Effectiveness of community-based DOTS strategy on tuberculosis treatment success rates in Namibia.

DOTS is a key pillar of the global strategy to end tuberculosis (TB). To assess the effectiveness of community-based compared with facility-based DOTS on TB treatment success rates in Namibia. Annual TB treatment success, cure, completion and case notification rates were compared between 1996 and 2015 using interrupted time series analysis. The intervention was the upgrading by the Namibian government of the TB treatment strategy from facility-based to community-based DOTS in 2005. The mean annual treatment success rate during the pre-intervention period was 58.9% (range 46-66) and increased significantly to 81.3% (range 69-87) during the post-intervention period. Before the intervention, there was a non-significant increase (0.3%/year) in the annual treatment success rate. After the intervention, the annual treatment success rate increased abruptly by 12.9% (P < 0.001) and continued to increase by 1.1%/year thereafter. The treatment success rate seemed to have stagnated at ∼85% at the end of the observation period. Expanding facility-based DOTS to community-based DOTS increased annual treatment success rates significantly. However, the treatment success rate at the end of the observation period had stagnated below the targeted 95% success rate. .

Population pharmacokinetic analysis of tacrolimus in the first year after pediatric liver transplantation.

PURPOSES: Tacrolimus (TAC) is the most widely used immunosuppressant for the prevention of acute rejection after solid organ transplantation. Its pharmacokinetics (PK) show considerable variability, making TAC a good candidate for therapeutic drug monitoring (TDM). The principal aim of the study was to describe the PK of TAC in pediatric patients during the first year after transplantation. METHODS: Routine TDM trough levels of TAC were obtained from 42 pediatric liver allograft recipients during the first year after transplantation. A population PK model was developed using nonlinear mixed-effects modeling to describe TAC PK during this period and to explain the observed variability by means of patients' demographics, biochemical test results and physiological characteristics. RESULTS: The PK of TAC were best described by a two-compartment model with first-order elimination. Apparent volumes of the central compartment, intercomparmental clearance and maximum blood clearance estimates were 253 L, 115 L/day and 314 L/day, respectively. The absorption first-order rate and volume of peripheral compartment were fixed to 4.5 h(-1) and 100 L, respectively. While hematocrit levels, time after transplantation and bodyweight influenced TAC clearance, bodyweight was the only covariate retained on volume of distribution. CONCLUSIONS: We developed a TAC population PK model in pediatrics covering the first year after liver transplantation that may serve as a tool for TAC dose individualization as part of TDM.

Application of dermal microdialysis for the determination of bioavailability of clobetasol propionate applied to the skin of human subjects.

Dermal microdialysis was used to assess the bioavailability of a topical corticosteroid, clobetasol propionate, following application onto the skin of human subjects. The penetration of clobetasol propionate from a 4% m/v ethanolic solution applied onto 4 sites on one forearm of healthy human volunteers was studied. A lipid emulsion, Intralipid®, was used as the perfusate and linear microdialysis probes with a 2-kDa cutoff were inserted intradermally at the designated sites. The results indicated that Intralipid could be used as a suitable perfusate for in vivo microdialysis of this lipophilic drug of interest. Furthermore, the study clearly demonstrated the application of dermal microdialysis as a valuable tool to assess the bioavailability/bioequivalence of clobetasol propionate penetration into the skin following topical application.

The effect of ageing on cytochrome p450 enzymes: consequences for drug biotransformation in the elderly.

Ageing is an aggravating factor leading to alterations in the biotransformation of drugs, and therefore their therapeutic efficacy and safety. In this review we discuss the influence of ageing on drug metabolizing enzymes in male Wistar rats. We report that drug metabolizing enzymes can be affected by ageing either by post-translational modifications or by transcriptional modifications. The post-translational modifications could be due to an increase of oxidative stress during ageing. Although it is now well established that transcriptional modifications are due to a change in the GH secretion profile in senescent rats, the intracellular mechanisms underlying these modifications are still unclear. In addition to the strong decrease in the activity of the main CYPs of male rats, we discuss the potential consequences on human drug metabolism in the elderly.

Generic substitution: the use of medicinal products containing different salts and implications for safety and efficacy.

In their quest to gain early entry of new generic products into the market prior to patent expiration, one of the strategies pursued by generic drug product manufacturers is to incorporate different salts of an approved active pharmaceutical ingredient (API) in a brand company's marketed dosage form and subject such dosage forms to bioequivalence assessment. These initiatives present challenges to regulatory authorities where the decision to approve bioequivalent products containing such pharmaceutical alternatives must be considered in the light of safety and efficacy, and more particularly, with respect to their substitutability. This article describes the various issues and contentions associated with the concept of pharmaceutical alternatives, specifically with respect to the uses of different salts and the implications for safety, efficacy and generic substitution.

Biowaiver monographs for immediate release solid oral dosage forms based on biopharmaceutics classification system (BCS) literature data: chloroquine phosphate, chloroquine sulfate, and chloroquine hydrochloride.

Literature data on the properties of chloroquine phosphate, chloroquine sulfate, and chloroquine hydrochloride related to the Biopharmaceutics Classification System (BCS) are reviewed. The available information indicates that these chloroquine salts can be classified as highly soluble and highly permeable, i.e., BCS class I. The qualitative composition of immediate release (IR) tablets containing these Active Pharmaceutical Ingredients (APIs) with a Marketing Authorization (MA) in Belgium (BE), Germany (DE), Finland (FI), and The Netherlands (NL) is provided. In view of these MA's and the critical therapeutic indication of chloroquine, it is assumed that the registration authorities had evidence that these formulations are bioequivalent to the innovator. It is concluded that IR tablets formulated with these excipients are candidates for a biowaiver.

In vivo tolerance assessment of skin after insertion of subcutaneous and cutaneous microdialysis probes in the rat.

The purpose of the study was to evaluate the trauma induced by insertion of the linear microdialysis probe in the subcutaneous and dermal tissue in the rat and to check if the microdialysis probe insertion affects transdermal drug delivery. Non-invasive bioengineering methods (TEWL, Laser Doppler Velocimeter, Chromameter) as well as histology were combined to characterize these effects. The results showed that the dermal and subcutaneous insertion of microdialysis probes did not change skin permeability, blood flow and color, confirming the safety of this technique. The probe depth did not influence the trauma. No significant physical damage after probe insertion was noticed. Thus, the present work validates the use of microdialysis in dermatopharmacokinetics studies after topical or systemic drug delivery.

Differential induction of midazolam metabolism in the small intestine and liver by oral and intravenous dexamethasone pretreatment in rat.

1. Midazolam is metabolized in the rat by CYP3A enzymes to 4-OH-midazolam (4-OH-MDZ) and 1'-OH-midazolam (1'-OH-MDZ). The induction of midazolam metabolism was studied in male Wistar rats treated with dexamethasone (50 mg kg(-1) day(-1)) during 4 days via the oral or intravenous routes. Microsomes were prepared from the liver and the proximal small intestine and in vitro metabolism of midazolam was determined. In addition, CYP3A1- and CYP3A2-like protein levels were measured by gel electrophoresis and immunoblotting. 2. The V(max)'s (mean SEM) for 4-OH-MDZ and 1'-OH-MDZ formation were much lower in intestinal (0.078 +/- 0.002 and 0.074 +/- 0.002 microM min(-1) mg(-1) protein, respectively) compared with hepatic microsomes prepared from the uninduced rat (0.870 +/- 0.007 and 0.310 +/- 0.020 microM min(-1) mg(-1) protein, respectively). Induction by oral or intravenous dexamethasone pretreatment led to significant increases in V(max) for 4-OH-MDZ and 1'-OH-MDZ by both intestinal and hepatic microsomes. Oral dexamethasone pretreatment via the oral route resulted in a more pronounced increase in V(max) compared with intravenous administration of the inducer. 3. CYP3A1 and CYP3A2 protein levels in liver microsomes were significantly increased following oral (3.7- and 3.2-fold, respectively) or intravenous (2.6- and 2.1-fold, respectively) pretreatment with dexamethasone. On the contrary, only oral dexamethasone pretreatment resulted in a significant change in intestinal CYP3A2-like protein (7.3-fold). A slight difference in the migration distance of the immunoreactive band for CYP3A2 was also observed for intestinal microsomes. 4. These results suggest that intestinal CYP3A enzymes in the rat differ from hepatic CYP3A1 and CYP3A2. They also demonstrate that systemic dexamethasone administration can induce intestinal microsome activity.

Validation of subcutaneous microdialysis sampling for pharmacokinetic studies of flurbiprofen in the rat.

The objective of this study was to validate subcutaneous (sc) microdialysis sampling to study flurbiprofen pharmacokinetics and plasma protein binding in the awake freely moving rat. A linear microdialysis probe was manufactured using a Hemophane hollow fiber which was tested in vitro and in vivo for the recovery of flurbiprofen and naproxen used as retrodialysis marker. Flurbiprofen was administered intraperitoneally and intravenously at a dose of 20 mg/kg in rats. In both cases, conventional blood sampling and sc microdialysis sampling were simultaneously performed. The microdialysates were analyzed on-line by high-pressure liquid chromatography. Naproxen, which was shown to have a similar in vivo loss by retrodialysis as flurbiprofen (71.5 +/- 0.9% and 71.0 +/- 0.8% respectively, n = 3), was used to continuously monitor probe recovery. Concentration-dependent protein binding of flurbiprofen was demonstrated in vivo based on experiments with a simultaneous sc microdialysis and blood sampling. Values of unbound fraction were similar to those reported previously by intravenous microdialysis sampling, demonstrating that the sc unbound concentrations are very similar to those in the central compartment. There was no significant difference among pharmacokinetic parameters (AUC, CL, t(1/2z), Vd) for total or unbound flurbiprofen determined after intraperitoneal and intravenous administration. Subcutaneous microdialysis is a simple yet powerful tool to study the pharmacokinetics and the in vivo plasma protein binding of flurbiprofen in the awake unrestrained rat.

In vitro immunosuppressive activity of tacrolimus dihydrodiol precursors obtained by chemical oxidation and identification of a new metabolite of SDZ-RAD by electrospray and electrospray-linked scan mass spectrometry.

Different tacrolimus epoxides and dihydrodiol epoxides arising from the chemical oxidation of the parent drug are described. Open-chain tautomeric forms involving the lactone function were identified for the tacrolimus epoxides. Moreover, the identification by electrospray and electrospray linked scan mass spectrometry of an SDZ-RAD C16-C27 O-demethyl 17, 18-19, 20-21, 22 tris-epoxide new metabolite isolated from pig liver microsomes is reported. The in vitro immunosuppressive activity, using mixed lymphocyte reactions of the two macrolide reported oxidation compounds are discussed.

Midazolam and cortisol metabolism before and after CYP3A induction in humans.

INTRODUCTION: CYP3A is responsible for the metabolism of numerous endogenous and exogenous compounds. Several substrates of CYP3A have been investigated to assess the CYP3A-metabolizing capacity of an individual in an attempt to predict the rate of metabolism of other CYP3A substrates. Two such tests of CYP3A activity are the midazolam plasma clearance after its intravenous administration and the 6beta-OH cortisol urinary ratio. Possible correlations between these 2 tests were investigated before and after treatment with rifampin in a group of healthy volunteers. METHODS: Pharmacokinetic parameters of midazolam and 6beta-OH cortisol urinary ratio were evaluated in 8 volunteers before and after 6 days treatment with rifampin, a potent inducer of CYP3A, and after cessation of rifampin treatment. RESULTS: Midazolam systemic clearance and the 6beta-OH cortisol urinary ratio were significantly higher at Days 7 and 10 than at Day 0. There was a strong positive correlation between these 2 parameters (r = 0.70, p < 0.001). In contrast, no correlation was observed between the ratio of the AUCs of 1'-OH midazolam vs. midazolam (AUC0-1(1'-OH)/AUC0-t(MDZ)) or the ratio of plasma concentration of 1'-OH midazolam vs. midazolam (C30 min(1'-OH)/C30 min(MDZ)) and the 6beta-OH cortisol urinary ratio (r = 0.05, p = 0.82; r = 0.04, p = 0.88, respectively). Considering only data obtained before or after treatment with rifampin, however, no correlation was observed between midazolam systemic clearance and the 6beta-OH cortisol urinary ratio. CONCLUSIONS: These data demonstrate that there is a strong positive correlation between systemic midazolam clearance and 6beta-OH cortisol urinary ratio before and after induction. This suggests that the 6beta-OH cortisol urinary ratio test is a non-invasive alternative to the use of systemic midazolam clearance for monitoring the time-course of CYP3A induction.

[Interactions of food and drug metabolism]. / Interactions entre alimentation et métabolisme des médicaments.

The nutritional state, and/or the ingestion of specific nutrients, is/are able to modify drug disposition, by interfering with drug absorption, distribution, storage, and metabolism. Recent data report that nutrients interfere with drug metabolism either by modifying key enzymes of phase I (cytochromeP450 dependent mixed function oxidase) and II (glucuronosyl, sulfonyl- ... transferases), or by modulating coenzymes availability (NADPH, UDPglucuronic acid...). Food components involved in drug metabolism modifications are either macro-nutrients (carbohydrates, lipids, proteins, ethanol), micronutriments (vitamins, minerals), or phytochemicals. Drug-nutrients interactions may be beneficials, and thus could constitute, i.e. a way to improve drug therapeutic index, or generate adverse effects.

Cryopreservation of rat precision-cut liver slices by ultrarapid freezing: influence on phase I and II metabolism and on cell viability upon incubation for 24 hours.

Several cryopreservation methods for precision-cut rat liver slices (PCLS) have been proposed, allowing a short-term (a few hours) maintainance of viability and functionality upon thawing. The aim of the present study was to test the metabolic capacity of PCLS cryopreserved by an ultrarapid method. The biotransformation of paracetamol to its glucuronide and sulfate conjugates and of midazolam to its hydroxylated metabolites was studied in thawed PCLS incubated for 24 hours at 37 degrees C in Williams' medium E. In addition, protein levels of the key enzymes involved in these metabolic reactions, i.e. UGT1A1, ST1A1, CYP2E1 and CYP3A2 were determinated. In addition, biological markers of cell function (ATP and glycogen levels) and toxicity (LDH leakage in the medium) were also measured. Compared to controls (non cryopreserved PCLS), CYP3A2 activity and content and CYP2E1 content were maintained at the same level all along the incubation, whereas paracetamol glucuronidation and sulfation dropped to 24 and 21% of the control value, respectively, immediately after thawing. Freezing-thawing conditions also modified cell functionality, leading to a lower intracellular ATP and glycogen content, and an increase in cell lysis, as shown by LDH released in the medium. The results of this study suggest that cryopreserved PCLS are able to maintain some phase I activities for 24 hours after thawing whereas some phase II metabolic capacities are not maintained.

Comparative clinical pharmacokinetics of tacrolimus in paediatric and adult patients.

Tacrolimus is a potent immunosuppressive agent used to prevent allograft rejection. The pharmacokinetics of tacrolimus have been studied in healthy volunteers and transplant recipients, mostly by using immunoassays to measure tacrolimus in plasma or blood. However, because of the cross-reactivity for certain tacrolimus metabolites of the antibodies used, these methods often lack specificity. This should be carefully taken into account when interpreting pharmacokinetic results for tacrolimus. In adult patients, tacrolimus is generally rapidly absorbed following oral administration (the time to reach maximum concentration is 1 to 2 hours), but in some patients absorption is slow or even delayed. Because of presystemic elimination, the oral bioavailability is low (around 20%) but may vary between 4 and 89%. Tacrolimus is highly bound to erythrocytes. Its binding to plasma proteins varies between 72 and 98% depending on the methodology used. Because of the extensive partitioning of tacrolimus into erythrocytes, its apparent volume of distribution (Vd) based on blood concentrations is much lower (1.0 to 1.5 L/kg) compared with values based on plasma concentrations (about 30 L/kg). Tacrolimus is metabolised by cytochrome P450 (CYP) 3A4 to at least 10 metabolites, some of which retain significant activity. Biliary excretion is the route of elimination of the tacrolimus metabolites. Systemic plasma clearance of tacrolimus is very high (0.6 to 5.4 L/h/kg), whereas blood clearance is much lower (0.03 to 0.09 L/h/kg). The terminal elimination half-life (t1/2beta) of tacrolimus is approximately 12 hours (with a range of 3.5 to 40.5 hours). Only limited information is available on the pharmacokinetics of tacrolimus in paediatric patients. The rate and extent of tacrolimus absorption after oral administration do not seem to be altered in paediatric patients. The Vd of tacrolimus based on blood concentrations in paediatric patients (2.6 L/kg) is approximately twice the adult value. Blood clearance of tacrolimus is also approximately twice as high in paediatric (0.14 L/h/kg) compared with adult (0.06 L/h/kg) patients. Consequently, t1/2beta does not appear modified in children, but oral doses need to be generally 2-fold higher than corresponding adult doses to reach similar tacrolimus blood concentrations. More pharmacokinetic studies in paediatric patients are, however, needed to rationalise the use of therapeutic drug monitoring for optimisation of tacrolimus therapy in this patient population.

Blood microdialysis in pharmacokinetic and drug metabolism studies.

Microdialysis is a sampling technique allowing measurement of endogenous and exogenous substances in the extracellular fluid surrounding the probe. In vivo microdialysis sampling offers several advantages over conventional methods of studying the pharmacokinetics and metabolism of xenobiotics, both in experimental animals and humans. In the first part of this review article various practical aspects related to blood microdialysis will be discussed, such as: probe design, surgical implantation techniques, methods to determine the in vivo relative recovery of the analyte of interest by the probe, special analytical considerations related to small volume microdialysate samples, and pharmacokinetic calculations based on microdialysis data. In the second part of this review a few selected applications of in vivo microdialysis sampling to investigate pharmacokinetic processes are briefly discussed: determination of in vivo plasma protein binding in small laboratory animals, distribution of drugs across the blood-brain barrier, the use of microdialysis sampling to study biliary excretion and enterohepatic cycling, blood microdialysis sampling in man and in the mouse, and in vivo drug metabolism studies.

High-performance liquid chromatographic assay of malagashanine in rat plasma and urine and its pharmacokinetic application.

A reversed-phase HPLC method was developed for quantitative analysis of malagashanine in rat plasma and urine. Malagashanine and internal standard were extracted from alkalinized rat plasma. Urine analysis was performed by direct injection onto the HPLC system. Acetonitrile-aqueous 25 mM sodium acetate solution at pH 6.25 (45:55, v/v) was used as the mobile phase. The eluate was monitored by using UV detection at 250 nm. The assay was linear within the concentration range of 10-1000 ng/ml. Both intra- and inter-day accuracy and precision were within acceptable limits. The method was applied to study the pharmacokinetics of malagashanine in rats.

Isolation from rat urine and human liver microsomes and identification by electrospray and nanospray tandem mass spectrometry of new malagashanine metabolites.

Malagashanine has been isolated from indigenous madagascan Strychnos myrtoides alkaloids used traditionally to treat malaria. This alkaloid was found to enhance the action of chloroquine against chloroquine-resistant strains of Plasmodium falciparum when combined with classical antimalarial drugs (chloroquine, quinine). The present study was carried out in order to investigate by electrospray mass and tandem mass spectrometry and NMR spectroscopy the structure of two new metabolites isolated from rat urine and human liver microsomes. We were able to demonstrate the presence of two new metabolites of malagashanine corresponding to a malagashanine N-demethylated metabolite and to the oxidation of malagashanine in the alpha-position of the N-methyl group to produce a carbinolamine function. The latter metabolite may be subject to ring and open-chain tautomerism effects and dimeric species were detected in the electrospray mass spectrum.

Isolation from pig liver microsomes, identification by tandem mass spectrometry and in vitro immunosuppressive activity of an SDZ-RAD 17,18,19,20,21,22-tris-epoxide.

Macrolide immunosuppressive drugs such as tacrolimus (FK506) and sirolimus (rapamycin) are compounds largely used in modern immunosuppressive therapy and considered as powerful immunosuppressive agents. Some of these molecules are still under clinical development as, for example, SDZ-RAD (40-O-(2-hydroxyethyl)rapamycin), an immunosuppressive drug closely related to rapamycin. SDZ-RAD has a molecular mass of 957.57 Da (C53H83NO14) and shares the same common intracellular receptor as tacrolimus, the FK-506 binding protein (FKBP-12). SDZ-RAD exerts its pharmacological effect by binding to a different effector protein, inhibits the S6p 70-kinase and interrupts a different signal transduction pathway than tacrolimus. Both SDZ-RAD and rapamycin are metabolized mainly by the cytochrome P-450 3A4-dependent mixed function oxygenase enzyme system to hydroxylated and demethylated metabolites. We describe here the isolation from pig liver microsomes of a novel SDZ-RAD metabolite identified by electrospray tandam mass spectrometry as a new SDZ-RAD 17,18,19,20,21,22-tris-epoxide metabolite. The in vitro immunosuppressive activity as measured by the mixed lymphocyte reaction is more or less comparable to that of SDZ-RAD, although its pharmacological mode of action may be different from that classically described for rapamycin.