Evaluation of drug interactions is an essential step in the new drug development process.Regulatory agencies, including U.S. Food and Drug Administrations and European Medicines Agency, have been published documents containing guidelines to evaluate potential drug interactions. Here, we have streamlined in vitro experiments to assess metabolizing enzymemediated drug interactions and provided an overview of the overall process to evaluate potential clinical drug interactions using v data. An experimental approach is presented when an investigational drug (ID) is either a victim or a perpetrator, respectively, and the general procedure to obtain in vitro drug interaction parameters is also described. With the in vitro inhibitory and/or inductive parameters of the ID, basic, static, and/or dynamic models were used to evaluate potential clinical drug interactions. In addition to basic and static models which assume the most conservative conditions, such as the concentration of perpetrators as C max , dynamic models including physiologically-based pharmacokinetic models take into account changes in in vivo concentrations and metabolizing enzyme levels over time.

Objective: Botulinum toxin was used to treat patients with difficulty in relaxation of the upper esophageal sphincter (UES), but the treatment did not always yield good results. We, therefore, attempted to investigate if there was any other factor affecting the outcome and hypothesized that this could be caused due to pharyngeal constriction. Methods: We conducted a retrospective study on a botulinum toxin injection treatment given to eleven patients with nasal backflow and pharyngeal stasis in the course of a videofluoroscopic swallowing study from August 2006 to December 2012. After the injection, the cases showing an esophageal passage of diluted barium regardless of aspiration were defined as “good”, and the cases showing no passage were defined as “bad”. Pharyngeal strength was measured using the pharyngeal constriction ratio (PCR), which was compared between the two groups using the Mann-Whitney U test for proving the hypothesis. Results: Five of the eleven patients showed esophageal passage after the injection treatment and were assigned to the “good” group. The remaining 6 were assigned to the “bad” group. When comparing the average PCR of each group, the ‘good’ group’s ratio was at 0.09±0.03 and the ‘bad’ group was at 0.29±0.16, showing a statistically significant difference (P＜0.05). Conclusion The strength of pharyngeal constriction could be considered to be an important factor influencing the outcome after botulinum toxin treatment for the difficulty in relaxation of the UES.

Background/Aims: Besifovir dipivoxil maleate (BSV), an acyclic nucleotide phosphonate, shows potent antiviral activity against hepatitis B virus. Our previous 48-week trial revealed that BSV has comparable antiviral efficacy to tenofovir disoproxil fumarate (TDF) and better safety profiles in terms of improved renal and bone safety. This extension study evaluated the prolonged efficacy and safety of BSV in treatment-naive chronic hepatitis B patients. Methods: Patients continued to participate in an open-label BSV study after an initial 48-week double-blind comparison of BSV and TDF treatment. The antiviral efficacy and drug safety was evaluated up to 192 weeks in two groups: patients continuing BSV treatment (BSV-BSV) and patients switching from TDF to BSV after 48 weeks (TDF-BSV). Results: Among 197 patients receiving randomized treatments, 170 (86%) entered the open-label phase and 152 (77%) entered the 192-week extension study. Virological response rates over 192 weeks were 92.50% and 93.06% in the BSV-BSV and TDF-BSV groups, respectively (P=0.90). Hepatitis B envelop antigen seroconversion and alanine aminotransferase normalization rates were similar between the groups (P=0.75 and P=0.36, respectively). There were no drug-resistant mutations to BSV. Bone mineral density and renal function were well preserved in the BSV-BSV group, whereas these initially worsened then recovered after switching therapy in the TDF-BSV group. Conclusions BSV maintained potent antiviral efficacy after 192 weeks and showed no evidence of drug resistance. BSV was safe, well tolerated, and effective in patients who switched from TDF to BSV. Trial Registration Number: NCT01937806 (date: 10 Sep 2013).

Background/Aims: Besifovir dipivoxil maleate (BSV), an acyclic nucleotide phosphonate, shows potent antiviral activity against hepatitis B virus. Our previous 48-week trial revealed that BSV has comparable antiviral efficacy to tenofovir disoproxil fumarate (TDF) and better safety profiles in terms of improved renal and bone safety. This extension study evaluated the prolonged efficacy and safety of BSV in treatment-naive chronic hepatitis B patients. Methods: Patients continued to participate in an open-label BSV study after an initial 48-week double-blind comparison of BSV and TDF treatment. The antiviral efficacy and drug safety was evaluated up to 192 weeks in two groups: patients continuing BSV treatment (BSV-BSV) and patients switching from TDF to BSV after 48 weeks (TDF-BSV). Results: Among 197 patients receiving randomized treatments, 170 (86%) entered the open-label phase and 152 (77%) entered the 192-week extension study. Virological response rates over 192 weeks were 92.50% and 93.06% in the BSV-BSV and TDF-BSV groups, respectively (P=0.90). Hepatitis B envelop antigen seroconversion and alanine aminotransferase normalization rates were similar between the groups (P=0.75 and P=0.36, respectively). There were no drug-resistant mutations to BSV. Bone mineral density and renal function were well preserved in the BSV-BSV group, whereas these initially worsened then recovered after switching therapy in the TDF-BSV group. Conclusions BSV maintained potent antiviral efficacy after 192 weeks and showed no evidence of drug resistance. BSV was safe, well tolerated, and effective in patients who switched from TDF to BSV. Trial Registration Number: NCT01937806 (date: 10 Sep 2013).

We have streamlined known in vitro methods used to predict the clearance (CL) of small molecules in humans in this tutorial. There have been many publications on in vitro methods that are used at different steps of human CL prediction. The steps from initial intrinsic CL measurement in vitro to the final application of the well-stirred model to obtain predicted hepatic CL (CLH ) are somewhat complicated. Except for the experts on drug metabolism and PBPK, many drug development scientists found it hard to figure out the entire picture of human CL prediction. To help readers overcome this barrier, we introduce each method briefly and demonstrate its usage in the chain of related equations destined to the CLH . Despite efforts in the laboratory steps, huge in vitro (predicted CLH )-in vivo (observed CLH ) discrepancy is not rare. A simple remedy to this discrepancy is to correct human predicted CLH using the ratio of in vitro-in vivo CLH obtained from animal species.

This tutorial introduces background and methods to predict the human volume of distribution (Vd ) of drugs using in vitro and animal pharmacokinetic (PK) parameters. The physiologically based PK (PBPK) method is based on the familiar equation: Vd = Vp + ∑T (VT × ktp ). In this equation, Vp (plasma volume) and VT (tissue volume) are known physiological values, and ktp (tissue plasma partition coefficient) is experimentally measured. Here, the ktp may be predicted by PBPK models because it is known to be correlated with the physicochemical property of drugs and tissue composition (fraction of lipid and water). Thus, PBPK models' evolution to predict human Vd has been the efforts to find a better function giving a more accurate ktp . When animal PK parameters estimated using i.v. PK data in ≥ 3 species are available, allometric methods can also be used to predict human Vd . Unlike the PBPK method, many different models may be compared to find the best-fitting one in the allometry, a kind of empirical approach. Also, compartmental Vd parameters (e.g., Vc , Vp , and Q) can be predicted in the allometry. Although PBPK and allometric methods have long been used to predict Vd, there is no consensus on method choice. When the discrepancy between PBPK-predicted Vd and allometry-predicted Vd is huge, physiological plausibility of all input and output data (e.g., r2 -value of the allometric curve) may be reviewed for careful decision making.

Predicting the rate and extent of oral absorption of drugs in humans has been a challenging task for new drug researchers. This tutorial reviews in vivo and PBPK methods reported in the past decades that are widely applied to predicting oral absorption in humans. The physicochemical property and permeability (typically obtained using Caco-2 system) data is the first necessity to predict the extent of absorption from the gut lumen to the intestinal epithelium (Fa). Intrinsic clearance measured using the human microsome or hepatocytes is also needed to predict the gut (Fg) and hepatic (Fh ) bioavailability. However, there are many issues with the correction of the inter-laboratory variability, hepatic cell membrane permeability, CYP3A4 dependency, etc. The bioavailability is finally calculated as F = F h × Fg × Fh . Although the rate of absorption differs by micro-environments and locations in the intestine, it may be simply represented by ka . The ka , the first-order absorption rate constant, is predicted from in vitro and in vivo data. However, human PK-predicting software based on these PBPK theories should be carefully used because there are many assumptions and variances. They include differences in laboratory methods, inter-laboratory variances, and theories behind the methods. Thus, the user's knowledge and experiences in PBPK and in vitro methods are necessary for proper human PK prediction.

This tutorial introduces background and methods to predict the human volume of distribution (Vd ) of drugs using in vitro and animal pharmacokinetic (PK) parameters. The physiologically based PK (PBPK) method is based on the familiar equation: Vd = Vp + ∑T (VT × ktp ). In this equation, Vp (plasma volume) and VT (tissue volume) are known physiological values, and ktp (tissue plasma partition coefficient) is experimentally measured. Here, the ktp may be predicted by PBPK models because it is known to be correlated with the physicochemical property of drugs and tissue composition (fraction of lipid and water). Thus, PBPK models' evolution to predict human Vd has been the efforts to find a better function giving a more accurate ktp . When animal PK parameters estimated using i.v. PK data in ≥ 3 species are available, allometric methods can also be used to predict human Vd . Unlike the PBPK method, many different models may be compared to find the best-fitting one in the allometry, a kind of empirical approach. Also, compartmental Vd parameters (e.g., Vc , Vp , and Q) can be predicted in the allometry. Although PBPK and allometric methods have long been used to predict Vd, there is no consensus on method choice. When the discrepancy between PBPK-predicted Vd and allometry-predicted Vd is huge, physiological plausibility of all input and output data (e.g., r2 -value of the allometric curve) may be reviewed for careful decision making.

Predicting the rate and extent of oral absorption of drugs in humans has been a challenging task for new drug researchers. This tutorial reviews in vivo and PBPK methods reported in the past decades that are widely applied to predicting oral absorption in humans. The physicochemical property and permeability (typically obtained using Caco-2 system) data is the first necessity to predict the extent of absorption from the gut lumen to the intestinal epithelium (Fa). Intrinsic clearance measured using the human microsome or hepatocytes is also needed to predict the gut (Fg) and hepatic (Fh ) bioavailability. However, there are many issues with the correction of the inter-laboratory variability, hepatic cell membrane permeability, CYP3A4 dependency, etc. The bioavailability is finally calculated as F = F h × Fg × Fh . Although the rate of absorption differs by micro-environments and locations in the intestine, it may be simply represented by ka . The ka , the first-order absorption rate constant, is predicted from in vitro and in vivo data. However, human PK-predicting software based on these PBPK theories should be carefully used because there are many assumptions and variances. They include differences in laboratory methods, inter-laboratory variances, and theories behind the methods. Thus, the user's knowledge and experiences in PBPK and in vitro methods are necessary for proper human PK prediction.

Background/Aims: This study examined the risk factors associated with mortality in cirrhotic patients hospitalized with variceal bleeding, and evaluated the effects of acute-on-chronic liver failure (ACLF) on the prognosis of these patients. Methods: This study was retrospectively conducted on patients registered in the Korean acute-on-chronic liver failure study cohort, and on 474 consecutive cirrhotic patients hospitalized with variceal bleeding from January 2013 to December 2013 at 21 university hospitals. ACLF was defined as described by the European Association for the Study of Liver-Chronic Liver Failure Consortium. Results: Among a total of 474 patients, 61 patients were diagnosed with ACLF. The cumulative overall survival (OS) rate was lower in the patients with ACLF than in those without (P<0.001), and patients with higher ACLF grades had a lower OS rate (P<0.001). The chronic liver failure-sequential organ failure assessment (CLIF-SOFA) score was identified as a significant prognostic factor in patients hospitalized with variceal bleeding (hazard ratio [HR], 1.40; 95% confidence interval [CI], 1.30–1.50; P<0.001), even in ACLF patients with variceal bleeding (HR, 1.32; 95% CI, 1.19–1.46, P<0.001). Concerning the prediction of the mortality risk at 28- and 90-day using CLIF-SOFA scores, c-statistics were 0.895 (95% CI, 0.829–0.962) and 0.897 (95% CI, 0.842–0.951), respectively, and the optimal cut-off values were 6.5 and 6.5, respectively. Conclusions In cirrhotic patients hospitalized with variceal bleeding, the prognosis was poor when accompanied by ACLF, especially depending upon CLIF-SOFA score. CLIF-SOFA model well predicted the 28-day or 90-day mortality for cirrhotic patients who experienced variceal bleeding.