Many people with schizophrenia struggle to adhere to their oral antipsychotic drug regimen.  It is thought that depot antipsychotic drugs (a special preparation of the medication, which is given by injection and is slowly released into the body over a number of weeks) may reduce relapse rates by improving adherence.

This systematic review searched for randomised controlled trials lasting at least 12 months in outpatients that compared depot with oral antipsychotics in schizophrenia. Data on relapse (primary outcome), rehospitalisation, non-adherence, and dropout due to any reason, inefficacy of treatment and adverse events were summarised in a meta-analysis using a random-effects model. Study quality was assessed with the Cochrane collaboration’s risk of bias tool, and publication bias with funnel plots.

Ten studies with 1700 participants met the inclusion criteria. Depot formulations significantly reduced relapses with relative and absolute risk reductions of 30% and 10%, respectively (RR 0.70, CI 0.57-0.87, NNT 10, CI 6-25, P=0.0009), and dropout due to inefficacy (RR 0.71, CI 0.57-0.89).

Limited data on non-adherence, rehospitalisation and dropout due to any reason and adverse events revealed no significant differences.

There were several potential sources of bias such as limited information on randomisation methods, problems of blinding and different medications in the depot and oral groups. Other studies reduced a potential superiority of depot by excluding non-adherent patients.

The reviewers concluded:

Depot antipsychotic drugs significantly reduced relapse. Due to a number of methodological problems in the single trials the evidence is, nonetheless, subject to possible bias.

Leucht C, Heres S, Kane JM, Kissling W, Davis JM, Leucht S. Oral versus depot antipsychotic drugs for schizophrenia–a critical systematic review and meta-analysis of randomised long-term trials. Schizophr Res. 2011 Apr;127(1-3):83-92. Epub 2011 Jan 22. [PubMed abstract]