Estimating the optimal dose of flupentixol decanoate in the maintenance treatment of schizophrenia-a systematic review of the literature.

The licensed dose range for the long-acting injectable antipsychotic flupentixol decanoate (Depixol®) in the treatment of schizophrenia is very broad. This provides little useful direction to prescribers and may ultimately result in patients receiving unnecessarily high doses. We aimed to estimate the effect of dose of flupentixol decanoate on relapse rates in schizophrenia and on tolerability by expanding on an earlier review and including non-RCT and German-language studies, as well as using pharmacokinetic and pharmacodynamic data to offer guidance on dosing. A literature review using EMBASE, Medline, PsycINFO and PubMed was conducted. Treatment success rates at 6 months were extracted or extrapolated from the studies and plotted against dose to estimate a dose-response curve. Data from 16 studies (n = 514) allowed estimation of a dose-response curve which rises steeply between the chosen placebo anchor (25% success rate) and 10 mg every 2 weeks before reaching a maximum between 20 and 40 mg every 2 weeks (80-95% success rates). Extrapyramidal side effects (EPSEs) were frequently seen (12-71% of participants) in that dose range. Two -weekly injections seem to provide the highest trough plasma concentration per dose administered and the lowest peak-to-trough concentration ratio. Plasma concentration varied up to 5-fold among individuals receiving the same dose. The optimal dose of flupentixol decanoate is likely to be between 20 mg and 40 mg every 2 weeks although higher doses may be required in some individuals owing to variation in drug handling. Doses of flupentixol should be individually established in the range of 10 to 40 mg every 2 weeks according to response and tolerability.