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Revision as of 16:41, 14 October 2010
Contents
Introduction
This article is about stimulants used in treatment of ADHD. See ADHD and DBDs articles for role of stimulants in the overall treatment strategies. A separate article addresses design and outcomes of the MTA study. Intoxication and overdose with stimulants is addressed separately.
Amphetamines
Amphetamine is a racemic compound (equal parts of D- and L-isomers). D-isomer (dextroamphetamine) is 3-4 times more potent than the L-isomer (levoamphetamine) as a CNS stimulant.[1] Stimulants used in ADHD are modified forms of amphetamine:
- Dexedrine is a dextroamphetamine (d-amphetamine) which is the D-isomer of amphetamine.
- Adderall is a mixture of salts of d-amphetamine and racemic amphetamine (d,l-amphetamine)
- Vyvanse is lesdexamphetamine, a prodrug metabolized by an enzyme on RBCs to d-amphetamine
Amphetamines have a short half-life (3-6 hours), necessitating TID dosing or use of extended-release preparations qAM.
Most (80%) is excreted unchanged by the kidneys, especially if urinary pH is low; acidifying urine increases rate of excretion (consider in overdose).
Methylphenidate
Methylphenidate (MPH) is a racemic compound derived from amphetamine:
- Concerta, Ritalin, Metadate, and Methylin are d,l-methylphenidate (MPH)
- Focalin is a D-isomer of MPH, or d-methylphenidate
- Daytrana is a transdermal MPH patch; it is placed on the skin for 9 hrs/day and can be effective for up to 12 hrs
Since D-isomer is beleived to be the active compund in CNS stimulation, 5 mg of Focalin has similar potency as 10mg of Ritalin,[1] while, theoretically, causing fewer side effects.
MPH has a half-life of 2-3 hours. 75% of MPH is metabolized (extensive 1st-pass metabolism) to inactive ritalinic acid.
Other stimulants
- Desoxyn is a methamphetamine (not MPH), approved for ADHD and exogenous obesity, but rarely prescribed
Mechanism of Action
Amphetamines and MPH increase synaptic concentrations of dopamine (DA), norepinephrine (NE), and serotonin via different mechanisms. Both MPH and amphetamines cause DA vessicles to relesase their contents at the synapse (amphetamines do this more selectively). MPH and amphetamines also block DA reuptake at the synapse. Amphetamines have more potent effect on the NE pathways than MPH does. [3]
Adverse Effects
Growth retardation is likely 2° to stimulant-induced appetite suppression. In the MTA study 2-year follow-up children on MPH were 1cm/year shorter and 1 kg lighter than children not taking stimulants. There is evidence that children "catch-up" once they enter puberty, or during "drug holidays," (e.g. if the medication is discontinued for the summer), however a cumulative deficit of about 1 inch may persist.[4] Significance of poor appetite can be minimized, if stimulants are taken with food (or after finishing breakfast).
Sleep disturbance is another common adverse effect. Management of this AE starts with sleep hygeine and stimulant dose adjustment. For children whose sleep troubles remain significant, adding an α-agonist (clonidine) qPM, switching to a different stimulant, or Intuniv are fair options.
Other common side effects include headache, GI symptoms, jitteriness, irritability, increase in HR and BP, dry mouth, blurred vision (anticholinergic AE).
Rarer and more concerning AE include depressed mood, emotional blunting/"zombie appearance"/"amphetamine look," hallucinations, tics, arrhythmias, leukopenia, and alopecia.
Clinical guidelines
Stimulants are contraindicated in patients with glaucoma, symptomatic CVD/HTN, hyperthyroidism, advanced atherosclerosis, and those taking MAO-I in the last 2 weeks.
Check BP and HR before starting a stimulant and at every dose increase. Obtain baseline and follow-up measure of symptom severity in two setting. [2][6] Baseline EKG is not part of the standard screening in the US.
Record height and weight and track yearly.
ADHD patients with manic symptoms can be put on a stimulant after the mood symptoms have been controlled with a mood-stabilizer. [2]
Ordering TSH and lead levels is only warranted if there is evidence of thyroid dysfunction or risk of lead exposure. [2]
Stimulants are generally safe in children with comorbid ADHD and tic disorder, however if tics worsen, or new tics appear, the stimulant should be changed or discontinued. [4]
MPH may lower seizure threshold; children with seizure disorders should be on an anticonvulsant.
Which stimulant to start with?
- Start a long-acting stimulant with the smallest marketed dose, titrate up q1-3 weeks.
- A stimulant that worked in a family member is a good first choice.
- MPH preparations are not recommended for children under age 6; start 5-year-olds on an amphetamine preparation.
Extended-Release Stimulants
Long-acting Stimulants approved for ADHD (methylphenidate and amphetamine preparations)
Medication
Mode of Delivery
Pill
Doses, mg
Typical Starting Dose
Max Dose per Day
Duration of Action
Ritalin SR (MPH)
Gradually released from wax matrix;
Pulse release; must swallow whole
20
10mg
60mg
7-8 hrs
Metadate ER
10, 20
Lesser than 2mg/kg/day or 60mg
Methylin ER (MPH)
10, 20
Metadate CD (MPH)
30% IR; 70% 3hrs later
Beaded pearls; can open and sprinkle
10, 20, 30, 40, 50, 60
20mg
8-9 hrs
Ritalin LA (MPH)
50% IR; 50% 4 hrs later
10, 20, 30, 40
20mg
60
7-9 hrs
Focalin XR (d-MPH)
Pearls; capsule
5, 10, 15, 20
5mg
Lesser than 1mg/kg/d or 30mg
Up to 12 hrsConcerta (MPH)
18% IR tab coating; 82% osmotically; mimics tid IR; ok if cap seen in stool
OROS Pump; don’t open
18, 27, 36, 54
18mg
Lesser than 2mg/kg/d or 72mg
Daytana (MPH)
Gradually releasing MPH
Trans-dermal film
10, 15, 20, 30
10mg
Lesser than 1mg/kg/d or 30mg
12 hrs
Adderall XR
50% IR; 50% 4hr later
Beaded pearls; can sprinkle
5, 10, 15, 20, 25, 30
10mg
Lesser than 1mg/kg or 30mg
10 hrs
Dexedrine
Initial dose released immediately; remainder gradually released
Beaded pearls
5, 10, 15
5-10mg q.d.to b.i.d.
Lesser than 1mg/kg or 40mg
10 hrs
Vyvanse (lisdexamphetamine)
Amphetamine w lysine attached; activated by GI cleavage of lysine
Capsule
20, 30, 40, 50, 60, 70
30mg
Lesser than 1mg/kg or 70mg
10 hrs
Abbreviations: OROS = osmotic-release oral system; IR = immediate release.
Notes: Concerta capsule should not be chewed or opened; pill may be seen in stool intact. Children with reduced GI absorption or transit time will benefit less. Patch: higher bioavailability (no first-pass metabolism).
[5]
Clinical Pearls
Stimulants are contraindicated in patients with glaucoma, psychosis, symptomatic CVD/HTN, hyperthyroidism, advanced atherosclerosis, and those taking MAO-I in the last 2 weeks.
Currently only stimulants, atomoxetine, and guanfacine ER (Intuniv) have approved FDA indications for ADHD.
Black-box warning was briefly considered for MPH-based drugs, because of cardiac-related adverse events, including sudden unexplained deaths.
Rebound is marked worsening of ADHD symptoms at the end of the day, as the blood level of a stimulant drop below a certain threshold. If the child is taking an extended-release stimulant, consider adding a small short-acting dose in the afternoon.
There is no increase in risk of future drug or alcohol abuse from appropriate stimulant use; in fact, children with untreated ADHD are at higher risk for substance use, than children taking stimulants for ADHD; however, stimulants are a Category II drugs, have substantial street value (particularly short-acting preparations), and can not be prescribed for more than 30 d (no refills).
Pemoline is not used due to hepatotoxicity.
When swithcing from MPH to d-amphetamine, half the dose for equivlent potency.
Prognosis
- parents often see general improvement within the first week, and up to 80% of children with ADHD respond to their first stimulant.
- About a third of children with ADHD will need to continue taking stimulants into adulthood to control symptoms
- Roughly another third will not have significant symptoms as adults
- Hyperactivity is the symptom most likely to be "outgrown"
Major studies
MTA study
The Multimodal Treatment Study of ADHD and its 2-year follow up is covered in a separate article.
PATS Study
Preschool ADHD Treatment Study (2006) was a radndomized placebo-controlled trial (RCT) in which 3 to 5.5yo children with symptoms of severe ADHD were prescribed MPH TID or placebo. There was marked decrease in ADHD symptoms. MPH was mostly well tolerated, but overall, 11% discontinued treatment due to AE. No episodes of mania, suicidality or serious cardiac events were observed.
Other CNS stimulants
- Cocaine
- Caffeine
- Nicotine
- Modafinil
- MDMA (Ecstasy)
- Crystal meth
References
[1] Labbate LA. Handbook of Psychiatric Drug Therapy 2010
[2] AACAP Practice Parameter JAACAP, 2007;46(7):894-921
[3] Martin A. Lewis's Child and Adolescent Psychiatry 4th edition pp.757-759
[4] Manos MJ. Managing ADHD ni a Fast-Paced World JManagCarePharm Nov.2007
[5] Information in the table is adopted from Lewis's Child and Adolescent Psychiatry 4th edition pp.443-446, [1], [6], and the PDR
[6] Bezchlibnyk-Butler KZ. Clinical Handbook of Psychotropic Drugs for Children and Adolescents 2nd ed. 2007
Copyright 2010 E. Grudnikoff
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