Parental reporting of adverse drug reactions associated with attention-deficit hyperactivity disorder (ADHD) medications in children attending specialist paediatric clinics in the UK

Background: The development of systems to ensure appropriate and informed use of medicines in children is a global priority. Current pharmacovigilance systems, such as the UK Yellow Card Scheme, are limited by opportunistic reporting of adverse drug reactions (ADRs), lack of a denominator and lower than expected reporting rates.

Objective: To develop a pharmacovigilance system able to target specific patient populations such as children, and specific medicines of interest, using specialist medical clinics.

Methods: Between January and March 2010, parents of 578 children (3-16 years of age) receiving pharmacological therapy for attention-deficit hyperactivity disorder and attending a child and adolescent clinic in the UK were sent an ADR questionnaire to elicit information on possible ADRs associated with their child's medication use. Two approaches, free text and a symptom tick list, were used to elicit possible ADRs.

Results: Two hundred and seven questionnaires were returned, of which 200 were evaluable, giving a response rate of 35.9%. 123 questionnaires reported a total of 213 free-text ADRs perceived by the parents to be due to the medications under study. Two-thirds of reported ADRs were considered to be ongoing at the time of reporting. Duration of reported ADRs ranged from 1 week to 3 years. 81 returned questionnaires reported 134 different ADRs for methylphenidate monotherapy. For methylphenidate, the most frequently reported ADRs were loss of appetite (34.3%), headache (17.9%), mood and emotional problems (14.9%), stomach upset (14.9%), sleep disturbance (10.4%), and rash and other skin problems (5.2%). 467 possible drug-related symptoms were reported using the tick-list approach. Using the tick list, the most frequently reported symptoms were mood and emotional problems (28.1% [131/467]), stomach and abdominal problems (13.3% [62/467]), insomnia (12.8% [60/467]) and lack of appetite (12.6% [59/467]). The symptom tick list identified a broader range of possible adverse effects not reported as free-text ADRs, such as schooling difficulties, hearing problems, cough and blurred vision.

Conclusions: The results of our study demonstrate the feasibility of using specialist clinics to target both at-risk patient populations and/or medicines of interest. We have also clearly demonstrated the practicality and feasibility of parental reporting. Parents reported common and less common ADRs, such as suicidal ideation, using both the free text and symptom tick-list approach.