A population pharmacokinetics analysis was performed after intravenous ganciclovir and oral valganciclovir in solid organ transplant patients with cytomegalovirus. Patients received ganciclovir at 5 mg/kg of body weight (5 days) and then 900 mg of valganciclovir (16 days), both twice daily with dose adjustment for renal function. A total of 382 serum concentrations from days 5 and 15 were analyzed with NONMEM VI. Renal function given by creatinine clearance (CL CR ) was the most influential covariate in CL. The final pharmacokinetic parameters were as follows: ganciclovir clearance (CL) was 7.49 ⅐ (CL CR /57) liter/h (57 was the mean population value of CL CR ); the central and peripheral distribution volumes were 31.9 liters and 32.0 liters, respectively; intercompartmental clearance was 10.2 liter/h; the first-order absorption rate constant was 0.895 h ؊1 ; bioavailability was 0.825; and lag time was 0.382 h. The CL CR was the best predictor of CL, making dose adjustment by this covariate important to achieve the most efficacious ganciclovir exposure.

The goal of this study was to establish the population pharmacokinetics (PK) of high-dose methotrexate (HD-MTX) treatment in children with osteosarcoma and to explore the influence of patient covariates and between-occasion variability on drug disposition. Patient covariates and concentration-time data were collected. PK data analysis from 209 HD-MTX cycles from 14 patients was performed using the population approach (NONMEM V). Internal and external validations were performed to confirm the model. PK of methotrexate was best described by a 2-compartment open PK model with first-order elimination from the central compartment. Between-subject variability (BSV) was included in total plasma clearance (CL) and in central compartment distribution volume (V1) [coefficient of variation (CV) 11.9% and 8.9%, respectively]. The CV of BSV in the residual error was 25.5%. Between-occasion variability was only retained for CL (CV 8.2%). RE consisted of a proportional error of 41.6%. Age and body weight in CL and body weight in V1 were identified as the appropriate covariates. The final estimates of total CL and V1 were given by the equations CL = 88.5.(AGE/15) + 27.4 x (WGT/50) L/d and V1 = 11.0 + 5.6 x (WGT/50) L, respectively. Internal validation results showed that the 95% confidence interval covered all the observed MTX concentrations. Mean bias and precision of the individual predicted concentrations, calculated in a validation dataset, resulted in -1.36% and 19.71%, respectively. A population PK model was developed for HD-MTX in children with osteosarcoma. Validation studies confirmed the suitability of the model for further dose individualization by means of a Bayesian approach.

The objectives of the current work were to develop a predictive population pharmacokinetic (PK)/pharmacodynamic (PD) model for the testosterone (TST) effects of triptorelin (TRP) administered in sustained-release (SR) formulations to patients with prostate cancer and determine the minimal required triptorelin serum concentration (C TRP_min ) to keep the testosterone levels of the patients below or equal to the level of castration (TST Յ0.5 ng/ml). A total of eight healthy male volunteers and 74 patients with prostate cancer received one or two doses of triptorelin injected subcutaneously or intramuscularly. Five different triptorelin formulations were tested. Pharmacokinetic (serum concentration of triptorelin) and pharmacodynamic (TST levels in serum) data were analyzed by using the population approach with NONMEM software (http://www.iconplc. com/technology/products/nonmem/). The PK/PD model was constructed by assembling the agonist nature of triptorelin with the competitive reversible receptor binding interaction with the endogenous agonist, a process responsible for the initial and transient TST flare-up, and triggering down-regulation mechanisms described as a decrease in receptor synthesis. The typical population values of K D , the receptor equilibrium dissociation constant of triptorelin, and C TRP_min to keep 95% of the patients castrated were 0.931 and 0.0609 ng/ml, respectively. The semimechanistic nature of the model renders the predictions of the effect of triptorelin on TST possible regardless the type of SR formulation administered, while exploring different designs during the development of new delivery systems.

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The pharmacokinetics/tolerability of lanreotide Autogel have been evaluated. Healthy volunteers (n = 24) first received immediate-release lanreotide as a single subcutaneous (s.c.) injection. After two days, 40 or 60 mg lanreotide Autogel was injected subcutaneously. Blood was sampled at various intervals for 56 days. Systemic/local adverse events and changes in biological profile/vital signs were recorded. Lanreotide Autogel produced a prolonged-release pharmacokinetic profile: mean area under the serum concentration-time curve from time 0 to infinity (AUC) was 53.73 +/- 8.99 and 79.48 +/- 13.06 ng mL(-1) day for 40 and 60 mg, respectively, mean peak serum concentration (C(max)) was 4.38 +/- 2.91 and 5.71 +/- 3.52 ng mL(-1), respectively, median time to reach C (minimum-maximum) was 0.50 (0.083-18.0) and 0.38 (0.083-9.01) days, respectively, mean apparent elimination half-life was 21.63 +/- 9.42 and 22.01 +/- 9.87 days, respectively, and relative bioavailability was 0.93 +/- 0.12 and 0.82 +/- 0.15, respectively. Thus, lanreotide Autogel exhibited linear pharmacokinetics for the doses studied. Pharmacokinetic profiles were similar in both genders, apart from statistically significant differences in C(max) and C(max)/AUC. The Autogel formulation of lanreotide was well tolerated, with systemic adverse events being mild/moderate. Erythema and a painless subcutaneous induration were the most common local adverse events. Lanreotide Autogel provided a prolonged dosing interval and good tolerability for treating acromegaly and carcinoid syndrome.

Steroid sulfatase (STS) inhibition may have a therapeutic role in suppression of endocrine-responsive breast cancer. This study aimed to determine the optimal biological dose and recommended dose (RD) of the STS inhibitor irosustat. A three-part, open-label, multicenter, dose escalation study of irosustat in estrogen receptor-positive breast cancer patients involved administration of a single dose of irosustat with a 7-day observation period; followed by a daily oral dose of irosustat for 28 days; and an extension phase, in which the daily oral dose of irosustat was continued at the discretion of the investigator and as long as the patient was benefitting from the treatment. Five doses of irosustat were tested (1, 5, 20, 40, and 80 mg) in 50 patients. After 28 days of daily administration of irosustat, all the evaluated patients in the 5, 20, 40, and 80 mg cohorts achieved ≥95 % STS inhibition in peripheral blood mononuclear cells and corresponding endocrine suppression. The maximum tolerated dose was not reached, and the 40 mg dose was established as the RD. The median time to disease progression in the 40 mg cohort was 11.2 weeks. Disease stabilization was achieved in 10 % of patients potentially indicative of drug activity. Dry skin was the most frequent adverse event. The RD of irosustat is 40 mg. Disease stabilization occurred in 10 % of this heavily pretreated patient population. A larger study is required to define an accurate response rate to irosustat as a single agent and whether co-administration with an aromatase inhibitor is needed.

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