Search

The aim of this work was to compare hepatocellular toxicity and pharmacological activity of amiodarone (2-n-butyl-3-[3,5 diiodo-4-diethylaminoethoxybenzoyl]-benzofuran; B2-O-Et-N-diethyl) and of eight amiodarone derivatives. Three amiodarone metabolites were studied, namely, mono-N-desethylamiodarone (B2-O-Et-NH-ethyl), di-N-desethylamiodarone (B2-O-Et-NH2), and (2-butyl-benzofuran-3-yl)-(4-hydroxy-3,5-diiodophenyl)-methanone (B2) carrying an ethanol side chain [(2-butylbenzofuran-3-yl)-[4-(2-hydroxyethoxy)-3,5-diiodophenyl]-methanone; B2-O-Et-OH]. In addition, five amiodarone analogs were investigated, namely, N-dimethylamiodarone (B2-O-Et-N-dimethyl), N-dipropylamiodarone (B2-O-Et-N-dipropyl), B2-O-carrying an acetate side chain [[4-(2-butyl-benzofuran-3-carbonyl)-2,6-diiodophenyl]-acetic acid; B2-O-acetate], B2-O-Et carrying an propionamide side chain (B2-O-Et-propionamide), and B2-Ocarrying an ethyl side chain [(2-butylbenzofuran-3-yl)-(4-ethoxy-3,5-diiodophenyl)-methanone; B2-O-Et]. A concentration-dependent increase in lactate dehydrogenase leakage from HepG2 cells and isolated rat hepatocytes was observed in the presence of amiodarone and of most analogs, confirming their hepatocellular toxicity. Using freshly isolated rat liver mitochondria, amiodarone and most analogs showed a dose-dependent toxicity on the respiratory chain and on β-oxidation, significantly reducing the respiratory control ratio and oxidation of palmitate, respectively. The reactive oxygen species concentration in hepatocytes increased time-dependently, and apoptotic/necrotic cell populations were identified using flow cytometry and annexin V/propidium iodide staining. The effect of the three least toxic amiodarone analogs on the human ether-a-go-go-related gene (hERG) channel was compared with amiodarone. Amiodarone, B2-O-acetate, and B2-O-Et-N-dipropyl (each 10 μM) significantly reduced the hERGtail current amplitude, whereas 10 μM B2-O-Et displayed no detectable effect on hERG outward potassium currents. In conclusion, three amiodarone analogs (B2-O-Et-N-dipropyl, B2-O-acetate, and B2-O-Et) showed a lower hepatocellular toxicity profile than amiodarone, and two of these analogs (B2-O-Et-N-dipropyl and B2-O-acetate) retained hERG channel interaction capacity, suggesting that amiodarone analogs with class III antiarrhythmic activity and lower hepatic toxicity could be developed.

Amiodarone (AMI) is a potent antiarrhythmic drug, but its metabolism has not yet been fully documented. Mono-N-desethylamiodarone (MDEA) is its only known metabolite. Our preliminary investigations using rabbit liver microsomes had shown that in vitro AMI was biotransformed to MDEA, and the latter was rapidly further biodegraded to other unknown products. The aim of the present study was to investigate the chemical structure of the biotransformed compound of MDEA. Upon incubation of MDEA with rabbit liver microsomes and NADPH as cofactor, MDEA was biotransformed into three unknown products: X1, X2, and X3. The products were purified using chromatography. The chemical structure of the major product, X1, was investigated in detail. HPLC-ESI-MS revealed that MDEA had been oxygenated. Hydrogen-deuterium exchange experiments showed that the X1 molecule contained one exchangeable hydrogen atom more than its precursor MDEA, indicating that MDEA had been hydroxylated. Further results from ESI-MS/MS analysis indicated that the site of hydroxylation was the n-butyl side chain. NMR analysis (1H NMR, one-dimensional-total correlation spectroscopy, and heteronuclear multiple-bond correlation spectroscopy) established the 3-position (ω-1) of the butyl moiety as the specific carbon atom that is hydroxylated. Rat liver microsomes were also able to catalyze MDEA hydroxylation. Compound X1, as analyzed by HPLC-ESI-MS and ESI-MS/MS, was detected in the liver, heart, lung, and kidney tissue of four rats receiving AMI, suggesting that the hydroxylated MDEA was a secondary metabolite of AMI. Conclusion: in mammals, MDEA is hydroxylated to the secondary metabolite of AMI {2-(3-hydroxybutyl)-3-[4-(3-ethylamino-1-oxapropyl)-3,5-diiodobenzoyl]-benzofuran}.

Angiotensin-converting enzyme (ACE) inhibitors are established as first-line therapy in chronic heart failure (CHF). However, little is known about the dosage-plasma-level relationship of ACE inhibitors in CHF and its relation to drug-induced adverse effects. We investigated 45 patients (age 55 ± 10 years) with stable CHF who presented with a maintenance dosage of enalapril of either 5 mg b.i.d. (E10, n= 16), 10 mg b.i.d. (E20, n= 18), or 20 mg b.i.d. (E40, n= 11). This dosage was changed three times to treat all patients with lower, higher, and, finally, the initial dosage for 4 weeks each. Patients were examined clinically, by questionnaire, and by spiroergometry. In addition, neurohormones (atrial and brain natriuretic peptide and norepinephrine), enalaprilat trough levels, and serum potassium and creatinine were measured. Enalaprilat trough levels differed significantly between the three groups at study entry but also varied markedly within each group. In addition to the dose of enalapril, serum creatinine, severity of CHF, basal metabolic rate, and body weight significantly influenced enalaprilat trough levels (R2=.84, p< .001). Within-patient comparisons revealed that serum creatinine (107 ± 26 versus 102 ± 20 μmol/liter) and potassium (3.8 ± 0.4 versus 3.7 ± 0.3mmol/liter) were higher, cough was more common (scored on a scale of 0–8: 1.7 ± 2.1 versus 1.4 ± 1.8), and blood pressure was lower (systolic, 112 ± 14 versus 117 ± 13 mm Hg; diastolic, 66 ± 9 versus 69 ± 11 mm Hg) on the highest than on the lowest enalaprilat trough level (all p< .05). Highly variable enalaprilat trough levels and the fact that adverse effects were more common on high enalaprilat trough levels provide a rationale for individually adjusting ACE-inhibitor dose in case of adverse effects.

Flecainide acetate, a class Ic antiarrhythmic agent, is eliminated to a larger extent by renal excretion and to a minor extent by the liver. In patients with impaired renal function or with elevated urinary pH, however, its elimination is dominated by hepatic metabolism. Recent evidence suggests that the in vivo metabolism of flecainide is controlled by the genetic polymorphism of the debrisoquin/sparteine type; i.e., it is a substrate of cytochrome P4501ID6. We investigated the inhibitory effect of flecainide on bufuralol 1‘-hydroxylation in human liver microsomes in vitro and on the metabolic dextromethorphan urinary ratio in eight healthy male volunteers. Both bufuralol and dextromethorphan are well-known substrates of cytochrome P450IID6. Microsomal bufuralol 1-hydroxylation was competitively inhibited by flecainide with an apparent Kiof 0.954 μmoUL. Moreover, a statistically significant increase in the urinary metabolic ratio (MR) of dextromethorphan/dextrorphan after 1 week of administration of oral flecainide was observed (p = 0.013) in all subjects. One individual increased the urinary MR to a value consistent with the poor metabolizer phenotype. We conclude that flecainide is a potent inhibitor of cytochrome P450IID6in vitro and in vivo and that careful drug monitoring is required with respect to renal function, debrisoquine phenotype, and concomitant drug administration.

A rapid and selective high-performance liquid chromatographic (HPLC) method using solid-phase extraction (SPE) for measuring piroximone in plasma samples has been developed. Human plasma and internal standard were pipetted onto a Bond Elut C18extraction cartridge conditioned with methanol and water. Impurities and proteins were washed out with water. Piroximone and internal standard were eluted with methanol. After evaporation, the residue was dissolved in the mobile phase and the aliquot injected into the HPLC system. Piroximone and its related compounds were separated on a reversed phase C18HPLC column maintained at 50°C using a mobile phase consisting of phosphate buffer and methanol. Piroximone-N-oxide, piroximone, and internal standard were detected spectrophotometrically at 340 nm. The extraction recovery for piroximone was 94. The within- and between-run coefficients of variation were <3 in the concentration range of 320–5,000 ng/ml and <17.5 at lower concentrations, e.g., 20 ng/ml. The limit of detection was 10 ng/ml.

Piroximone is a new phosphodiesterase III inhibitor that combines inotropic and vasodilator properties. To elucidate the optimal dose regimen and the dose-concentration-effect relationships, we studied eight patients with congestive heart failure of New York Heart Association class IV during a continuous multistage infusion over a 24-h period followed by a 4-h washout. After a bolus of 0.5 mg/kg, infusions at a rate of 2.5, 5.0, and 10.0 μg/kg/min for 8 h each were given to determine the maintenance dose of piroximone required to achieve an increase in cardiac index ≥ 30. Serial assessment of hemodynamics, plasma piroximone levels, and ventricular ectopic beats was performed. Following the loading dose and at higher infusion rates (5 and 10 μg/kg/min) Piroximone produced significant hemodynamic changes compared to baseline, i.e., a maximum increase in cardiac index from 2.2 ± 0.4 to 3.6 ± 0.8 L/min/m2(67 ± 21), decreases in right atrial pressure from 14 ± 3 to 9 ± 3 mm Hg (40 ± 16), pulmonary capillary wedge pressure from 29 ± 5 to 23 ± 7 mm Hg (28 ± 18), pulmonary vascular resistance from 249 ± 93 to 151 ± 59 (45 ± 19), and systemic vascular resistance from 1,330 ± 442 to 752 ± 272 dyn s/cm5(44 ± 19). Piroximone increased the heart rate by 10 at the highest dose and produced a decrease in mean arterial pressure by 13. There was a slight increase in ventricular ectopy in two patients (2.2 and 3 VPBs/min) and no change in the remaining six. Two hours after discontinuation of the piroximone infusion, hemodynamic parameters returned to baseline in parallel to decreasing plasma levels. Plasma concentrations of piroximone reached a steady state at infusion rates of 2.5 and 5.0 μg/kg/min but continued to rise disproportionately at the highest dose. The terminal elimination half-life was 1.4 ± 0.3 h. Our findings indicate a close relationship between piroximone plasma concentrations and hemodynamic effects in patients with severe congestive heart failure. The rising plasma concentrations at an infusion rate of 10 μg/kg/min are suggestive of nonlinear pharmacokinetics, with the risk of excessive accumulation during prolonged administration.

The impact of ECG presentations of acute myocardial infarction (AMI) in cardiogenic shock is unknown.