A systematic review and combined analysis of therapeutic drug monitoring studies for oral paliperidone

<p><b>Introduction</b>: This article includes a combined analysis of therapeutic drug monitoring (TDM) studies and a review of the marketer’s data on pharmacological mechanisms.</p> <p><b>Areas covered</b>: 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.</p> <p><b>Expert Commentary</b>: 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.</p

A systematic review and combined analysis of therapeutic drug monitoring studies for long-acting risperidone

<p><b>Introduction</b>: This systematic review of therapeutic drug monitoring (TDM) identifies three long-acting injectable (LAI) risperidone formulations.</p> <p><b>Areas covered</b>: Limited data is available on two formulations (RBP-7000 and <i>in Situ</i> 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.</p> <p><b>Expert commentary</b>: 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.</p

Pharmacokinetic correlates of clinical response in a naturalistic sample of escitalopram-treated patients

We assessed pharmacokinetic correlates of treatment response to escitalopram using a large therapeutic drug monitoring database. A large naturalistic sample of patients receiving escitalopram was analyzed. Responders were defined as ‘very much improved’ or ‘much improved’ based on the Clinical Global Impression – Improvement score, CGI-I. We compared responders (n = 83) vs. non-responders (n = 388) with the primary outcome being the escitalopram plasma concentration and concentration corrected by the daily dose (C/D ratio). Effects of age, sex, body-mass-index (BMI), and C/D ratio were assessed in a multivariate logistic regression model predicting response. There were no statistically significant differences in clinical and demographic characteristics between responders vs. non-responders. There were also no differences between escitalopram daily doses or plasma concentrations, while C/D ratios were significantly higher in non-responders than in responders (1.6 ± 1.7 vs. 1.2 ± 0.9 (ng/mL)/(mg/day), p = 0.007); C/D ratios (odds ratio 0.52, 95% confidence interval 0.34–0.80, p Patients with low clearance of escitalopram as reflected upon high C/D ratios may be less likely respond to escitalopram. Identifying these patients during dose titration may support clinical decision-making, including switching to a different antidepressant instead of increasing daily dose.</p