Antihistamines in the treatment of ADHD and allergy.

The prevalence of attention-deficit/hyperactivity disorder (ADHD) has increased enormously over the last decade. Recent studies showed a significant association between ADHD and atopic diseases such as asthma, rhinitis, and eczema. Recently, we confirmed the association in the General Practitioner Research Database, a large British database in which prescription data of boys who were prescribed ADHD medication were compared with matched controls. We found a significant increase of risk for having an atopic disease in patients with ADHD.
One explanation for the association could be that histamine and histamine-receptors play a role in both ADHD and allergic diseases. For allergic diseases it has been established that histamine plays a key role in allergic reactions; in fact, systemic antihistamines are used as first line drugs to treat allergic symptoms such as those of allergic rhinitis. Histamine-receptors are present in every organ system and histamine is an important neurotransmitter.

Pelsser and coworkers treated boys with ADHD with a diet low of allergens and found a significant decrease in ADHD-symptoms. We hypothesize that the use of systemic antihistamines will decrease ADHD symptoms as well as allergic symptoms in children with ADHD who are treated with methylphenidate and who have comorbid asthma and/or allergic rhinitis and/or eczema. For this trial we will use alimemazine, a registered systemic antihistaminic drug that has been used for long times in many children in and outside the Netherlands, and which has an acceptable safety profile.

We hypothesized that adding alimemazine to existing ADHD treatment will decrease ADHD-symptoms as reported by parents and school teachers as well as allergic symptoms.

We hypothesized that adding alimemazine to existing ADHD treatment will decrease ADHD-symptoms as reported by parents and school teachers as well as allergic symptoms.

At inclusion, 4 weeks after start of treatment and 4 weeks after crossover.

The study is designed as a randomized cross-over study. Participants aged 6-12 years are using methylphenidate and will be asked to continue their treatment as prescribed by their physician throughout the study. The intervention consists of the extra use of a tablet of 5 mg alimemazine, a H1-receptorantagonist or a placebo (vitamin B) complex as add-on therapy over one month, followed by use of the alternative compound over a month, in a 1:1 ratio randomly in either order.