When children with ADHD don’t respond well to Methylphenidate (Ritalin) doctors often increase the dose. Now a new review shows that increasing the dose may not always be the best option, as it may have no effect on some of the functional impairments associated with ADHD. The researchers caution against increasing the doses is based on findings that this effect may only be observed for behavioral factors (such as reduction in attention and/or hyperactivity/impulsivity) and not for the child’s ability to control their impulses. This work is presented at the ECNP Conference held in Copenhagen.
Methylphenidate (MPH) has been commonly used as a first line medication to treat children with ADHD since the 1990s. It is generally effective and well tolerated, but around 30% of children taking MPH don’t respond to standard doses, often leading doctors to consider increasing the dose.
Like all drugs, MPH carries the risk of side effects, which may become more significant at increased dose and with long-term use. These side effects include growth retardation and difficulty in gaining weight: 3 years of MPH use can cause a child to be 2cm shorter and 2.7 kg lighter than normal.
To understand and distil the effects of the drug on children with ADHD, Karen Vertessen (MD & PhD student at the Vrije Universiteit Amsterdam) and colleagues undertook a review of all the scientific literature (a metanalysis) relating to dose effects of MPH on inhibitory control (an aspect of impulsiveness) in children and adolescents.
They managed to identify 18 studies, comprising in total 606 subjects with ADHD. They were able to classify the MPH doses reported as low, medium, or high dose. Results showed that a medium dose of MPH had the strongest beneficial effects on inhibitory control. However, increasing the dose past the medium dose did not make the drug work more effectively.
Vertessen said, “Scientifically, this is an interesting result. Generally, high doses of MPH do not help the child or adolescent keep their inhibitions under better control, although an increased dose, in general, does have a greater effect on the core behavioural symptoms of ADHD.
Even though inhibitory control is just one aspect of impulsivity, we suggest that medically we need to be cautious about just increasing the dose when a child does not instantly respond to the drugs. Children are more vulnerable than adults in these cases, especially since they will be just beginning to receive treatment, and so many treatment variables will still need to be established. If clinicians decide to start therapy with MPH, they need to keep a close eye on the patient and objectively evaluate every dose, to make sure that the higher dose is actually having an effect.
“Current ADHD evaluation only uses behavioural outcomes, whereas we suggest adding neurocognitive outcomes to this evaluation, given that these outcomes are important for, among others, academic functioning. In other words, checking for whether or not MPH is dealing with inhibitory control might allow us to see if increasing the dose makes sense. To see to what extent these findings might have a clinical impact, we are currently investigating the other most relevant neurocognitive factors related to ADHD”, Vertessen said.