Stéphane Mouly

P-glycoprotein increases from proximal to distal regions of human small intestine.

AbstractPurpose. The contribution of the efflux transporter P-glycoprotein (P-gp) as a barrier to drug absorption may depend on its level of expression at the site of absorption. Accordingly, the distribution of P-gp was examined along the entire length of the human small intestine. Methods. Homogenates prepared from mucosal scrapings from every other 30-cm segment of four unrelated human donor small intestines were analyzed for P-gp and the control protein villin by Western blot. Results. In each donor intestine, relative P-gp expression (P-gp/villin integrated optical density ratio) progressively increased from proximal to distal regions. Among individuals, relative P-gp levels varied 2.1-fold in the duodenal/proximal jejunal region, 1.5- to 2.0-fold in the middle/distal jejunal region, and 1.2- to 1.9-fold in the ileal region. Within-donor variation was somewhat greater, from 1.5- to 3.0-fold. Conclusions. These results provide further evidence that the site of absorption can represent another source for the interindividual variation in the oral bioavailability of drugs.

Variation in oral clearance of saquinavir is predicted by CYP3A5*1 genotype but not by enterocyte content of cytochrome P450 3A5

Saquinavir, a widely prescribed human immunodeficiency virus 1 protease inhibitor, has a low and variable oral bioavailability that has been attributed to extensive first‐pass extraction mediated by hepatic or intestinal cytochrome P450 (CYP) 3A4 and intestinal P‐glycoprotein (P‐gp). The polymorphic CYP3A5 has also been shown to influence the saquinavir metabolite/parent urinary ratio, suggesting a role for CYP3A5.

Effect of Variations in the Amounts of P-Glycoprotein (ABCB1), BCRP (ABCG2) and CYP3A4 along the Human Small Intestine on PBPK Models for Predicting Intestinal First Pass

It is difficult to predict the first-pass effect in the human intestine due to a lack of scaling factors for correlating in vitro and in vivo data. We have quantified cytochrome P450/3A4 (CYP3A4) and two ABC transporters, P-glycoprotein (P-gp, ABCB1) and the breast cancer resistant protein BCRP (ABCG2), throughout the human small intestine to determine the scaling factors for predicting clearance from intestinal microsomes and develop a physiologically based pharmacokinetic (PBPK) model. CYP3A4, P-gp and BCRP proteins were quantified by Western blotting and/or enzyme activities in small intestine samples from 19 donors, and mathematical trends of these expressions with intestinal localization were established. Microsome fractions were prepared and used to calculate the amount of microsomal protein per gram of intestine (MPPGI). Our results showed a trend in CYP3A4 expression decrease from the upper to the lower small intestine while P-gp expression is increasing. In contrast, BCRP expression did not vary significantly with position, but varied greatly between individuals. The MPPGI (mg microsomal protein per centimeter intestine) remained constant along the length of the small intestine, at about 1.55 mg/cm. Moreover, intrinsic clearance measured with specific CYP3A4 substrates (midazolam and an in-house Servier drug) and intestinal microsomes was well correlated with the amount of CYP3A4 (R(2) > 0.91, p < 0.01). In vivo data were more accurately predicted using PBPK models of blood concentrations of these two substrates based on the segmental distributions of these enzymes and MPPGI determined in this study. Thus, these mathematical trends can be used to predict drug absorption at different intestinal sites and their metabolism can be predicted with the MPPGI.

Amiodarone concentrations in plasma and fat tissue during chronic treatment and related toxicity

AIMS To determine if amiodarone, highly lipophilic, accumulates in excess with respect to dose in fat tissue during long-term administration, and study if plasma and fat tissue concentrations are correlated with adverse effects. METHODS Trough concentrations of amiodarone and N-desethyl-amiodarone were measured simultaneously in plasma and fat tissue, in 30 consecutive patients treated with amiodarone for 3 months to 12 years. Subcutaneous adipose tissue was obtained by needle aspiration from lumbar and abdominal areas. Concentrations were measured by liquid chromatography-tandem mass spectrometry. RESULTS Plasma levels of amiodarone and N-desethyl-amiodarone were significantly correlated with daily maintenance doses (R= 0.52, P= 0.003). Amiodarone concentrations in fat tissue were four to 226 times (mean 55) higher than in plasma, and well correlated with plasma levels (R= 0.68, P < 0.001). Concentrations of amiodarone and N-desethyl-amiodarone in adipose tissue did not significantly increase with higher total cumulated doses or longer treatment duration. Nine of 12 patients who had received amiodarone for > or =2 years developed clinically important adverse effects, predominantly hypothyroidism (n= 6), compared with two of 18 patients treated for less time (relative risk 6.75; 95% confidence interval 1.8, 26). The incidence of those adverse effects was not significantly associated with amiodarone concentrations, whether in plasma or in adipose tissue. CONCLUSIONS We found no evidence of excessive or unexpected accumulation of amiodarone in fat tissue on long-term administration. Late amiodarone adverse effects, particularly hypothyroidism, are associated with longer exposure times, but do not seem to be explained by higher concentrations in plasma or in fat tissue.

A meta-analysis of bed rest versus early ambulation in the management of pulmonary embolism, deep vein thrombosis, or both

BACKGROUND Bed rest is often recommended as part of the management of deep vein thrombosis (DVT) and pulmonary embolism (PE), though this recommendation is not clearly evidence-based. METHODS Using the Cochrane Central Register of Controlled Trials, Medline, and Embase, this meta-analysis considered all randomized studies and prospective registries that compared the outcomes of patients with DVT, PE, or both, managed with bed rest versus early ambulation, in addition to anticoagulation. For each study, data regarding the incidence of new PE, new or progression of DVT, and death from all causes, were used to calculate relative risks (RR) and 95% confidence intervals (CI). RESULTS The 5 studies retained in this analysis included a total of 3048 patients. When compared to bed rest, early ambulation was not associated with a higher incidence of a new PE (RR 1.03; 95% CI 0.65-1.63; p=0.90). Furthermore, early ambulation was associated with a trend toward a lower incidence of new PE and new or progression of DVT than bed rest (RR 0.79; 95% CI 0.55-1.14; p=0.21) and lower incidence of new PE and overall mortality (RR 0.79; 95% CI 0.402-1.56; p=0.50). CONCLUSIONS Compared with bed rest, early ambulation of patients with DVT, PE or both, was not associated with a higher risk of progression of DVT, new PE or death. This meta-analysis does not support the systematic recommendation of bed rest as part of the early management of patients presenting with DVT, PE of both.

Mini-series: I. Basic science. Uncertainty and inaccuracy of predicting CYP-mediated in vivo drug interactions in the ICU from in vitro models: focus on CYP3A4

Drug–drug interactions (DDIs) contribute significantly to the incidence of adverse drug reactions. Important advances in the knowledge of human drug-metabolizing enzymes have fueled the integration of in vitro drug metabolism and clinical DDIs studies for use in drug development programs and in the clinical setting. The activity of cytochrome P450 (CYP) 3A4 and P-glycoprotein are critical determinant of drug clearance, interindividual variability in drug disposition and clinical efficacy, and appears to be involved in the mechanism of numerous clinically relevant DDIs. Cell-based in vitro models are being increasingly applied in elucidating the pharmacokinetic profile of drug candidates during the preclinical steps of drug development. Human liver, intestinal samples and recombinant human CYP3A4 are now readily available as in vitro screening tools to predict the potential for in vivo DDIs. Although it is easy to determine in vitro metabolic DDIs, the interpretation and extrapolation of in vitro interaction data to in vivo situations requires a good understanding of pharmacokinetic principles. Clinicians and pharmacokineticists should recognize that in vitro models may not be clinically relevant in all situations. In the current article, research will be presented on drug metabolism and DDIs along with examples illustrating the utility of specific in vitro or in vivo approaches. In addition, the impact and clinical relevance of complexities such as dosing-route dependent effects, multi-site kinetics of drug-metabolizing enzymes and non-CYP determinants of metabolic clearance will be addressed.

Improving HIV Infection Management Using Antiretroviral Plasma Drug Levels Monitoring: A Clinicians Point of View

Due to genetic and environmental factors, there are wide inter-patient differences when measuring drug exposure to a standard dose. If there is a relationship between drug exposure and efficacy or toxicity, this inter-patient variability carries various risks to develop toxicity or failure. Therapeutic drug monitoring is an attempt to adjust the dose to obtain a level within a therapeutic range consisting in a minimum plasma concentration needed to be efficacious and a maximum plasma concentration not to exceed to avoid toxicity. Many studies have shown a relationship between various pharmacokinetic parameters and drug toxicity or efficacy for HIV protease inhibitors (PIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs). Therapeutic drug monitoring (TDM) proves to be a useful tool to assess adherence, to investigate drug-drug interactions between antiretroviral (ARV) drugs or with co-medications, to prevent some ARV drug toxicities, to adjust the dosage in particular populations, and to increase ARV efficacy of some drugs in naive patients. The integration of virological and pharmacological parameters, using inhibitory quotients, looks promising to improve therapy in ARV-experienced patients. Effective and non-toxic target concentrations will be determined for all present and future antiretroviral drugs covering the extended spectrum of naive patients to multiple failures. In this article, we review the rationale of TDM for antiretroviral drugs, the retrospective and prospective studies assessing plasma drug concentrations in relation with antiretroviral toxicity or efficacy, and the actually recommended or proposed indications for TDM. We also highlight the benefits and limits of this tool as an adjunct in the care of HIV-infected patients.

Management of xerostomia in older patients : a randomised controlled trial evaluating the efficacy of a new oral lubricant solution.

BackgroundXerostomia is a subjective sensation of mouth dryness that may frequently occur in older patients.ObjectiveTo compare the clinical efficacy and acceptability of a new oxygenated glycerol triester (OGT) oral spray taken five times daily with that of a commercially available saliva substitute (Saliveze®) in the treatment of xerostomia.MethodsForty-one institutionalised patients (28 women, 13 men; mean age 84 ± 7 years) were randomly assigned to receive either OGT or Saliveze® in a 2-week, randomised, parallel-group study. Clinical assessment of xerostomia included evaluation of mouth dryness using a self-rated, 10cm long visual analogue scale (VAS), objective assessment of oral tissue condition using a four-point ordinal scale and subjective assessment of symptoms of xerostomia using dichotomous responses to a questionnaire. The primary endpoint was the day (D) 14 patient-based mouth dryness score measured on a self-rated VAS.ResultsAt D14, OGT resulted in significantly greater efficacy with respect to mouth dryness (mean between-treatment difference 2.1 ± 0.1, 95% CI 1.9, 2.3; p = 0.001), swallowing difficulty (1.8 ± 0.3, 95% CI 1.5, 2.1; p = 0.001), speech difficulty (1.1 ± 0.2, 95% CI 1.0, 2.4; p = 0.04) and overall sensation of symptom relief (2.7 ± 1.2, 95% CI 1.9, 3.8; p = 0.001). Objective assessment of oral tissues also showed significantly better improvement with OGT spray with respect to dryness (p = 0.01), stickiness (p = 0.005) and dullness (p = 0.001) of oral mucosa; severity of mucositis (p = 0.01); and thickening of the tongue (p = 0.03). A significant difference in taste acceptability was also noted in favour of OGT (1.4 ± 0.6, 95% CI 1.2, 1.9; p = 0.04).ConclusionOGT lubricant oral spray was superior to Saliveze® in improving xerostomia and oral tissue condition in older institutionalised patients.

Methadone dose in heroin‐dependent patients: role of clinical factors, comedications, genetic polymorphisms and enzyme activity

AIMS Methadone is characterized by wide intersubject variability regarding the dose needed to obtain full therapeutic response. We assessed the influence of sociodemographic, ethnic, clinical, metabolic and genotypic variables on methadone maintenance dose requirement in opioid-dependent responder patients. METHODS Eighty-one stable patients (60 men and 21 women, 43.7 ± 8.1 years old, 63.1 ± 50.9 mg day(-1) methadone), divided into quartiles with respect to the median daily dose, were enrolled and underwent clinical examination, treatment history and determination of liver/intestinal cytochrome P450 (CYP) 3A4 activity measured by the midazolam test, R,S-methadone trough concentration and clinically significant polymorphisms of the OPRM1, DRD2, COMT, ABCB1, CYP2B6, CYP3A5, CYP2C19 and CYP2D6 genes. RESULTS Methadone maintenance dose was correlated to the highest dose ever used (r(2) = 0.57, P < 0.0001). Fractioned methadone intake (odds ratio 4.87, 95% confidence interval 1.27-18.6, P = 0.02), bodyweight (odds ratio 1.57, 95% confidence interval 1.01-2.44, P = 0.04), history of cocaine dependence (80 vs. 44 mg day(-1) in never-addict patients, P = 0.005) and ethnicity (Asian > Caucasian > African, P = 0.04) were independently associated with high-dose methadone in multiple regression analysis. A modest correlation was observed between liver/intestinal CYP3A4 activity and methadone dose at steady state (Spearman rank correlation coefficient [rs ] = 0.21, P = 0.06) but not with highest dose ever used (rs = 0.15, P = 0.18) or dose-normalized R,S-methadone trough concentrations (rs = -0.05, P = 0.64). Concomitant CYP3A4 inhibitors only affected the relationship between methadone dose and R,S-methadone trough concentration. None of the genetic polymorphisms explored was predictive of the methadone maintenance dose. CONCLUSIONS Methadone maintenance dose was predicted by sociodemographic and clinical variables rather than genetic polymorphisms or liver/intestinal CYP3A4 activity in stable patients.

Development of Sarcoidosis Following Completion of Treatment for Hepatitis C with Pegylated Interferon-α2a and Ribavirin: A Case Report and Literature Review

Sarcoidosis is a chronic inflammatory multisystem disease of unknown etiology. We report on a woman, aged 57 years, presenting with typical sarcoidosis occurring two months after completion of a six-month course of interferon-α and ribavirin for chronic hepatitis C virus infection. The current observation is interesting with regard to the time elapsed between the occurrence of symptoms and antiviral treatment withdrawal, and spontaneous recovery after ten months of follow-up. Pathophysiological mechanisms involved in the development of antiviral therapy-induced sarcoidosis are discussed.