Clinical pharmacokinetics of quinidine

Analysis of nonlinear tissue distribution of quinidine in rats by physiologically based pharmacokinetics

The nonlinear tissue distribution of quinidine in rats was investigated by a physiologically based pharmacokinetic model. Serum protein binding of quinidine showed a nonlinearity over the in vivo plasma concentration range. The blood-to-plasma concentration ratio (Cb/Cp) of quinidine also showed a concentration dependence. The steady-state volume of distribution (Vss) determined over the plasma concentration range from 0.5 to 10 micrograms/ml was 6.0 +/- 0.45 L/kg. The tissue-to-plasma partition coefficient (Kp) of muscle, skin, liver, lung, and gastrointestinal tract (GI) showed a nonlinearity over the in vivo plasma concentration range of quinidine, suggesting saturable tissue binding. The concentration of quinidine in several tissues and plasma was predicted by a physiologically based pharmacokinetic model using in vitro plasma protein binding and the Cb/Cp of quinidine. The tissue binding parameters were estimated from in vivo Kp values. The predicted concentration curves of quinidine in each tissue and in plasma showed good agreement with the observed values.

Independent and interactive effects of digoxin and quinidine on the atrial fibrillation threshold in dogs

To assess the effects of digoxin as single therapy and in combination with quinidine in the treatment of atrial fibrillation, the atrial fibrillation threshold was determined from the right atrial appendage and Bachmann's bundle in 11 open chest dogs. In group 1 (six dogs), the atrial fibrillation threshold was determined at baseline, post-quinidine (10 mg/kg intravenously) and then post-digoxin (50 micrograms/kg intravenously). In group 2 (five dogs), the order of drug administration was reversed. The results of this study were: 1) Digoxin had no significant effect on the atrial fibrillation threshold when given alone. 2) Quinidine significantly increased the atrial fibrillation threshold (p less than 0.002) and the addition of digoxin resulted in a further increase in threshold (p less than 0.002). 3) Quinidine produced greater suppression of atrial fibrillation induction at the right atrial site than at the Bachmann's bundle site, suggesting differential effects of quinidine on atrial fibers.

Intravenous quinidine for the treatment of severe falciparum malaria. Clinical and pharmacokinetic studies

Quinidine has proved more effective than quinine against chloroquine-resistant Plasmodium falciparum both in vitro and in patients with uncomplicated disease. To examine the effectiveness and pharmacokinetics of quinidine for this use, we treated 14 patients who had severe falciparum malaria with intravenous quinidine gluconate; a loading dose of 15 mg of the base per kilogram of body weight was followed by 7.5 mg per kilogram every eight hours. Two of the five patients with cerebral malaria died, but parasitemia was eliminated in the 12 survivors. Two patients had recurrent parasitemia on Days 25 and 28. Times required for parasite clearance and elimination of fever (49.4 +/- 17.8 and 69.5 +/- 18.7 hours, respectively) were comparable to those in earlier studies with a loading dose of quinine. Quinidine appears to have a larger volume of distribution than quinine. The elimination half-life was 12.8 hours, the volume of distribution was 1.68 liters per kilogram, total clearance was 1.75 ml per kilogram per minute, and urinary clearance was 0.62 ml per kilogram per minute. Electrocardiographic changes were common but there were no dysrhythmias. In two patients, blood pressure fell during the initial infusion of quinidine. Quinidine gluconate is more widely available than quinine in many countries, and our findings show that it is effective in severe falciparum malaria.

Diltiazem, verapamil, and quinidine in patients with chronic atrial fibrillation

The comparative effects of diltiazem and verapamil in 30 patients with long-standing atrial fibrillation were evaluated in a prospective clinical trial. After a one- to two-day washout period during which drugs other than digoxin were withdrawn, patients were randomly assigned to diltiazem or verapamil treatment groups. All therapy was double blind. Both drugs were given in ascending doses as follows: days 1-6 (part I): diltiazem, 180 mg/d, or verapamil, 240 mg/d; days 7-12 (part II): diltiazem, 360 mg/d, or verapamil, 480 mg/d. Patients failing to convert to sinus rhythm after 12 days had dosage reduced to 180 mg/d of diltiazem or 240 mg/d of verapamil, and quinidine, 750 mg/d, was coadministered for another six days (part III). Medication compliance was verified by frequent measurement of serum drug concentrations. Three verapamil patients dropped out during part I due to adverse reactions (dyspnea, pulmonary congestion, skin rash, or hepatotoxicity). The higher dosage of either verapamil or diltiazem in part II was not well tolerated, and in eight patients part III had to be initiated early due to symptomatic bradycardia. Only one patient in the diltiazem group converted to sinus rhythm, whereas five converted with verapamil (two with verapamil alone, three when combined with quinidine). Thus, diltiazem and verapamil alone are unlikely to convert atrial fibrillation to sinus rhythm. The combination of verapamil and quinidine, however, is a potentially useful pharmacologic approach, having converted atrial fibrillation to sinus rhythm in nearly 50% of patients.

Comparison of the erythrocyte partitioning method with two classical methods for estimating free drug fraction in plasma

A modification of the erythrocyte partitioning method for the rapid estimation of plasma-free drug fractions (fu) is described and applied to five basic drugs. In the procedure, which uses readily available clinical laboratory equipment, fu is calculated from measurements of drug partitioning between plasma and erythrocytes, and between buffer and erythrocytes. Results obtained are compared with those from equilibrium dialysis or ultrafiltration techniques for amitriptyline, imipramine, quinidine, lidocaine, and propranolol. For each drug, the mean value of fu obtained with the erythrocyte partitioning procedure was not found to be significantly different from that determined by one of the two other classical techniques. The erythrocyte partitioning method lead to reproducible (mean C.V. = 6.25) and precise values of fu when compared to the other methods; its clinical application to lidocaine gave results which agreed with those obtained by equilibrium dialysis.

Comparison of two long-acting forms of quinidine

The bioequivalence of two forms of long acting quinidine compounds was assessed (Kinidin durules and Longacor) using drug plasma level and QT ECG changes. Six healthy volunteers received each preparation on two occasions in random order. The wash out period between successive experiments was at least 7 days. There was no difference in tmax, Cmax and AUC for plasma level and adjusted QT. However, between patient variability was large. A 20% difference in plasma levels could not be excluded but the difference in QT max and QT AUC between the two preparations did not exceed 20% (P less than 0.05, Westlake's method). This study illustrates the fact that pharmacodynamic equivalence, let alone therapeutic equivalence, does not necessarily imply plasma level equivalence, as assessed by the current method.

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.

Drug prescribing in renal failure: dosing guidelines for adults

The data base for rational guidelines to safe, efficacious drug prescribing in adults with renal insufficiency are presented in tabular form. Current medical literature was extensively surveyed to provide as much specific information as possible. When information is lacking, however, recommendations are based on pharmacokinetic variables in normal subjects. Nephrotoxicity, important adverse effects, and special considerations in renal patients are noted. Adjustments are suggested for hemodialysis and peritoneal dialysis when appropriate.

Effect of quinidine on digoxin distribution and elimination in guinea pigs

The effect of quinidine on the distribution and elimination of digoxin was examined by comparing the change in the steady-state volume of distribution (Vdss), determined both from in vivo plasma elimination and tissue distribution and in vitro serum binding studies, with that in the total body clearance (CLtot) determined from biliary, renal, and metabolic clearances in guinea pigs. The plasma disappearance of digoxin after a 250-micrograms/kg iv dose followed a triexponential decline in both the control and quinidine-treated guinea pigs. In the quinidine-treated guinea pigs, the pharmacokinetic parameters Vdss and CLtot significantly decreased to approximately half of that for the control guinea pigs. The tissue-to-plasma partition coefficients (Kp) of all tissues studied, i.e. liver, heart, muscle, and brain, at 6 hr after bolus injection of digoxin decreased in the presence of quinidine. The serum free fraction and the plasma-to-blood concentration ratio of digoxin in the therapeutic range did not show a significant alteration in the presence of quinidine. This suggested that the decrease of Kp is due mainly to the inhibition of tissue distribution of digoxin by quinidine. The biliary clearance (CLB) and renal clearance (CLR) also significantly decreased in the presence of quinidine. It was concluded that quinidine caused a inhibition of digoxin in the tissue binding or uptake, which significantly decreased the Kp values of digoxin; this result may explain the significant decrease of Vdss. Moreover quinidine may be the cause of a reduction of biliary, renal, and metabolic clearances, which significantly decrease the CLtot of digoxin.

Quinine disposition kinetics

Intravenous quinine dihydrochloride (5 mg kg-1 over 5 min) was given to seven healthy male volunteers. There were minor subjective symptoms in all subjects but no significant changes in pulse or blood pressure. There was significant prolongation of the electrocardiographic QRS and rate corrected QT intervals which was greatest between 1 and 4 min after completion of the quinine infusion. Values then returned towards baseline. Plasma concentrations of quinine were measured spectrophotofluorimetrically after benzene extraction. Peak plasma concentrations (mean +/- 1 s.d.) after the infusion were 5.1 +/- 1.3 mg 1(-1). Pharmacokinetic analysis fitted a two compartment open model in each case; distribution half-time (t 1/2, lambda 1) was 1.89 +/- 0.54 min (mean +/- 1 s.d.), elimination half-time (t 1/2, z) 11.1 +/- 2.1 h, apparent volume of the central compartment (V1) 0.57 +/- 0.32 1 kg-1, total apparent volume of distribution 1.80 +/- 0.37 1 kg-1 and total clearance 1.92 +/- 0.45 ml min-1 kg-1.

Urinary excretion kinetics of intact quinidine and 3-OH-quinidine after oral administration of a single oral dose of quinidine gluconate in the fasting and non-fasting state

To obtain more precise urinary excretion data of intact quinidine (D) and its main metabolite, 3-OH-quinidine (DM), the specific HPLC method of Bonora et al has been used to follow its urinary excretion kinetics. In a cross-over study, 2 commercial dosage forms of quinidine gluconate, fast- and slow-release, were administered to 18 healthy subjects who had fasted for 10 hours in 3 treatments which were administered during the fasting period (T1), and before (T2) of after (T3) a standard breakfast. The urine was collected at fixed time intervals for 72 hours after the administration of a single dose (405 mg of quinidine base). The difference between the drug release characteristics of the two products was studied by analysing the cumulative amount of D and DM excreted as a function of time, and the time required to reach the maximum value for the urinary excretion rate of intact quinidine. A food effect could be noticed among treatments with the conventional fast-release dosage form when comparing the maximum values of the urinary excretion rate of D (T2 greater than T1). There was no significant difference in the percentage of drug absorbed from the 2 products, according to the data on the cumulative amount of D and DM. The parameters estimated for quinidine and the metabolite were: the apparent half-life of elimination, the urinary excretion rates and the time to reach a maximum value in the urinary excretion rate. The urinary excretion rate constant and the renal clearance were also quantified for quinidine by combining urinary parameters with the corresponding serum data previously reported.

Effect of food and an antacid on quinidine bioavailability

Two 200 mg quinidine sulfate tablets were administered to nine healthy male subjects in the fasting state, immediately after a balanced meal, and with 30 ml of aluminum hydroxide gel using a complete crossover design. Serum and urine samples were taken over 32 and 60 h, respectively. Quinidine concentrations were measured using a high-performance liquid chromatography assay specific for quinidine. Computer fitting of the data to several models indicated that a one-compartment model with zero-order absorption and a lag time best fit all the data. Quinidine elimination and urine pH were unaffected by the study conditions. While the maximum serum concentration (Cmax) and area under the serum concentration-time curve (AUC) were unaffected by administration of quinidine with food or antacid, there was a 44 per cent increase (p less than 0.10) in time to Cmax (tmax) following quinidine administration with food. Thus, while the extent of quinidine absorption was unaffected by food or the antacid used, the rate of quinidine absorption was significantly reduced by food as reported earlier.

A calculator program to determine k and V from measured serum drug concentrations by a two point curve fitting method

A calculator program is presented which determines k and V from two drugs levels or k from an assumed V and one drug level during maintenance dosing with any of four dosing schedules: intermittent, fixed interval; intermittent, two fixed intervals; intermittent, non-uniform dose, non-uniform interval; continuous intravenous infusion/sustained release. A loading dose and or one additional level taken before maintenance dosing begins can be taken into account for additional flexibility. Steady state concentrations are projected when dosage regimen and pharmacokinetic parameters are known.

Serum quinidine determination: comparison of mass-spectrometric and extraction-fluorescence methods

A comparison of two analytical methods of quinidine plasma determination--the modified extraction fluorometric method and the mass spectrometric method--was made. Plasma supplies collected at steady state from normal human volunteers participating in a bioavailability study were analyzed, using both methods. A total of 359 samples were analyzed. Comparison of both sets of values, by linear regression, yielded an r2 value of 0.84. The results of this comparison were consistent with the results reported by others, confirming that the commonly used extraction fluorometric method of quinidine determination is sufficiently accurate for monitoring quinidine plasma concentrations in the patient care setting, as well as for bioavailability comparisons between products.

Quinidine in falciparum malaria

Fourteen patients with falciparum malaria were successfully treated with oral quinidine. Twelve of these patients were followed for 35 days without recrudescence. In six patients the infection had already recrudesced after antimalarial treatment, which in two cases had included a full course of quinine. Quinidine caused no cardiotoxicity, although the electrocardiogram QTc interval was prolonged by more than 25% in four patients. In-vitro cultures from nine of these patients and a further seven patients with falciparum malaria showed that the minimum inhibitory concentration was consistently lower for quinidine than for quinine. Quinidine is an effective antimalarial drug for Plasmodium falciparum infections and may be more potent than quinine.

The specificity of the extraction fluorescence assay for serum or plasma quinidine

A series of 26 randomly selected serum samples from patients receiving long-term antiarrhythmic therapy with oral quinidine preparation were assayed by both a modification of the extraction fluorescence technique and high-pressure liquid chromatography, with highly comparable results (r = 0.98). A review of the literature on comparing the extraction fluorescence technique's results with other methods indicates a high degree of agreement. However, because variations from study to study exist, investigators using the extraction fluorescence technique should assess the specificity of the method in their own laboratory.

Intravenous quinidine in congestive cardiomyopathy

Eight male patients with compensated congestive cardiomyopathy received single 300-mg doses of intravenous quinidine by 15-min infusion. Left ventricular (LV) performance was evaluated by echocardiography at multiple points in time during the next 24 h. Quinidine kinetics and protein binding were determined from multiple serum samples drawn for up to 36 h after dosage. LV function was not impaired. Instead, quinidine transiently increased ejection fraction (mean: +39%) and rate of circumferential shortening (mean: +46%). Endsystolic and end-diastolic LV internal diameter likewise were decreased (means: -13% and -7%). Blood pressure and ventricular rate were not significantly altered. Compared to 8 healthy controls matched for age, sex, and weight, quinidine volume of distribution among patients was smaller (means: 2.27 vs 1.90 l/kg), as was total quinidine clearance (3.49 vs 2.84 ml/min/kg); however, differences were not statistically significant. Well-controlled, slow intravenous infusion of quinidine does not impair LV performance and is safe for patients with compensated congestive cardiomyopathy. However, such patients may have reduced quinidine clearance and hence require lower doses than expected based on age and weight.

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.