Treatment-completion rates with olanzapine long-acting injection versus risperidone long-acting injection in a 12-month, open-label treatment of schizophrenia: indirect, exploratory comparisons

International Journal of General Medicine, 05/10/2012

Ascher–Svanum H et al. – Using treatment–completion rates as a proxy measure of medication effectiveness, olanzapine long–acting injection did not differ significantly from risperidone long–acting injection when including all eligible studies. However, the findings of this exploratory analysis should be interpreted with caution, considering the methodological limitations of these indirect, cross–study comparisons.

Methods

  • Indirect, cross–study comparisons between olanzapine long–acting injection and risperidone long–acting injection used 12–month treatment–completion rates, because discontinuation of an antipsychotic for any cause is a recognized proxy measure of the medication's effectiveness in treating schizophrenia.
  • Following a systematic review of the literature, two indirect comparisons were conducted using open–label, single–cohort studies in which subjects were stabilized on an antipsychotic medication before depot initiation.
  • The first analysis compared olanzapine long–acting injection (one study) with pooled data from nine identified risperidone long–acting injection studies.
  • The second analysis was a “sensitivity analysis,” using only the most similar studies, one for olanzapine long–acting injection and one for risperidone long–acting injection, which shared near–identical study designs and involved study cohorts with near–identical patient characteristics.
  • Pearson Chi–square tests assessed group differences on treatment–completion rates.

Results

  • Comparison of olanzapine long–acting injection data (931 patients) with the pooled data from the nine risperidone long–acting injection studies (3950 patients) provided almost identical 12–month treatment–completion rates (72.7% versus 72.4%; P = 0.87).
  • When the two most similar studies were compared, the 12–month completion rate for olanzapine long–acting injection was significantly higher than for risperidone long–acting injection (81.3% versus 47.0%; P < 0.001).
  • However, any conclusions drawn from this comparison may be limited by differences in the studies' geographic catchment areas.

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