Current Drug Metabolism - Volume 21, Issue 2, 2020

Background: Overactive bladder syndrome is a broadly occurring urological disorder with a distressing impact on the quality of life. The commonly used antimuscarinic drugs show poor patient compliance because of unsatisfactory potency, tolerability and high occurrence of adverse effects such as dry mouth, blurred vision, constipation, dizziness etc. Mirabegron is the first approved β3-adrenoreceptor agonist, used as mono or in combination therapies for overactive bladder syndrome. Objective: The present review provides an insight into the mechanism, pharmacokinetics, toxicokinetics, clinical trials and the development of various conventional and modified-release dosage forms of mirabegron for the treatment of overactive bladder syndrome. Results: The clinical trials of phase II and phase III of mirabegron demonstrated symptomatic relief from the overactive bladder without disturbing the micturition cycle. To date, mirabegron showed promising results for safety, tolerability and efficacy in patients with overactive bladder syndrome. The modified-release tablet dosage form of mirabegron appear to be a proficient and suitable replacement for antimuscarinics and revealed the tremendous potential to overcome the adverse effects of conventional antimuscarinic drugs like Oxybutyline chloride ER, Detrol LA, VESIcare, etc. Conclusion: Mirabegron shows a distinct mode of action, i.e., targeting β3-adrenoreceptors and improving bladder storage without altering void contractions. The limited side effects, high safety, efficacy and tolerability of mirabegron present an adequate substitute to antimuscarinics. However, long-term analysis and clinical studies are prerequisites for assessing the safety, tolerability and efficacy profile of mirabegron.

Background: Nobel laureate Sir James Black’s molecule, propranolol, still has broad potential in cardiovascular diseases, infantile haemangiomas and anxiety. A comprehensive and systematic review of the literature for the summarization of pharmacokinetic parameters would be effective to explore the new safe uses of propranolol in different scenarios, without exposing humans and using virtual-human modeling approaches. Objective: This review encompasses physicochemical properties, pharmacokinetics and drug-drug interaction data of propranolol collected from various studies. Methods: Clinical pharmacokinetic studies on propranolol were screened using Medline and Google Scholar databases. Eighty-three clinical trials, in which pharmacokinetic profiles and plasma time concentration were available after oral or IV administration, were included in the review. Results: The study depicts that propranolol is well absorbed after oral administration. It has dose-dependent bioavailability, and a 2-fold increase in dose results in a 2.5-fold increase in the area under the curve, a 1.3-fold increase in the time to reach maximum plasma concentration and finally, 2.2 and 1.8-fold increase in maximum plasma concentration in both immediate and long-acting formulations, respectively. Propranolol is a substrate of CYP2D6, CYP1A2 and CYP2C19, retaining potential pharmacokinetic interactions with co-administered drugs. Age, gender, race and ethnicity do not alter its pharmacokinetics. However, in renal and hepatic impairment, it needs a dose adjustment. Conclusion: Physiochemical and pooled pharmacokinetic parameters of propranolol are beneficial to establish physiologically based pharmacokinetic modeling among the diseased population.

Background: Dabigatran etexilate (DE) was approved by the FDA in 2010 to reduce the risk of stroke and systemic embolism in adults with Non-valvular Atrial Fibrillation (NVAF). Compared with warfarin, a traditional anticoagulant drug, DE exhibits a shorter half-life, improved dose-effect relationship, fewer food and drug interactions, and can be taken orally without monitoring the conventional coagulation index. DE can also prevent or reduce the severity of adverse events, such as attenuated drug efficacy or bleeding. It is convenient for patients to take DE due to low levels of individual variation. This review aims to application of Dabigatran etexilate in specific populations. Methods: Fifty-five papers were included in the review. Results: We review the pharmacological mechanisms, pharmacokinetics and drug interactions, as well as the application of DE for different clinical populations, and provide clinical guidelines. Conclusion: When using DE, one should consider the risk of bleeding, age, renal function, drug interactions, and other factors.

Background: Bioequivalence studies are a vital part of drug development. The average bioequivalence approach is the standard method of assessment to conclude whether the generic product is bioequivalent to the innovator product. Of late, debates are on whether the average bioequivalence approach adequately addresses drug interchangeability as it considers only population mean for the evaluation especially when highly variable drug products and narrow therapeutic index drugs are dealt with. Hence, the alternative approaches like population bioequivalence and individual bioequivalence assessment approaches emerge as they consider inter/intra-subject variance and subject- by-formulation variance along with population mean. Objectives: The objective of the study was to apply different bioequivalence assessment approaches in a replicate bioequivalence study to evaluate the drug interchangeability. Methods: This was an open-label, single-dose, randomized, balanced, two-treatment, three-period, three-sequence, partial replicate crossover bioequivalence study of omeprazole enteric-coated tablet 20 mg conducted on 48 normal healthy subjects under fed conditions. The plasma concentration of omeprazole was analyzed by a validated bioanalytical method to determine the pharmacokinetic and statistical parameters to assess average bioequivalence, population bioequivalence, and individual bioequivalence. Results: In this study, test formulation was shown to be bio-inequivalent to the reference formulation by average bioequivalence, population bioequivalence, and individual bioequivalence approaches. Conclusion: The outcome of the evaluation clearly states that the bioequivalence outcome of all these approaches are the same. Obviously, it does not mean that these three approaches provide the same outcome though the consideration of variances varies. Certainly, population bioequivalence and individual bioequivalence approach will be more accurate for the assessment of drug interchangeability.

Background: Clobazam (CLBZ) metabolized primarily by Cytochrome P-450 isoenzyme CYP3A4 than with CYP2C19, Whereas Levetiracetam (LEV) is metabolized by hydrolysis of the acetamide group. Few CYP enzymes are inhibited by Proton Pump Inhibitors (PPIs) Pantoprazole, Esomeprazole, and Rabeprazole in different extents that could affect drug concentrations in blood. The aim of the present study was to evaluate the effect of these PPIs on the plasma concentrations of LEV and CLBZ. Methods: Blood samples from 542 patients were included out of which 343 were male and 199 were female patients and were categorized as control and test. Plasma samples analyzed using an HPLC-UV method. Plasma concentrations were measured and compared to those treated and those not treated with PPIs. One way ANOVA and games Howell post hoc test used by SPSS 20 software. Results: CLBZ concentrations were significantly 10 folds higher in patients treated with Pantoprazole (P=0.000) and 07 folds higher in patients treated with Esmoprazole and Rabeprazole (P=0.00). Whereas plasma concentration of LEV control group has no statistical and significant difference when compared to pantoprazole (P=0.546) and with rabeprazole and esomeprazole was P=0.999. Conclusion: The effect of comedication with PPIs on the plasma concentration of clobazam is more pronounced for pantoprazole to a greater extent when compared to esomeprazole and rabeprazole. When pantoprazole is used in combination with clobazam, dose reduction of clobazam should be considered, or significance of PPIs is seen to avoid adverse effects.

Background: The translation of Pharmacokinetics (PK)/Pharmacodynamics (PD) from preclinical models to the clinic has not been studied in detail for drugs used to treat complicated urinary tract infections (cUTI). Objective: The PK/PD of Ciprofloxacin (CIP), a drug used to treat cUTI, was evaluated in a mouse model of cUTI infected with Escherichia coli, and compared with clinical PK/PD in cUTI patients. Methods: Streptozotocin induced diabetic female BALB/c mice were infected transurethrally with Escherichia coli. Four hours post infection, CIP oral doses of 3, 10, 30,100, and 300 mg/kg, were administered as single doses (for PK and dose response) and repeated doses (PD and PK/PD). Bacterial burden in kidneys, bladder, urine, body temperature, and other clinical signs were assessed twenty-four hours post-treatment. Results: CIP displayed linear PK with dose proportional increase in Cmax and AUCinf in plasma. In PD time course studies, CIP showed rapid onset, intensity and duration of anti-bacterial effect in target tissues. In intrinsic PD studies, CIP showed a maximum effect at plasma AUC/MIC=1705 (300 mg/kg, twice daily) for bacterial load in bladder (r2=0.979), kidney (r2=0.951) and rectal temperature (r2=0.67). A plasma AUC/MIC ratio of 412 was associated with maximum PD effect of Imax=3.7 Log10CFU/bladder and Imax=1.97 Log10CFU/kidney. In dose fractionation studies, plasma AUC/MIC ratio showed highest correlation with efficacy in bladder (r2=0.77) and kidney (r2=0.80) followed by Cmax/MIC ratio in bladder (r2=0.68). Conclusion: Plasma AUC/MIC showed the highest correlation with the efficacy of Ciprofloxacin on E. coli in diabetic mice with cUTI.

Background and Objectives: Inflammatory bowel disease (IBD) is a set of chronic inflammatory gastrointestinal disorders, which include ulcerative colitis (UC) and Crohn’s disease (CD) that affects many patients worldwide with a peak incidence in early adult life. The immunosuppressant drug Azathioprine (AZA) represents one of the most useful drugs in the management of IBD. It is metabolized by many enzymes like AOX1, and XDH enzymes, the variation in the metabolism of AZA may contribute to inter-individual variation in response to this treatment. This study aims to find out if there is an association between certain AOX1 and XDH polymorphisms and AZA response in Jordanian IBD patients. Methods: One hundred IBD patients aged between (17-72) years and taking AZA were enrolled and genotyped for AOX13404G, XDH1936C and XDH2107C polymorphisms using DNA Sequencing (Sanger) method. Results and Conclusion: This study revealed that 16% of our patients were non-responders to AZA; they needed an alternative therapy (biological agent) or steroids along with AZA. There was no statistically significant association (p-value>0.05) between the AOX1 3404G, XDH 1936C and XDH 2107C polymorphisms and the response to AZA among Jordanian IBD patients. Finally, the study showed an association between the age of the patient and the response to AZA (p-value=0.013).

Background: DMPK data and knowledge are critical in maximising the probability of developing successful drugs via the application of in silico, in vitro and in vivo approaches in drug discovery. Methods: The evaluation, optimisation and prediction of human pharmacokinetics is now a mainstay within drug discovery. These elements are at the heart of the ‘right tissue’ component of AstraZeneca’s ‘5Rs framework’ which, since its adoption, has resulted in increased success of Phase III clinical trials. With the plethora of DMPK related assays and models available, there is a need to continually refine and improve the effectiveness and efficiency of approaches best to facilitate the progression of quality compounds for human clinical testing. Results: This article builds on previously published strategies from our laboratories, highlighting recent discoveries and successes, that brings our AstraZeneca Oncology DMPK strategy up to date. We review the core aspects of DMPK in Oncology drug discovery and highlight data recently generated in our laboratories that have influenced our screening cascade and experimental design. We present data and our experiences of employing cassette animal PK, as well as re-evaluating in vitro assay design for metabolic stability assessments and expanding our use of freshly excised animal and human tissue to best inform first time in human dosing and dose escalation studies. Conclusion: Application of our updated drug-drug interaction and central nervous system drug exposure strategies are exemplified, as is the impact of physiologically based pharmacokinetic and pharmacokinetic-pharmacodynamic modelling for human predictions.