Antipsychotic Drug Side Effects More Frequent With Intellectual Disability

Patients taking warfarin had an increased risk of developing dementia.
Patients taking warfarin had an increased risk of developing dementia.
UK researchers evaluated extrapyramidal side effects of antipsychotic medication in patients with and without intellectual disability.

A cohort study drawing on a large UK, nationally representative database – The Health Improvement Network (THIN) – recorded movement side effects significantly more often among patients taking prescription antipsychotic medications who have intellectual disability (ID) than among those without ID, according to the study reported in the British Medical Journal.

The researchers identified 9039 patients with ID and selected a cohort of 34,242 patients without ID similar in age (≥18 years), sex, level of social deprivation, and history of movement disorder for entry into the study. The movement disorders recorded included parkinsonism, acute dystonias, akathisia, tardive dyskinesia, and neuroleptic malignant syndrome – all those seen as side effects of oral antipsychotic medications. Taken together, the groups provided 148,709 patient-years of data between January 1999 and December 2014.

The incidence of recorded movement side effects was 275 per 10,000 patient-years (95% CI, 256-296) in the ID group and 248 per 10,000 patient-years (95% CI, 237-260) in the non-ID group. After adjustment, the incidence rate of any movement disorder was significantly greater – 30% higher – among people with ID compared with those without ID (incidence rate ratio 1.30; 94% CI, 1.18-1.42, <.001). The incidence of neuroleptic malignant syndrome, akathisia, and parkinsonism was higher in the ID group compared with the non-ID group.  Parkinsonism was the most commonly recorded movement side effect in both study groups. 

Movement side effects were significantly more likely to be recorded among people with ID than those without, regardless of whether they were taking first-generation or  second-generation antipsychotics. The incidence of such side effects fell significantly over the study period in both groups. Each calendar year was associated with a 5% decline for people with ID and a 7% decline for those without ID who were prescribed antipsychotic medications.

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Sheehan R, Horsfall L, Strydom A, Osborn D, Walters K, Hassiotis A. Movement side effects of antipsychotic drugs in adults with and without intellectual disability: UK population-based cohort study. BMJ Open. 2017;7(8):e017406