Schizophrenia, a disabling yet relatively common mental illness, is often controlled by antipsychotic drugs. However, long-term treatments are subject to non-adherence and consequent treatment failure. Non-adherence can be reduced by administration of slow-release drugs such as intramuscularly injected (IM) paliperidone palmitate. Considerable inter- and intra-individual variation in serum drug concentration exists, whose effect on clinical efficacy remains unclear. We report two cases of off-label use resulting in serum paliperidone levels greatly exceeding the recommended therapeutic window. A 20- and 31-year-old male were treated with 150 mg IM paliperidone palmitate/21 days. After one and two years, blood drug concentrations were 240 nmol/l and 610 nmol/l, respectively. Neither patient exhibited major adverse effects. Thus paliperidone serum levels greatly in excess of recommended targets can be well tolerated, although we urge caution with off-label use of paliperidone palmitate as it is not always the most appropriate way to achieve the control of schizophrenia.
Keywords: antipsychotic agents; clinical efficacy; injections; intramuscular; off-label use; paliperidone palmitate; schizophrenia; treatment outcome.