The central stimulants methylphenidate and dextroamphetamine are highly effective in the short-term treatment of childhood-onset disorders involving symptoms of inattention, hyperactivity, and impulsivity.(3) There is also evidence, albeit less comprehensive, that pemoline has short-term benefits for such symptoms.(4) In many countries, these three drugs can only be prescribed on a named-patient basis (or may not even be available).

About 75 per cent of children treated with stimulants show improved 'behaviour', measured in various ways. Conversely, about 25 per cent show no clinical response or their behaviour deteriorates while on such drugs. Sustained attention and persistence of effort to assigned tasks are augmented, and restlessness and motor overactivity decrease. Very often, the classroom behaviour of children with attention-deficit hyperactivity is normalized. (5) The drugs also enhance performance on tasks requiring fine motor co-ordination, vigilance, and impulse control and tend to reduce reaction times. In addition, and clinically of considerable importance, stimulants improve the quality of social interactions between children with attention-deficit hyperactivity and their parents, teachers, and peers. (3)

The support for continuation treatment for this class of medications is much less convincing. However, one longer-term double-blind placebo-controlled study indicated the continued usefulness of amphetamine 15 months after starting treatment,(6) with remaining positive effects on general behaviour, inattention, hyperactivity and learning, good treatment compliance, and few serious adverse events. The presence of comorbid tics, autistic-type symptoms, or mild mental retardation did not decrease the likelihood of a positive treatment response.

Common side-effects include decreased appetite, insomnia, and mild to moderate abdominal pain. These can usually be tolerated after titration of the dosage or decreasing/increasing the number of doses per day. They also tend to diminish within 1 to 2 weeks of beginning medication even without dosage adjustment. Rarer adverse effects, such as severe headaches, hallucinations, or the induction of a 'zombie' state (with overcontrolled aloof behaviours and a lack of spontaneity) can usually be controlled by dose reduction and disappear soon after the treatment is discontinued. Tics can be provoked by stimulant treatment, but probably only in individuals liable to tics or Tourette's syndrome. Caution is warranted when using stimulants for the treatment of attention-deficit hyperactivity in individuals who have an individual or family history of tics, but they should not be regarded a priori as contraindicated in such cases. (7)

Stimulants are given orally and are swiftly absorbed from the gastrointestinal tract. Behavioural effects are noticeable within 20 to 60 min, peak around 2 h after ingestion, and usually dissipate within 4 to 5 h. Pemoline has a somewhat longer half-life than dextroamphetamine and methylphenidate. In addition, the half-life tends to increase with chronic use, possibly accounting for the considerably delayed behavioural effects (up to several weeks) of this medication. Tolerance to these drugs has not been established, but anecdotal evidence suggests that it might exist in individual cases. (8) Sustained-release forms have obvious benefits from the point of view of administration of a drug, but there is evidence that they may be less effective than the standard preparations. (9) In many cases, pharmacotherapy can be discontinued during vacations, and sometimes even on weekends. However, it is often preferable to keep the child on about half the regular dose on Saturdays and Sundays to maintain habituation to side-effects, therefore avoiding a major problem in this respect at school on Monday mornings.

High levels of inattention (such as measured on the Kauffman freedom from distractibility factor of the Wechsler Intelligence Scale for Children), restless and acting-out behaviours, poor motor coordination, and young age, but not anxious/depressed mood or family/socio-economic variables, tend to predict a good response to stimulant treatment/3,1 d1

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