Introduction: This article includes a combined analysis of therapeutic drug monitoring (TDM) studies and a review of the marketer’s data on pharmacological mechanisms. Areas covered: An article search led to the inclusion of 21 paliperidone studies in the systematic review plus 2 case reports. Paliperidone clearance was calculated from: 1) steady-state studies using concentration/dose (C/D) ratios, and 2) single-dose studies describing 24-h area under the curve calculations. The marketed extended-release formulation has 28% bioavailability. Calculated mean C/D ratios (ng/ml/mg/d) were: 1) 4.09 in 6 studies of 221 non-Korean and non-geriatric adult patients, 2) 2.59 in 2 studies of 100 Korean adult patients, and 3) 6.89 in 1 study with 15 elderly Japanese patients. The limited drug–drug interaction studies indicated that carbamazepine is a clinically relevant inducer requiring three times the dosage, and that valproate, probably an inhibitor, requires half the dosage. Renal impairment markedly decreased paliperidone elimination, and other antipsychotics should be considered. Expert Commentary: We recommend more use of: 1) paliperidone TDM in clinical practice, 2) TDM when moving from oral to long-acting paliperidone, 3) better designs for paliperidone TDM studies, 4) laboratory studies on paliperidone pharmacokinetic mechanisms, and 5) TDM studies comparing paliperidone and risperidone dosing.

Introduction: This article includes a combined analysis of therapeutic drug monitoring (TDM) studies and a review of the marketer’s data on pharmacological mechanisms. Areas covered: An article search led to the inclusion of 21 paliperidone studies in the systematic review plus 2 case reports. Paliperidone clearance was calculated from: 1) steady-state studies using concentration/dose (C/D) ratios, and 2) single-dose studies describing 24-h area under the curve calculations. The marketed extended-release formulation has 28% bioavailability. Calculated mean C/D ratios (ng/ml/mg/d) were: 1) 4.09 in 6 studies of 221 non-Korean and non-geriatric adult patients, 2) 2.59 in 2 studies of 100 Korean adult patients, and 3) 6.89 in 1 study with 15 elderly Japanese patients. The limited drug–drug interaction studies indicated that carbamazepine is a clinically relevant inducer requiring three times the dosage, and that valproate, probably an inhibitor, requires half the dosage. Renal impairment markedly decreased paliperidone elimination, and other antipsychotics should be considered. Expert Commentary: We recommend more use of: 1) paliperidone TDM in clinical practice, 2) TDM when moving from oral to long-acting paliperidone, 3) better designs for paliperidone TDM studies, 4) laboratory studies on paliperidone pharmacokinetic mechanisms, and 5) TDM studies comparing paliperidone and risperidone dosing.

Introduction: 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).

Introduction: 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).

Introduction: This systematic review of therapeutic drug monitoring (TDM) identifies three long-acting injectable (LAI) risperidone formulations. Areas covered: Limited data is available on two formulations (RBP-7000 and in Situ Microparticle), but 20 TDM articles on the microsphere formulation were found. Risperidone TDM includes the serum concentrations of risperidone and its active metabolite, 9-hydroxyrisperidone, used for calculating: 1) the risperidone/9-hydroxyrisperidone (R/9-OH-R) ratio (a measure of CYP2D6; values >1 are indicative of a CYP2D6 poor metabolizer) and 2) the total risperidone concentration-to-dose (C/D) ratio (a measure of risperidone clearance with a normal value around 7 in oral risperidone). The weighted mean R/9-OH-R ratio was 0.48 (approximately twice that of oral risperidone TDM) in a combined analysis from 329 patients in 6 risperidone LAI studies without major confounders. The total C/D ratios from 297 patients in 6 risperidone LAI studies ranged from 7.4 to 9.7 ng/ml/mg/day with a weighted mean of 8.8 ng/ml/mg/day. Expert commentary: Clinicians using TDM for risperidone LAI microsphere formulation need to: 1) consider steady state to be reached ≥ 6 weeks after the first injection, 2) pay attention to a) co-medications with inducers/inhibitors, b) severe inflammations/infections, and c) hepatic/renal impairment, and 3) use Castberg’s recommendation to calculate risperidone dosing.

Introduction: This systematic review of therapeutic drug monitoring (TDM) identifies three long-acting injectable (LAI) risperidone formulations. Areas covered: Limited data is available on two formulations (RBP-7000 and in Situ Microparticle), but 20 TDM articles on the microsphere formulation were found. Risperidone TDM includes the serum concentrations of risperidone and its active metabolite, 9-hydroxyrisperidone, used for calculating: 1) the risperidone/9-hydroxyrisperidone (R/9-OH-R) ratio (a measure of CYP2D6; values >1 are indicative of a CYP2D6 poor metabolizer) and 2) the total risperidone concentration-to-dose (C/D) ratio (a measure of risperidone clearance with a normal value around 7 in oral risperidone). The weighted mean R/9-OH-R ratio was 0.48 (approximately twice that of oral risperidone TDM) in a combined analysis from 329 patients in 6 risperidone LAI studies without major confounders. The total C/D ratios from 297 patients in 6 risperidone LAI studies ranged from 7.4 to 9.7 ng/ml/mg/day with a weighted mean of 8.8 ng/ml/mg/day. Expert commentary: Clinicians using TDM for risperidone LAI microsphere formulation need to: 1) consider steady state to be reached ≥ 6 weeks after the first injection, 2) pay attention to a) co-medications with inducers/inhibitors, b) severe inflammations/infections, and c) hepatic/renal impairment, and 3) use Castberg’s recommendation to calculate risperidone dosing.