Browsing by Author "Abdelhady, Ahmed M."

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    Efavirenz inhibits the human ether-a-go-go related current (hERG) and induces QT interval prolongation in CYP2B6*6*6 allele carriers
    (Wiley, 2016-10) Abdelhady, Ahmed M.; Shugg, Tyler; Thong, Nancy; Li Lu, Jessica Bo; Kreutz, Yvonne; Jaynes, Heather A.; Robarge, Jason D.; Tisdale, James E.; Desta, Zeruesenay; Overholser, Brian R.; Pharmacology and Toxicology, School of Medicine
    Background Efavirenz (EFV) has been associated with torsade de pointes despite marginal QT interval lengthening. Since EFV is metabolized by the cytochrome P450 (CYP) 2B6 enzyme, we hypothesized that EFV would lengthen the rate-corrected QT (QTcF) interval in carriers of the CYP2B6*6 decreased functional allele. Objective The primary objective of this study was to evaluate EFV-associated QT interval changes with regard to CYP2B6 genotype and to explore mechanisms of QT interval lengthening. Methods EFV was administered to healthy volunteers (n=57) as a single 600 mg dose followed by multiple doses to steady-state. Subjects were genotyped for known CYP2B6 alleles and ECGs and EFV plasma concentrations were obtained serially. Whole-cell, voltage-clamp experiments were performed on cells stably expressing hERG and exposed to EFV in the presence and absence of CYP2B6 expression. Results EFV demonstrated a gene-dose effect and exceeded the FDA criteria for QTcF interval prolongation in CYP2B6*6/*6 carriers. The largest mean time-matched differences ΔΔQTcF were observed at 6 hrs (14 ms; 95% CI [1; 27]), 12 hrs (18 ms; 95% CI [−4; 40] and 18 hrs (6 ms; 95% CI [−1; 14]) in the CYP2B6*6/*6 genotype. EFV concentrations exceeding 0.4 µg/mL significantly inhibited outward hERG tail currents (P<0.05). Conclusions This study demonstrates that homozygous carriers of CYP2B6*6 allele may be at increased risk for EFV-induced QTcF interval prolongation via inhibition of hERG.
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    Pharmacokinetics of Procainamide and N-acetylprocainamide during Continuous Renal Replacement Therapy
    (Elsevier, 2013) Mohamed, Ahmed N.; Abdelhady, Ahmed M.; Spencer, Dustin; Sowinski, Kevin M.; Tisdale, James E.; Overholser, Brian R.; Medicine, School of Medicine
    Procainamide and its major metabolite, N-acetyl procainamide (NAPA), prolong the QTc interval and can promote potentially fatal ventricular arrhythmias. Excretion of procainamide and NAPA is reduced in patients with chronic kidney disease (CKD) resulting in drug accumulation and toxicity. The elimination of procainamide or NAPA in patients undergoing continuous renal replacement therapy (CRRT) has not been evaluated increasing the risk for subtherapeutic or toxic dosing regimens. This case report describes a patient undergoing CRRT who was administered procainamide for recurring ventricular tachycardia (VT) over approximately a 36 hour period. The patient required increased vasopressor therapy and developed QTc prolongation during procainamide administration. The VT resided following pacemaker adjustments, procainamide administration, and multiple direct current cardioversion attempts. Procainamide and NAPA concentrations were determined over a 120 hour period as part of routine clinical care and a pharmacokinetic (PK) model was developed using NONMEM. The developed PK model was used to simulate several procainamide dosing regimens to optimize therapy during CRRT. Based on the model-based simulations, a 50% reduction in the procainamide maintenance dose (2 mg/min) in CKD patients on CRRT can achieve therapeutic plasma procainamide and combined procainamide/NAPA concentrations.