BACKGROUND: Asthma exacerbations are major contributors to asthma morbidity and rather difficult to treat. There is inconclusive evidence that macrolide antibiotics may have an effect on asthma exacerbations through their antibacterial and/or anti-inflammatory properties. The aim of the study was to evaluate the efficacy of clarithromycin on medium-term asthma activity when given as an add-on therapy in children with acute asthma. METHODS: This pilot, open-labeled, randomized, prospective study included 40 school-aged children, with intermittent or mild persistent asthma, presenting with an acute exacerbation. Children were randomized to receive 15 mg/kg of clarithromycin for 3 wk, in addition to their regular (GINA-guided) exacerbation treatment. The microbial trigger of exacerbations was assessed by serology and PCR. Children were followed up with diary cards for 12 wk; lung function was assessed at entry, 3, and 12 wk after the exacerbation. RESULTS: Children in the clarithromycin group had significantly more symptom-free days (78 ± 2 vs. 69 ± 6 days, p