title: Effects of combined treatment with sildenafil and itraconazole on the cardiovascular system in telemetered conscious dogs.
abstract: Sildenafil, a potent PDE5 inhibitor, is widely prescribed as a treatment of erectile dysfunction. Itraconazole is an inhibitor of CYP3A4, a metabolic enzyme of sildenafil. In the current study, we investigated the effects of single treatment with sildenafil and combined treatment with sildenafil and itraconazole on blood pressure, heart rate, and QT interval in conscious beagle dogs. After a transmitter was implanted to beagle dogs for conscious state experiments, a single oral dose of sildenafil was administered to the beagle dogs at dose levels of 3, 15, and 30 mg/kg. Blood pressure, heart rate, and lead II ECG were measured prior to dosing and at 0.5, 1, 2, 4, 6, and 24 h postdosing. In the study of combined treatment with sildenafil and itraconazole, the 100 mg/kg dose of itraconazole was orally administered 1 h prior to oral administration of sildenafil. No changes in blood pressure were observed at any doses in animals receiving either single treatment with sildenafil or combined treatment with sildenafil and itraconazole. Increased heart rate from 0.5 h to 6 h postdosing and decreased QT interval were observed in animals receiving single treatment with sildenafil at 15 or 30 mg/kg. When 30 mg/kg of sildenafil was coadministered with 100 mg/kg of itraconazole, drug-related effects such as increased heart rate and decreased QT interval were significantly enhanced as compared to sildenafil-alone administration at 6 h postadministration. These results demonstrated that increased heart rate and decreased QT interval, the adverse effects of sildenafil, were enhanced and prolonged when sildenafil was coadministered with itraconazole. Therefore, caution should be taken when sildenafil is coadministered with itraconazole, a CYP3A4 inhibitor, or when administered to elderly patients or patients with hepatic or renal impairment who cannot metabolize and excrete sildenafil normally.
authors.affiliation: Department of Pharmacology and National Research Laboratory, Korea Institute of Toxicology, Korea Research Institute of Chemical Technology, Yuseong, Daejeon, Korea. ejkim@kitox.re.kr
authors.forename: Eun-Joo
authors.initials: EJ
authors.lastname: Kim
authors.forename: Joung-Wook
authors.initials: JW
authors.lastname: Seo
authors.forename: Ji-Yoon
authors.initials: JY
authors.lastname: Hwang
authors.forename: Sang-Seop
authors.initials: SS
authors.lastname: Han
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000037:antagonists & inhibitors; D000284:Administration, Oral; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D004285:Dogs; D004357:Drug Synergism; D004562:Electrocardiography; D004791:Enzyme Inhibitors / Q000633:toxicity*; D006339:Heart Rate / Q000187:drug effects*; D017964:Itraconazole / Q000633:toxicity*; D008297:Male; D010879:Piperazines / Q000633:toxicity*; D011687:Purines; D000068677:Sildenafil Citrate; D013450:Sulfones; D013686:Telemetry
chemical_list: D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D010879:Piperazines; D011687:Purines; D013450:Sulfones; D017964:Itraconazole; D000068677:Sildenafil Citrate; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; C517381:PDE5A protein, human