Few studies are available comparing the effectiveness of Risperidone long-acting injection (RLAI) against conventional depot antipsychotics. We aimed to study patients who were prescribed the long-acting injections Risperidone and Zuclopenthixol decanoate in routine clinical practice, to identify predictors of continuing longer-term treatment.

From a data set of 11,250 electronic patient records, we retrospectively identified all secondary care psychiatric patients Risperidone and Zuclopenthixol depots during a three years period (2002-2005). We calculated the duration of treatment ratio (DoTR) (duration of mention of medication divided by total duration of psychiatric record) as a measure of effectiveness. We examined clinical and demographic variables associated with high and low DoTRs, i.e. patients likely to continue versus those likely to discontinue treatment.

98 records were identified for Risperidone LAI, 70 for Zuclopenthixol. Patients who continued longer-term treatment were similar for both compounds in terms of age, sex, diagnosis, length of contact with services, previous Clozapine treatment and co-prescription with other psychotropics. Individuals continuing on RLAI long-term were on a higher maximum mean dose (42 mg every 2 weeks) compared to those who discontinued early (30 mg every 2 weeks) p=0.0002. Discontinuation due to adverse effects was less with RLAI than with Zuclopenthixol (26% versus 63%, p=0.06).

Both RLAI and Zuclopenthixol depot are clinically effective in longer-term treatment of psychotic disorders. Patients established on higher dose RLAI (37.5 mg and 50 mg per fortnight) were more likely on to continue long-term treatment.