Influence of partial hepatectomy on theophylline pharmacokinetics in rats

Besifloxacin-loaded ocular nanoemulsions: design, formulation and efficacy evaluation

The purpose of this study was to develop and evaluate nanoemulsions (NEs) containing besifloxacin for ocular drug delivery. Pseudo ternary phase diagrams were constructed using Triacetin (oil), Cremophor® RH 40 (surfactant), and Transcutol®P (co-surfactant) to identify NE regions. Six formulations were developed by low-energy emulsification method and then evaluated for size, refractive index, pH, osmolality, viscosity, and drug release. After accelerated physical stability and bovine conrneal permeation studies, NE2 was chosen as optimized formulation forantimicrobial efficacy, and hen's egg test-chorioallantoic membrane (HET-CAM) tests. The particle size of optimum NE was 14 nm with a narrow size distribution. Moreover, other physicochemical characterizations were in the acceptable range for ocular administration. Besifloxacin-loaded NEs demonstrated sustained release pattern and 1.7-fold higher permeation compared with the control suspension in the ex vivo transcorneal permeation study. HET-CAM test indicated no irritation, and HL% revealed no damage to the tissue, so the optimum NE is well tolerated by the eye. In vitro antimicrobial evaluation, showed comparative efficacy of lower drug-loaded NE (0.2%) versus 0.6% besifloxacin suspension (equal concentration to commercial besifloxacin eye drop). In conclusion, besifloxacin-loaded NEs could be considered as a suitable alternative to the marketed suspension for treating bacterial eyeinfections.

Pharmacokinetics of drugs in adult living donor liver transplant patients: regulatory factors and observations based on studies in animals and humans

INTRODUCTION

Limited information is available on the pharmacokinetics of drugs in the donors and recipients following adult living donor liver transplantation (LDLT). Given that both the donors and recipients receive multiple drug therapies, it is important to assess the pharmacokinetics of drugs used in these patients.

AREAS COVERED

Pathophysiological changes that occur post-surgery and regulatory factors that may influence pharmacokinetics of drugs, especially hepatic drug metabolism and transport in both LDLT donors and the recipients are discussed. Pharmacokinetic data in animals with partial hepatectomy are presented. Clinical pharmacokinetic data of certain drugs in LDLT recipients are further reviewed.

EXPERT OPINION

It takes up to six months for the liver volume to return to normal after LDLT surgery. In the LDLT recipients, drug exposure generally is higher with lower clearance during early period post-transplant; lower initial dosages of immunosuppressants are used than deceased donor liver transplant recipients during the first six months post-transplantation. In animals, the activities of hepatic drug metabolizing enzymes and transporters are known to be altered differentially during liver regeneration. Future studies on the actual hepatic function with reference to drug metabolism, drug transport, and biliary secretion in both LDLT donors and recipients are required.

Contribution of presystemic hepatic extraction to the low oral bioavailability of green tea catechins in rats

Green tea and green tea catechins have been shown to possess potent cancer-preventive activities in rodent cancer models. At present, epidemiological evidence of the protective effect of green tea consumption against the development of human cancers is not conclusive. Oral bioavailability of green tea catechins has been shown to be low in animals and possibly in humans. This study is designed to determine the contribution of first-pass hepatic elimination to the low oral bioavailability of green tea catechins. Green tea catechin mixture was dosed to rats by intravenous or intraportal infusion. Blood samples were collected after dosing and analyzed using high-performance liquid chromatography with the coulometric electrode array detection system. The systemic clearance of epigallocatechin gallate (EGCG), epigallocatechin (EGC), and epicatechin (EC) was 8.9, 6.3, and 9.4 ml/min, respectively. The steady state volume of distribution (V(ss)) of EGCG, EGC, and EC was 432, 220, and 187 ml, respectively. We found that high percentage of green tea catechins escaped first-pass hepatic elimination, with 87.0, 108.3, and 94.9% of EGCG, EGC, and EC, respectively, available in the systemic blood following intraportal infusion. Our results suggest that factors within the gastrointestinal tract such as limited membrane permeability, transporter mediated intestinal secretion, or gut wall metabolism may contribute more significantly to the low oral bioavailability of green tea catechins.

Influence of hepatic regeneration after partial hepatectomy on theophylline pharmacokinetics in rats

The influence of hepatic regeneration after partial hepatectomy on theophylline pharmacokinetics has been studied on the rat. At different times after partial hepatectomy, theophylline was administered intravenously as a single dose of 6 mg/Kg. Drug plasma levels were determined by HPLC and pharmacokinetic parameters were obtained. Physiological parameters were also measured. Following hepatectomy, an increase in mass liver was observed and 15 days after surgery, liver mass was 78% of nonhepatectomized rats. Initial theophylline concentrations varied during the regeneration period, as well as the distribution volume at steady-estate (Vss). Elimination half-life (t 1/2), notably increased after hepatectomy (7.27+/-1.38 h), decreased with time (6.70+/-1.18 h, 6.47+/-0.69 and 5.17+/-0.87 h after 24 h, 3 days and 15 days post-hepatectomy, respectively) to reach a value close to that of the control group (4.30+/-1.37 h). The increase in elimination half-life led to a decrease in the mean residence time during the period of liver regeneration. However, the intrinsic clearance hardly varied during regeneration period. We could establish the following relationship between liver weight (LW) and the elimination half-life: t 1/2 (h)=-0.358*LW (g)+8.6168 (R2=0.9906). For the mean residence time (MRT) this relationship was: MRT (h) =-0.5173*LW (g)+12.433 (R2=0.991).