Pharmacokinetic and pharmacodynamic implications of P-glycoprotein modulation

Ivermectin Toxicokinetics in Rainbow Trout (Oncorhynchus mykiss) following P-glycoprotein Induction

Alterations in ivermectin (IVM, 22,23-dihydro avermectin B1a+22,23-dihydro avermectin B1b) toxicokinetics following P-glycoprotein (P-gp) induction by clotrimazole (CTZ) were examined in rainbow trout (Oncorhynchus mykiss) to assess the potential importance of P-gp activity levels in xenobiotic distribution and kinetics in fish. Control and fish pretreated with CTZ (30 µmol/kg) were administered 175 µg/kg 3H-IVM into the caudal vasculature. At various time points (0.25, 0.5, 1, 3, 24, 48, 96, and 168 h) following injection, tissues (blood, liver, kidney, gill, intestines, brain [5 regions], eye, gonad and fat) were removed analyzed for IVM-derived radioactivity. IVM concentration declined in blood, liver, kidney and gill, and concentrations in other tissues remained constant over the sampling period. The highest measured concentrations were found in kidney, followed by liver, with the lowest values found in brain, eye and gonad. The highest % of the administered dose was found in the liver and kidney in the immediate hours post-administration, and in the intestines and fat at 24 h post-administration. P-gp induction by CTZ did not alter IVM distribution or any calculated toxicokinetic parameter (AUC, mean residence time, T1/2, clearance rate, volume of distribution), suggesting that P-gp induction may be limited or that P-gp plays a lesser role in xenobiotic kinetics in fish compared to mammals.

The effects of P-glycoprotein induction on ivermectin-induced behavioural alterations in zebrafish (Danio rerio) under varying diets

The neuroprotective effects of inducing the blood-brain barrier ATP-binding cassette protein transporter P-glycoprotein (P-gp) with clotrimazole (CTZ) in both fed and fasted zebrafish (Danio rerio) against the CNS-toxicant ivermectin (IVM, 22,23-dihydro avermectin B1a + 22,23-dihydro avermectin B1b) were examined. Zebrafish were administered 2 μmol/kg IVM intraperitoneally, and various behavioural assays (swimming performance, exploratory behaviour, olfactory responses, motor coordination, and escape responses) were used to measure neurological dysfunction. IVM administration alone caused a decrease in mean swim speed (91 % of controls), maximal speed (71 %), passage rate (81 %), 90° turns (81 %), and response to food stimulus (39 %). IVM exposure also increased the percent time that fish spent immobile (45 % increase over controls) and the percent of lethargic fish (40 % increase). Fish administered 30 μmol/kg of the P-gp inducer CTZ intraperitoneally 3 d prior to IVM exposure exhibited a change in only the % time spent immobile. These data indicate that P-gp induction may be limited in protecting the zebrafish CNS from IVM over baseline. Fasted fish did not differ from fed fish in the effects of IVM on behaviour, and no differences were seen following P-gp induction with CTZ. These results suggest that this chemical defence system is not downregulated when fish are challenged with limited energy availability.

Characterization of P-glycoprotein orthologs from human, sheep, pig, dog, and cat

The ATP-binding cassette transporter P-glycoprotein (P-gp) limits the oral bioavailability of many drugs. Although P-gp has been well studied in humans and mice, little is known about the substrate specificities of many of its species orthologs. To address this, we performed in vitro analysis of P-gp transporter function using HEK293 cells stably expressing human, ovine, porcine, canine, and feline P-gp. We also employed a human physiologically based pharmacokinetic (PBPK) model to assess variations in digoxin exposure resulting from altered P-gp function. Compared to human P-gp, sheep P-gp had significantly less digoxin efflux (2.3-fold ±0.04 vs. 1.8-fold ±0.03, p < .0001) and all species orthologs had significantly less quinidine efflux compared with human P-gp (p < .05). Human P-gp also had significantly greater efflux of talinolol compared to sheep and dog P-gp (1.9-fold ±0.04 vs. 1.6-fold ±0.06, p = .003 and 1.6-fold ±0.05, p = .0002, respectively). P-gp expression protected all lines against paclitaxel-induced toxicity, with sheep P-gp being significantly less protective. The inhibitor verapamil demonstrated dose-dependent inhibition of all P-gp orthologs. Finally, a PBPK model showed digoxin exposure was sensitive to altered P-gp activity. Overall, our study found that species differences in this major drug transporter exist and that the appropriate species ortholog of P-gp should be evaluated during veterinary drug development.

In Vitro Evaluation of P-gp-Mediated Drug-Drug Interactions Using the RPTEC/TERT1 Human Renal Cell Model

BACKGROUND AND OBJECTIVES

In vitro evaluation of the P-glycoprotein (P-gp) inhibitory potential is an important issue when predicting clinically relevant drug-drug interactions (DDIs). Located within all physiological barriers, including intestine, liver, and kidneys, P-gp plays a major role in the pharmacokinetics of various therapeutic classes. However, few data are available about DDIs involving renal transporters during the active tubular secretion of drugs. In this context, the present study was designed to investigate the application of the human renal cell line RPTEC/TERT1 to study drug interactions mediated by P-gp.

METHODS

The P-gp inhibitory potentials of a panel of drugs were first determined by measuring the intracellular accumulation of rhodamine 123 in RPTEC/TERT1 cells. Then four drugs were selected to assess the half-maximal inhibitor concentration (IC50) values by measuring the intracellular accumulation of two P-gp-substrate drugs, apixaban and rivaroxaban. Finally, according to the FDA guidelines, the [I₁]/IC50 ratio was calculated for each combination of drugs to assess the clinical relevance of the DDIs.

RESULTS

The data showed that drugs which are known P-gp inhibitors, including cyclosporin A, ketoconazole, and verapamil, caused great increases in rhodamine 123 retention, whereas noninhibitors did not affect the intracellular accumulation of the P-gp substrate. The determined IC50 values were in accordance with the inhibition profiles observed in the rhodamine 123 accumulation assays, confirming the reliability of the RPTEC/TERT1 model.

CONCLUSIONS

Taken together, the data demonstrate the feasibility of the application of the RPTEC/TERT1 model for evaluating the P-gp inhibitory potentials of drugs and consequently predicting renal drug interactions.

IAF, QGF, and QDF Peptides Exhibit Cholesterol-Lowering Activity through a Statin-like HMG-CoA Reductase Regulation Mechanism: In Silico and In Vitro Approach

In this study, in silico approaches are employed to investigate the binding mechanism of peptides derived from cowpea β-vignin and HMG-CoA reductase. With the obtained information, we designed synthetic peptides to evaluate their in vitro enzyme inhibitory activity. In vitro, the total protein extract and <3 kDa fraction, at 5000 µg, support this hypothesis (95% and 90% inhibition of HMG-CoA reductase, respectively). Ile-Ala-Phe, Gln-Gly-Phe, and Gln-Asp-Phe peptides were predicted to bind to the substrate binding site of HMGCR via HMG-CoAR. In silico, it was established that the mechanism of HMG-CoA reductase inhibition largely entailed mimicking the interactions of the decalin ring of simvastatin and via H-bonding; in vitro studies corroborated the predictions, whereby the HMG-CoA reductase activity was decreased by 69%, 77%, and 78%, respectively. Our results suggest that Ile-Ala-Phe, Gln-Gly-Phe, and Gln-Asp-Phe peptides derived from cowpea β-vignin have the potential to lower cholesterol synthesis through a statin-like regulation mechanism.

Characterization of P-Glycoprotein Inhibitors for Evaluating the Effect of P-Glycoprotein on the Intestinal Absorption of Drugs

For developing oral drugs, it is necessary to predict the oral absorption of new chemical entities accurately. However, it is difficult because of the involvement of efflux transporters, including P-glycoprotein (P-gp), in their absorption process. In this study, we conducted a comparative analysis on the inhibitory activities of seven P-gp inhibitors (cyclosporin A, GF120918, LY335979, XR9576, WK-X-34, VX-710, and OC144-093) to evaluate the effect of P-gp on drug absorption. GF120918, LY335979, and XR9576 significantly decreased the basal-to-apical transport of paclitaxel, a P-gp substrate, across Caco-2 cell monolayers. GF120918 also inhibited the basal-to-apical transport of mitoxantrone, a breast cancer resistance protein (BCRP) substrate, in Caco-2 cells, whereas LY335979 hardly affected the mitoxantrone transport. In addition, the absorption rate of paclitaxel after oral administration in wild-type mice was significantly increased by pretreatment with LY335979, and it was similar to that in mdr1a/1b knockout mice. Moreover, the absorption rate of topotecan, a BCRP substrate, in wild-type mice pretreated with LY335979 was similar to that in mdr1a/1b knockout mice but significantly lower than that in bcrp knockout mice. These results indicate that LY335979 has a selective inhibitory activity for P-gp, and would be useful for evaluating the contribution of P-gp to drug absorption.

Role of membrane-embedded drug efflux ABC transporters in the cancer chemotherapy

One of the major problems being faced by researchers and clinicians in leukemic treatment is the development of multidrug resistance (MDR) which restrict the action of several tyrosine kinase inhibitors (TKIs). MDR is a major obstacle to the success of cancer chemotherapy. The mechanism of MDR involves active drug efflux transport of ABC superfamily of proteins such as Pglycoprotein (P-gp/ABCB1), multidrug resistance-associated protein 2 (MRP2/ABCC2), and breast cancer resistance protein (BCRP/ABCG2) that weaken the effectiveness of chemotherapeutics and negative impact on the future of anticancer therapy. In this review, the authors aim to provide an overview of various multidrug resistance (MDR) mechanisms observed in cancer cells as well as the various strategies developed to overcome these MDR. Extensive studies have been carried out since last several years to enhance the efficacy of chemotherapy by defeating these MDR mechanisms with the use of novel anticancer drugs that could escape from the efflux reaction, MDR modulators or chemosensitizers, multifunctional nanotechnology, and RNA interference (RNAi) therapy.

The effect of genetic variations on ribavirin pharmacokinetics and treatment response in HCV-4 Egyptian patients receiving sofosbuvir/daclatasvir and ribavirin

PURPOSE

This study aimed to investigate the effect of single nucleotide polymorphisms (SNPs) of genes involved in ribavirin (RBV) transport (SLC28A2 gene, ABCB1 gene and ABCB11 gene) on the clinical outcome and pharmacokinetics of ribavirin in HCV- 4 Egyptian patients.

METHOD

100 patients treated with sofosbuvir/daclatasvir and ribavirin for 12 weeks. The SNP genotyping was performed by real-time PCR using high resolution melting analysis. Ribavirin plasma trough concentrations were determined at week 4 of therapy using a liquid chromatography/tandem mass spectrometry (LC-MS/MS). For clinical outcomes, sustained virological response (SVR), liver function tests (ALT and AST), total bilirubin, albumin, serum creatinine, hemoglobin, leukocyte count, and platelet count were measured.

RESULTS

Concerning RBV pharmacokinetics, ABCB1 2677 G > T SNP and ABCB11 1331 T > C SNP were statistically associated with RBV C_trough levels after 4 weeks of therapy. ABCB11 1331 T > C SNP revealed significant association with clinical outcomes (SVR). SLC28A2-146 A > T SNP has not showed any statistically significant association with RBV plasma levels or response.

CONCLUSION

SNP genotyping for ABCB1 and ABCB11 genes can help in better personalized medicine for maximizing response for ribavirin as explored by the significant association between polymorphism in ABCB1 and ABCB11 genes and ribavirin pharmacokinetics and the significant association of ABCB11 1331 T > C SNP with clinical response.

Pharmacogenetics of the anti-HCV drug sofosbuvir: a preliminary study

Background

Sofosbuvir is a potent nucleotide HCV NS5B polymerase inhibitor that is also a P-glycoprotein (encoded by the ABCB1 gene) and breast cancer resistance protein (encoded by the ABCG2 gene) substrate. Concerning previous anti-HCV therapies, pharmacogenetics had a significant impact, particularly considering the association of interleukin28B polymorphisms with dual-therapy (ribavirin + pegylated IFN) outcomes.

Objectives

In this work, we investigated the association between sofosbuvir and its prevalent metabolite (GS-331007) plasma concentrations at 1 month of therapy and genetic variants (SNPs) in genes encoding transporters and nuclear factors (ABCB1, ABCG2 and HNF4α) related to sofosbuvir transport.

Patients and methods

Allelic discrimination was performed through real-time PCR, whereas plasma concentrations were evaluated through liquid chromatography. One hundred and thirteen patients were enrolled.

Results

Sofosbuvir concentrations were below the limit of quantification since the drug was converted into its GS-331007 metabolite. ABCB1 2677 G>T (P = 0.044) and HNF4α 975 C>G (P = 0.049) SNPs were associated with GS-331007 metabolite plasma concentrations. In linear multivariate analysis, liver stiffness, insulin resistance, baseline haemoglobin and haematocrit and SNPs in the ABCB1 gene (3435 CT/TT and 1236 TT genotypes) were significant predictors of GS-331007 concentrations. Furthermore, we performed sub-analyses considering the anti-HCV concomitant drug and HCV genotype, identifying specific polymorphisms associated with GS-331007 plasma concentrations: ABCB1 3435 C>T and HNF4α975 C>G in patients treated with daclatasvir, ABCB1 2677 G>T with ledipasvir and ABCB1 3435 C>T, ABCB1 2677 G>T, ABCG2 421 C>A and ABCG2 1194 + 928 C>A with ribavirin.

Conclusions

In this study we suggested sofosbuvir GS-331007 metabolite plasma levels were affected by variants in the ABCB1 and HNFα genes.

Strategy for the Prediction of Steady-State Exposure of Digoxin to Determine Drug-Drug Interaction Potential of Digoxin With Other Drugs in Digitalization Therapy

Digoxin, a narrow therapeutic index drug, is widely used in congestive heart failure. However, the digitalization therapy involves dose titration and can exhibit drug-drug interaction. Ctrough versus area under the plasma concentration versus time curve in a dosing interval of 24 hours (AUC0-24h) and Cmax versus AUC0-24h for digoxin were established by linear regression. The predictions of digoxin AUC0-24h values were performed using published Ctrough or Cmax with appropriate regression lines. The fold difference, defined as the quotient of the observed/predicted AUC0-24h values, was evaluated. The mean square error and root mean square error, correlation coefficient (r), and goodness of the fold prediction were used to evaluate the models. Both Ctrough versus AUC0-24h (r = 0.9215) and Cmax versus AUC0-24h models for digoxin (r = 0.7781) showed strong correlations. Approximately 93.8% of the predicted digoxin AUC0-24h values were within 0.76-fold to 1.25-fold difference for Ctrough model. In sharp contrast, the Cmax model showed larger variability with only 51.6% of AUC0-24h predictions within 0.76-1.25-fold difference. The r value for observed versus predicted AUC0-24h for Ctrough (r = 0.9551; n = 177; P < 0.001) was superior to the Cmax (r = 0.6134; n = 275; P < 0.001) model. The mean square error and root mean square error (%) for the Ctrough model were 11.95% and 16.2% as compared to 67.17% and 42.3% obtained for the Cmax model. Simple linear regression models for Ctrough/Cmax versus AUC0-24h were derived for digoxin. On the basis of statistical evaluation, Ctrough was superior to Cmax model for the prediction of digoxin AUC0-24h and can be potentially used in a prospective setting for predicting drug-drug interaction or lack of it.

ABCB1 and ABCC11 confer resistance to eribulin in breast cancer cell lines

This study aimed to elucidate the mechanisms underlying the resistance of breast cancer to eribulin. Seven eribulin-resistant breast cancer cell lines (MCF7/E, BT474/E, ZR75-1/E, SKBR3/E, MDA-MB-231/E, Hs578T/E, and MDA-MB-157/E) were established. mRNA and protein expression of ATP-binding cassette subfamily B member 1 (ABCB1) and subfamily C member 11 (ABCC11) increased in all eribulin-resistant cell lines compared to the parental cell lines. When ABCB1 or ABCC11 expression was inhibited by small interfering RNA in MCF7/E, BT474/E, and MDA-MB-231/E cells, eribulin sensitivity was partially restored. Moreover, eribulin resistance was attenuated additively by inhibiting ABCB1 and ABCC11 in MCF7/E cells. Additionally, overexpression of exogenous ABCB1 or ABCC11 in HEK293T cells conferred resistance to eribulin. MCF7/E and MDA-MB-231/E cells showed cross-resistance to paclitaxel, doxorubicin, and fluorouracil. Inhibition of ABCB1 partially restored paclitaxel and doxorubicin sensitivity. Partial restoration of fluorouracil sensitivity was induced by inhibiting ABCC11 in MCF7/E and MDA-MB-231/E cells. Both ABCB1 and ABCC11 are involved in the development of eribulin resistance in breast cancer cells in vitro regardless of the breast cancer subtype. Thus, ABCB1 and ABCC11 expression may be used as a biomarker for predicting the response to eribulin in patients with breast cancer. Concomitant inhibition of ABCB1 and ABCC11 might help enhance the antitumor effects of eribulin.

Systematic Therapeutic Drug Monitoring for Linezolid: Variability and Clinical Impact

Linezolid serum trough (C_min) and peak (C_max) levels were determined prospectively in 90 patients. Adequate exposure was defined as a C_min of 2 to 8 mg/liter. Therapy was empirical (73.3%) or targeted (26.7%). Wide interindividual variability in linezolid C_min levels was recorded (0.1 to 25.2 μg/ml). Overall, 65.5% of the patients had out-of-range, 41.1% had subtherapeutic, and 24.4% had supratherapeutic trough levels. We did not find a correlation between abnormal levels and adverse events, in-hospital mortality, or overall poor outcome.

Role of vitamin D pathway gene polymorphisms on rifampicin plasma and intracellular pharmacokinetics

AIM

We retrospectively evaluate the pharmacogenetic role of single nucleotide polymorphisms involved in rifampicin transport (SLCO1B1, MDR1 and PXR genes) and vitamin D (VDR, CYP24A1 and CYP27B1 genes) metabolism and activity on drug plasma and intracellular concentrations.

PATIENTS & METHODS

Rifampicin C_max and C_trough were measured at weeks 2 and 4 using Ultra-Performance Liquid Chromatography-tandem mass spectroscopy methods. Allelic discrimination was performed by real-time polymerase chain reaction.

RESULTS

Twenty-four patients were enrolled. At week 2, OATP1B1 521TT and CYP27B1 +2838CC/CT considering plasma and BsmIAA for intraperipheral blood mononuclear cells C_max, remained in regression analysis. Concerning week 4, TaqITC/CC and CYP24A1 22776CT/TT were retained in plasma C_max regression model.

CONCLUSION

This study confirms the role of SLCO1B1 and it suggests the involvement of vitamin D pathway gene polymorphisms in rifampicin pharmacokinetics.

Oral Contraceptives after Bariatric Surgery

OBJECTIVE

Bariatric surgery offers a highly effective mode of treatment for obese patients. Some procedures such as bypass cause an alteration in normal gastrointestinal tract with possible consequences for the uptake of orally administered drugs.

METHODS

We assessed the literature to ascertain whether the use of oral drugs and especially oral contraceptives is effective and adequate after bariatric surgery.

RESULTS

The bioavailability of drugs could be affected by the solubility and pH of the modified medium after bariatric surgery and by the loss of gastrointestinal transporters. Bariatric surgery could potentially result in a transient change in the absorption of drugs such as analgesics, antibiotics, antiarrhythmics, anticoagulants, psychotropic, and oral contraceptive drugs. Effective contraception is especially critical in the postoperative period, and implants might be representing a safe contraceptive method in women undergoing bariatric surgery.

CONCLUSION

Each drug will have to be evaluated with respect to its site of absorption and its mechanism of absorption, with special attention on parameters influencing the effectiveness of the absorption processes.

The Evolving Paradigm of Individualized Postresuscitation Care After Cardiac Arrest

The postresuscitation period after a cardiac arrest is characterized by a wide range of physiological derangements. Variations between patients include preexisting medical problems, the underlying cause of the cardiac arrest, presence or absence of hemodynamic and circulatory instability, severity of the ischemia-reperfusion injury, and resuscitation-related injuries such as pulmonary aspiration and rib or sternal fractures. Although protocols can be applied to many elements of postresuscitation care, the widely disparate clinical condition of cardiac arrest survivors requires an individualized approach that stratifies patients according to their clinical profile and targets specific treatments to patients most likely to benefit. This article describes such an individualized approach, provides a practical framework for evaluation and triage at the bedside, and reviews concerns specific to all members of the interprofessional postresuscitation care team.

Pharmacokinetic and pharmacodynamic evaluation of linagliptin for the treatment of type 2 diabetes mellitus, with consideration of Asian patient populations

Our aims were to summarize the clinical pharmacokinetics and pharmacodynamics of the dipeptidyl‐peptidase‐4 inhibitor, linagliptin, and to consider how these characteristics influence its clinical utility. Differences between linagliptin and other dipeptidyl‐peptidase‐4 inhibitors were also considered, in addition to the influence of Asian race on the pharmacology of linagliptin. Linagliptin has a xanthine‐based structure, a difference that might account for some of the pharmacological differences observed with linagliptin versus other dipeptidyl‐peptidase‐4 inhibitors. The long terminal half‐life of linagliptin results from its strong binding to dipeptidyl‐peptidase‐4. Despite this, linagliptin shows a short accumulation half‐life, as a result of saturable, high‐affinity binding to dipeptidyl‐peptidase‐4. The pharmacokinetic characteristics of linagliptin make it suitable for once‐daily dosing in a broad range of patients with type 2 diabetes mellitus. Unlike most other dipeptidyl‐peptidase‐4 inhibitors, linagliptin has a largely non‐renal excretion route, and dose adjustment is not required in patients with renal impairment. Furthermore, linagliptin exposure is not substantially altered in patients with hepatic impairment, and dose adjustment is not necessary for these patients. The 5‐mg dose is also suitable for patients of Asian ethnicity. Linagliptin shows unique pharmacological features within the dipeptidyl‐peptidase‐4 inhibitor class. Although most clinical trials of linagliptin have involved largely Caucasian populations, data on the pharmacokinetic/pharmacodynamic properties of linagliptin show that these features are not substantially altered in Asian populations. The 5‐mg dose of linagliptin is suitable for patients with type 2 diabetes mellitus irrespective of their ethnicity or the presence of renal or hepatic impairment.

Effects of berberine on pharmacokinetics of midazolam and rhodamine 123 in rats in vivo

Aim

To evaluate whether berberine hydrochloride (BBR) could modify the pharmacokinetic profiles of midazolam (MDZ), a substrate of CYP3A, and rhodamine 123 (Rh123), a substrate of P-glycolprotein (P-gp), in male rats.

Methods

The rats were given with varied does of BBR or 75 mg/kg ketoconazole as a positive control for 10 days by intragastric administration. Single-pass duodenum perfusion of 20 mg/kg MDZ and inguinal artery canulated rats were used in the study. Plasma concentrations of MDZ and 1′-hydroxymidazolam (1′-OH-MDZ) were analyzed by high performance liquid chromatography (HPLC). The rats were given with varied does of BBR or 4 mg/kg verapamil as a positive control for 10 days by intragastric administration. Blood was obtained from the caudal vein of rats after single-pass intragastric administration of 5 mg/kg Rh123. HPLC was used to analyze the plasma concentrations of Rh123.

Results

BBR produced similar results as the ketoconazole (positive control group) with a dose-dependent increase in the AUC_(0−t) and AUMC _(0−t) of midazolam except at the dose of 50 mg/kg (p < 0.01). And BBR could significantly increase the peak plasma concentrations (C_max) of MDZ (p < 0.01), but reduce the clearance rate (CL_z) and the apparent volume of the distribution (V_z) of MDZ (p < 0.05). The results also indicated that BBR had no significant impact on the half-life period (t_1/2) and the time to reach peak concentration (t_max). Meanwhile, BBR could dose-dependently decrease AUC_(0−t) and AUMC_(0−t) of 1′-OH-MDZ significantly (p < 0.05), and expedite the clearance rate of 1′-OH-MDZ while gaining its apparent volume of distribution (p < 0.05), but had no significant impact on t_1/2 and T_max. The result also showed that BBR, except at the dose of 50 mg/kg, and the positive verapamil group could significantly increase the AUC_(0−t) and AUC_(0−∞) of Rh123 (p < 0.001), meanwhile raise C_max of Rh123 and shorten its V_z inversely (p < 0.05). Additionally, pre-treatment with BBR had no significant influence with the half-life period of Rh123, while significantly reduced its clearance rate (p < 0.05).

Conclusion

The metabolism of MDZ and Rh123 was controlled by BBR. The results were most likely due to the inhibition by BBR on CYP3A enzymes and P-gp transporter.

Ethambutol plasma and intracellular pharmacokinetics: A pharmacogenetic study

We evaluated ethambutol plasma and intracellular pharmacokinetic according to single nucleotide polymorphisms in ABCB1, OATP1B1, PXR, VDR, CYP24A1 and CYP27B1 genes. Mycobacterium tubercolosis infected patients were enrolled. Standard weight-adjusted antitubercular treatment was administered intravenously for 2 weeks and then orally. Allelic discrimination was performed by real-time PCR. Ethambutol plasma and intracellular concentrations were measured by UPLC-MS/MS methods. Twenty-four patients were included. Considering weeks 2 and 4, median plasma Ctrough were 73 ng/mL and 247 ng/mL, intracellular Ctrough were 16,863 ng/mL and 13,535 ng/mL, plasma Cmax were 5627 ng/mL and 2229 ng/mL, intracellular Cmax were 133,830 ng/mL and 78,544 ng/mL. At week 2, ABCB1 3435 CT/TT (p=0.023) and CYP24A1 8620 AG/GG (p=0.030) genotypes for plasma Ctrough, BsmI AA (p=0.036) for intracellular Ctrough and BsmI AA (p<0.001) and ApaI AA (p=0.048) for intracellular Cmax, remained in linear regression analysis as predictive factors. Concerning week 4 only ABCB1 3435 CT/TT (p=0.035) and Cdx2 AG/GG (p=0.004) genotypes for plasma Ctrough and BsmI AA (p=0.028) for plasma Cmax were retained in final regression model. We reveal, for the first time, the possible role of single nucleotide polymorphisms on ethambutol plasma and intracellular concentrations; this may further the potential use of pharmacogenetic for tailoring antitubercular treatment.

Mammalian drug efflux transporters of the ATP binding cassette (ABC) family in multidrug resistance: A review of the past decade

Multidrug resistance (MDR) is a serious phenomenon employed by cancer cells which hampers the success of cancer pharmacotherapy. One of the common mechanisms of MDR is the overexpression of ATP-binding cassette (ABC) efflux transporters in cancer cells such as P-glycoprotein (P-gp/ABCB1), multidrug resistance-associated protein 2 (MRP2/ABCC2), and breast cancer resistance protein (BCRP/ABCG2) that limits the prolonged and effective use of chemotherapeutic drugs. Researchers have found that developing inhibitors of ABC efflux transporters as chemosensitizers could overcome MDR. But the clinical trials have shown that most of these chemosensitizers are merely toxic and only show limited or no benefits to cancer patients, thus new inhibitors are being explored. Recent findings also suggest that efflux pumps of the ABC transporter family are subject to epigenetic gene regulation. In this review, we summarize recent findings of the role of ABC efflux transporters in MDR.

Effect of resveratrol on the pharmacokinetics of fexofenadine in rats: Involvement of P-glycoprotein inhibition

BACKGROUND

Resveratrol (RSV) is a natural occurring antioxidant has been found to possess P-glycoprotein (P-gp) inhibition activity in vitro and in vivo, which may have the potential to cause drug-phytochemical interactions. The purpose of the present study was to evaluate the effect of RSV on the pharmacokinetics of fexofenadine (FEX), P-gp substrate in rats.

METHODS

A mechanistic evaluation was undertaken using in vitro non-everted sac and in situ intestinal perfusion studies to determine the FEX intestinal transport and permeability. These results were confirmed by an in vivo pharmacokinetic study of oral administered FEX (10mg/kg) in rats.

RESULTS

The intestinal transport and apparent permeability (Papp) of FEX were increased significantly in duodenum, jejunum and ileum of RSV and verapamil (VER) pretreated groups when compared to FEX alone group. Similarly absorption rate constant (Ka), fraction absorbed (Fab) and effective permeability (Peff) of FEX were increased significantly in ileum of RSV and VER pretreated groups when compared to FEX alone group. In comparison with FEX alone, RSV pretreatment significantly increased maximum plasma concentration (Cmax) and area under the concentration-time curve (AUC), while there was no significant change was observed in T1/2 and Tmax of FEX.

CONCLUSIONS

RSV significantly enhanced the exposure of FEX in rats likely by the inhibition of P-glycoprotein (P-gp) mediated efflux during the intestinal absorption, suggesting that there is a potential pharmacokinetic interaction between RSV and FEX. Therefore, further studies are recommended to evaluate the potential drug-phytochemical interactions in humans.

Intracellular accumulation of boceprevir according to plasma concentrations and pharmacogenetics

Boceprevir (BOC) is a directly-acting antiviral agent for the treatment of hepatitis C virus genotype 1 (HCV-1) infection. It is a mixture of two stereoisomers, the inactive R and the active S isomers. No data have previously been published on BOC intracellular accumulation. In this study, BOC isomer concentrations in peripheral blood mononuclear cells (PBMCs) and plasma were determined. The influence of various single nucleotide polymorphisms (SNPs) on plasma and intracellular drug exposure at Week 4 of triple therapy were also evaluated. Plasma and intracellular BOC concentrations were determined at the end of the dosing interval (C(trough)) using a UPLC-MS/MS validated method. Allelic discrimination was performed through real-time PCR. Median plasma concentrations were 65.97 ng/mL for the S isomer and 36.31 ng/mL for the R isomer; the median S/R plasma concentration ratio was 1.66. The median PBMC concentration was 2285.88 ng/mL for the S isomer; the R isomer was undetectable within PBMCs. The median S isomer PBMC/plasma concentration ratio was 28.59. A significant positive correlation was found between plasma and PBMC S isomer concentrations. ABCB1 1236, SLC28A2 124 and IL28B rs12979860 SNPs were associated with the S isomer PBMC/plasma concentration ratio. In regression models, S isomer plasma levels and FokI polymorphism were able to predict S isomer intracellular exposure, whereas SNPs in AKR1, BCRP1 and SLC28A2 predicted the S isomer PBMC/plasma concentration ratio. No similar data regarding BOC pharmacogenetics and pharmacokinetics have been published previously. This study adds a novel and useful overview of the pharmacological properties of this drug.

Identification of Possible Binding Sites for Morphine and Nicardipine on the Multidrug Transporter P-Glycoprotein Using Umbrella Sampling Techniques

The multidrug transporter P-glycoprotein (P-gp) is central to the development of multidrug resistance in cancer. While residues essential for transport and binding have been identified, the location, composition, and specificity of potential drug binding sites are uncertain. Here molecular dynamics simulations are used to calculate the free energy profile for the binding of morphine and nicardipine to P-gp. We show that morphine and nicardipine primarily interact with key residues implicated in binding and transport from mutational studies, binding at different but overlapping sites within the transmembrane pore. Their permeation pathways were distinct but involved overlapping sets of residues. The results indicate that the binding location and permeation pathways of morphine and nicardipine are not well separated and cannot be considered as unique. This has important implications for our understanding of substrate uptake and transport by P-gp. Our results are independent of the choice of starting structure and consistent with a range of experimental studies.

Dapagliflozin in patients with type 2 diabetes mellitus

Dapagliflozin is a selective and reversible inhibitor of sodium-glucose linked transporter type 2 (SGLT2), which mediates approximately 90% of active renal glucose reabsorption in the early proximal tubule of the kidney. Dapagliflozin significantly reduces glucose reabsorption and decreases serum glucose concentration in an insulin-independent manner. The decrease of glucose reabsorption by dapagliflozin has also been associated with a reduction in body weight. Furthermore, the drug modestly reduces blood pressure levels through weight loss and its action as osmotic diuretic. Dapagliflozin has been approved as monotherapy in patients with type 2 diabetes mellitus (T2DM) who cannot tolerate metformin or in combination with other antidiabetic drugs, with the exception of pioglitazone due to the theoretical increased risk of bladder cancer. The drug should not be prescribed in patients with moderate or severe renal impairment or in patients at risk for developing volume depletion. Dapagliflozin is associated with increased incidence of genital and lower urinary tract infections, but these infections are usually mild to moderate and respond to standard antimicrobial treatment. Based on current evidence, dapagliflozin is a useful drug for patients with T2DM with a favorable safety profile. However, further research regarding the effects of dapagliflozin on cardiovascular outcomes is needed.

Modulation of P-glycoprotein efflux pump: induction and activation as a therapeutic strategy

P-glycoprotein (P-gp) is an ATP-dependent efflux pump encoded by the MDR1 gene in humans, known to mediate multidrug resistance of neoplastic cells to cancer therapy. For several decades, P-gp inhibition has drawn many significant research efforts in an attempt to overcome this phenomenon. However, P-gp is also constitutively expressed in normal human epithelial tissues and, due to its broad substrate specificity, to its cellular polarized expression in many excretory and barrier tissues, and to its great efflux capacity, it can play a crucial role in limiting the absorption and distribution of harmful xenobiotics, by decreasing their intracellular accumulation. Such a defense mechanism can be of particular relevance at the intestinal level, by significantly reducing the intestinal absorption of the xenobiotic and, consequently, avoiding its access to the target organs. In this review, the current knowledge on this important efflux pump is summarized, and a new focus is brought on the therapeutic interest of inducing and/or activating P-gp for limiting the toxicity caused by its substrates. Several in vivo and in vitro studies validating the use of such a therapeutic strategy are discussed. An extensive literature search for reported P-gp inducers/activators and for the experimental models used in their characterization was conducted. Those studies demonstrate that effective antidotal pathways can be achieved by efficiently promoting the P-gp-mediated efflux of deleterious xenobiotics, resulting in a significant reduction in their intracellular levels and, consequently, in a significant reduction of their toxicity.

ABCB11 and ABCB1 gene polymorphisms impact on telaprevir pharmacokinetic at one month of therapy

In 2011 direct-acting antivirals, including telaprevir, have been developed to achieve a better antiviral effect. It was reported that telaprevir is a substrate of P-glycoprotein (ABCB1) and cytochrome P450 3A4. The aim of this retrospective study was the evaluation of the influence of some single nucleotide polymorphisms (SNPs) of genes (ABCB1, SLC28A2/3, SLC29A1) involved in TLV and RBV transport and their correlation with plasma TLV drug exposure at 1 month of therapy. We also investigated the association of a SNP in ABCB11 gene, whose role in TLV transport was not yet shown. Twenty-nine HCV-1 patients treated with telaprevir, ribavirin and pegylated-interferon-α were retrospectively analyzed; allelic discrimination was performed by real-time PCR. Telaprevir Ctrough levels were influenced by Metavir score (P=0.023), ABCB1 2677 G>T (P=0.006), ABCB1 1236 C>T (P=0.015) and ABCB11 1131 T>C (P=0.033) SNPs. Regarding ABCB1 3435 C>T, a not statistically significant trend in telaprevir plasma concentration was observed. Metavir score (P=0.002, OR -336; 95% CI -535;-138), ABCB1 2677 (P=0.020, OR 497; 95% CI 86; 910), ABCB11 1131 (P=0.002, OR 641; 95% CI 259;1023) and CNT2 -146 (P=0.006, OR -426; 95% CI -721;-132) were able to predict telaprevir plasma levels in the regression analysis. Other SNPs showed no association. This study reveals BSEP implication in telaprevir transport and confirms the involvement and influence of P-glycoprotein on telaprevir plasma levels. To date, no similar data concerning pharmacogenetics and pharmacokinetics were published, but further studies in different and bigger cohorts are needed.

Drug activity prediction using multiple-instance learning via joint instance and feature selection

Background

In drug discovery and development, it is crucial to determine which conformers (instances) of a given molecule are responsible for its observed biological activity and at the same time to recognize the most representative subset of features (molecular descriptors). Due to experimental difficulty in obtaining the bioactive conformers, computational approaches such as machine learning techniques are much needed. Multiple Instance Learning (MIL) is a machine learning method capable of tackling this type of problem. In the MIL framework, each instance is represented as a feature vector, which usually resides in a high-dimensional feature space. The high dimensionality may provide significant information for learning tasks, but at the same time it may also include a large number of irrelevant or redundant features that might negatively affect learning performance. Reducing the dimensionality of data will hence facilitate the classification task and improve the interpretability of the model.

Results

In this work we propose a novel approach, named multiple instance learning via joint instance and feature selection. The iterative joint instance and feature selection is achieved using an instance-based feature mapping and 1-norm regularized optimization. The proposed approach was tested on four biological activity datasets.

Conclusions

The empirical results demonstrate that the selected instances (prototype conformers) and features (pharmacophore fingerprints) have competitive discriminative power and the convergence of the selection process is also fast.

The tumor microenvironment and strategies to improve drug distribution

The microenvironment within tumors is composed of a heterogeneous mixture of cells with varying levels of nutrients and oxygen. Differences in oxygen content result in survival or compensatory mechanisms within tumors that may favor a more malignant or lethal phenotype. Cells that are rapidly proliferating are richly nourished and preferentially located close to blood vessels. Chemotherapy can target and kill cells that are adjacent to the vasculature, while cells that reside farther away are often not exposed to adequate amounts of drug and may survive and repopulate following treatment. The characteristics of the tumor microenvironment can be manipulated in order to design more effective therapies. In this review, we describe important features of the tumor microenvironment and discuss strategies whereby drug distribution and activity may be improved.

Effect of ketoconazole on the pharmacokinetics of the 11β-hydroxysteroid dehydrogenase type 1 inhibitor ABT-384 and its two active metabolites in healthy volunteers: population analysis of data from a drug-drug interaction study

ABT-384 [1-piperazineacetamide, N-[5-(aminocarbonyl) tricyclo[3.3.1.13,7]dec-2-yl]-α,α-dimethyl-4-[5-(trifluoromethyl)-2-pyridinyl]-,stereoisomer] is a potent and selective inhibitor of 11β-hydroxysteroid dehydrogenase type 1 (HSD-1). ABT-384 has been shown to be safe and well tolerated in humans at doses up to 100 mg daily, and to fully inhibit both peripheral and brain HSD-1 at a dose of 2 mg daily. The effect of ketoconazole on the pharmacokinetics of ABT-384 and its two active metabolites, A-1331480 and A-847082, was investigated in healthy volunteers. When 10 mg of ABT-384 was coadministered with ketoconazole, ABT-384 exposures increased 18-fold for area under the plasma concentration-time curve from time 0 to infinity and 3.5-fold for Cmax. The results suggest that ABT-384 is a sensitive substrate of CYP3A. After ketoconazole coadministration, exposures of A-1331480 and A-847082 were also greatly increased. A population pharmacokinetic model was constructed for ABT-384 and its metabolites using NonMEM. A two-compartment model with three transit absorption compartments best described ABT-384 data. The model predicted a 69.3% decrease in ABT-384 clearance and 91.1% increase in the volume of distribution of ABT-384 in the presence of ketoconazole. A-1331480 was shown to be formation rate-limited and A-847082 was elimination rate-limited. Both metabolites were characterized by a one-compartment model with first-order rate constants of formation and elimination. Overall the model adequately captured the concentration-time profiles of ABT-384, A-1331480, and A-847082 in both ABT-384-alone and ketoconazole-coadministration conditions. Although ABT-384 exposures were greatly increased in the presence of ketoconazole, coadministration of ABT-384 with ketoconazole or other strong/moderate CYP3A inhibitors is not expected to contribute to any major clinical safety issues considering the favorable safety profile of ABT-384.

Oral treatment with etoposide in small cell lung cancer - dilemmas and solutions

Background

Etoposide is a chemotherapeutic agent, widely used for the treatment of various malignancies, including small cell lung cancer (SCLC), an aggressive disease with poor prognosis. Oral etoposide administration exhibits advantages for the quality of life of the patient as well as economic benefits. However, widespread use of oral etoposide is limited by incomplete and variable bioavailability. Variability in bioavailability was observed both within and between patients. This suggests that some patients may experience suboptimal tumor cytotoxicity, whereas other patients may be at risk for excess toxicity.

Conclusions

The article highlights dilemmas as well as solutions regarding oral treatment with etoposide by presenting and analyzing relevant literature data. Numerous studies have shown that bioavailability of etoposide is influenced by genetic, physiological and environmental factors. Several strategies were explored to improve bioavailability and to reduce pharmacokinetic variability of oral etoposide, including desired and undesired drug interactions (e.g. with ketoconazole), development of suitable drug delivery systems, use of more water-soluble prodrug of etoposide, and influence on gastric emptying. In addition to genotype-based dose administration, etoposide is suitable for pharmacokinetically guided dosing, which enables dose adjustments in individual patient.

Further, it is established that oral and intravenous schedules of etoposide in SCLC patients do not result in significant differences in treatment outcome, while results of toxicity are inconclusive. To conclude, the main message of the article is that better prediction of the pharmacokinetics of oral etoposide may encourage its wider use in routine clinical practice.

Sucralose, a synthetic organochlorine sweetener: overview of biological issues

Sucralose is a synthetic organochlorine sweetener (OC) that is a common ingredient in the world's food supply. Sucralose interacts with chemosensors in the alimentary tract that play a role in sweet taste sensation and hormone secretion. In rats, sucralose ingestion was shown to increase the expression of the efflux transporter P-glycoprotein (P-gp) and two cytochrome P-450 (CYP) isozymes in the intestine. P-gp and CYP are key components of the presystemic detoxification system involved in first-pass drug metabolism. The effect of sucralose on first-pass drug metabolism in humans, however, has not yet been determined. In rats, sucralose alters the microbial composition in the gastrointestinal tract (GIT), with relatively greater reduction in beneficial bacteria. Although early studies asserted that sucralose passes through the GIT unchanged, subsequent analysis suggested that some of the ingested sweetener is metabolized in the GIT, as indicated by multiple peaks found in thin-layer radiochromatographic profiles of methanolic fecal extracts after oral sucralose administration. The identity and safety profile of these putative sucralose metabolites are not known at this time. Sucralose and one of its hydrolysis products were found to be mutagenic at elevated concentrations in several testing methods. Cooking with sucralose at high temperatures was reported to generate chloropropanols, a potentially toxic class of compounds. Both human and rodent studies demonstrated that sucralose may alter glucose, insulin, and glucagon-like peptide 1 (GLP-1) levels. Taken together, these findings indicate that sucralose is not a biologically inert compound.

Implementation of multiple-instance learning in drug activity prediction

BACKGROUND

In the context of drug discovery and development, much effort has been exerted to determine which conformers of a given molecule are responsible for the observed biological activity. In this work we aimed to predict bioactive conformers using a variant of supervised learning, named multiple-instance learning. A single molecule, treated as a bag of conformers, is biologically active if and only if at least one of its conformers, treated as an instance, is responsible for the observed bioactivity; and a molecule is inactive if none of its conformers is responsible for the observed bioactivity. The implementation requires instance-based embedding, and joint feature selection and classification. The goal of the present project is to implement multiple-instance learning in drug activity prediction, and subsequently to identify the bioactive conformers for each molecule.

METHODS

We encoded the 3-dimensional structures using pharmacophore fingerprints which are binary strings, and accomplished instance-based embedding using calculated dissimilarity distances. Four dissimilarity measures were employed and their performances were compared. 1-norm SVM was used for joint feature selection and classification. The approach was applied to four data sets, and the best proposed model for each data set was determined by using the dissimilarity measure yielding the smallest number of selected features.

RESULTS

The predictive abilities of the proposed approach were compared with three classical predictive models without instance-based embedding. The proposed approach produced the best predictive models for one data set and second best predictive models for the rest of the data sets, based on the external validations. To validate the ability of the proposed approach to find bioactive conformers, 12 small molecules with co-crystallized structures were seeded in one data set. 10 out of 12 co-crystallized structures were indeed identified as significant conformers using the proposed approach.

CONCLUSIONS

The proposed approach was proven not to suffer from overfitting and to be highly competitive with classical predictive models, so it is very powerful for drug activity prediction. The approach was also validated as a useful method for pursuit of bioactive conformers.

A plausible explanation for enhanced bioavailability of P-gp substrates in presence of piperine: simulation for next generation of P-gp inhibitors

P-glycoprotein (P-gp) has a major role to play in drug pharmacokinetics and pharmacodynamics, since it effluxes many cytotoxic hydrophobic anticancer drugs from gastrointestinal tract, brain, liver and kidney. Piperine is known to enhance the bioavailability of curcumin, as a substrate of P-gp by at least 2000%. Besides these at least 50 other substrates and inhibitors of P-gp have been reported so far. All P-gp inhibitors have diverse structures. Although little is known about binding of some flavonoids and steroids at the NBD (nucleotide binding domain) of P-gp in the vicinity of ATP binding site inhibiting its hydrolysis, a valid explanation of how P-gp accommodates such a diverse set of inhibitors is still awaited. In the present study, piperine up to 100 μM has not shown observable cytotoxic effect on MDCK cell line, and it has been shown to accumulate rhodamine by fluorescence microscopy and fluorescent activated cell sorter in MDCK cells. Computational simulation for piperine and some first and second generation P-gp inhibitors has shown that these dock at the NBD site of P-gp. A comparative simulation study has been carried out regarding their docking and binding energies. Binding conformation of P-gp co-crystallized complexes with ADP, AMP-PNP (Adenylyl-imidodiphosphate), and ATP were compared with piperine. The receptor based E-pharmacophore of docked piperine has been simulated to find common features amongst P-gp inhibitors. Finally it has been concluded that piperine could be utilized as base molecule for design and development of safe non-toxic inhibitor of P-gp in order to enhance the bioavailability of most of its substrates.

Enhancement of cellular uptake and cytotoxicity of curcumin-loaded PLGA nanoparticles by conjugation with anti-P-glycoprotein in drug resistance cancer cells

AIM

To compare the anti-cancer activity and cellular uptake of curcumin (Cur) delivered by targeted and non-targeted drug delivery systems in multidrug-resistant cervical cancer cells.

METHODS

Cur was entrapped into poly (DL-lactide-co-glycolide) (PLGA) nanoparticles (Cur-NPs) in the presence of modified-pluronic F127 stabilizer using nano-precipitation technique. On the surface of Cur-NPs, the carboxy-terminal of modified pluronic F127 was conjugated to the amino-terminal of anti-P-glycoprotein (P-gp) (Cur-NPs-APgp). The physical properties of the Cur-NPs, including particle size, zeta potential, particle morphology and Cur release kinetics, were investigated. Cellular uptake and specificity of the Cur-NPs and Cur-NPs-APgp were detected in cervical cancer cell lines KB-V1 (higher expression of P-gp) and KB-3-1 (lower expression of P-gp) using fluorescence microscope and flow cytometry, respectively. Cytotoxicity of the Cur-NPs and Cur-NPs-APgp was determined using MTT assay.

RESULTS

The particle size of Cur-NPs and Cur-NPs-APgp was 127 and 132 nm, respectively. The entrapment efficiency and actual loading of Cur-NPs-APgp (60% and 5 μg Cur/mg NP) were lower than those of Cur-NPs (99% and 7 μg Cur/mg NP). The specific binding of Cur-NPs-APgp to KB-V1 cells was significantly higher than that to KB-3-1 cells. Cellular uptake of Cur-NPs-APgp into KB-V1 cells was higher, as compared to KB-3-1 cells. However, the cellular uptake of Cur-NPs and Cur-NPs-IgG did not differ between the two types of cells. Besides, the cytotoxicity of Cur-NPs-APgp in KB-V1 cells was higher than those of Cur and Cur-NPs.

CONCLUSION

The results demonstrate that Cur-NPs-APgp targeted to P-gp on the cell surface membrane of KB-V1 cells, thus enhancing the cellular uptake and cytotoxicity of Cur.

ABCB1 gene variants influence tolerance to selective serotonin reuptake inhibitors in a large sample of Dutch cases with major depressive disorder

P-glycoprotein (P-gp), an ATP-driven efflux pump in the blood-brain barrier, has a major impact on the delivery of antidepressant drugs in the brain. Genetic variants in the gene ABCB1 encoding for P-gp have inconsistently been associated with adverse effects. In order to resolve these inconsistencies, we conducted a study in a large cohort of patients with major depressive disorder with the aim to unravel the association of ABCB1 variants with adverse effects of antidepressants and in particular with selective serotonin reuptake inhibitors (SSRIs), which display affinity as substrate for P-gp. The Netherlands Study of Depression and Anxiety (NESDA) study was used as a clinical sample. For 424 patients data were available on drug use, side effects. We selected six ABCB1 gene variants (1236T>C, 2677G>T/A, 3435T>C, rs2032583, rs2235040 and rs2235015) and analyzed them for association with adverse drug effects using multinomial regression analysis for both single variants and haplotypes. We found a significant association between the number of SSRI-related adverse drug effects and rs2032583 (P=0.001), rs2235040 (P=0.002) and a haplotype (P=0.002). Moreover, serotonergic effects (sleeplessness, gastrointestinal complaints and sexual effects) were significantly predicted by these variants and haplotype (P=0.002/0.003). We conclude that adverse drug effects with SSRI treatment, in particular serotonergic effects, are predicted by two common polymorphisms of the ABCB1 gene.

Pharmacokinetic considerations in Roux-en-Y gastric bypass patients

PURPOSE

Pharmacokinetic considerations in patients who have undergone Roux-en-Y gastric bypass (RYGB) are explored.

SUMMARY

The prevalence of obesity, especially morbid obesity, has dramatically increased in recent years. In response, the number of bariatric surgeries performed has risen sharply, as this surgery is the technique demonstrated as being the most effective for sustained treatment of morbid obesity. RYGB, the most popular technique in the United States, combines the principle of restriction (dramatically decreasing stomach size) with malabsorption (bypassing the entire duodenum). It stands to reason that a decrease in gastric and intestinal absorptive surface area may considerably affect oral bioavailability of some drugs. Drugs that require a more acidic environment for absorption, uncoating, or activation and drugs that rely on intestinal transporters located in the duodenum for proper absorption would be most affected. Practitioners looking for guidance in tailoring pharmacotherapy to the RYGB patient will find little help in the primary literature at this time. Until more pharmacokinetic studies are available, practitioners may apply and log P of individual the principles of pK(a) drugs in the attempt to predict the potential impact of the RYGB on a drug's absorption. Likewise, if a drug relies on certain transporters located with highest frequency in the duodenum, alternative therapies can be selected that do not rely on such transport mechanisms for absorption.

CONCLUSION

The pK(a), log P, and intestinal transport mechanisms should be considered when determining which drugs may have altered pharmacokinetics in patients who have undergone RYGB.