threo-methylphenidate) is a preparation of the RR enantiomer of methylphenidate.[56][57] In theory, D-TMP (d-threo-methylphenidate) can be anticipated to be twice the strength of the racemic product.[58][53]

Compd[59] DAT (Ki) DA (IC50) NET (Ki) NE (IC50)
D-TMP 161 23 206 39
L-TMP 2250 1600 >10K 980
DL-TMP 121 20 51 788

Pharmacology

Dexmethylphenidate has a 4-6 hour duration of effect (a long-acting formulation, Focalin XR, which spans 12 hours is also available and has been shown to be as effective as DL (dextro-, levo-)-TMP (threo-methylphenidate) XR (extended release) (Concerta, Ritalin LA), with flexible dosing and good tolerability.[60][61]) It has also been demonstrated to reduce ADHD symptoms in both children[62] and adults.[63] d-MPH has a similar side-effect profile to MPH[64] and can be administered without regard to food intake.[65]

References

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    The strong correlation between chronic drug exposure and ΔFosB provides novel opportunities for targeted therapies in addiction (118), and suggests methods to analyze their efficacy (119). Over the past two decades, research has progressed from identifying ΔFosB induction to investigating its subsequent action (38). It is likely that ΔFosB research will now progress into a new era – the use of ΔFosB as a biomarker. ...

    Conclusions
    ΔFosB is an essential transcription factor implicated in the molecular and behavioral pathways of addiction following repeated drug exposure. The formation of ΔFosB in multiple brain regions, and the molecular pathway leading to the formation of AP-1 complexes is well understood. The establishment of a functional purpose for ΔFosB has allowed further determination as to some of the key aspects of its molecular cascades, involving effectors such as GluR2 (87,88), Cdk5 (93) and NFkB (100). Moreover, many of these molecular changes identified are now directly linked to the structural, physiological and behavioral changes observed following chronic drug exposure (60,95,97,102). New frontiers of research investigating the molecular roles of ΔFosB have been opened by epigenetic studies, and recent advances have illustrated the role of ΔFosB acting on DNA and histones, truly as a ‘‘molecular switch’’ (34). As a consequence of our improved understanding of ΔFosB in addiction, it is possible to evaluate the addictive potential of current medications (119), as well as use it as a biomarker for assessing the efficacy of therapeutic interventions (121,122,124). Some of these proposed interventions have limitations (125) or are in their infancy (75). However, it is hoped that some of these preliminary findings may lead to innovative treatments, which are much needed in addiction.
     
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External links

  • Information from the U.S. National Institute of Health
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