Impact of food administration on lopinavir-ritonavir bioequivalence studies.

A bioequivalence study in 16 Caucasian healthy volunteers (eight male, eight female), comparing plasma drug concentrations after a single oral dose of lopinavir and ritonavir (400 and 100mg, respectively), was carried out following a two-period, two-sequence, two-treatment, randomized crossover design. Formulations were given 15 min after a moderate-fat breakfast in order to diminish both the intrinsic highly-variable performance and the sex differences observed in bioequivalence trials under fasting conditions. Ninety percent confidence intervals for the Test/Reference (T/R) ratio of geometric means for area under concentration-time curve (AUC) and maximum concentration (C(MAX)), either for lopinavir or ritonavir, were within the range of 0.80-1.25. Coprandial administration of formulations not only reduced the number of subjects required for bioequivalence assessment, reducing both ethical and economic cost of the trial, but also the sex differences in the T/R ratio of means.

Comparative drug systemic exposure and clinical efficacy against resistant nematodes in lambs treated with different albendazole formulations.

A pharmaco-parasitological assessment of four different albendazole (ABZ) formulations was carried out in lambs infected with multiple resistant gastrointestinal (GI) nematodes. The comparative drug systemic exposure profiles (ABZ sulphoxide plasma concentrations) and anthelmintic efficacies (clinical endpoint measured through the faecal nematode eggs reduction counts) were determined for a reference formulation (RF) and three different test (T1, T2, T3) generic ABZ preparations. Fifty (50) Corriedale lambs naturally infected with multiple resistant GI nematodes were allocated into five experimental groups (n = 10). Animals in each group received treatment with either the RF, one of the test ABZ formulations (5 mg/kg by the intraruminal route) or were kept as untreated control. Blood samples were collected over 48 h post-treatment. ABZ parent drug was not recovered in the bloodstream. The ABZ sulphoxide (ABZSO) and sulphone (ABZSO(2) ) metabolites were measured in plasma by ultraviolet high-performance liquid chromatography over 36-48 h post-treatment. A faecal nematode egg count reduction test (FECRT) was performed at day 10th post-treatment to lambs from all treated and untreated groups, which indicated the predominance of nematodes with high level of resistance to ABZ. Both ABZSO C(max) and AUC(0-LOQ) values obtained for the RF (pioneer product) were significantly higher (P < 0.05) than those obtained for the T1 and T3 preparations. Based on the currently available bioequivalence criteria, the test (generic) ABZ formulations under evaluation could not be considered equivalent to the RF regarding the rate (C(max) ) and extent (AUC(0-LOD) ) of drug absorption (indirectly estimated through the ABZSO metabolite). A large variation in nematode egg counts did not permit to obtain statistically significant differences among formulations. However, a favourable trend in the efficacy against the most resistant nematodes was observed for the formulations with the highest ABZSO systemic exposure.

Total, unbound plasma and salivary phenytoin levels in critically ill patients / Níveis totais, livres em plasma, e salivares de fenitoína em doentes graves

OBJECTIVE: To assess the reliability of salivary phenytoin (PHT) concentrations and predicted free PHT levels by Sheiner-Tozer equation in order to substitute measured free PHT concentrations in critically ill patients. METHODOLOGY: Twenty-four neurocritically ill adult patients receiving intravenous PHT were included in the study. Analyses of total, free plasma and saliva PHT concentrations were performed by fluorescence polarization immunoassay. Plasma albumin levels were also determined. RESULTS: Free PHT concentrations as well as salivary levels better correlate to clinical effect than total drug concentrations. Linear regression analysis showed a strong correlation between estimated free PHT concentrations by Sheiner-Tozer and measured free PHT levels (r=0.835; p<0.001) and salivary PHT concentrations and measured free PHT concentrations (r=0.964; p<0.001). Sheiner-Tozer equation could be misleading in the presence of displacing drugs. CONCLUSIONS: Saliva may serve as a feasible fluid to plasma in order to be used as a surrogate for free concentration monitoring of PHT in this population.

OBJETIVO: Avaliar a confiabilidade de concentrações salivares de fenitoina (PHT) e níveis livres de PHT pronosticado por equação de Sheiner-Tozer, o efeito da substituição das concentrações medidas livres de PHT em doentes graves. MÉTODO: Vinte e quatro doentes adultos que recebem PHT intravenoso forem incluídos no estudo. Análises de PHT total, livre em plasma e saliva foram realizadas por uma técnica de imune fluorescência polarizassem. Os níveis de albumina em plasma foram também determinados. RESULTADOS: Concentrações livres de PHT em plasma e saliva correlacionam melhor ao efeito clínico que concentrações de fármaco total. Análise de regressão lineal mostrou uma correlação forte entre concentrações livres de PHT estimadas por Sheiner-Tozer e os níveis livres de PHT medidos (r=0.835; p<0.001), e entre concentrações em saliva de PHT e concentrações livres medidas de PHT (r=0.964; p<0.001). A equação de Sheiner-Tozer poderia ser inadequada na presença de fármacos competidores da ligação às proteínas. CONCLUSÕES: Saliva pode servir como substituto do plasma para ser utilizado no controle de concentração livre de PHT em plasma nesta população.

Therapeutic drug monitoring of vancomycin in severe sepsis and septic shock.

BACKGROUND: The sudden changes (increase in capillary permeability, edema formation, vasodilation and hypotension) observed in septic patients and the measurements taken in order to revert this situation make vancomycin concentrations difficult to interpret. Therapeutic drug monitoring (TDM) of vancomycin is routinely performed at steady state, target concentrations are peaks between 20 and 40 mg/l and troughs of 5-10 mg/l. Lately, continuous infusion of vancomycin (CIV) has been used as an alternative mode of administration mainly in critically ill patients with sepsis or septic shock. Despite this novel mode of administration, the need of drug monitoring in this population is under discussion. OBJECTIVE: The aim of our study was to test the usefulness of a multi-compartment model in order to understand the rapid changes that occur in critically ill patients. MATERIALS AND METHODS: A prospective, cohort study was carried out in the intensive care unit of the University Hospital. 25 intensive care unit adults patients with severe sepsis or septic shock receiving vancomycin in CIV modality for documented gram-positive infections were included in the study. Once the infusion was started, blood samples were drawn periodically and analyzed by fluorescence polarisation immunoassay (FPIA, TDx, Abbott Laboratories, Chicago, IL, USA). A multi-compartment model was used to predict vancomycin level evolution throughout the treatment of patients with sepsis. RESULTS: High doses of vancomycin were administered in order to rescue patients from septic shock. Plasma drug concentration dropped while clinical condition of patients worsened. Conversely, drug levels increased spontaneously once the infection was reverted. The theoretical model provided greater insight into pharmacokinetic features related with the use of vancomycin in septic patients. CONCLUSIONS: There was consistency between the model based prediction and the experimental data so dose adjustment was performed in order to reach target concentrations above 20 mg/l and an initial dose of 3 grams of vancomycin per day was recommended to reach these levels.

Monitoreo de vancomicina administrada intraventricularmente en lactantes durante el tratamiento de ventriculitis / Monitoring of intraventricularly administered vancomycin in infants in the treatment of ventriculitis

El objetivo de este estudio fue establecer pautas para el monitoreo de Vancomicina cuando la misma es administrada intraventricularmente en lactantes. En este estudio se incluyeron once pacientes con derivaciones ventrículo-peritoneal. Todos los pacientes recibieron una dosis de Vancomicina intraventricular (IVT). Las muestras de líquido cefalorraquídeo (LCR) fueron analizadas y se calcularon los parámetros farmacocinéticos: constante de velocidad de eliminación (ke) y volumen de distribución (Vd) para poder llevar a cabo un ajuste posológico. Las medias referidas al Vd y a la semivida de eliminación para estos pacientes fueron de 244(±162) mL y 37.1(±23.3) horas respectivamente. En algunos pacientes se observó una gran variabilidad en el Vd. Este cambio en Vd se correlacionó con problemas en el tamaño ventricular o con ventrículos septados. En todos los casos, se propuso una nueva dosis de acuerdo a los parámetros calculados. Debido a variaciones en el sistema a lo largo de la terapia, se propuso un protocolo para la recolección de muestras de LCR de forma tal de individualizar la dosis de Vancomicina con los parámetros farmacocinéticos obtenidos

The objective of this study was to establish guidelines for the monitoring of intraventricularly administered Vancomycin in infants. Eleven patients with ventriculo-peritoneal shunts who developed ventriculitis were included in the study. All patients were given an intraventricular (IVT) dose of Vancomycin. Cerebrospinal fluid (CSF) samples were analysed and pharmacokinetic parameters: elimination rate constant (ke) and distribution volume (Vd) were calculated in order to adjust the dose. Mean values of Vd and elimination half-life for these patients were 244 (± 162) mL and 37.1 (±23.3) hours respectively. A great variability in the Vd was observed in some patients. This change in Vd correlates with problems in the ventricle size or with septated ventricles. In all cases a new dose was suggested according to the calculated parameters. Due to variations in the system throughout therapy, a protocol for CSF samples collection was proposed in order to individualise Vancomycin dosage according to pharmacokinetic parameters

In vitro approach to study the influence of the cardiac output distribution on drug concentration.

Blood flow is not constant during the day, not only due to cardiac output variation but to the variable blood flow fraction supplied to the organs. To what extent these variations could affect the relative drug concentration between two different tissues, is the purpose of this work. In order to study that, a device was designed which took into account different fluid flows towards two flasks. Connections between flasks and pump are shown in text (figure 1). At the bottom of each flask a non-miscible liquid (dichloromethane: CH2Cl2, 100 mL, places 2 and 3) with the circulating fluid (water, 1350 mL, places 1, A, B) was placed. Malachite Green (MG) was introduced as solute into the system (place 1, 5 mL, 700 mg/L aqueous solution). The pump output was set at 1080 mL/min, serving more fluid (five times) to flask A than to flask B. Samples were drawn from compartments 1, A and B, and from organic compartments, during experiences taking several hours. MG concentrations were colorimetrically measured at 619 nm. Room temperature was between 15-25 degrees C. CH2Cl2 MG concentration ratio([2]/[3]) was similar to fluid flow ratio (sigma/(1-sigma)) all over the experience time. Other experiences changing the stop time, room temperature, CH2Cl2 volumes and places, pump output distribution, led us to different evidences that supported a theoretical model. As a conclusion, the most important feature was that whereas MG concentrations in water (1, A, B) were close, in CH2Cl2 these were very different. So, is drug effect prediction reliable by monitoring free drug concentrations in blood?

Lipidic matrix of albendazole: an alternative for systemic infections.

Albendazole is a poorly water soluble drug, with low oral bioavailability, used in pharmacological treatment of a systemic disease as hydatid parasitosis. Lipidic matrices of Gelucires (44/14 and 35/02) were developed. After "in vitro" studies, one formulation was chosen for a single dose study in 8 healthy volunteers, with a cross-over and randomised design, taking a commercially available tablet as reference. Drug absorption was followed by albendazole sulphoxide dosage in urine by high pressure liquid chromatography. Neither albendazole nor albendazole sulphoxide were recovered in urine after tablet administration while 0.18% (+/- 0.06) of dose was recovered after lipidic matrix administration in the first 24 hours. Besides ageing control were performed up to 18 months post-elaboration. Lipidic matrix with Gelucire 44/14 was revealed as a promising attempt for oral pharmaceutical form in albendazole systemic treatment.

Average parameters as a trend to reduce the residual variability in bioequivalence trials.

Bioavailability and bioequivalence evaluations of drug products carried out using the experimental maximum concentration (Cmax) and the experimental time to reach Cmax (Tmax), are not advisable for slow-release formulations and for trials performed with saliva as biologic fluid. When slow-release curves are considered the drug concentration profiles usually show multiple peaks, making it difficult to compute a Cmax,Tmax value. The saliva profile throughout time shows a high variability observed as more than one peak in the saliva concentration versus time curves. In both cases, even if there is a major peak, when the statistical analysis of the data is performed, an important variability in Cmax results in high values in the residual variance of the ANOVA test. Consequently, the power of the bioequivalence test decreases and sometimes it is not possible to conclude on bioequivalence. The average concentration (Cav), the average maximum concentration (Cmax,av) and Cmax,av/Cav x 100 (%Cmax,av) are proposed in this paper as possible parameters in order to evaluate the profile of the concentration-time curves, as they reduce the residual variability in bioequivalence studies.

Average parameters in bioavailability studies: an application to slow-release amitriptyline formulation.

In order to assess the extent and the rate of absorption in bioavailability studies, area under the curve (AUC), experimental maximum concentration (Cmax) and experimental time to reach Cmax (Tmax), are used. But when slow-release formulations are considered, the drug concentration-time curves usually show multiple peaks, and it is difficult to compute a Cmax and Tmax value. In case a Cmax value is computed, important variability in this parameter results in high values in the residual variance of the ANOVA test. So in order to decrease the high variability, average parameters: average concentration (Cav), average maximum concentration (Cmax,av) and Cmax,av x 100/Cav (%Cmax,av), are proposed. These new parameters were applied in a bioavailability study of slow-release amitriptyline formulation.

Lipidic matrix of albendazole sulphoxide: is it an alternative for systemic infections?

As albendazole sulphoxide (ABZS) shows better dissolution properties than albendazole (ABZ), a lipidic matrix with this drug was formulated in order to evaluate if its absorption and so systemic infection chemotherapy could be improved. A cross-over, randomised study in 8 healthy volunteers was carried out, after single administration of 1 g of albendazole or albendazole sulphoxide in lipidic matrix of Gelucire 44/14 (ABZLM and ABZSLM). Absorption was followed performing albendazole sulphoxide dosage in urine samples by high pressure liquid chromatography analysis, during 48 hours. Significant differences were found (p = 0.02) between the urinary recoveries (% E48), being 1.74% and 0.19% the percentage of dose recovered when ABZSLM or of ABZLM were respectively administered. In a previous study of our group similar values were obtained of urinary recovery percentages after albendazole sulphoxide powder administered to another group of healthy volunteers. Lipidic matrix does not improve the physicochemical properties of albendazole sulphoxide powder.

Bioavailability comparison between albendazole and albendazole sulphoxide in rats and man.

Albendazole (ABZ) is a broad spectrum anthelmintic benzimidazole with very low bioavailability, and its activity is due to its main metabolite, Albendazole sulphoxide (ABZS). This work demonstrates the improvement of bioavailability when the ABZS is directly administered, compared with the ABZ administration, both orally given. This observation may be used as an interesting target in the design of new drugs with antihelmintic activity in systemic diseases, using ABZS as a parent drug.

Influence of the emulsion sign in phenytoin bioavailability.

To study the influence of the emulsion sign in phenytoin bioavailability, two emulsions (w/o and o/w) were prepared. Bioavailability studies were carried out with both emulsions in Wistar male rats. The study was of a randomized two-way cross over design. A radiotracer technique was chosen as analytical procedure, due to the small blood sample collected. 14C-phenytoin was synthesized with a high yield and suitable radiochemical purity. It is concluded, from a biopharmaceutic point of view, that the emulsion sign does not seem to affect the amount of phenytoin absorbed, as it is shown through the comparison of the areas under curve up to 24 h. An emulsion with oil as an external phase is responsible of a longer absorption, taking into account the apparent elimination constant rates.

Bioavailability study of furosemide prodrugs in rats.

According to the hydrolysis performance "in vitro" and lipophylicity, two Furosemide (F) prodrugs were chosen from a series of acyloxymethylesters of F synthesized previously: P1 (acetyloxymethyl-4-chloro-N-furfuryl-5-sulfamoylanthranilate ) and P4 (pivaloyloxymethyl-4-chloro-N-furfuryl-5-sulfamoylanthranilate+ ++). The bioavailability studies were assayed over two groups of eight male Wistar rats as a randomized two-way crossover and balanced design: group 1) a solution of P1 in propylenglycol/ethyl acetate vs an aqueous solution of F, and group 2) P1 vs. P4 solutions in oleic acid (P1#, P4#). These assays showed a better absorption performance of P1 and P4 than F, while the two prodrugs showed a similar bioavailability. The oleic acid seems to be responsible for the delay in the recovery of 50% of the total amount of F excreted in urine (T50%). When the monitoring is done in plasma after the administration of P1#, P1 was not detected as circulating prodrug. The analytical determinations of F in urine and plasma were done by high performance liquid chromatography (HPLC). From the urinary excretion data, a slope that indicates a slow elimination was found with a half-life of 12 hours approximately.

Development of absorption furosemide prodrugs: synthesis, in vitro and in vivo evaluation.

Six acyloxymethyl esters of Furosemide were synthesized and the structures were determined by chemical and spectroscopic methods. Lipophilicity parameters were analysed by high performance liquid chromatography (HPLC). Hydrolysis performances in human plasma and intestinal fluids anticipate their properties as absorption prodrugs of Furosemide. A bioavailability study carried out with 8 male Wistar rats with one of the synthesized prodrug (acetyloxymethyl 4-chloro-N-furfuryl-5-sulfamoylanthranilate) showed a greater absorption in relation to Furosemide. The percentages of mean urinary recovery of Furosemide for the prodrug and for the standard solution of the drug were 20.84 and 14.36 respectively. The doses were 10 mg/Kg in Furosemide. The analytical determinations of Furosemide in biological fluids were done by HPLC.

Linear relationships in systems with non linear kinetics.

The elimination rate of drug from a capacity-limited one-compartment model can be expressed by equation (1): [formula: see text] Traditionally equation (1) was linearized according to equation (2): [formula: see text] Here, an alternative linear relationships between concentration and the area under the curve of C/(Km + c]) is proposed: [formula: see text] By iteration of Km into equation (3) until the statistic of analysis of variance for the regression is maximized, both Km and Vmax can be obtained. Several cases were considered: a) Intravenous bolus (single dose): Km (mg/L), Vmax (mg/L h), Vd (L) and V (mg/h) can be estimated. b) Extravascular administration (single dose): by the method of residuals it is possible to make additional estimations of FD/Vd (mg/L) and Ka (1/h). c) Bioequivalence studies: with parameters obtained at single dose, the simulated levels at steady-state are considered for the bioequivalence assessments. d) Km, Vmax estimation with two (C,t) points (single dose): double iteration (Km values and interpolated fictitious third points) are needed. e) Multiple dose: [formula: see text] If t2-t1 = T (interval of administration) it is possible to calculate operatives Km, Vmax, FD/Vd and to estimate Css (steady-state concentration). C1 and C2 correspond to different intervals. All the areas were calculated by the trapezoidal rule.

Alternative approach to relative bioavailability and bioequivalence evaluation, with drugs following Michaelis-Menten elimination kinetics.

An alternative approach to bioavailability and bioequivalence assessment is presented. By a modified Wagner-Nelson procedure, the parameters of a monocompartmental model are calculated, after single oral dose administration trials. The usefulness of the procedure described here is that it permits comparison between two different brands of drug in multiple doses, without the need to administer repeated doses. Only one dose is necessary in order to calculate model parameters and infer steady-state levels.