Gastropathy and ketoconazole malabsorption in the acquired immunodeficiency syndrome (AIDS)

Applications of bio-predictive dissolution tools for the development of solid oral dosage forms: Current industry experience

Development and optimization of orally administered drug products often require bio-predictive tools to help with informing formulation and manufacturing decisions. Reliable bio-predictive dissolution toolkits not only allow rational development of target formulations without having to conduct excessive in vivo studies but also help in detecting critical material attributes (CMAs), critical formulation variables (CFVs), or critical process parameters (CPPs) that could impact a drug's in vivo performance. To provide early insights for scientists on the development of a bio-predictive method for drug product development, this review summarizes current phase-appropriate bio-predictive dissolution approaches applicable to address typical concerns on solubility-limited absorption, food effect, achlorhydria, development of extended-release formulation, clinically relevant specification, and biowaiver. The selection of an in vitro method which can capture the key rate-limiting step(s) of the in vivo dissolution and/or absorption is considered to have a better chance to produce a meaningful in vitro-in vivo correlation (IVIVC) or in vitro-in vivo relationship (IVIVR).

The Overview on the Pharmacokinetic and Pharmacodynamic Interactions of Triazoles

Second generation triazoles are widely used as first-line drugs for the treatment of invasive fungal infections, including aspergillosis and candidiasis. This class, along with itraconazole, voriconazole, posaconazole, and isavuconazole, is characterized by a broad range of activity, however, individual drugs vary considerably in safety, tolerability, pharmacokinetics profiles, and interactions with concomitant medications. The interaction may be encountered on the absorption, distribution, metabolism, and elimination (ADME) step. All triazoles as inhibitors or substrates of CYP isoenzymes can often interact with many drugs, which may result in the change of the activity of the drug and cause serious side effects. Drugs of this class should be used with caution with other agents, and an understanding of their pharmacokinetic profile, safety, and drug-drug interaction profiles is important to provide effective antifungal therapy. The manuscript reviews significant drug interactions of azoles with other medications, as well as with food. The PubMed and Google Scholar bases were searched to collect the literature data. The interactions with anticonvulsants, antibiotics, statins, kinase inhibitors, proton pump inhibitors, non-nucleoside reverse transcriptase inhibitors, opioid analgesics, benzodiazepines, cardiac glycosides, nonsteroidal anti-inflammatory drugs, immunosuppressants, antipsychotics, corticosteroids, biguanides, and anticoagulants are presented. We also paid attention to possible interactions with drugs during experimental therapies for the treatment of COVID-19.

Proton pump inhibitor usage reduces sustained viral response rates for veterans with HIV/HCV coinfection on ledipasvir/sofosbuvir: a real-world study from a multicentre VA cohort

Previous studies have reported an association of proton pump inhibitor (PPI) use and decreased sustained viral response rate (SVR) in patients taking ledipasvir/sofosbuvir (LDV/SOF). The relationship between PPI usage and SVR is less clear in patients with HIV/HCV coinfection, where concomitant antiretrovirals may result in more complex drug interactions. This retrospective study evaluates the effects of acid suppression medications (PPI or H₂ -receptor antagonist [H₂ B]) use and SVR rates in patients with HIV/HCV or HCV and taking LDV/SOF in a large multicentre veteran cohort. Patients in the Veterans Affairs Health Care System who received LDV/SOF ± ribavirin from 10/10/2014 to 12/31/2015 were included. The odds ratios (OR) of PPI or H₂ B use for SVR were adjusted for clinical factors and with inverse probability of treatment weighting for non-random treatment selection for acid suppression medication use. There were 9703 veterans included in our final analysis. After adjustment of other clinical factors, PPI use is associated with a lower SVR in the overall cohort (95.0% vs. 96.1%, OR: 0.86, 95% CI: 0.74-0.99, p = .03, number needed to harm 90.9) and HIV/HCV coinfection subgroup (93.4% vs. 96.9%, OR: 0.47, 95% CI: 0.26-0.85, p = .01, number needed to harm 28.6). This present study reveals PPI use is associated with reduced SVR after LDV/SOF treatment, with a more significant impact in the subgroup of patients with HIV/HCV coinfection. Precautions need to be taken when using PPI and LDV/SOF in this group of patients.

Formulation technologies and advances for oral delivery of novel nitroimidazoles and antimicrobial peptides

Antibiotic resistance has become a global crisis, driving the exploration for novel antibiotics and novel treatment approaches. Among these research efforts two classes of antibiotics, bicyclic nitroimidazoles and antimicrobial peptides, have recently shown promise as novel antimicrobial agents with the possibility to treat multi-drug resistant infections. However, they suffer from the issue of poor oral bioavailability due to disparate factors: low solubility in the case of nitroimidazoles (BCS class II drugs), and low permeability in the case of peptides (BCS class III drugs). Moreover, antimicrobial peptides present another challenge as they are susceptible to chemical and enzymatic degradation, which can present an additional pharmacokinetic hurdle for their oral bioavailability. Formulation technologies offer a potential means for improving the oral bioavailability of poorly permeable and poorly soluble drugs, but there are still drawbacks and limitations associated with this approach. This review discusses in depth the challenges associated with oral delivery of nitroimidazoles and antimicrobial peptides and the formulation technologies that have been used to overcome these problems, including an assessment of the drawbacks and limitations associated with the technologies that have been applied. Furthermore, the potential for supercritical fluid technology to overcome the shortcomings associated with conventional drug formulation methods is reviewed.

Management of Diabetic Bacterial Foot Infections with Organic Extracts of Liverwort Marchantia debilis from Cameroon

Diabetic bacterial foot infections (DBFIs) are limb-threatening complications in patients with diabetes mellitus, accounting for 50% of diabetes related lower limb amputations in developing countries, representing approximately 20 percent of all diabetes-related hospital admissions with significant healthcare-related costs involved. The widespread problem of bacterial resistance to most commonly used antibiotics places a huge economic burden on the healthcare system, with both increased morbidity and mortality among diabetic patients with foot infections. In this study, the antibacterial activity of organic extracts of the fresh liverwort Marchantia debilis from the North West Region of Cameroon is reported. An exit pool system, where patients presenting with DBFIs consented to be involved in the use of phytomedicines, after long term treatment of ulcers with antibiotics and not yielding significant long term benefit, presented themselves at the Phytobiotechnology Research clinic (PRF). Continuous culture of swabs from foot and toe wounds from 30 infected patients on nutrient agar and MacConkey agars in triplicate as well as Gram stain microscopy, revealed the presence of Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Proteus mirabilis and Bacillus species. Light petroleum and methanol extracts of the whole bryophyte plants at 100% concentration were tested. In vitro inhibition of the tested bacterial isolates from the diabetic foot ulcers by M. debilis was observed only with the light petroleum extract. No inhibition by the extracts was observed for the Pseudomonas aeruginosa isolate. The light petroleum extract of M. debilis was formulated into a petroleum oil based cream named BryoCreamTM. This was administered to 20 of the patients with 90% cure rate in a three week time period. The main nonpolar components were determined by GCMS as lepidozene and β-barbatene, and by NMR as stigmasterol and β-sitosterol. In conclusion, nonpolar extracts from bryophytes from Cameroon could, potentially, be used to treat diabetic bacterial foot infections.

Pharmacokinetic considerations in treating invasive pediatric fungal infections

INTRODUCTION

Despite the increased availability of systemic antifungal agents in recent years, the management of invasive fungal disease is still associated with significant morbidity and mortality. Knowledge of a drug's pharmacokinetic behavior is critical for optimizing existing treatment strategies.

AREAS COVERED

This review examines the pharmacokinetics of the major drug classes used to treat invasive mycoses including the echinocandins, imidazoles, triazoles, nucleoside analogs, and polyenes. It examines the mechanisms behind dose-exposure profiles that differ in children as compared with adults and explores the utility of pharmacogenetic testing and therapeutic drug monitoring.

EXPERT OPINION

Lifesaving medical advances for oncologic and autoimmune conditions have resulted in a significant increase in the frequency of opportunistic fungal infections. Owing to the high rate of treatment failures observed when managing invasive fungal infections, strategies to optimize antifungal therapy are critical when caring for these complex patients. Opportunities to maximize positive outcomes include dose refinement based on age or genetic status, formulation selection, co-administration of interacting medications, and administration with regard to food. The application of therapeutic drug monitoring for dose individualization is a valuable strategy to achieve pharmacodynamic targets.

Physiologically based pharmacokinetic models for the optimization of antiretroviral therapy: recent progress and future perspective

Anti-HIV therapy is characterized by the chronic administration of antiretrovirals (ARVs), and consequently, several problems can arise during the management of HIV-positive patients. ARV disposition can be simulated by combining system data describing a population of patients and in vitro drug data through physiologically based pharmacokinetic (PBPK) models, which mathematically describe absorption, distribution, metabolism and elimination. PBPK modeling can find application in the investigation of clinically relevant scenarios, while providing the opportunity for a better understanding of the mechanisms regulating drug distribution. In this review, we have analyzed the most recent applications of PBPK models for ARVs and highlighted some of the most interesting areas of use, such as drug–drug interaction, pharmacogenetics, factors regulating absorption and tissue penetration, as well as therapy optimization in special populations. The application of the PBPK modeling approach might not be limited to the investigation of hypothetical clinical issues, but could be used to inform future prospective clinical trials.

ESCMID* guideline for the diagnosis and management of Candida diseases 2012: patients with HIV infection or AIDS

Mucosal candidiasis is frequent in immunocompromised HIV-infected highly active antiretroviral (HAART) naive patients or those who have failed therapy. Mucosal candidiasis is a marker of progressive immune deficiency. Because of the frequently marked and prompt immune reconstitution induced by HAART, there is no recommendation for primary antifungal prophylaxis of mucosal candidiasis in the HIV setting in Europe, although it has been evidenced as effective in the pre-HAART era. Fluconazole remains the first line of therapy for both oropharyngeal candidiasis and oesophageal candidiasis and should be preferred to itraconazole oral solution (or capsules when not available) due to fewer side effects. For patients who still present with fluconazole-refractory mucosal candidiasis, oral treatment with any other azole should be preferred based on precise Candida species identification and susceptibility testing results in addition to the optimization of HAART when feasible. For vaginal candidiasis, topical therapy is preferred.

Itraconazole: Precautions regarding drug interactions and bioavailability

OBJECTIVE

To describe patients with fungal infections in whom drug interactions and bioavailability problems were associated with itraconazole treatment failure.

DESIGN

Retrospective chart review.

SETTING

Two tertiary care university-affiliated teaching hospitals.

POPULATION STUDIED

Itraconazole-treated patients between 1990 and 1992.

MAIN RESULTS

Four patients treated with itraconazole were identified in whom suboptimal serum itraconazole levels were associated with relapse of disseminated histoplasmosis, treatment failure of invasive aspergillosis or development of superficial mycoses. Low serum itraconazole levels were associated with concurrent therapy with rifampin or agents inhibiting gastric acid secretion, with administration of itraconazole capsule contents through a nasogastric tube or with the presence of aids.

CONCLUSIONS

It is recommended that serum itraconazole levels be measured in patients with potentially life-threatening mycoses if coexistent factors may interfere with itraconazole therapy.

Using absorption simulation and gastric pH modulated dog model for formulation development to overcome achlorhydria effect

Impaired absorption of weakly basic drugs in patients with reduced gastric acidity can lead to loss of efficacy of the therapeutic agent. Hence, a robust formulation which can provide adequate exposure in achlorhydric patients is imperative to achieve the desired efficacy. In this report, formulation development of a weakly basic Merck compound A is described. Compound A shows lower solubility at higher pH and thus is prone to reduced exposure under conditions of achlorhydria, as the compound's solubility increases only in environments of less than pH 2. Several formulations with or without an acidifier were developed and characterized by in vitro dissolution and in gastric pH modified dog model to assess their bioperformance in high gastric pH conditions. To predict the bioperformance of these formulations in humans, a dissolution based absorption model was developed and validated against the observed PPI-interaction data in the clinic and the gastric pH-adjusted dog data. An additional absorption model was developed to allow for incorporation of the dog PK data to provide translation of preclinical to clinical exposure. Based on the in vitro dissolution, in silico absorption modeling and preclinical in vivo data, a citric acid-based formulation (F2) was selected for a human pharmacokinetic study. This study showed that exposures from F2 were not meaningfully different in the presence of proton pump inhibitor (PPI) as compared to non-PPI, thus confirming that the F2 formulation was successful in overcoming the achlorhydria effect. These efforts also highlighted that the complementary use of in vitro/in silico/in vivo (IVISIV) tools may be a helpful strategy in the development of formulations to overcome the achlorhydria effect and achieve adequate exposure in patients with high gastric pH.

Clinical pharmacology profile of raltegravir, an HIV-1 integrase strand transfer inhibitor

Raltegravir is an HIV-1 integrase inhibitor approved to treat HIV infection in adults in combination with other antiretrovirals. Data from healthy volunteers demonstrate that raltegravir is rapidly absorbed with a mean half-life of approximately 7 to 12 hours, with steady state achieved in approximately 2 days. Raltegravir is characterized by both high intra- and interindividual variabilities, although neither gender, race, age, body mass index, food intake, nor renal or hepatic insufficiency has a clinically meaningful effect on raltegravir pharmacokinetics. Raltegravir lacks activity as a perpetrator of drug-drug interactions and demonstrates a low propensity to be subject to drug-drug interactions. Raltegravir is metabolized primarily by UGT1A1 and is not affected by P450 inhibitors or inducers. Inhibitors of UGT1A1 (eg, atazanavir) can increase plasma concentrations of raltegravir, although this increase has not been found to be clinically meaningful. Likewise, inducers of UGT1A1 (eg, rifampin) can reduce plasma concentrations of raltegravir, and the clinical significance of this reduction is being investigated in ongoing clinical studies. Raltegravir demonstrates favorable clinical pharmacology and a drug interaction profile that permits administration to a wide, demographically diverse patient population and coadministration with many other therapeutic agents, including antiretroviral agents and supportive medications, without restrictions or dose adjustment.

Effects of omeprazole on plasma levels of raltegravir

Raltegravir, a human immunodeficiency virus type 1 (HIV-1) integrase inhibitor, has pH-dependent solubility. Raltegravir plasma concentration increases with omeprazole coadministration in healthy subjects; this is likely secondary to an increase in bioavailability attributable to increased gastric pH. Increased gastric pH has been reported in HIV-1-infected individuals, and the effects of omeprazole in this intended population may be diminished. Further investigation is necessary.

Emerging pharmacology: inhibitors of human immunodeficiency virus integration

The first integrase inhibitor licensed to treat HIV-1 infection was approved in late 2007, more than a decade after the introduction of the first inhibitors of the HIV-1 reverse transcriptase and protease. The unique biochemical and molecular mechanism of action of this novel class of antiretroviral drugs is the fundamental basis for their activity in treating multidrug-resistant HIV-1 infection and is important for understanding both the cellular and in vivo pharmacology and metabolism of these agents. In addition, available pharmacokinetic and drug interaction data for raltegravir and elvitegravir, the two integrase inhibitors that are the most advanced in clinical development to date, are reviewed.

Population-based mechanistic prediction of oral drug absorption

The bioavailability of drugs from oral formulations is influenced by many physiological factors including gastrointestinal fluid composition, pH and dynamics, transit and motility, and metabolism and transport, each of which may vary with age, gender, race, food, and disease. Therefore, oral bioavailability, particularly of poorly soluble and/or poorly permeable compounds and those that are extensively metabolized, often exhibits a high degree of inter- and intra-individual variability. While several models and algorithms have been developed to predict bioavailability in an average person, efforts to accommodate intrinsic variability in the component processes are less common. An approach that incorporates such variability for human populations within a mechanistic framework is described together with examples of its application to drug and formulation development.

The use of an in vitro dissolution and absorption system to evaluate oral absorption of two weak bases in pH-independent controlled-release formulations

The aim of this study was to compare the oral absorption of two weak bases including their pH-independent controlled-release preparations using an in vitro evaluation system. This system is able to simulate dissolution of drugs, pH change and permeation of drugs through the epithelial cell membrane in the gastrointestinal tract. Albendazole-polymers solid dispersion and pH-independent sustained-release granules of dipyridamole were prepared by using a solvent method. Elution profiles and predicted absorption of these preparations in gastric pH conditions similar to those in healthy subjects and patients with achlorhydria were compared with those of a physical mixture and commercial tablets. When a physical mixture or commercial tablets were used, the elution profile and predicted absorption of both albendazole and dipyridamole were extremely pH-dependent. On the other hand, when a solid dispersion and granules were used, elution and predicted absorption were not affected by changes in pH of the flowing solution in a drug-dissolving vessel. These results are in agreement with the results of our previous in vivo study using gastric acidity-controlled rabbits. Our results suggest that this in vitro system is useful for the evaluation of oral absorption of pH-independent controlled-release preparations.

Disseminated dermatophytosis caused by Microsporum gypseum in an AIDS patient: response to terbinafine and amorolfine. Fallbericht. Disseminierte Dermatophytose durch Microsporum gypseum bei einem AIDS- Patienten mit Ansprechen auf Terbinafin und Amorolfin

A 51-year-old white male, native of Rio de Janeiro, Brazil, with advanced AIDS and in chronic use of imidazoles for oral candidosis, presented erythematous, desquamative, pruriginous plaques of 1 month evolution on the trunk, inguinal/crural region, and lower limbs. The diagnosis of dermatophytosis was based on the isolation of Microsporum gypseum from scales scraped from the skin lesions. The lesions regressed after 30 days treatment with itraconazole, 100 mg day(-1). After interruption of this antifungal, the mycosis recurred 2 months later, along with a toe onychomycosis also caused by M. gypseum. Attempted reintroduction of itraconazole at higher dose was unsuccessful. Patient responded well to treatment with terbinafine 250 mg day(-1) for 45 days. However, the medication had to be interrupted as a result of the emergence of a disseminated erythematous/papulous rash. Topical treatment with amorolfine cream was then performed, with a good clinical and mycological response.

Pharmacokinetics of posaconazole coadministered with antacid in fasting or nonfasting healthy men

Posaconazole is a potent broad-spectrum azole antifungal agent in clinical development for the treatment of invasive fungal infections. This study evaluated the potential for a pH-dependent pharmacokinetic interaction between posaconazole and an antacid (Mylanta), under fasting and nonfasting conditions. Twelve men completed this randomized, four-period crossover, single-dose study. Subjects received 200 mg of posaconazole following a 10-h fast, with 20 ml of Mylanta and a 10-h fast, with 20 ml of Mylanta and a high-fat breakfast, and with a high-fat breakfast alone. Antacid coadministration had no statistically significant effects on posaconazole bioavailability under fasting or nonfasting conditions. In the fasting state, antacid slightly increased the relative oral bioavailability of posaconazole by 15% (P = 0.296); in the nonfasting state, antacid decreased the relative bioavailability of posaconazole by 12% (P = 0.352). Food increased the relative oral bioavailability of posaconazole by 400% (P = 0.001). In conclusion, the effect of antacid on posaconazole exposure in the fasting or nonfasting state was small and is not considered clinically significant.

Gastric function in the elderly: effects on absorption of ketoconazole

The authors studied effects of age-related changes in gastric function on absorption of ketoconazole. Eighteen men and women age 65 years or older swallowed 200 mg ketoconazole on two occasions, once as tablets with water and once as tablets crushed in acidic juice. The sequence was randomly determined. Gastric pH was measured by radiotelemetry and gastric emptying rate by radiolabeled technetium with a gamma camera. Plasma ketoconazole was assayed by high-performance liquid chromatography (HPLC). Subjects with gastric pH less than or equal to 4.5 absorbed ketoconazole equally well from intact tablets and tablets crushed in acid. When pH was 5.0 or higher, ketoconazole was absorbed well from acid-crushed tablets but not from intact tablets. Gastric emptying was shown to be rapid in all subjects. Since the prevalence of such hypoacivity is approximately 5% in the elderly, and other parameters of gastric function are usually normal, impaired absorption of drugs such as ketoconazole should be uncommon with normal aging.

Expandable gastroretentive dosage forms

Expandable gastroretentive dosage forms (GRDFs) have been designed for the past 3 decades. They were originally created for possible veterinary use, but later the design was modified for enhanced drug therapy in humans. These GRDFs are easily swallowed and reach a significantly larger size in the stomach due to swelling or unfolding processes that prolong their gastric retention time (GRT). After drug release, their dimensions are minimized with subsequent evacuation from the stomach. Gastroretentivity is enhanced by the combination of substantial dimensions with high rigidity of the dosage form to withstand the peristalsis and mechanical contractility of the stomach. Positive results were obtained in preclinical and clinical studies evaluating GRT of expandable GRDFs. Narrow absorption window drugs compounded in such systems have improved in vivo absorption properties. These findings are an important step towards the implementation of expandable GRDFs in the clinical setting. The current review deals with expandable GRDFs reported in articles and patents, and describes the physiological basis of their design. Using the dog as a preclinical screening model prior to human studies, relevant imaging techniques and pharmacokinetic-pharmacodynamic aspects of such delivery systems are also discussed.

Delavirdine malabsorption in HIV-infected subjects with spontaneous gastric hypoacidity

To determine the impact of gastric hypoacidity and acidic beverages on delavirdine mesylate pharmacokinetics in HIV-infected subjects, matched subjects with (n = 11) and without (n = 10) gastric hypoacidity received delavirdine 400 mg tid with either water or an acidic beverage (usually orange juice). The pharmacokinetics of delavirdine and its N-desalkyl metabolite were determined over 8 hours after 14 days of each treatment. Gastric pH was measured at baseline and during each pharmacokinetic evaluation. Delavirdine exposure (Cmax, AUC0-->8 h, and Cmin) was approximately 50% lower and the extent of delavirdine metabolism was higher in subjects with gastric hypoacidity. Orange juice produced a lower mean gastric pH compared to water and increased delavirdine absorption by 50% to 70% in subjects with gastric hypoacidity. However, orange juice had a marginal impact on delavirdine exposure in subjects without gastric hypoacidity. HIV-infected subjects with gastric hypoacidity significantly malabsorb delavirdine. Delavirdine administration with acidic beverages improves, but dose not normalize, absorption in these subjects.

Pharmacokinetic and other drug interactions in patients with AIDS

A variety of medications are used in treating patients infected with the human immunodeficiency virus (HIV). These medications are used to control viremia and to prevent and treat opportunistic infections. An individual is often required to take numerous drugs at the same time and thus clinicians are confronted with potential drug interactions, some of which are significant. Three different groups of anti-HIV drugs are used to treat patients. These groups include nucleoside reverse transcription inhibitors, non-nucleoside reverse transcription inhibitors, and protease inhibitors. This article reviews the most relevant drug interactions that occur during the treatment of HIV-infected patients with traditional and also alternative drugs. The role of therapeutic drug monitoring in the routine management of HIV-infected patients is discussed.

Effect of pharmacotechnical design on the in vitro interaction of ketoconazole tablets with non-systemic antacids

In certain polytherapy programs, ketoconazole can be administered with some antacids that could modify its dissolution rate and reduce its absorption leading to therapeutic failures. The aim of this work was to evaluate the influence of some excipients on this interaction in vitro. In this way, six formulations of directly compressible ketoconazole tablets were developed. The results confirmed that the dissolution rate of ketoconazole tablets was significantly reduced in the presence of antacids. Nevertheless this interaction was remarkably avoided in some of the formulations checked and in some conditions. In this way, the inclusion of a disintegrant (sodium starch glycolate) not only increased the dissolution rate of ketoconazole in the tablets, as expected, but it also modified the degree in which the dissolution rate was decreased in the presence of antacids. It was proved that a suitable selection of the excipients and therefore the modification in the rate in which the drug was released, could play an important role to modify a pharmacokinetic interaction based on a reduction of the solubility of the drug as a function of the pH value of the medium.

Increased oral ganciclovir bioavailability in HIV-infected patients with chronic diarrhoea and wasting syndrome--a population pharmacokinetic study

AIMS

Despite a lack of data, the antiviral agent ganciclovir is not indicated in AIDS patients with diarrhoea because of its presumed poor oral bioavailability. To assess the effect of diarrhoea on ganciclovir intestinal absorption, we conducted a pharmacokinetic study in 42 HIV-infected patients categorized into three groups: A, HIV stage A and B (n = 15); B, AIDS stage C (n = 13); C, AIDS with chronic diarrhoea and wasting syndrome (n = 14).

METHODS

Each patient was evaluated for nutritional (body mass index, albumin, transferrin serum levels), inflammatory (haptoglobin, orosomucoid), immunological (CD4 count, plasma viral load) and intestinal (D-xylose test, faecal fat and nitrogen output, intestinal permeability) status. Ganciclovir (1 g) was administered orally to fasted patients. Six blood samples were collected over 24 h. Serum was analysed for ganciclovir by h.p.l.c. Population pharmacokinetic analysis was performed using a nonlinear mixed effects modelling program, MP2.

RESULTS

Mean intestinal permeability (lactulose/mannitol urinary ratio) was increased in group C (0.2) compared with group A (0.05) and B (0.1) patients. Drug concentration-time profiles were best described by a two-compartment model. Apparent oral clearance (CL/F) and central volume of distribution (V1/F) were influenced by clinical status (group). For groups A and B combined, final parameter estimates of CL/F and V1/F were 256 +/- 98 l h(-1) and 1320 +/- 470 l, respectively. Final parameter estimates for group C were 118 +/- 108 l h(-1) and 652 +/- 573 l for CL/F and V1/F, respectively. The 95% confidence intervals on differences between A and B combined and C were statistically significant ([ + 70, + 206] for CL/F, and [+ 314, + 1022] for V1/F). Compared with groups A and B, ganciclovir CL/F was significantly decreased in group C patients.

CONCLUSIONS

AIDS patients with diarrhoea and severe disease may benefit from ganciclovir therapy, but a dose adjustment may be required according to their digestive and immunological status.

Influence of physicochemical properties on dissolution of drugs in the gastrointestinal tract

The rate-limiting step to absorption of drugs from the gastrointestinal (GI) tract is often dissolution from the dosage form. Consideration of the Noyes-Whitney dissolution model shows that drug diffusivity, solubility in the gastrointestinal contents, the surface area of the solid wetted by the lumenal fluids and the GI hydrodynamics all play a role in determining the in vivo dissolution rate. Solubility in the GI contents is determined by aqueous solubility, crystalline form, drug lipophilicity, solubilization by native surfactants and co-ingested foodstuffs, and pK(a) in relation to the GI pH profile. Compounds with aqueous solubilities lower than 100 microg/ml often present dissolution limitations to absorption. The dose:solubility ratio of the drug provides an estimate of the volume of fluids required to dissolve an individual dose, and when this volume exceeds 1 l, dissolution is often problematic. The surface area of a drug available for dissolution depends on the particle size of the solid and its ability to be wetted by lumenal fluids. Other physiological factors that can play a role in dissolution include the viscosity of the lumenal contents, through its effect on the diffusivity, and mixing and flow patterns within the gut. In order to better predict in vivo dissolution of drugs, dissolution tests which more adequately simulate the physiological conditions are needed.

Systemic antifungal therapy

Systemic antifungal therapy for superficial mycoses has advanced greatly since the introduction of griseofulvin in 1958. The discovery of the azole antifungal compounds, ketoconazole, itraconazole, and fluconazole, allowed for a broader spectrum of treatment and a shorter treatment duration. Terbinafine, through a unique mechanism of action, has a fungicidal power not seen previously in the other antifungals. It is important to use our knowledge of the pharmacology in combination with clinical experience and cost of therapy in order to select the proper drug. The search to identify new oral antifungal agents should continue, since none of the five currently used drugs fulfill the criteria of the "ideal" antifungal.

Oral ganciclovir systemic exposure is enhanced in HIV-infected patients with diarrhea and weight loss

OBJECTIVE

To determine whether diarrhea and intestinal malabsorption during HIV infection alter oral ganciclovir systemic exposure.

METHODS

We studied the oral disposition of ganciclovir in 42 HIV-infected patients stratified into three groups: A (n = 15), HIV (stage A and B); B (n = 13), AIDS (stage C); and C (n = 14), AIDS with chronic diarrhea and wasting syndrome (10% or more weight loss). Each patient was evaluated for nutritional (body mass index, serum albumin and transferrin), immunologic (CD4 count, plasma viral load) and intestinal status (D-xylose test, fecal fat and nitrogen excretion, and intestinal permeability). Following an overnight fast, 1 g oral ganciclovir was given to patients. Six blood samples were collected over 24 hours. Serum was analyzed for ganciclovir by high performance liquid chromatography. Drug disposition was characterized using a population pharmacokinetic approach.

RESULTS

Mean intestinal permeability increased as HIV disease progressed (0. 05, 0.1, and 0.2 for groups A, B, and C, respectively). Average weight-adjusted maximum concentration (Cmax) in group C was twofold more than that in group A and B patients (12.5 versus 6 and 6.4 ng/ml/kg), and average area under the curve (AUC0-infinity) was threefold greater in group C patients (193 versus 59 and 65 ng. hour/ml/kg in groups A and B, respectively). Mean oral clearance was threefold lower in group C (96 versus 258 and 212 L/hour in groups A and B, respectively).

CONCLUSION

Because systemic exposure of oral ganciclovir is enhanced in AIDS patients with diarrhea and wasting syndrome, oral ganciclovir therapy may benefit these patients.

AIDS in Latin America

The epidemic in Latin America has placed an unexpected additional burden on the health care systems and national economies, already weak and affected by severe problems. Specific regional diseases in addition to common opportunistic infections, and particularly the high incidence of TB, produce a different picture compared with the United States and Europe. Access to ARV therapy is far from being universal in Latin America; nevertheless, some countries are providing HAART to all eligible patients, showing that it is not impossible to improve quality of care for people living with HIV infection in the region. Before assuming as definitive and irreversible that at least one or two generations will be sacrificed on the altar of inequity of our uneven world, we as acting scientists should join the struggle of millions of human beings claiming their right to be treated with the best drugs that science can offer today.

Pharmacokinetics of rifabutin in HIV-infected patients with or without wasting syndrome

AIMS

The purpose of the study was to compare the pharmacokinetic parameters of rifabutin obtained in a group of patients without wasting syndrome (NWS) with those obtained in a group with wasting syndrome (WS).

METHODS

A single dose of 300 mg rifabutin was administered in the fasting state to the patients in both study groups and blood samples were scheduled to be collected at the following times: 0 (predose), 0.5, 1, 2, 3, 4, 6, 8, 24, 48, 72 and 96 h following administration. Data were analysed using noncompartmental methods. The pharmacokinetic parameters of rifabutin in patients with and without wasting syndrome were compared using the Mann-Whitney U-test.

RESULTS

Cmax was 0.34+/-0. 14 mg l-1 in NWS patients and 0.55+/-0.16 mg l-1 (P=0.01) in patients with WS. tmax was 4.2+/-1.5 and 3.3+/-2.3 h (P=0.17) in NWS and WS patients, respectively. The AUCs were similar in the two study groups. V/F was 2905+/-1646 l in NWS patients and 1701+/-492 l (P=0.07) for the WS group. These differences are less pronounced following normalization of V/F to patients body weight (43.7+/-20.1 vs 35.4+/-10.3 l kg-1 ). t1/2,lambdaz tended to be shorter in patients with WS (31.4+/-12.9 vs 46.0+/-23.5 h, P=0.12).

CONCLUSIONS

Our study suggests that the pharmacokinetics of rifabutin in patients with wasting syndrome are not altered to a degree that is clinically important.

The relationship between ritonavir plasma levels and side-effects: implications for therapeutic drug monitoring

OBJECTIVES

To assess whether the neurological or gastrointestinal adverse effects of ritonavir correlate with parameters of ritonavir systemic exposure.

METHODS

Peak (Cmax) and trough (Cmin) ritonavir plasma levels were compared in 11 patients experiencing side-effects (group A) versus 10 patients without side-effects (group B). Ritonavir was administered with the following escalation dosing scheme: 300, 400, 500 mg twice a day for 3, 4, and 5 days, respectively, then the full dose of 600 mg twice a day. Blood sampling was done in group A within 24 h of the occurrence of side-effects and in group B after at least 3 days of the full dosage regimen.

RESULTS

Both Cmax and Cmax were significantly higher (Mann-Whitney U test) in patients with side-effects. Cmax was [median (interquartile range)] 26.7 (22.7-33.3) mg/l versus 16.2 (13.4-17.0) mg/l (P = 0.001) and Cmin was 12.6 (9.1-13.9) versus 7.5 (4.9-8.6) mg/l (P = 0.002).

CONCLUSION

Patients with higher ritonavir concentrations are at a higher risk of experiencing neurological or gastrointestinal side-effects. Individualization of the dosage regimen, e.g. a downward titration of the ritonavir dose in patients with side-effects, guided by plasma level monitoring, may result in a substantial increase in the percentage of patients tolerating ritonavir without increasing the risk of treatment failure as a result of suboptimal systemic exposure.

Antifungal agents. Part II. The azoles

Before 1978, amphotericin B and flucytosine were the only drugs available for the treatment of systemic fungal infections. The imidazoles, miconazole and ketoconazole, were introduced during the next 3 years. Intravenously administered miconazole served a limited therapeutic role and is no longer available. Orally administered ketoconazole, an inexpensive, effective, and convenient option for treating mucosal candidiasis, was widely used for a decade because it was the only available oral therapy for systemic fungal infections. During the 1990s, use of ketoconazole diminished because of the release of the triazoles--fluconazole and itraconazole. Fluconazole is less toxic and has several pharmacologic advantages over ketoconazole, including penetration into the cerebrospinal fluid. In addition, it has superior efficacy against systemic candidiasis, cryptococcosis, and coccidioidomycosis. Despite a myriad of drug interactions and less favorable pharmacologic and toxicity profiles in comparison with fluconazole, itraconazole has become a valuable addition to the antifungal armamentarium. It has excellent activity against sporotrichosis and seems promising in the treatment of aspergillosis. Itraconazole has replaced ketoconazole as the therapy of choice for nonmeningeal, non-life-threatening cases of histoplasmosis, blastomycosis, and paracoccidioidomycosis and is effective in patients with cryptococcosis and coccidioidomycosis, including those with meningitis. Further investigation into the development of new antifungal agents is ongoing.

Penetration of clindamycin and its metabolite N-demethylclindamycin into cerebrospinal fluid following intravenous infusion of clindamycin phosphate in patients with AIDS

Clindamycin, which is usually used in combination with pyrimethamine, has been proven effective in the treatment of cerebral toxoplasmosis in human immunodeficiency virus-infected patients. However, it is not known if clindamycin achieves inhibitory concentrations at the site of infection. Also, it has been hypothesized that the activity of clindamycin against Toxoplasma gondii may be due, at least in part, to a metabolite. We evaluated the penetration of clindamycin and its major metabolite, N-demethylclindamycin (NDC), into cerebrospinal fluid (CSF) of AIDS patients undergoing lumbar puncture for diagnostic purposes. A single, 1,200-mg dose of clindamycin was administered as a 45-min intravenous infusion beginning at 1.5 or 2.5 h before CSF sampling. The concentrations of clindamycin in CSF ranged from 0.091 to 0.429 mg/liter at 1.5 h and from 0.120 to 0.283 mg/liter at 2.5 h following the beginning of the infusion. The concentrations of clindamycin in CSF were well above the 50% inhibitory concentration of 0.001 mg/liter and the parasiticidal concentration of 0.006 mg/liter. NDC was undetectable both in plasma and in CSF. Our study provides a pharmacokinetic rationale for the clinical efficacy of clindamycin in the treatment of cerebral toxoplasmosis.