Low-molecular-weight heparin pharmacokinetics: a dual absorption model approach.

OBJECTIVE: The aim of this study was to develop a novel population pharmacokinetic (PPK) model of dalteparin after subcutaneous (s.c.) injection, to describe the impact of the "flip-flop" phenomenon and to demonstrate any ethnic difference between Asian and Caucasian subjects. MATERIALS AND METHODS: The PPK model was constructed based on data collected from Asian (Japanese) and Caucasian (French) subjects with a total of 931 plasma anti-Xa activity measurements. After s.c. injection, the apparent elimination half-life of the dalteparin was about 4 hours, longer than that reported after intravenous (i.v.) injection, indicating a "flip-flop" phenomenon. In addition, following the mono-exponential decline profile after s.c. injection, a longer secondary phase was apparently observed in 70% of subjects. To investigate the phenomenon, we applied a dual absorption model including fast first-order and slow zero-order inputs as the structural model. RESULTS: The PPK model for s.c. injection provided the half-life consistent with that of i.v. injection and could account for the observed bi-phasic profile. Body weight and gender for clearance and body weight for volume of distribution were identified as covariates. Due to lower body weight in Asian subjects, an ethnic difference might occur but it would not be reflected by per kg body weight injection. CONCLUSIONS: Dalteparin PK profiles after s.c. injection were described reasonably by the novel PPK model based on flip-flop pharmacokinetics and a dual absorption process.

Safety and pharmacokinetics of PF-04360365 following a single-dose intravenous infusion in Japanese subjects with mild-to-moderate Alzheimer's disease: a multicenter, randomized, double-blind, placebo-controlled, dose-escalation study.

OBJECTIVE: PF-04360365 is a humanized IgG(2)Δa anti-amyloid ß (Aß) antibody designed to improve outcome in Alzheimer's disease (AD). Single doses of 0.1 - 10 mg/kg were safe and well tolerated in Western (mostly Caucasian) subjects with mild-to-moderate AD. This Phase 1, multicenter, randomized, double-blind, dose-escalation study was the first to evaluate the safety, pharmacokinetics, pharmacodynamics, and immunogenicity of PF-04360365 in Japanese subjects. MATERIALS AND METHODS: 30 subjects with mild-to-moderate AD were enrolled. In each cohort, 3 subjects received PF-04360365 (0.1, 0.5, 1, 5, or 10 mg/kg) and 1 subject received placebo as a single 2-hour intravenous infusion. Subjects were monitored as inpatients for 24 hours and then as outpatients for 1 year. RESULTS: All subjects completed the study. There were no serious or National Cancer Institute Common Terminology Criteria for Adverse Events grade ≥ 3 adverse events, hypersensitivity reactions, or antidrug antibodies. No clinical or MRI evidence of brain microhemorrhage, cerebral edema, or encephalitis was observed. PF-04360365 plasma concentrations increased with dose, and pharmacokinetics were consistent with a small steady-state volume of distribution, slow clearance, and long elimination half-life. Cerebrospinal fluid (CSF):plasma ratios were < 0.5%. Plasma Aß species showed dose-dependent increases in C(max) and AUC(∞), but CSF biomarkers did not differ clearly between treatment arms. CONCLUSIONS: PF-04360365 was safe and well tolerated in Japanese subjects. Pharmacokinetics and plasma pharmacodynamic responses in Japanese subjects were comparable to those in Western subjects. *No longer affiliated with Pfizer.

[A new anti-mycobacterial agent, rifabutin].

This is a review of non-clinical and clinical study results of rifabutin (Mycobutin, RBT) which was approved as a new anti-mycobacterial agent 38 years after rifampicin (RFP) was approved in Japan. The anti-bacterial actions of RBT were similar to those of RFP, but its potency was stronger (4 to 32 times in MIC90). RBT showed excellent penetration in cells (9 times in neutrophil, 15 times in monocyte, against plasma concentration) and in tissues (5 to 10 times in pulmonary tissue). Clinical efficacy of RBT (150 mg, as well as 300 mg daily) was comparable to that of RFP 600 mg daily, in the treatment of newly diagnosed tuberculosis, drug-resistant tuberculosis, and the NTM diseases. In addition, RBT 300 mg showed significant prophylactic effect on the development of disseminated MAC infection in HIV positive subjects. Most of the adverse events of RBT were the same as those of RFP, including drug-drug interactions related to the induction of CYP3A4. The concomitant use of RBT (over 450 mg) with clarithromycin induces uveitis, which warrants special attention. It is expected that the efficacy and safety of RBT in Japanese subjects will be evaluated in Japan through the accumulation of clinical experience.

Population pharmacokinetic analysis of linezolid in patients with infectious disease: application to lower body weight and elderly patients.

Linezolid (Zyvox), belonging to oxazolidinone antibiotics, is commonly used for the treatment of patients infected with methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci. Although linezolid has been approved worldwide, the Japanese pharmacokinetic (PK) profile has not been characterized in detail. The objective of this study is to develop a population PK model for linezolid that can be applied to a Japanese population. This population PK model was established based on the 1 Japanese phase III and 4 Caucasian phase II/III studies. A total of 2539 linezolid plasma concentration measurements from 455 patients, aged 18 to 98 years and body weight 30 to 190.5 kg, were used for the analysis. The data were analyzed using nonlinear mixed effects modeling. Body weight (BW), age, ethnicity, and gender were investigated as covariates. The final model was validated by the bootstrap technique. The PK profiles of linezolid were described with a 1-compartment PK model with first-order absorption and first-order elimination. In the final population PK model, BW and age were influential covariates on clearance, and the distribution volume was affected by BW. The present population PK model of linezolid described well the PK profiles in Japanese patients who have lower BW and are relatively older compared with those in the United States/European Union.

Current status and future perspective on preclinical pharmacokinetic and pharmacodynamic (PK/PD) analysis: Survey in Japan pharmaceutical manufacturers association (JPMA).

Preclinical pharmacokinetic/pharmacodynamic (PK/PD) analysis is an efficient tool for the translational research and proof of mechanism/concept in animals. The questionnaire survey on the practice of preclinical PK/PD analysis was conducted in the member companies of the Japan Pharmaceutical Manufacturers Association (JPMA). According to the survey, 60% of companies conducted preclinical PK/PD analysis and its impact for drug development was different between each of the companies. The frequently analyzed therapeutic areas of preclinical PK/PD analysis were neurology, inflammation and metabolic disease, and those are different from the therapeutic area (infectious disease and oncology) in which PK/PD analysis was considered as effective by the present survey. Many companies which have used preclinical PK/PD analysis for the translation to human PK/PD and for the prediction of dose/regimen had good communication with other research & development (R&D) departments (e.g. pharmacology/clinical pharmacology). The increase in resources for preclinical PK/PD analysis including education was highly demanded. As a future perspective, the closer collaboration between pharmacokinetics scientists, pharmacologists, toxicologists and clinical pharmacologists and the increase in resources including upskilling and the comprehension of preclinical PK/PD analysis by the project team are considered to lead to efficient contributions to improve the success ratio of drug discovery and development.