Risk Factors, Incidence, and Outcomes of Neuroleptic Malignant Syndrome on Long-Acting Injectable vs Oral Antipsychotics in a Nationwide Schizophrenia Cohort

Introduction: Long-acting injectable antipsychotics (LAIs) are associated with multiple positive outcomes in psychosis, but it is unclear whether LAIs are associated with worse outcomes if neuroleptic malignant syndrome (NMS), a potentially lethal adverse effect, occurs.Methods: We used nationwide and nationally representative databases of healthcare encounters in Finland to study the incidence and outcome predictors of NMS in patients diagnosed with schizophrenia/schizoaffective disorder between January 01, 1972 and December 31, 2017. Using a nested case-control design, we also explored differences by anti-psychotic formulation (LAI vs oral antipsychotic [OAP]) and class (first-generation antipsychotic [FGA] vs second-generation antipsychotic [SGA]).Results: One hundred seventy-two NMS cases and 1441 sex-, age-, and diagnosis-matched controls were included (age = 58.8 +/- 13.1 years, males = 59.9%). Incidence of NMS was 1.99 (1.98-2.00) per 10 000 person-years. The likelihood of developing NMS did not differ by antipsychotic formulation (adjusted odds ratio [aOR]: 0.89, 95% confidence intervals [95% CI]: 0.59-1.33, for LAIs vs OAPs) or class (FGA-OAP vs SGA-OAP [aOR: 1.08, 95% CI: 0.66-1.76], FGA-LAI [aOR: 0.89, 95% CI: 0.52-1.53], SGA-LAI [aOR: 1.35, 95% CI: 0.58-3.12]). NMS risk factors included antipsychotic treatment change: increased number (odds ratios [OR]: 5.00, 95% CI: 2.56-9.73); decreased number/switch (OR: 2.43, 95% CI: 1.19-4.96); higher antipsychotic dose (>2DDDs-OR: 3.15, 95% CI: 1.61-6.18); co-treatment with anticholinergics (OR: 2.26, 95% CI: 1.57-3.24), lithium (OR: 2.16, 95% CI: 1.30-3.58), benzodiazepines (OR: 2.02, 95% CI: 1.44-3.58); and comorbid cardiovascular disease (OR: 1.73, 95% CI: 1.22-2.45). Within 30 days, 4.7% of cases with NMS died (15.1% within 1 year) without differences by antipsychotic formulation. NMS reoccurred in 5 of 119 subjects (4.2%), after a median = 795 (range = 77-839) days after rechallenge with antipsychotics.Conclusion: NMS remains a potentially life-threatening risk, yet these results should further contribute to mitigate concerns about LAI safety regarding NMS onset or outcomes, including mortality.