Placebo-controlled pilot trial of mecamylamine for treatment of autism spectrum disorders

Abstract

Objective: To explore possible benefits of a nicotinic acetylcholine receptor (nAChR) agent for autistic symptoms based on postmortem observation of nAChR abnormalities (deficient α4β2 nAChRs, excess α7 nAChRs) in brains of patients with autism.

Method: Mecamylamine, because of its safety record in children with other disorders, was chosen for this first exploration. Twenty children with autism spectrum disorder age 4-12 years were randomly assigned for 14 weeks to placebo (n=8) or mecamylamine (n=12) in ascending fixed doses: 0.5 mg/day for 6 weeks, 2.5 mg for 2 weeks, then 5 mg/day for 6 weeks. Improvement was rated by a blinded independent evaluator. Because of small sample, data analysis was descriptive.

Results: Eighteen participants (10 mecamylamine, 8 placebo) completed the study. All doses were well tolerated; the only side effect of note was constipation (50% compared with 25% of placebo group). Three children had clinically nonsignificant electrocardiographic QT prolongation. Both groups showed modest to moderate improvement, but differences between groups were negligible. On the primary outcome measure, the Ohio Autism Clinical Impressions Scale, 90% of the active treatment group showed improvement at some point (but only 40% sustained it), compared with 62% on placebo. Of the four in active treatment that sustained improvement, three had a maximum dose of 0.13-0.15 mg/kg/day, while those who regressed had doses ≥0.18 mg/kg/day. Graphed means suggested better outcome with lower mg/kg and longer medication duration. Four parents spontaneously reported reduced hyperactivity and irritability and better verbalization and continued mecamylamine at their own expense.

Conclusion: Mecamylamine appeared to be safe, but not very effective in autism. The suggestion of better results at lower doses and longer exposure warrants consideration for future trials. The next step would be exploration of a more specific α4β2 nAChR agonist, such as varenicline.

FIG. 1.

Ohio Autism Clinical Impressions Scale-I (OACIS-I) Item Mean by Dose, Duration, and Weight. Lower score is better. Week 6=0.5 mg/day; week 8=2.5 mg/day; week 14=5 mg/day. Left panel: Lower mg/kg dose and longer duration are associated with better outcome. Better result at 14 weeks could be higher dose or longer duration of dosing because dose and duration are confounded, but duration seems the most likely association in view of the better outcome at lower mg/kg doses. Right panel: Association of better outcome with higher body weight (resulting in lower mg/kg doses in this fixed-dose titration). Results are not statistically significant at this sample size.