Hsiu-Ying Yu

Triamcinolone permeation from different liposome formulations through rat skin in vitro

Abstract The permeation of triamcinolone acetonide (TRMA) from various liposome formulations through rat skin was studied in vitro. The penetrated amount, permeability and intradermal retention of TRMA were compared among various lipid compositions, different vesicle sizes (0.2, 0.4 and 1 μm), charges (positive, negative and neutral), as well as between multilamellar vesicles (MLV) and small unilamellar vesicles (SUV). All of the liposome formulations resulted in significantly higher flux and permeability of TRMA than a commercial TRMA ointment. The ‘skin lipid’ liposome provided the most effective transdermal delivery of incorporated TRMA. Presence or absence of cholesterol in the lipid bilayers did not reveal any difference in transdermal delivery of the associated TRMA. The flux and permeability of TRMA through skin were not influenced by the vesicle size of MLV, but was significantly increased by negative SUV. Intradermal retention of TRMA from positive MLV was significantly higher, while that from neutral SUV was significantly lower, than from other formulations. Liposomal lipid was not detectable on the receptor compartment. These results suggest that liposome itself may not penetrate through the skin, but that it does enhance the transfer of incorporated TRMA. Liposomal lipid composition is the most important factor affecting the efficiency of transdermal delivery of incorporated drugs, but was not correlated with its phase transition temperature.

Propofol concentration monitoring in plasma or whole blood by gas chromatography and high-performance liquid chromatography.

We compared the measurement of propofol concentrations in plasma or whole blood by high-performance liquid chromatography (HPLC) to that of gas chromatography (GC). Blood samples were collected from patients who had received bolus injection or continuous infusion of propofol. The results showed that the two methods correlated well both in plasma and whole blood samples. However, significant biphasic differences of propofol concentrations between plasma and whole blood specimens were observed in the bolus injection group. Differences were larger in the infusion group. This discrepancy in concentrations resulted from the infusion or clearance of propofol, and the lag of redistribution across blood cell membranes. In conclusion, monitoring of propofol concentrations by the methods of GC and HPLC gives equivalent results. For propofol concentration monitoring, plasma samples are preferred, but immediate centrifugation is needed. (Anesth Analg 1995;81:175-8)

Kinetic and dynamic studies of liposomal bupivacaine and bupivacaine solution after subcutaneous injection in rats.

The pharmacodynamics and pharmacokinetics of bupivacaine in solution and in liposome preparations following subcutaneous administration were studied in rats. Multilamellar vesicles entrapping bupivacaine solution were prepared. The local anaesthetic effect was estimated by the tail‐flick test in Wistar rats treated with 1 mg bupivacaine in 0.2‐ml. preparations. Plasma concentrations of bupivacaine were determined by high‐performance liquid chromatography. The results showed that both bupivacaine solution and bupivacaine liposomes revealed local anaesthetic effects in the initial tail‐flick test (15 min after injection). With bupivacaine liposomes, the duration of action was 5‐fold (447 ± 28.9 vs 87 ± 6.7 min), the maximum possible effect was 2‐fold (100 ± 0 vs 47.6 ± 13%), and the peak plasma concentration (Cmax) was less than one‐fifth (0.12 ± 0.04 vs 0.65 ± 0.04 μg mL−1) that with bupivacaine solution. The sensory block effect of bupivacaine solution completely resolved at 90 min, while the plasma concentration of bupivacaine was still more than half the Cmax. Bupivacaine liposomes resulted in a low and relatively constant plasma level (approx. 0.1 μg mL−1) and a pronounced local anaesthetic effect throughout the experimental period (> 7 h). In conclusion, bupivacaine liposomes elevated the intensity and prolonged the duration of the local anaesthetic effect of bupivacaine, and suppressed the systemic absorption rate of encapsulated bupivacaine.

Clinical implications of serum protein binding in epileptic children during sodium valproate maintenance therapy.

Steady-state serum levels of total and unbound valproic acid as well as unbound fraction in epileptic children were studied in a clinical setting. Valproic acid binding parameters were analyzed and compared with in vitro findings. Daily doses of sodium valproate ranging from 29 to 73 mg/kg/day were administered per os. Considerable variation in total and unbound concentrations and unbound fractions within and between subjects was observed. In subjects evaluated in this study, serum level of total and unbound valproic acid ranged from 279 to 1,196 μmol/L and from 37 to 410 μmol/L, respectively. The unbound fraction ranged from 10.32 to 48.39%. In vivo binding parameters obtained from clinical material were as follows: association constant, Ka = 4.984 L/mmol; total binding sites, NP = 1.451 mmol/L, where P is the molar concentration of albumin; number of binding sites per molecule of albumin, N = 2.48. Using spiked sera, binding parameters of Ka = 8.032 L/mmol, NP = 1.262 mmol/L, and N = 1.86 were found in the in vitro study. The association constant obtained from in vivo and in vitro studies were not significantly different (p > 0.05) from each other. The unbound fraction of valproic acid was concentration dependent even within the therapeutic range. An equation for estimating unbound concentration (Cf‘) or unbound fraction (fp’) from total concentration (Ct) of valproic acid is derived. The ratio of observed unbound fraction to the estimated unbound fraction (fp/fp’) was used to evaluate the variation in valproate serum binding of that clinical sample. Nine samples from hospitalized patients whose medication and diet were closely supervised showed an fp/fp’ ratio very close to 1 (mean ± SD = 1.04 ± 0.24). It is suggested that a clinical sample showing a value of fp/fp’ greater than 1.76 (mean ± 3 SD) should be evaluated for the cause of the decrease in serum binding and for the associated pharmacokinetic alterations. Therefore, in clinical monitoring of valproate, determination of both total and unbound drug levels was preferable to determination of either one alone. Furthermore, an understanding of the unbound fraction of valproic acid would significantly contribute to the effective management of epileptic patients.

Application of Rat In Situ Single-pass Intestinal Perfusion in the Evaluation of Presystemic Extraction of Indinavir Under Different Perfusion Rates

BACKGROUND/PURPOSE First-pass effect has been an important concern for oral pharmaceuticals. An in vivo system was developed for measuring different concentrations of pharmaceuticals in the portal vein and hepatic vein (via the inferior vena cava) for delineating presystemic metabolism under different perfusion rates by using indinavir as an exemplary agent. METHODS An in situ single-pass intestinal perfusion technique was modified from previous studies to concomitantly obtain portal and hepatic venous bloods. Portal and hepatic venous samples were simultaneously taken from rats at appropriate time points using the perfusion model of 1 mg/mL indinavir at flow rates of 0.05, 0.1, 0.5 and 1.0 mL/min. The indinavir concentrations were assayed by binary-gradient high-pressure liquid chromatography with UV detection. RESULTS The mean indinavir concentrations in portal vein concentration-time profiles at different perfusion times under various flow rates were all higher than those obtained for hepatic veins. At flow rates of 0.5 and 1.0 mL/min, in particular, the area under the curve (AUC) and maximal concentration (Cmax) of indinavir absorption were significantly different between portal veins and hepatic veins (p < 0.05), indicating considerable hepatic involvement in the presystemic extraction of indinavir. The system also has potential for use when estimating the hepatic extraction ratio (E(H)) and hepatic clearance (Cl(H)). CONCLUSION This in vivo approach could provide another useful tool for improving our basic understanding of the absorption kinetics and hepatic metabolism of pharmaceuticals under development and facilitating the clinical application of such.

Prolonged local anesthetic effect of bupivacaine liposomes in rats

Abstract The purpose of the present study was to develop a sustained release local anesthetic formulation that would localize the local anesthetic drug at target sites and produce a prolonged sensory block by a single usual dose. Bupivacaine aqueous solution was encapsulated in multilamellar vesicles (MLV) of liposomes by mechanical shaking method. Wister rats (240±30 g body weight) were given an injection of 0.2 ml liposomal bupivacaine (5 mg/ml), bupivacaine solution (5 mg/ml) or blank liposome. The duration of sensory analgesia was quantified using the tail flick test, and compared among the three preparations. Blank liposomes did not show any sensory block action. The duration of sensory block and the antinociceptive index (AI) in the rats treated with liposomal bupivacaine were 447±19.6 min and 54±5%, respectively, and that in the rats treated with bupivacaine solution was 87±6.7 min and 30±8%, respectively. Liposomal bupivacaine significantly ( p

Quantitation of propofol in plasma by capillary gas chromatography

A rapid, accurate and sensitive gas chromatographic method is described for measuring plasma concentrations of propofol. The technique required only 200 microliters of plasma and a single extraction process, using chloroform containing pentadecane (500 ng/ml) as an internal standard. Quantitation was achieved on an SGE BP-1 fused-silica capillary column (25 m x 0.33 mm I.D., 0.5 micron film thickness) with flame ionization detector. The peak response was linear over a wide concentration range (10-10,000 ng/ml) and the limit of quantitation was 10 ng/ml. The absolute recoveries were over 96% (n = 3). The method is applicable for both research and routine plasma level monitoring.

Effects of St. John's wort extract on indinavir pharmacokinetics in rats: differentiation of intestinal and hepatic impacts.

AIMS To evaluate the possible herb-drug interaction of St. Johns wort (SJW) extracts with indinavir in rats and to set up a model for characterizing pre-systemic sites for the interactions between orally administered herbs and pharmaceuticals. MAIN METHODS The in vivo pharmacokinetic study and in situ single-pass intestinal perfusion model were employed in the research. Plasma indinavir concentration and cytochrome P450 3A activities were measured by high-pressure liquid chromatography and spectrophotometric assays, respectively. KEY FINDINGS Oral administration of either 150 or 300 mg/day SJW for 15 days significantly reduced indinavir plasma levels with certain pharmacokinetic parameter changes. The cytochrome P450 3A analysis suggested that this interaction was attributable to the induction of indinavir metabolism. Further perfusion study demonstrated that both small intestine and the liver contributed significantly to the reduction of indinavir bioavailability and was flow rate-dependent. Moreover, the small intestine was the major site for the pre-systemic metabolism of indinavir, whether with or without SJW pretreatment. SIGNIFICANCE Herb-drug pharmacokinetic interactions between SJW and indinavir can be clearly observed in the Wistar rat model. Particularly, the respective first-pass effect contributed by the small intestine and the liver could be differentiated and quantified. The application of the animal model to investigating herb-drug interactions or other relevant research purposes is envisioned.

Changes in Pharmacokinetics of Valproic Acid in Guinea Pigs from Birth to Maturity

Summary: Pharmacokinetic variations of valproic acid in guinea pigs from birth to maturity were investigated. Male guinea pigs were classified into three groups according to age, and each group was fürther divided into two to three subgrups. The suckling group included three subgroups of 3, 6, and 10 days of age; the juvenile group, three subgroups of 14, 21, and 28 days of age; and the adult group, two subgroups of 42 and 56 days of age. The bile was exteriorized to exclude the factor of enterohepatic circulation during the experiment. Pharmacokinetic parameters were studied and statistically analyzed after an intravenous single dose of 20 mg/kg of sodium valproate. A significantly (p < 0.01) longer elimination half‐life (t1/2) in guinea pigs <10 days of age compared with other groups was observed. Total clearance (Cltot) was significantly smaller (p < 0.01) in the suckling group than in the juvenile group. Volume of distribution at steady state (Vss) was not significantly different between the suckling and juvenile grups, but was significantly smallest (p < 0.01) in the adult group. In vitro study showed that the blood‐to‐plasma concentraction ratio, ranging from 0.81 to 0.84, and the plasma unbound fraction (fu), ranging from 0.24 to 0.38, of valproic acid around therapeutic levels (50–100 μg/ml) were not significantly different among different age groups. It is obvious that the longer t1/2 in the suckling group is not related to either fu or Vss. Therefore, lwo metabolic capacity, i. e., low intrinsic clearance, which was estimated from Cltot and fu, might be the mechanism for the long t1/2 of valproic acid in the suckling stage of guinea pigs.

Dose-dependent inhibition in plasma protein binding of valproic acid during continued treatment in Guinea-pigs

Abstract— Plasma protein binding of valproic acid over a wide range of steady‐state plasma concentration (11·3 α 2·6–130·3–0 α 122·9 μg mL−1: s.e.m., n = 5) in guinea‐pigs has been studied. Valproic acid was given by intravenous constant infusion. At steady‐state the plasma protein binding of valproic acid was analysed. Nonlinear binding was observed. Unbound fraction (fu) of valproic acid increased from 25 to 95% with the increase of steady‐state plasma concentration (Css). The plasma protein‐bound drug concentration (Cb) of valproic acid increased initially with Css but decreased after the Css exceeded 345·0 μg mL−1, where the Cb was 152·5 α 26·8 μg mL−1. At a Css of 1303·3 α 122·9 μg mL−1 the Cb was significantly (P < 0·05) decreased to 72·8 α 20·2 μg mL−1. Binding characteristics of valproic acid in‐vitro were studied using drug‐free guinea‐pig plasma with added valproic acid (10–1000 μg mL−1). The binding behaviour was also nonlinear in‐vitro. The fu increased from 14 to 79% with the increase of valproate concentrations. No decrease in Cb was observed throughout the range. The study demonstrated that binding characteristics of valproic acid in‐vivo and in‐vitro are not parallel. The results suggest that valproic acid may produce or induce plasma protein binding competitors; metabolites of valproic acid may be implicated.