Solubility vs Dissolution in Physiological Bicarbonate Buffer.

BACKGROUND: Phosphate buffer is often used as a replacement for the physiological bicarbonate buffer in pharmaceutical dissolution testing, although there are some discrepancies in their properties making it complicated to extrapolate dissolution results in phosphate to the in vivo situation. This study aims to characterize these discrepancies regarding solubility and dissolution behavior of ionizable compounds. METHODS: The dissolution of an ibuprofen powder with a known particle size distribution was simulated in silico and verified experimentally in vitro at two different doses and in two different buffers (5 mM pH 6.8 bicarbonate and phosphate). RESULTS: The results showed that there is a solubility vs. dissolution mismatch in the two buffers. This was accurately predicted by the in-house simulations based on the reversible non-equilibrium (RNE) and the Mooney models. CONCLUSIONS: The results can be explained by the existence of a relatively large gap between the initial surface pH of the drug and the bulk pH at saturation in bicarbonate but not in phosphate, which is caused by not all the interfacial reactions reaching equilibrium in bicarbonate prior to bulk saturation. This means that slurry pH measurements, while providing surface pH estimates for buffers like phosphate, are poor indicators of surface pH in the intestinal bicarbonate buffer. In addition, it showcases the importance of accounting for the H2CO3-CO2 interconversion kinetics to achieve good predictions of intestinal drug dissolution.

Novel food drug interaction mechanism involving acyclovir, chitosan and endogenous mucus.

Drug absorption from drug products may be affected by pharmaceutical excipients and/or food additives through different mechanisms. Chitosan is a recognized nutraceutical, with potential as an excipient due to its permeability enhancer properties. While chitosan properties have been evaluated in in vitro and pre-clinical models, studies in humans are scarce. Unexpectedly, a controlled clinical trial showed chitosan actually reduced acyclovir bioavailability. The effect seems to be related to an interaction with gastrointestinal mucus that prevents further absorption, although more in depth research is needed to unravel the mechanism. In this paper, we propose a mechanism underlying this excipient effect. The mucus - chitosan interaction was characterized and its effect on acyclovir diffusion, permeation and bioaccessibility was investigated. Further, pharmacokinetic modeling was used to assess the clinical relevance of our findings. Results suggest that in situ coacervation between endogenous mucus and chitosan rapidly entrap 20-30% of acyclovir dissolved dose in the intestinal lumen. This local reduction of acyclovir concentration together with its short absorption window in the small intestine would explain the reduction in acyclovir Cmax and AUC. This study highlights the importance of considering mucus in any biorelevant absorption model attempting to anticipate the effect of chitosan on drug absorption.

In Vitro Methodologies for Evaluating Colon-Targeted Pharmaceutical Products and Industry Perspectives for Their Applications.

Several locally acting colon-targeted products to treat colonic diseases have been recently developed and marketed, taking advantage of gastrointestinal physiology to target delivery. Main mechanisms involve pH-dependent, time-controlled and/or enzymatic-triggered release. With site of action located before systemic circulation and troublesome colonic sampling, there is room for the introduction of meaningful in vitro methods for development, quality control (QC) and regulatory applications of these formulations. A one-size-fits-all method seems unrealistic, as the selection of experimental conditions should resemble the physiological features exploited to trigger the release. This article reviews the state of the art for bio-predictive dissolution testing of colon-targeted products. Compendial methods overlook physiological aspects, such as buffer molarity and fluid composition. These are critical for pH-dependent products and time-controlled systems containing ionizable drugs. Moreover, meaningful methods for enzymatic-triggered products including either bacteria or enzymes are completely ignored by pharmacopeias. Bio-predictive testing may accelerate the development of successful products, although this may require complex methodologies. However, for high-throughput routine testing (e.g., QC), simplified methods can be used where balance is struck between simplicity, robustness and transferability on one side and bio-predictivity on the other. Ultimately, bio-predictive methods can occupy a special niche in terms of supplementing plasma concentration data for regulatory approval.

Predicting Pharmacokinetics of Multisource Acyclovir Oral Products Through Physiologically Based Biopharmaceutics Modeling.

Highly variable disposition after oral ingestion of acyclovir has been reported, although little is known regarding the underlying mechanisms. Different studies using the same reference product (Zovirax ®) showed that Cmax and AUC were respectively 44 and 35% lower in Saudi Arabians than Europeans, consistent with higher frequencies of reduced-activity polymorphs of the organic cation transporter (OCT1) in Europeans. In this study, the contribution of physiology (i.e., OCT1 activity) to the oral disposition of acyclovir immediate release (IR) tablets was hypothesized to be greater than dissolution. The potential role of OCT1 was studied in a validated physiologically-based biopharmaceutics model (PBBM), while dissolution of two Chilean generics (with demonstrated bioequivalence) and the reference product was assessed in vitro. The PBBM suggested that OCT1 activity could partially explain population-related pharmacokinetic differences. Further, dissolution of generics was slower than the regulatory criterion for BCS III IR products. Remarkably, virtual bioequivalence (incorporating in vitro dissolution into the PBBM) correctly and robustly predicted the bioequivalence of these products, showcasing its value in support of failed BCS biowaivers. These findings suggest that very-rapid dissolution for acyclovir IR products may not be critical for BCS biowaiver. They also endorse the relevance of cross-over designs in bioequivalence trials.

Biowaiver Monograph for Immediate-Release Solid Oral Dosage Forms: Carbamazepine.

Literature relevant to assessing whether BCS-based biowaivers can be applied to immediate release (IR) solid oral dosage forms containing carbamazepine as the single active pharmaceutical ingredient are reviewed. Carbamazepine, which is used for the prophylactic therapy of epilepsy, is a non-ionizable drug that cannot be considered "highly soluble" across the range of pH values usually encountered in the upper gastrointestinal tract. Furthermore, evidence in the open literature suggests that carbamazepine is a BCS Class 2 drug. Nevertheless, the oral absolute bioavailability of carbamazepine lies between 70 and 78% and both in vivo and in vitro data support the classification of carbamazepine as a highly permeable drug. Since the therapeutic and toxic plasma level ranges overlap, carbamazepine is considered to have a narrow therapeutic index. For these reasons, a BCS based biowaiver for IR tablets of carbamazepine cannot be recommended. Interestingly, in nine out of ten studies, USP dissolution conditions (900 mL water with 1% SLS, paddle, 75 rpm) appropriately discriminated among bioinequivalent products and this may be a way forward to predicting whether a given formulation will be bioequivalent to the comparator product.

Poloxamer 188-Coated Ammonium Methacrylate Copolymer Nanocarriers Enhance Loperamide Permeability across Pgp-Expressing Epithelia.

Loperamide is a µ-opioid agonist with poor gastrointestinal absorption, mainly because of its modest aqueous solubility and being a P-glycoprotein (Pgp) efflux substrate. Nevertheless, studies associated with therapeutic effects strongly suggest that loperamide holds potential pharmacological advantages over traditional µ-opioid agonists commonly used for analgesia. Thus, in this Communication, we assessed in MDCK-hMDR1 cell lines the effects over loperamide uptake and efflux ratio, when loaded into Eudragit RS (ERS) nanocarriers coated with poloxamer 188 (P188). ERS was chosen for enhancing loperamide aqueous dispersibility and P188 as a potential negative Pgp modulator. In uptake assays, it was observed that Pgp limited the accumulation of loperamide into cells and that preincubation with P188, but not coincubation, led to increasing loperamide uptake at a similar extent of Pgp pharmacological inhibition. On the other hand, the efflux ratio displayed no alterations when Pgp was pharmacologically inhibited, whereas ERS/P188 nanocarriers effectively enhanced loperamide uptake and absorptive transepithelial transport. The latter suggests that loperamide transport across cells is significantly influenced by the presence of the unstirred water layer (UWL), which could hinder the visualization of Pgp-efflux effects during transport assays. Thus, results in this work highlight that formulating loperamide into this nanocarrier enhances its uptake and transport permeability.

Metformin Transport in Native MDCK-Wt and MDCK-II Monolayers Unveils Functional Inter-Strains Differences Influencing Drug Permeability.

PURPOSE: MDCK cells are commonly used to assess drug permeability, but the existence of various strains merits a comparative functional study. Since metformin absorption is largely mediated by transporters and paracellular diffusion, we used it to functionally compare MDCK-wt and MDCK-II. METHODS: Uptake, bidirectional transport and efflux experiments were performed using different buffers, pH, and a panel of transporter inhibitors. Relative contributions to total transport in both strains were estimated. RESULTS: Metformin uptake into MDCK-wt was linear but saturable in MDCK-II. Uptake into MDCK-wt or -II was promoted at pH 5.4 or 8.4, respectively. Quinidine and cimetidine similarly inhibited uptake in both strains. Lopinavir (PMAT specific) at pH 5.4 or pyrimethamine (MATE specific) at pH 8.4 differentially inhibited MDCK-wt or -II, respectively. Transport at pH 7.4 was absorptive regardless of strains, but secretory (MDCK-II) or absorptive (MDCK-wt) at pH 5.4. Efflux was largely basolateral in both strains. While paracellular permeability was similar between strains, total transport was dominated by transporters in MDCK-II or paracellular diffusion in MDCK-wt. CONCLUSIONS: Metformin transport revealed functional differences between MDCK strains. Apical uptake was governed by MATE in MDCK-II or PMAT in MDCK-wt, such that metformin transport was either secretory or absorptive, respectively.

In vitro prediction of in vivo absorption of ibuprofen from suspensions through rational choice of dissolution conditions.

Two ibuprofen suspension formulations were investigated for their dissolution in various bicarbonate, phosphate and acetate buffers. Phosphate and acetate gave faster release than bicarbonate at comparable molarities. Nevertheless, mass transport modelling using the reversible non-equilibrium (RNE) approach enabled the calculation of phosphate molarities that gave good matches to physiological bicarbonate in terms of ibuprofen dissolution. This shows that developing surrogate buffers for bicarbonate that are devoid of the technical difficulties associated with the bicarbonate-CO2 systems is possible. In addition, the intestinal dissolution kinetics of the tested suspensions were determined by applying compartmental pharmacokinetic modelling to plasma profiles that were previously obtained for these suspensions in an in vivo study performed on healthy human volunteers. The in vitro dissolution profiles in bicarbonate compared reasonably well with the profiles representing the in vivo intestinal dissolution kinetics of the tested suspensions when applied to healthy human volunteers in a pharmacokinetic study. This shows the possible potential toward extending biowaivers so that they include BCS class IIa compounds.

The effect of chitosan on the bioaccessibility and intestinal permeability of acyclovir.

Chitosan is object of pharmaceutical research as a candidate permeability enhancer. However, chitosan was recently shown to reduce the oral bioavailability of acyclovir in humans. The effect of chitosan on two processes determining the oral bioavailability of acyclovir, bioaccessibility and intestinal absorption, was now investigated. Acyclovir's bioaccessibility was studied using the dynamic TNO gastro-Intestinal Model (TIM-1). Four epithelial models were used for permeability experiments: a Caco-2 cell model in absence and presence of mucus and both rat and porcine excised intestinal segments. Study concentrations of acyclovir (0.8 g/l) and chitosan (1.6 g/l and 4 g/l) were in line with those used in the aforementioned human study. No effect of chitosan was measured on the bioaccessibility of acyclovir in the TIM-1 system. The results obtained with the Caco-2 models were not in line with the in vivo data. The tissue segment models (rat and porcine intestine) showed a negative trend of acyclovir's permeation in presence of chitosan. The Ussing type chamber showed to be the most biopredictive, as it did point to an overall statistically significantly reduced absorption of acyclovir. This model thus seems most appropriate for pharmaceutical development purposes, in particular when interactions between excipients and drugs are to become addressed.

Reformas de sector salud en el camino de la integración: aprendizaje y perspectivas

Documento presentado Seminario Internacional Reformas del Sector Salud en el Camino de la Integración que contiene informes de representantes de la salud de cada país de la región andina abordando las cuestiones del sistema de salud como su contexto histórico, político y económico. Documento en formato PDF, requer Acrobat Reader.

Documento de consenso sobre el tratamiento de la exposición a tuberculosis y de la infección tuberculosa latente en niños / Treatment of tuberculosis exposure and latent tuberculosis infection in children

Introducción La pobreza, la infección por el virus de la inmunodeficiencia humana (VIH), la resistencia a fármacos y la diseminación a partir de pacientes con infección latente son las causas más importantes de la pandemia actual de tuberculosis. En los países industrializados, la población inmigrante procedente de países en desarrollo y la falta de programas eficaces de control son las causas principales del incremento de la enfermedad. La situación de los niños es todavía más grave por ser más vulnerables a la enfermedad que los adultos. El mayor riesgo de contraer tuberculosis lo tienen los niños autóctonos que conviven con adultos que tienen factores de riesgo de tuberculosis y los niños inmigrantes y adoptados del tercer mundo. A pesar de que los niños desarrollan la enfermedad no son prácticamente nunca bacilíferos, el tratamiento adecuado de la exposición a tuberculosis bacilífera y de la infección tuberculosa latente en niños contribuye a crear una vigilancia estrecha de los núcleos familiares que asegura un riguroso estudio de contactos y contribuye a evitar formas graves de tuberculosis, más frecuentes en el niño. Objetivo El objetivo de este segundo documento de consenso del Grupo de Trabajo de Tuberculosis de la Sociedad de Infectología Pediátrica (SEIP) es unificar criterios para el tratamiento de las situaciones de exposición a tuberculosis e infección tuberculosa latente en niños y sensibilizar a las autoridades sanitarias acerca de la necesidad de acometer programas muy estrictos de detección de tuberculosis en población de riesgo

Introduction The most important causes of the current tuberculosis pandemic are poverty, HIV infection, drug resistance, and the spread of infection by patients with latent tuberculosis infection. In industrialized countries, the main reasons for the increase of this disease are immigration from developing countries and the lack of effective surveillance programs. The situation of children is even more serious as they are more vulnerable to the disease than adults. The children most at risk are those who live with adults at risk for tuberculosis, immigrant children, and adoptees from developing countries. Although children are bacilliferous only exceptionally, the appropriate management of bacilliferous tuberculosis exposure and latent tuberculosis infection in children contributes to the creation of close surveillance of nuclear families and rigorous study of contacts. Moreover, it could prevent serious forms of the disease, which are more frequent in children. Objective The principal objective of this second consensus document of the Spanish Society of Pediatric Infectious Diseases (Sociedad Española de Infectología Pediátrica [SEIP]) is to unify the criteria for the treatment of tuberculosis exposure and latent tuberculosis infection in children. A further aim is to increase awareness of the need for strict detection measures in high-risk populations among health authorities

Validation of two rating scales for attention-deficit hyperactivity disorder diagnosis in Colombian children.

This study assesses the validity of the Behavioral Assessment System for Children-parent and teacher questionnaires for attention-deficit hyperactivity disorder diagnosis in a randomized sample of 344 Colombian children (145 cases, 199 controls), males and females, ages 6 to 11, with an estimated Wechsler Full Scale Intelligence Quotient over 70. The assessment protocol for both groups included psychiatric, neurologic, and psychological interviews, parent and teacher rating forms, and an Attention-Deficit Hyperactivity Disorder Checklist. All Behavioral Assessment System for Children-parent and teacher dimensions, except withdrawal and somatization, significantly differentiated cases and controls. Parents and teachers rated attention-deficit hyperactivity disorder combined type children as significantly more aggressive. Both questionnaires had good discriminant accuracy for detecting cases and control children, but accuracy for discriminating between attention-deficit hyperactivity disorder subtypes was poor. The Behavioral Assessment System for Children-parent and teacher questionnaires for 6- to 11-year-olds may be useful tools for diagnosing the presence of attention-deficit hyperactivity disorder. Additional assessment methods will be needed to discriminate between the subtypes.

[Acute meningococcal disease. Its prognostic assessment]. / Enfermedad meningocócica aguda. Valoración pronóstica.

We have studied 50 children affected with acute meningococcal disease (AMD). The ages of the children varied between 4 months and 12.58 years, with a mean age of 4.58 years. By using the shock state and DIC syndrome, both of which are indications of the severity of the illness, an evaluation of the discriminatory capacity was done with regard to significantly associate variables and 3 scores, Bjorvatn, Leclerc and PRISM, throughout 8 intervals within the first 48 hours of hospital treatment. We observed a very high survival rate (98%) associated with the early treatment for shock. Leukopenia and disseminated purpura were the best variables in order to discriminate shock and DIC, respectively. The greatest capacity for the diagnosis of the shock state and DIC syndrome were registered during the 0-6 hour period and the 0-12 hour period, respectively. The prognosis improved if the child remained alive 12 hours after the treatment had begun.