Current Drug Metabolism - Volume 22, Issue 5, 2021

Background: Hydroxymethyl glutaryl-CoA (HMG-CoA) reductase inhibitors (Statins) are used to treat dyslipidemia. Generally, the statins are the substrates of CYP enzymes, P-glycoprotein (P-gp), and organic anion transporting polypeptides transporters (OATP1B1). Objective: This review article focuses on the clinical significance of statins, and their interactions in real practice. Methods: The databases like Medline/PubMed Central/PubMed, Google Scholar, Science Direct, Cochrane Library, Directory of open access journals (DOAJ), and reference lists were searched to identify relevant articles. Results: Most of the drug interactions of statins result in elevated plasma concentrations and toxicity of statins due to the inhibition of CYP3A4, P-gp and/or OATP1B1 transporters. The toxicity of statins includes myopathy, rhabdomyolysis, elevated liver enzymes, acute kidney injury, and diabetes. The statins like simvastatin, lovastatin, and atorvastatin are substrates of CYP3A4 enzyme and P-glycoprotein and their concomitant use with the drugs inhibiting or inducing them would result in changes in plasma concentrations and toxicity/efficacy. However, the statins like pravastatin, rosuvastatin and pitavastatin are not substrates of CYP enzymes and hence the concomitant use of CYP inhibitors or inducers does not affect them. Almost all the statins are the substrates of OATP1B1 transporter, and the co-prescription of inhibitors of OATP1B1 elevates the plasma concentrations and muscle toxicity of statins. Conclusion: Understanding the interacting potential of each statin will enable the prescribers, pharmacists, and other health care professionals to use statins effectively without compromising patient safety.

Background: Graft acceptance against immunity is one of the major challenges in solid organ transplant. Immunosuppressive medications have effectively improved the post-transplantation outcome however, it has its own limitations. Genetic polymorphisms in drug-metabolizing enzymes have been identified as the potential targets in developing a pharmacogenetic strategy, to individualize drug dose and also in preventing the adverse events. Objective: The rationale of the study was to explore polymorphisms in tacrolimus and mycophenolate metabolic pathways that influence the adverse clinical outcomes in renal transplant recipients. Methods: A total of 255 renal transplant recipients were analyzed for the pharmacogenetic determinants of tacrolimus (CYP3A5*3 ABCB1 1236 T>C ABCB1 2677 G>A/T ABCB1 3435 T>C) and mycophenolate (UGT1A8*3 UGT1A9 IMPDH I IMPDH II c.787C>T ABCC2 -24 C>T and c.3972C>T) using Sanger sequencing. Results: Acute rejection (AR) was observed in 5.88% of the transplant recipients whereas acute tubular necrosis (ATNs) was observed in 7.45% of the patients within early stage of the maintenance phase. Infections such as urinary tract infection (UTI) and cytomegalovirus (CMV) infection were observed in 11.37% and 12.16% of the patients. The AUC of mycophenolate was significantly higher in patients with increased risk for infections. ABCC2 -24 C>T c.3972C>T polymorphisms and ABCB1 3435 C-allele were associated with reduced risk for infections. ABCC2 rs3740066 was associated with 2.06-fold all-cause mortality risk. CYP3A5 AG- and UGT1A9-440 CC-genotypes showed increased risk and ABCC 3972C>T CC-genotype showed protection against adverse events. Conclusion: Genetic variants in tacrolimus and mycophenolate metabolic pathways were found to influence the morbidity and mortality in renal transplant recipients.

Background: The role of multidrug resistance-associated protein 3 (Mrp3) in the transport of bile acid (BA) in drug-induced cholestasis has not been well studied. Objective: In this study, wild type and Mrp3 knockout (Mrp3^-/-) mice under normal physiological and lithocholic acid (LCA)-induced cholestatic conditions were employed to investigate the role of Mrp3 in BA transport. Methods: The levels of BA in serum, liver, gallbladder, intestine, kidney, feces and urine were quantified in both wild type and Mrp3^-/- mice via ultra-high performance liquid chromatography triple quadrupole mass spectrometry (UHPLC-MS/MS). Quantitative real-time PCR (RT-PCR) analysis was used to measure the expression of genes related to the transport and synthesis of BA. Results: The results showed that the liver did not suffer more serious damage as a result of cholestasis when Mrp3 was depleted. The level of some individual bile acids changed apparently in the compartments of enterohepatic circulation (EHC) between the two control and model groups, respectively, but the level of serum total bile acid was only slightly reduced for Mrp3^-/- groups. In addition, the level of BA-related efflux transporters and synthases increased significantly when Mrp3 was knocked out under normal physiological conditions, but a negligible alteration appeared under cholestatic conditions. Conclusion: Our results indicated that Mrp3 could be responsible for the transport of some specific bile acids, and part of the Mrp3 role could be compensated for by other transporters. Moreover, Mrp3 deficiency has a direct effect on the expression of BA-related synthases and efflux transporters under normal physiological conditions, but this effect could be less prominent under cholestatic conditions. This study could provide much valuable insight into the physiological function of Mrp3 in the transport of bile acids.

Background: Fixed-dose combination of artemisinin and naphthoquine (NQ) is a new artemisinin- based combination therapy for the treatment of uncomplicated Plasmodium falciparum. NQ absorption has been reported to be affected by food in humans. Objectives: The effect of gastric pH on NQ pharmacokinetics and antiplasmodial activity was investigated. Methods: The pharmacokinetic profiles of NQ were studied in healthy rodents after an oral dose of NQ with or without gastric pH modulators, i.e., pentagastrin (stimulator) and famotidine (suppressant). The effect of gastric pH on NQ exposures in humans was predicted using a physiologically-based pharmacokinetic (PBPK) model. The effect of gastric pH on the antiplasmodial activity of NQ was evaluated in mice infected with Plasmodium yoelii. Results: Neither pentagastrin nor famotidine affected NQ absorption (AUC0-t and Cmax) significantly (P > 0.05) in rodents. The predicted PK profiles of NQ in humans did not show an effect of gastric pH. Compared to pure NQ (ED90, 1.2 mg/kg), the combination with pentagastrin showed non-significantly (< 1.5-fold) higher antimalarial potency (ED90, 1.1 mg/kg). Correspondingly, the elevation of gastric pH (up to pH 5) by famotidine treatment resulted in a relatively weaker antimalarial potency for NQ (ED90, 1.4 mg/kg). Such a difference is within the acceptable range of variability in NQ pharmacokinetics and antiplasmodial activity. Conclusions: Although the food was found to significantly impact NQ pharmacokinetics, other factors except for gastric pH should account for the result, and the warning of careful use of NQ in patients with the acid-related disease is not expected to be clinically meaningful.

Background: Dermorphin is a heptapeptide with an analgesic potential higher than morphine that does not present the same risk for the development of tolerance. These pharmacological features make dermorphin a potential doping agent in competitive sports and it is already prohibited for racehorses. For athletes, the development of an efficient strategy to monitor for its abuse necessitates an investigation of the metabolism of dermorphin in humans. Methods: Here, human liver microsomes and zebrafish were utilized as model systems of human metabolism to evaluate the presence and kinetics of metabolites derived from dermorphin. Five hours after its administration, the presence of dermorphin metabolites could be detected in both models by liquid chromatography coupled to highresolution mass spectrometry. Results: Although the two models showed common results, marked differences were also observed in relation to the formed metabolites. Six putative metabolites, based on their exact masses of m/z 479.1915, m/z 501.1733, m/z 495.1657, m/z 223.1073, m/z 180.1017 and m/z 457.2085, are proposed to represent the metabolic pattern of dermorphin. The major metabolite generated from the administration of dermorphin in both models was YAFG-OH (m/z 457.2085), which is the N-terminal tetrapeptide previously identified from studies on rats. Conclusion: Its extensive characterization and commercial availability suggest that it could serve as a primary target analyte for the detection of dermorphin misuse. The metabolomics approach also allowed the assignment of other confirmatory metabolites.

Background: Clinical mastitis is an important production disease of dairy animals, causing significant economic losses. Objective: Disposition kinetics of ceftriaxone was conducted in healthy lactating and staphylococcal mastitic crossbred cows in field condition following single-dose intravenous administration of only ceftriaxone. Methods: A single dose of ceftriaxone at 20 mg kg^-1 body weight was administered intravenously through jugular vein to six clinically healthy and six mastitic crossbred cows after proper diagnosis and three mastitic cows remained untreated (positive control). Blood and milk samples were collected at 0 (pre-dosing), 5, 15, 30 min, and 1, 24, 48, 72, 96 and 120 h post drug administration and analyzed for ceftriaxone and its active metabolite (ceftizoxime) by high-performance liquid chromatography. Results: Ceftriaxone achieved a peak mean plasma concentration of 131.67±1.83 μg mL^-1 at 5 min, which decreased sharply until 1 h (35.56±0.44 μg mL^-1) and was below detection limit at 24 h post drug administration in mastitic crossbred cows. On the other hand, ceftizoxime (active metabolite of ceftriaxone) achieved a peak level of 55.42±3.34 μg mL^-1 at 72 h and could not be detected at 120 h post drug administration in the milk of those mastitic crossbred cows. The Staphylococcus aureus colony count in mastitic crossbred cows was 49.33±6.55 × 10⁵ c.f.u./mL and the lowest colony count was achieved at 72 h with no colony at 120 h post drug administration. All the staphylococcal mastitis affected crossbred cows were cured on day 5. Conclusion: Ceftriaxone may prove to be effective in the treatment of staphylococcal mastitis in crossbred cows following single-dose intravenous administration at 20 mg kg^-1 body weight.

Background: Both clotrimazole and ketoconazole have been verified to have an inhibitory effect on CYP3A4. hCE2 is an enzyme closely related to the side effects of several anti-cancer drugs. However, the interactions between hCE2, clotrimazole, and ketoconazole remain unclear. Objective: The objective of this study was to investigate and compare the inhibition behaviors of the two antifungal agents, ketoconazole and clotrimazole, on the human liver microsome hCE2 and to explore their underlying mechanism. Methods: The inhibitory effects were investigated in human liver microsomes (HLMs) using fluorescein diacetate (FD), N-(2-butyl-1,3-dioxo-2,3-dihydro-1H-phenalen-6-yl)-2-chloroacetamide (NCEN) and irinotecan (CPT- 11) as substrates of hCE2. Results: Clotrimazole significantly inhibited the hCE2 activity, which was manifested by attenuated fluorescence when the substrates were FD and NCEN. The inhibitory effect of clotrimazole towards hCE2 was much stronger than that of ketoconazole, and the inhibitory behaviors displayed substrate-dependent inhibition. The IC50 value of clotrimazole, with CPT-11 as the substate, increased by 5 and 37 times more than that with FD and NCEN, respectively. Furthermore, the inhibitions of clotrimazole towards hCE2-mediated hydrolysis of FD, NCEN, and CPT-11 were all in competitive mode with the Ki values of 0.483 μM, 8.63 μM, and 29.0 μM, respectively. Molecular docking result of clotrimazole binding to hCE2 illustrated that clotrimazole could efficiently orient itself in the Z site cavity of hCE2. Conclusion: Clotrimazole displayed a strong inhibitory effect against hCE2, which might be used as a potential combined agent co-administrated with CPT-11 to alleviate the hCE2-mediated severe side effects.

Background: Aprocitentan is an orally active, dual endothelin receptor antagonist that may offer a new therapeutic option for the treatment of difficult-to-control hypertension. Objective: To investigate safety, tolerability, mass balance, absorption, distribution, metabolism, and excretion of aprocitentan. Methods: In this single-center, open-label study, a single oral dose of 25 mg containing 3.7 MBq of ¹⁴C-radiolabeled aprocitentan was administered to 6 healthy male subjects. Metabolites were identified using mass spectrometry and, where possible, confirmed and quantified with reference compounds. Results: Aprocitentan was well tolerated and there were no clinically significant findings for any safety variable. The geometric mean cumulative recovery of radioactivity from urine and feces over 14 days was 77% of the administered radioactive dose, with 52.1% cumulative recovery from urine and 24.8% from feces. Concentrations of total radioactivity in whole blood were markedly lower compared to plasma. In plasma, 94.3% of total radioactivity was aprocitentan. In urine and feces, 5 and 2, respectively (in feces one being aprocitentan) main products were identified. Metabolism data of aprocitentan identified two main elimination pathways, glucosidation to M3 and hydrolysis to M1, representing approximately 25% and 32% of the radioactive dose, respectively. Conclusions: Based on these metabolism data, aprocitentan can be concomitantly administered without dose adjustment with drugs that are inhibitors or inducers of any metabolizing enzyme, specifically cytochrome P450 enzymes.