Acetylcholinesterase inhibitors for autistic spectrum disorders

Background Autism spectrum disorder (autism) is a neurodevelopmental condition characterised by impairments in social communication and interaction, plus restricted, repetitive patterns of behaviour and interests. Whilst some people embrace autism as part of their identity, others struggle with their difficulties, and some seek treatment. There are no current interventions that result in complete reduction of autism features. Acetylcholine is a neurotransmitter for the cholinergic system and has a role in attention, novelty seeking, and memory. Low levels of acetylcholine have been investigated as a potential contributor to autism symptomatology. Donepezil, galantamine, and rivastigmine (commonly referred to as acetylcholinesterase inhibitors) all inhibit acetylcholinesterase, and have slightly different modes of action and biological availability, so their effectiveness and side‐effect profiles may vary. The effect of various acetylcholinesterase inhibitor on core autism features across the lifespan, and possible adverse effects, have not been thoroughly investigated. Objectives To evaluate the efficacy and harms of acetylcholinesterase inhibitors for people with the core features (social interaction, communication, and restrictive and repetitive behaviours) of autism. To assess the effects of acetylcholinesterase inhibitors on non‐core features of autism. Search methods In November 2022, we searched CENTRAL, MEDLINE, Embase, eight other databases, and two trials registers. We also searched the reference lists of included studies and relevant reviews, and contacted authors of relevant studies. Selection criteria Randomised controlled trials (RCTs), comparing acetylcholinesterase inhibitors (e.g. galantamine, donepezil, or rivastigmine) of varying doses, delivered orally or via transdermal patch, either as monotherapy or adjunct therapy, with placebo. People of any age, with a clinical diagnosis of autism were eligible for inclusion. Data collection and analysis We used standard methodological procedures expected by Cochrane. Our primary outcomes were core features of autism and adverse effects. Secondary outcomes were language, irritability, hyperactivity, and general health and function. We used GRADE to assess certainty of evidence. Main results We included two RCTs (74 participants). One study was conducted in Iran, the second in the USA, although exact location in the USA is unclear. Galantamine plus risperidone versus placebo plus risperidone One study compared the effects of galantamine plus risperidone to placebo plus risperidone (40 participants, aged 4 years to 12 years). Primary and secondary outcomes of interest were measured postintervention, using subscales of the Aberrant Behavior Checklist (score 0 to 3; higher scores = greater impairment). Very low‐certainty evidence showed there was little to no difference between the two groups postintervention for social communication (mean difference (MD) ‐2.75, 95% confidence interval (CI) ‐5.88 to 0.38), and restricted and repetitive behaviour (MD ‐0.55, 95% CI ‐3.47 to 2.37). Overall autism features were not assessed. Adverse events may be higher in the galantamine plus risperidone group (75%) compared with the placebo plus risperidone group (35%): odds ratio 5.57, 95% CI 1.42 to 21.86, low‐certainty evidence. No serious adverse events were reported. Low‐certainty evidence showed a small difference in irritability (MD ‐3.50, 95% CI ‐6.39 to ‐0.61), with the galantamine plus risperidone group showing a greater decline on the irritability subscale than the placebo group postintervention. There was no evidence of a difference between the groups in hyperactivity postintervention (MD ‐5.20, 95% CI ‐10.51 to 0.11). General health and function were not assessed. Donepezil versus placebo One study compared donepezil to placebo (34 participants aged 8 years to 17 years). Primary outcomes of interest were measured postintervention, using subscales of the Modified Version of The Real Life Rating Scale (scored 0 to 3; higher scores = greater impairment). Very low‐certainty evidence showed no evidence of group differences immediately postintervention in overall autism features (MD 0.07, 95% CI ‐0.19 to 0.33), or in the autism symptom domains of social communication (MD ‐0.02, 95% CI ‐0.34 to 0.30), and restricted and repetitive behaviours (MD 0.04, 95% CI ‐0.27 to 0.35). Significant adverse events leading to study withdrawal in at least one participant was implied in the data analysis section, but not explicitly reported. The evidence is very uncertain about the effect of donepezil, compared to placebo, on the secondary outcomes of interest, including irritability (MD 1.08, 95% CI ‐0.41 to 2.57), hyperactivity (MD 2.60, 95% CI 0.50 to 4.70), and general health and function (MD 0.03, 95% CI ‐0.48 to 0.54) postintervention. Across all analyses within this comparison, we judged the evidence to be very low‐certainty due to high risk of bias, and very serious imprecision (results based on one small study with wide confidence intervals). The study narratively reported adverse events for the study as a whole, rather than by treatment group. Authors' conclusions Evidence about the effectiveness of acetylcholinesterase inhibitors as a medication to improve outcomes for autistic adults is lacking, and for autistic children is very uncertain. There is a need for more evidence of improvement in outcomes of relevance to clinical care, autistic people, and their families. There are a number of ongoing studies involving acetylcholinesterase inhibitors, and future updates of this review may add to the current evidence.