Search

Several studies have evaluated the association between individual polymorphisms and response to methylphenidate (MPH) in subjects with attention-deficit/hyperactivity disorder (ADHD). There are few replication studies for each polymorphism of interest and results are sometimes inconsistent in this field. Although data collection from multiple international sites would allow large sample sizes, this approach has been criticized for introducing sampling variability due to differences in ethnicity and methodology between studies. To examine these issues, we aggregated nine pharmacogenetic studies from four different continents and conducted a two stage analysis: (a) we evaluated the role of methodological aspects in the variability of ADHD symptom improvement between studies using meta-regression analysis; (b) we assessed the role of individual characteristics of the subjects in the variability of ADHD symptoms improvement using multivariate regression analysis in the same data sets. At the study level, from five evaluated factors, only the design of the study (open studies vs. randomized controlled trials) was significantly associated with heterogeneity of results (P = 0.001). At the individual level, age (P < 0.001), comorbid oppositional defiant disorder (P < 0.001), and pre-treatment scores (P < 0.001) were associated with change of ADHD scores with treatment in the final multivariate model. Our results suggest that joint analyses of pharmacogenetic studies are feasible and promising, since fixed variables, such as the site where the study was conducted, were not related to results. Nevertheless, stratified analyses according to the design of the study must be preferentially conducted and the role of individual factors such as demographic data and comorbid profile as confounders should be assessed., (Copyright 2008 Wiley-Liss, Inc.)

Background This study examined the effects of atomoxetine ( ATX) and OROS methylphenidate ( MPH) on laboratory measures of inhibitory control and attention in youth with attention-deficit/hyperactivity disorder ( ADHD). It was hypothesized that performance would be improved by both treatments, but response profiles would differ because the medications work via different mechanisms. Methods One hundred and two youth (77 male; mean age = 10.5 ± 2.7 years) with ADHD received ATX (1.4 ± 0.5 mg/kg) and MPH (52.4 ± 16.6 mg) in a randomized, double-blind, crossover design. Medication was titrated in 4-6-week blocks separated by a 2-week placebo washout. Inhibitory control and attention measures were obtained at baseline, following washout, and at the end of each treatment using Conners' Continuous Performance Test II ( CPT- II), which provided age-adjusted T-scores for reaction time ( RT), reaction time variability ( RT variability), and errors. Repeated-measures analyses of variance were performed, with Time (premedication, postmedication) and Treatment type ( ATX, MPH) entered as within-subject factors. Data from the two treatment blocks were checked for order effects and combined if order effects were not present. Clinical trial registration: Clinicaltrials.gov: NCT00183391. Results Main effects for Time on RT ( p = .03), RTSD ( p = .001), and omission errors ( p = .01) were significant. A significant Drug × Time interaction indicated that MPH improved RT, RTSD, and omission errors more than ATX ( p < .05). Changes in performance with treatment did not correlate with changes in ADHD symptoms. Conclusions MPH has greater effects than ATX on CPT measures of sustained attention in youth with ADHD. However, the dissociation of cognitive and behavioral change with treatment indicates that CPT measures cannot be considered proxies for symptomatic improvement. Further research on the dissociation of cognitive and behavioral endpoints for ADHD is indicated. [ABSTRACT FROM AUTHOR]

Reflecting on the accompanying article by Jans et al., we draw the following thoughts. Future research on multiplex ADHD families is needed to elucidate mechanisms, timing, and a sequencing of interventions, preferably in treatment naïve participants. Furthermore, in addition to symptom measures, it is likely that multi‐informant measures of functional impairments such as parenting and parent‐child observations may help elucidate the complex mechanisms linking maternal and child ADHD, and eventually lead to more targeted, efficient, and feasible prevention and intervention strategies. [ABSTRACT FROM AUTHOR]