Population Pharmacokinetic− Pharmacodynamic Modeling of Carvedilol to Evaluate the Effect of Cytochrome P450 2D6 Genotype on the Heart Rate Reduction

Background@#Carvedilol is a beta-adrenergic receptor antagonist primarily metabolized by cytochromes P450 (CYP) 2D6. This study established a carvedilol population pharmacokinetic (PK)–pharmacodynamic (PD) model to describe the effects of CYP2D6 genetic polymorphisms on the inter-individual variability of PK and PD. @*Methods@#The PK–PD model was developed from a clinical study conducted on 21 healthy subjects divided into three CYP2D6 phenotype groups, with six subjects in the extensive metabolizer (EM, *1/*1, *1/*2), seven in the intermediate metabolizer-1 (IM-1, *1/*10, *2/*10), and eight in the intermediate metabolizer-2 (IM-2, *10/*10) groups. The PK–PD model was sequentially developed, and the isoproterenol-induced heart rate changes were used to establish the PD model. A direct effect response and inhibitory E max model were used to develop a carvedilol PK–PD model. @*Results@#The carvedilol PK was well described by a two-compartment model with zeroorder absorption, lag time, and first-order elimination. The carvedilol clearance in the CYP2D6*10/*10 group decreased by 32.8% compared with the other groups. The inhibitory concentration of carvedilol estimated from the final PK–PD model was 16.5 ng/mL regardless of the CYP2D6 phenotype. @*Conclusion@#The PK–PD model revealed that the CYP2D6 genetic polymorphisms were contributed to the inter-individual variability of carvedilol PK, but not PD.

Evaluation of Vancomycin TDM Strategies: Prediction and Prevention of Kidney Injuries Based on Vancomycin TDM Results

The current guidelines for therapeutic drug monitoring (TDM) of vancomycin suggest a target 24-hour area under the curve (AUC 0-24 ) of 400 to 600 mg*h/L for serious methicillinresistant Staphylococcus aureus infections. In this study, the predictabilities of acute kidney injury (AKI) of various TDM target parameters, target levels, and sampling methods were evaluated in patients who underwent TDM from January 2020 to December 2020. The AUC 0-24 and trough values were calculated by both one- and two-point sampling methods, and were evaluated for the predictability of AKI. Among the AUC 0-24 cutoff comparisons, the threshold value of 500 mg*h/L in the two sampling methods was statistically significant (P = 0.042) when evaluated for the predictability of AKI. Analysis by an receiver operating characteristic curve estimated an AUC 0-24 cutoff value of 563.45 mg*h/L as a predictor of AKI, and was proposed as the upper limit of TDM target.

A validated simple LC-MS/MS method for quantifying trimethylamine N-oxide (TMAO) using a surrogate matrix and its clinical application

Trimethylamine N-oxide (TMAO) is a small molecular amine oxide generated from dietary choline and carnitine through intestinal microbial metabolism. Recently, TMAO has attracted much public attention as its role in disease progression has been proven in many clinical studies. The plasma concentration of TMAO in humans was found to be positively associated with the increased risk of many diseases including cardiovascular diseases and chronic kidney diseases. To achieve accurate and sensitive quantitation of TMAO for clinical applications, we established and validated a simple quantitative method using a liquid chromatography tandem mass spectrometry (LC-MS/MS) system. We constructed an eight-point calibration curve in an artificial surrogate matrix instead of the commonly used biological matrices to avoid interference from the endogenous TMAO. The calibration curve showed excellent linearity in the range of 1 to 5,000 ng/mL, with a correlation coefficient (R2 ) higher than 0.996 in each validation batch. Moreover, both the intra-day and inter-day assays achieved satisfactory precision and accuracy results ranging from 1.65–7.15% and 96.36–111.43%, respectively. Further, this method was cross-validated using a human plasma matrix and applied to a clinical pharmacology study. Overall, these results demonstrate that the developed quantitation method is applicable in clinical research for monitoring disease progression and evaluating drug effects.

Development and validation of a method for the simultaneous quantification of endogenous steroids metabolized by CYP3A

Cytochrome P450 (CYP) 3A enzymes, the most important phase 1 drug-metabolizing enzymes, are responsible for 50% of the metabolism of clinically used drugs. CYP3A activity varies widely among individuals, which can affect the probability of adverse drug reactions and drug-drug interactions mediated by the induction or inhibition of the enzyme. Hence, it is important to be able to predict CYP3A activity in individuals to reduce the incidence of unexpected drug responses. To specifically and quickly measure CYP3A activity, we developed method based on gas chromatography interfaced with triple-quadrupole mass spectrometry for the quantification of cortisol, cortisone, 6β-hydroxycortisol, and 6β-hydroxycortisone simultaneously in urine and 4β-hydroxycholesterol in plasma. The results were calculated based on charcoal-stripped steroid-free urine and plasma control samples. The accuracy and precision were 93.18% to 110.0% and 1.96% to 5.34%, respectively. This method was then applied to measure endogenous steroids from urine and plasma samples of healthy Korean males and females. The calibration curves of all analytes showed good linearity with a correlation coefficient (r2) that ranged from 0.9953 to 0.9999. Therefore, this validated method can be used to measure endogenous biomarkers to predict CYP3A activity and might be applicable in the prediction of CYP3A-mediated drug interactions of new drug candidates.

Digital therapeutics and clinical pharmacology

Digital therapeutics (DTx) is a new subsection of digital health that is primarily driven by software and will be of great interest to clinical pharmacologists. In this article, an overview of DTx, including definition, position in the landscape of therapeutics, product categories, benefits, and challenges, is provided. Discussions from the point of view of clinical pharmacology are presented, as DTx should have exposure-response relationships. The principles of clinical pharmacology can be applied to DTx as they are comparable to pharmacotherapy. Clinical pharmacology has great potential in the development, application, and regulation of DTx.

Development of a physiologically-based pharmacokinetic model for cyclosporine in Asian children with renal impairment

This study aimed to assess the pharmacokinetics of cyclosporine A (CsA) in Asian children with renal impairment (RI) by developing a physiologically-based pharmacokinetic (PBPK) model with Simcyp Simulator. The PBPK model of Asian children with RI was developed by modifying the physiological parameters of the built-in population libraries in Simcyp Simulator. The ratio of healthy and RI populations was obtained for each parameter showing a difference between the populations. Each ratio was multiplied by the corresponding parameter in healthy Asian children. The model verification was performed with published data of Korean children with kidney disease given multiple CsA administrations. Simulations were performed with different combinations of ethnicity, age, and renal function to identify the net impact of each factor. The simulated results suggested that the effect of RI was higher in children than adults for both Caucasian and Asian. In conclusion, the constructed model adequately characterized CsA pharmacokinetics in Korean children with RI. Simulations with populations categorized by ethnicity, age, and renal function enabled to assess the net impact of each factor on specific populations.

Effect of plasma membrane monoamine transporter genetic variants on pharmacokinetics of metformin in humans

Metformin, an oral hypoglycemic agent belonging to biguanide class, is widely used to treat type 2 diabetes mellitus, and several drug transporters such as organic cation transporters (OCTs), multidrug and toxin extrusion transporter (MATE), and plasma membrane monoamine transporter (PMAT) are thought to affect its disposition. We evaluated the role of PMAT genetic variations on the pharmacokinetic characteristics of metformin in a Korean population. In this retrospective study, 91 healthy subjects from four different metformin pharmacokinetic studies were analyzed; in each study, the subjects were administered two oral doses of metformin at intervals of 12 hours and dose-normalized pharmacokinetic parameters were compared between the subjects' genotypes. Subjects who had more than one allele of c.883-144A>G single nucleotide polymorphism (SNP) in PMAT gene (rs3889348) showed increased renal clearance of metformin compared to wild-type subjects (814.79 ± 391.73 vs. 619.90 ± 195.43 mL/min, p=0.003), whereas no differences in metformin exposure were observed between the PMAT variant subjects and wild-type subjects. Similarly, subjects with variant rs316019 SNP in OCT2 showed decreased renal clearance of metformin compared to wild-type subjects (586.01 ± 160.54 vs. 699.13 ± 291.40 mL/min, p=0.048). Other SNPs in PMAT and MATE1/2-K genes did not significantly affect metformin pharmacokinetics. In conclusion, the genetic variation of c.883-144A>G SNP in PMAT significantly affects the renal clearance of metformin in healthy Korean male subjects.

A post hoc analysis of intra-subject coefficients of variation in pharmacokinetic measures to calculate optimal sample sizes for bioequivalence studies

Because bioequivalence studies are performed using a crossover design, information on the intra-subject coefficient of variation (intra-CV) for pharmacokinetic measures is needed when determining the sample size. However, calculated intra-CVs based on bioequivalence results of identical generic drugs produce different estimates. In this study, we collected bioequivalence results using public resources from the Ministry of Food and Drug Safety (MFDS) and calculated the intra-CVs of various generics. For the generics with multiple bioequivalence results, pooled intra-CVs were calculated. The estimated intra-CVs of 142 bioequivalence studies were 14.7±8.2% for AUC and 21.7±8.8% for Cmax. Intra-CVs of Cmax were larger than those of area under the concentration-time curve (AUC) in 129 studies (90.8%). For the 26 generics with multiple bioequivalence results, the coefficients of variation of intra-CVs between identical generics (mean±sd (min ~ max)) were 38.0±24.4% (1.9 ~ 105.3%) for AUC and 27.9±18.2% (4.0 ~ 70.1%) for Cmax. These results suggest that substantial variation exists among the bioequivalence results of identical generics. In this study, we presented the intra-CVs of various generics with their pooled intra-CVs. The estimated intra-CVs calculated in this study will provide useful information for planning future bioequivalence studies. (This is republication of the article 'Transl Clin Pharmacol 2017;25:179-182' retracted from critical typographic errors. See the 'Retraction and Republication section of this issue for further information)

Retraction and Republication: A post hoc analysis of intra-subject coefficients of variation in pharmacokinetic measures to calculate optimal sample sizes for bioequivalence studies

The retraction has been agreed upon due to critical typographical errors throughout the contents from accidents at the manuscript editing step.

A post hoc analysis of intra-subject coefficients of variation in pharmacokinetic measures to calculate optimal sample sizes for bioequivalence studies

Because bioequivalence studies are performed using a crossover design, information on the intra-subject coefficient of variation (intra-CV) for pharmacokinetic measures is needed when determining the sample size. However, calculated intra-CVs based on bioequivalence results of identical generic drugs produce different estimates. In this study, we collected bioequivalence results using public resources from the Ministry of Food and Drug Safety (MFDS) and calculated the intra-CVs of various generics. For the generics with multiple bioequivalence results, pooled intra-CVs were calculated. The estimated intra-CVs of 142 bioequivalence studies were 14.7±8.2% for AUC and 21.7±8.8% for C(max). Intra-CVs of C(max) were larger than those of area under the concentration-time curve (AUC) in 129 studies (90.8%). For the 26 generics with multiple bioequivalence results, the coefficients of variation of intra-CVs between identical generics (mean±sd (min ~ max)) were 38.0±24.4% (1.9 ~ 105.3%) for AUC and 27.9±18.2 % (4.0 ~ 70.1%) for C(max). These results suggest that substantial variation exists among the bioequivalence results of identical generics. In this study, we presented the intra-CVs of various generics with their pooled intra-CVs. The estimated intra-CVs calculated in this study will provide useful information for planning future bioequivalence studies.

Evaluation of factors associated with drug-induced liver injury using electronic medical records

The causes and attributing factors of drug-induced liver injury (DILI) remain unclear as a result of exclusion-based diagnosis and low incidence. The aim of this study was to explore and evaluate potential drug-related causes and factors associated with DILI. Using electronic medical records (EMR) from the Seoul National University Bundang Hospital from 2003 to 2014, patients with DILI events were identified based on liver function test results. All patients with hepatic or biliary diseases were excluded. Patient characteristics, including demographics, clinical patterns, and severity of DILI were summarized and their associations were evaluated. Drugs frequently prescribed to patients exhibiting DILI within the month before their first DILI event compared to the total patient population were identified and the probabilities of hepatotoxicity associated with their use were assessed through examination of available reports. Among the 1,835 patients with laboratory test results, 1,023 were male and 1,053 were 65 years of age or older. Moderate DILI was dominant in older or male patients and cholestatic DILI tended to be more frequently identified in older patients of either sex. Cytarabine was the most frequently prescribed drug in DILI patients, followed by aprotinin and dopamine. Among the 30 most frequently prescribed drugs in DILI patients, 15 (50%) were identified as known hepatotoxic agents. In conclusion, this study evaluated differences in features of DILI among groups based on demographics and explored candidate drugs with possible associations with DILI, which has potential value reflecting real-world clinical practice.

Erratum: Pharmacokinetics and bioequivalence of two different 20 mg olmesartan tablets: A randomized, single-dose, two-period crossover study in healthy Korean male volunteers

In the published version of this article, an error in the sponsor's identity was discovered in the acknowledgment section.

Pharmacokinetics and bioequivalence of two different 20 mg olmesartan tablets: A randomized, single-dose, two-period crossover study in healthy Korean male volunteers

Olmesartan is an angiotensin receptor blocker (ARB) and is widely used in clinical practice to treat hypertension. To compare the pharmacokinetic (PK) parameters and tolerability of two oral formulations of olmesartan (test drug: OMETAN(R) 20 mg tablet, reference drug: OLMETEC(R) 20 mg tablet) and assess their bioequivalence, a randomized, single dose, two-treatment crossover clinical study was conducted. At each period, 40 subjects received the test drug or the reference drug. Blood samples were collected at pre-dose and up to 48 h after study drug administration of each period. Plasma concentrations of olmesartan were measured using liquid chromatography-tandem mass spectrometry. To evaluate PK profiles, maximum plasma concentration (C(max)) and area under the concentration-time curve from zero to last measurable time (AUC(last)) were estimated using a non-compartmental method. Tolerability was evaluated based on the incidence of adverse events, vital signs, electrocardiograms, and laboratory tests. A total of 39 subjects completed the study. The geometric mean ratio and 90% confidence intervals (CI) of test drug to reference drug were 1.027 (0.969-1.088) for C(max) and 1.014 (0.957-1.074) for AUC(last), respectively. There were no serious adverse events and both formulations of olmesartan were well tolerated. The OMETAN 20 mg tablet was judged to be bioequivalent to the OLMETEC 20 mg tablet.

Geriatric clinical pharmacology and clinical trials in the elderly

The aging process is linked to changes in the physiological function of organs and changes in body composition that alter the pharmacokinetics of drugs and pharmacodynamic responses. Comorbidity and polypharmacy in the elderly decreases tolerability of drugs, leading to greater vulnerability to adverse drug reactions than that observed in younger adults. In geriatric pharmacotherapy, the general recommendation is dose reduction and slow titration, which is based on pharmacokinetic considerations and concern for adverse drug reactions, rather than clinical trial data. Older patients are under-represented in clinical trials. In the absence of evidence, extrapolation of risk-benefit ratios from younger adults to geriatric populations is not necessarily valid. Sound evidence through prospective clinical trials is essential, and geriatric societies, governments, and patient advocacy groups should collaborate to promote the inclusion of older people in clinical trials. It is believed that all involved in clinical trials have both an obligation and an opportunity to eliminate age discrimination in clinical trial practice.

Current State and Future Improvement of the Elderly Participation in Clinical Trials

BACKGROUND: Clinical trials are widely used to approve the efficacy and discover adverse reactions of new drugs. However, there has been much concern about the unjustified exclusion of the older adults in clinical trials. The purpose of this study was to assess ageism in clinical trials and to find solution to any discovered discrimination. METHODS: An online questionnaire was completed by 1,650 experts including doctors, pharmaceutical staff, and contract research organization members. An offline inquiry was conducted by 250 experienced professors from a single tertiary hospital and other allied professions. The questions covered the current state of elderly participation, possible reasons for under-representation, and plans for its solution. RESULTS: Among 1,900 subjects, 246 (12.9%) individuals completed the survey. We excluded the six subjects who did not answer more than 10 questions, and analyzed the remaining 240 respondents. They agreed that there are tendencies to exclude the aged from clinical trials (69.2%), and that under-representation would cause difficulties for doctors and geriatric patients. Most people (84.6%) thought that treating older adults with the results from trials which exclude aged participants is inappropriate. Because respondents had difficulties explaining the trial process and obtaining informed consent, they thought establishing a geriatric clinical trial team would be highly effective. Experts also believed that financial inducements and legal regulations are required to increase elderly enrollment. CONCLUSION: Because the elderly have a unique physiology, the participation of older adults in clinical research is indispensable for verifying efficacy and determining potential adverse reactions. Consequently, clinical research professionals should be concerned about the participation of older subjects, and the authorities must begin to care about age discrimination in research fields.

Pregnane X Receptor agonist Increases the Expression Levels of the Plasma Membrane Monoamine Transporter

We evaluated the effect of the pregnane X receptor agonist, pregnenolone 16 alpha-carbonitrile (PCN) on the expression levels of plasma monoamine transporter (PMAT) in the intestine. Male C57/BL6 mice were divided into two 2 groups: mice in the PCN group (n=3) were administered PCN once a day for 4 days, while those in the control group (n=3) received the same volume of vehicle once a day for 4 days. After the mice were killed 24 h after administration of the last dose of PCN or vehicle, and the expression levels of PMAT in the intestine tissues were isolated and measured the expression level of PMAT using immunohistochemical and western blotting analyses. The expression level of PMAT expression levels in the small intestine increased after PCN treatment. These results suggest that the induction of PMAT may play a clinically significant role by increasing intestinal absorption of PMAT substrates such as metformin.

A Randomized, Open Label, 2-Way Crossover Study to Assess the Pharmacokinetic Characteristics and Skin Irritation of Murupe(R) Patch Compared with Trast(R) Patch in Healthy Volunteers

BACKGROUND: A piroxicam patch has been widely used to treat musculoskeletal pain. The aim of this study was to assess the pharmacokinetic (PK) characteristics and skin irritation of Murupe(R) patch (piroxicam 96 mg) compared with Trast(R) patch (piroxicam 96 mg) in healthy volunteers. METHODS: A randomized, open-label, 2-way crossover study was conducted in 12 healthy Korean male subjects. They were allocated to one of the two treatment sequences of RT and TR (R, reference drug, Trast(R) patch; T, test drug, Murupe(R) patch). Each patch was applied to the subject once during 48 hours. Serial blood samples were collected up to 72 hours after removing the patch and plasma concentrations were determined by high performance liquid chromatography. Safety was monitored and the skin irritation potential was assessed. RESULTS: The plasma concentration-time profile during 48 hours showed an exponential increase in both of two patch products. Mean C(max) and AUC(last) values were not statistically different between two patch groups. Mean AUC[0-48h] was lower in Murupe(R) patch group than that in Trast(R) patch group; 806.4 and 1196.5 ng.h/mL. However, the mean AUC[48-120h] value tended to be higher in Murupe(R) patch group, implying more delayed excretion than in Trast(R) patch group; 2724.7 ng.h/mL and 1989.2 ng.h/mL. The overall results of skin irritation potential test showed no clinically significant differences between two patch groups. CONCLUSION: Mean Cmax and AUC(last) values in Murupe(R) patch group were comparable to those in Trast(R) patch group. Murupe(R) patch was safe and well tolerated in healthy male subjects.

A Randomized, Placebo Controlled, Double Blind, Parallel Group, Multiple Dosing, Dose Escalation Clinical Study to Evaluate Pharmacokinetics/Pharmacodynamics and Tolerability of Zofenopril in Healthy Korean Subjects

BACKGROUND: Zofenopril is a new Angiotensin Converting Enzyme (ACE) inhibitor for the treatment of the patients with hypertension and congestive heart failure. This study aimed to evaluate the pharmacokinetics (PKs)/pharmacodynamics (PDs) and tolerability of zofenopril in healthy Korean subjects. METHODS: A randomized, double blind, placebo-controlled, multiple dosing parallel group study with two dosage groups (zofenopril 30 mg or 60 mg) was conducted in healthy Korean male subjects. Each dosage group consisted of 10 subjects and they were randomly assigned to receive zofenopril or placebo with a ratio of 4:1. PK characteristics of zofenopril and its active metabolite, zofenoprilat, were evaluated after single or multiple dosing. Serum ACE activities and blood pressures were measured for PD evaluation. Adverse events, clinical laboratory tests, electrocardiograms, vital signs and physical examinations were performed for tolerability evaluation. RESULTS: The PK characteristics of zofenopril and zofenoprilat after single dose and multiple doses were similar to one another. The metabolic ratio of zofenoprilat to zofenopril after single dose and multiple doses were 12.4 and 14.9, respectively, in the 30 mg dosage group, and were 6.8 and 6.6, respectively, in the 60 mg dosage group. Complete serum ACE activity inhibition was observed within 1 hour in both doses but it was maintained longer in the 60 mg dosage group compared to the 30 mg dosage group. There were no clinically significant abnormalities in tolerability evaluations. CONCLUSION: The PK/PD characteristics of zofenopril and zofenoprilat after single or multiple administrations were explored. Zofenopril was well tolerated after multiple administrations in healthy Korean subjects.

A Placebo-Controlled, Single and Multiple Dose Study to Investigate the Appropriate Parameters for Evaluation of Pharmacodynamic Equivalence of Voglibose in Healthy Korean Volunteers

BACKGROUND: Voglibose is an alpha-glucosidase inhibitor. The purpose of this study was to evaluate the pharmacodynamic characteristics of voglibose for determining the appropriate study design and parameters for a pharmacodynamic equivalence study of voglibose. METHODS: This study consisted of two studies. The single dose study had an open and single sequence design. Nineteen subjects received placebo and then one tablet of voglibose on two consecutive days with sucrose. The multiple dose study was performed with the similar design, except that it was a multiple dose of the single dose study. Nine subjects who showed an effective response in the single dose study received placebo three times and then voglibose 4 times on two consecutive days. Serial blood samples for pharmacodynamic parameters were taken until 180 mins after each administration. The baseline adjusted maximum serum glucose level (G(max)) and area under the serum glucose level-time profiles were determined and compared. RESULTS: In the single dose study, the difference in G(max) was -10.6 +/- 28.7 mg/dL. The area under the serum glucose concentration-time curve (AUGC(0-1h)) of placebo and voglibose were 7825.0 +/- 1145.3 mg.min/dL, 7907.5 +/- 917.2 mg.min/dL, respectively. In the multiple dose study, the difference in G(max) was 46.6 +/- 16.1 mg/dL. The AUGC(0-1h) of placebo and voglibose were 8138.6 +/- 721.9 mg.min/dL and 6499.7 +/- 447.2 mg.min/dL, respectively. The G(max) and AUGC(0-1h) of the multiple dose study was significantly different between placebo and voglibose in paired t-test. CONCLUSION: The differences in G(max) and AUGC(0-1h) are suitable for pharmacodynamic parameters to evaluate bioequivalence of voglibose.

Percutaneous Nephrolithotomy: Comparison of the Efficacies and Feasibilities of Regional and General Anesthesia

PURPOSE: To compare surgical outcomes and complications after percutaneous nephrolithotomy (PCNL) under regional or general anesthesia. MATERIALS AND METHODS: One hundred and one patients who underwent PCNL as a first-line treatment for kidney calculi between June 2004 and June 2013 were enrolled in this retrospective study. Patients were classified into two groups by anesthetic method: 77 were allocated to the regional anesthesia group and 24 to the general anesthesia group. Patient general characteristics, stone features, surgical outcomes, and complications were compared between the two groups. RESULTS: The two groups were similar in terms of mean age and stone size, number, and type. Furthermore, they did not differ significantly in terms of general characteristics, treatment outcomes, or complications excluding postoperative fever. However, mean hospital stay was significantly shorter in the regional anesthesia group than in the general anesthesia group (8.9+/-3.2 days vs. 11.5+/-6.9 days, respectively, p=0.025). Also, the postoperative fever rate was significantly higher in the general anesthesia group (53.2% vs. 83.3%, respectively, p=0.007). CONCLUSIONS: Regional anesthesia is as effective as general anesthesia during percutaneous nephrolithotomy and is associated with shorter hospital stays and lower rates of postoperative fever.