Pharmacokinetics of dihydroquinidine in congestive heart failure patients after intravenous quinidine administration

Pharmacokinetics of hydroxy-3(S)-dihydroquinidine in healthy volunteers after intravenous and oral administration

The pharmacokinetics of hydroxy-3(S)-dihydroquinidine (HDHQ) were studied in 6 healthy volunteers following a 15 min intravenous infusion of a 300 or 400 mg dose, a 300 mg oral dose in solution and a 300 mg tablet administration on three separate occasions (random order) with at least one week intervals. Using a specific HPLC assay for HDHQ, the post-infusion and post-absorption plasma HDHQ concentrations declined bi-exponentially. Both oral forms of HDHQ were absorbed rapidly (tmax 1 h-1.2 h) with an absolute bioavailability of the oral solution (F = 0.54 to 0.93) which was not significantly different from that of the tablet (F = 0.66 to 0.90). HDHQ was rapidly and extensively distributed to the tissues with a high steady-state volume of distribution (6.82 +/- 1.85 l X kg-1). Mean elimination half-life was 6.7 +/- 1.4 h after IV infusion, 8.4 +/- 1.7 h after the oral solution and 11.3 +/- 4.4 h after the tablet administration. HDHQ was partially eliminated from the body in the unchanged non-conjugated form by the urine and renal clearance represented approximately 50% of the total body clearance. These results show that HDHQ is rapidly and almost completely absorbed and has potential for a twice daily administration regimen for the treatment of cardiac arrhythmias.

Determination of quinidine in serum by spectrofluorometry, liquid chromatography and fluorescence scanning thin-layer chromatography

Quinidine is determined in serum by direct and extraction spectrofluorometry, by reflectance fluorescence scanning thin-layer chromatography (TLC), and by high-performance liquid chromatography (HPLC). Least-squares analyses of patients' sera (n = 62) analyzed first by direct fluorometry (x) and then HPLC (y) gave a slope of 0.52, an y-intercept of -0.40, a standard error of estimate of 0.65, and a correlation coefficient of 0.83. Comparison of patients' sera (n = 59) determined by extraction fluorometry (x) and then HPLC (y) gave a slope of 0.998, an y-intercept of -0.175, a standard error of estimate of 0.30, and a correlation coefficient of 0.96. Comparison of patients' sera (n = 36) by HPLC (x) and then reflectance fluorescence scanning TLC (y) gave a slope of 0.837, an y-intercept of 0.152, and a correlation coefficient of 0.94. Methaqualone and oxazepam interfere with HPLC. Within-run precision is 1.6, 1.0, 5.2 and 3.0% by direct fluorometry, extraction fluorometry, TLC and HPLC while between-run precision is 5, 3.5, 9 and 6.0%, respectively.

Determination of the quinidine analog, 7'-trifluoromethyldihydrocinchonidine-2HCl in plasma and urine by high-performance liquid chromatography

A rapid and specific high-performance liquid chromatographic (HPLC) assay was developed for the determination of the antiarrhythmic quinidine analog, 7'-trifluoromethyldihydrocinchonidine.2HCl ([I].2HCl) in plasma and urine. The overall recovery of [I] from plasma was 86 +/- 9% with a sensitivity limit of detection of 0.2 microgram/ml. The assay involves extraction of [I] into benzene--methylene chloride (9:1) from plasma or urine made alkaline with 0.1 N sodium hydroxide (pH 13) and saturated sodium chloride, the residue of which is dissolved in methylene chloride, an aliquot of which is analyzed by HPLC using adsorption chromatography on silica gel with UV detection at 254 nm. The mobile phase composed of methylene chloride--methanol--conc. ammonium hydroxide (95.5:4:0.5) yields baseline resolution of quinidine used as the internal (reference) standard, compound [I] and dihydroquinidine, a common contaminant in quinidine. The assay was applied to the analysis of plasma and urine samples taken from a dog administered a single 20 mg/kg dose via intravenous and oral routes. The stability of [I] in human plasma for up to 37 days of storage at -17 degrees C was also demonstrated.