This is a combined analysis of therapeutic drug monitoring (TDM) studies of long-acting injectable paliperidone formulations: monthly (PP1M) and three-month (PP3M) injections. Areas covered: Fourteen PP1M articles and one PP3M article were identified. Using the paliperidone concentration/dose (C/D) ratio as a measure of clearance provided a weighted mean of 7.7 ng/ml per mg/day among 69 patients from three steady-state PP1M studies (twice as high as oral paliperidone). C/D ratios were: 1) higher by a factor of 1.26 in 12 geriatric patients, 2) lower in obese patients, and 3) 50% lower in three patients taking carbamazepine. No clinically meaningful PP3M pharmacokinetic data have been published. Expert commentary: Half-life studies and more TDM PP1M studies using steady state are urgently needed. Early TDM studies may help orient PP1M dosing but steady state may not be reached until after the ninth injection (8 months). PP3M may take > 1 year to reach steady state. Any clinician considering switching patients to PP1M: 1) should switch from oral risperidone to PP1M rather than from oral paliperidone to PP1M, and 2) become proficient in paliperidone TDM to use during switches. TDM is highly recommended for patients with abnormal clearance (from obesity, geriatric age, or potent inducers).
Keywords: Antipsychotic agents/administration & dosage; antipsychotic agents/pharmacology; delayed-action preparations; drug monitoring; injections; paliperidone palmitate; risperidone/administration & dosage; risperidone/blood; risperidone/metabolism; risperidone/pharmacokinetics; schizoaffective disorder/drug therapy; schizophrenia/drug therapy.