The influence of age and smoking on the elimination of disopyramide

Pharmacokinetic determinants for the right dose of antiarrhythmic drugs

INTRODUCTION

Antiarrhythmic drugs (AADs) show a narrow therapeutic range and marked intersubject variability in pharmacokinetics (PK), which may lead to inappropriate dosing and drug toxicity.

AREAS COVERED

The aim of the present review is to describe PK properties of AADs, discussing the main changes in different clinical scenarios, such as the elderly and patients with obese, chronic kidney, liver, and cardiac disease, in order to guide their right prescription in clinical practice.

EXPERT OPINION

There are few data about PK properties of AADs in a special population or challenging clinical setting. The use and dose of AADs is commonly based on physicians' clinical experience observing the clinical effects rather than being personalized on the individual patients PK profiles. More and updated studies are needed to validate a patient centered approach in the pharmacological treatment of arrhythmias based on patients' clinical features, including pharmacogenomics, and AAD pharmacokinetics.

What really declines with age? The Hayflick Lecture for 2006 35th American Aging Association

In order to understand the basic mechanisms underlying the organismic aging process, considerable efforts have been devoted in the last half-century to biochemical (enzyme activity) alterations in specific tissues and organs of various organisms associated with aging. When a decline in enzyme activities with age has been found in a study, especially for key enzymes such as antioxidant enzymes, the results have often been interpreted as a cause for the aging of the entire body. Retrospectively, however, these changes turned out to be so variable--depending on species, strains and sexes of animals--that the interpretation of these results in general terms of aging became invalid. Further, unlike the prediction for the whole human body, many enzyme activities in a vital organ, such as the liver, remained unchanged, as long as the old subjects remained healthy. However, enzyme activities in old animals and humans are often more susceptible to morbidities and frailties, which themselves are often accompanied by infections and malnutrition. Despite the rather stable enzyme functions in the liver with age, a distinct and progressive decline in the lateral diffusion coefficient of proteins of hepatocyte plasma membranes has been demonstrated by fluorescence recovery after photobleaching (FRAP), which was implicated as the cause for the decline of hepatocyte functions such as ouabain (and taurocholate) hepatic uptake and their eventual biliary excretion. Since a similar decline in protein diffusion coefficients was observed in brain and muscle cells, it is likely that these changes are occurring in common with many cell types of the body, thus causing a delay in transmembrane transport of endogenous and exogenous substances whose transports are mediated by membrane proteins. In attempts to prolong the life spans of animals other than by calorie restriction, but instead using deprenyl or tetrahydrocurcumin, works by the author and coworkers are introduced and discussed. Despite limited success along these lines thus far, further attempts are encouraged, primarily to understand the mechanisms underlying organismic aging processes and to find a practical way to prolong the health span of the elderly.

Pharmacokinetics in older persons

BACKGROUND

Physiologic changes and disease-related alterations in organ function occur with aging. These changes can affect drug pharmacokinetics in older persons.

OBJECTIVE

This article reviews age-related changes in pharmacokinetics and their clinical relevance.

METHODS

A PubMed search was conducted using the terms elderly and pharmacokinetics. Other reviews were also included for literature searching. The review includes literature in particular from 1990 through April 2004. Some articles from before 1990 were included to help illustrate principles of age-related pharmacokinetics.

RESULTS

There are minor changes in drug absorption with aging. The effect of aging on small-bowel transporter systems is not yet fully established. Bioavailability of highly extracted drugs often is increased with age. Transdermal absorption may be delayed, especially in the case of water-soluble compounds. Fat-soluble drugs may distribute more widely and water-soluble drugs less extensively in older persons. Hepatic drug metabolism shows wide interindividual variation, and in many cases, there is an age-related decline in elimination of metabolized drugs, particularly those eliminated by the cytochrome enzyme system. Any decrement in cytochrome enzyme metabolism appears nonselective. Synthetic conjugation metabolism is less affected by age. Pseudocapillarization of the sinusoidal endothelium in the liver, restricting oxygen diffusion, and the decline in liver size and liver blood flow may influence age-related changes in rate of hepatic metabolism. Frailty, physiological stress, and illness are important predictors of drug metabolism in older individuals. Inhibition of drug metabolism is not altered with aging, but induction is reduced in a minority of studies. Renal drug elimination typically declines with age, commensurate with the fall in creatinine clearance. Renal tubular organic acid transport may decline with age, while the function of the organic base transporter is preserved but may be less responsive to stimulation.

CONCLUSION

Changes in pharmacokinetics occur due to age-related physiologic perturbations. These changes contribute to altered dose requirements in older persons, particularly in the case of drugs eliminated by the kidney. Interindividual variation, disease, frailty, and stress may overshadow age-related changes.

Aging of the liver: facts and theories

Although most theories of aging assume that cellular functions decline with aging, many intracellular functions in the liver, such as enzyme activities, stay fairly stable in old age. This does not appear to be an antifact caused by in vitro experimental design, since in vivo pharmacokinetic data also demonstrate that most, if not all, biotransformation capacities of the liver remain stable during the aging process, if we take the decline in liver volume with age into account. Thus, many theories to explain the decline in cellular functions during aging appear to be based on erroneous assumptions. The stability of cellular function in old age does not necessarily mean, however, that all cellular functions are identical for young and old organisms. Once unfavorable conditions, such as malnutrition, infection, etc., are involved, the response of the liver is quite different for young and old subjects, demonstrating a more efficient and versatile response in young animal livers in comparison to old livers. Large differences in enzyme activities between young and old organisms appear during stress and especially during recovery from stress. Accordingly, any aging theory needs to explain a potential difference in liver functions (such as response capability) rather than the difference in basal functions. In contrast to rather stable intracellular functions, the uptake function of the hepatocyte surface membranes was found to be progressively decreased with age. This was shown for at least two different types of carrier systems in the surface membranes. Although the decrease of carrier unit number for these substances remains a possible causal factor, we suggest that the decline in hepatic uptake with age is at least partially the result of a gradual decrease in the mobility of surface membrane proteins, which can be shown by the fluorescence recovery after photobleaching (FRAP) technique. Theories of aging need to be elaborated on the basis of unbiased observations on the actual manifestations of cellular aging.

Cardiovascular Drug Therapy in Elderly Patients

An increasing number of elderly patients are exposed to cardiovascular drugs for the treatment of acute and/or chronic conditions. This is a result of the progressive aging of the population, a common feature in most industrialised countries, and an improvement in primary and secondary cardiovascular prevention strategies with increased survival rates. Traditionally, most elderly patients receiving cardiovascular drugs had advanced cardiac, liver and kidney disease that significantly influenced drug pharmacokinetic and pharmacodynamic parameters. Currently, however, many patients without significant organ impairment receive cardiovascular therapy for primary or early secondary prevention (i.e. increased vascular risk, asymptomatic left ventricular dysfunction, poststroke phase, type 2 diabetes mellitus), highlighting the need for a better understanding of specific age-related pharmacokinetic and pharmacodynamic effects. A systematic review has been conducted on the specific effects of aging, in the absence of major co-morbidities, on the pharmacokinetic and pharmacodynamic properties of traditional and newer cardiovascular drugs. Currently, the evidence available is poor or nonexisting for several drugs and mainly derived from very small and underpowered studies, thus limiting data interpretation. In particular, there is very little information on patients >80 years of age, thus raising important concerns about the correct use of these drugs in this constantly growing population.

Age, environmental factors and drug metabolism

Both ageing and the environment have a significant impact on xenobiotic metabolism. Furthermore, there is some evidence from in vivo studies that the elderly respond to environmental changes to a lesser degree than younger individuals. This article reviews the available evidence and concentrates on possible underlying mechanisms.

Extent and variability of the first-pass elimination of adinazolam mesylate in healthy male volunteers

The pharmacokinetics of adinazolam and N-desmethyladinazolam (NDMAD) were studied in 14 healthy male volunteers who received 15 mg adinazolam mesylate orally as a solution and 5 mg adinazolam mesylate intravenously in a crossover design. Two weeks prior to the crossover study, each subject received 5 mg/kg indocyanine green (ICG) as an intravenous bolus injection to estimate liver blood flow. The absolute bioavailability (F), calculated as the dose-corrected ratio of oral to iv adinazolam area under the curve (AUC) values, was found to be 39%. NDMAD AUC values were similar following oral and iv administration, and adinazolam mean absorption time was approximately 0.77 hr. Thus, adinazolam is completely and rapidly absorbed after oral administration in man; the incomplete bioavailability is due to first-pass metabolism. Mean liver blood flow, adinazolam systemic clearance, blood/plasma ratio, and extraction ratio were 1189 ml/min, 498 ml/min, 0.70, and 0.57, respectively. The extraction ratio agrees with that calculated as 1-F (0.62), suggesting that the liver is primarily responsible for first-pass metabolism of adinazolam. The unbound fraction of adinazolam in plasma was 0.31 (range, 0.25-0.36); adinazolam free intrinsic clearance (a reflection of metabolic capacity) was 4285 ml/min (range, 2168-6312 ml/min). These results suggest that the majority of the variability in adinazolam plasma concentrations following oral administration is due to the variability in the metabolic capacity of the liver for adinazolam, rather than variability in plasma protein binding.

Hepatic drug metabolism and aging

Although there is considerable variation in the effect of age on drug biotransformation, the metabolism of many drugs is impaired in the elderly. Age-related physiological changes, such as a reduction in liver mass, hepatic metabolising enzyme activity, liver blood flow and alterations in plasma drug binding may account for the decreased elimination of some metabolised drugs in the elderly. It is difficult, however, to separate an effect of aging from a background of marked variation in the rate of metabolism due to factors such as individual metabolic phenotype, environmental influences, concomitant disease states and drug intake. The prevailing data suggest that initial doses of metabolised drugs should be reduced in older patients and then modified according to the clinical response. In most studies the elderly appear as responsive as young individuals to the effects of compounds which induce or inhibit the activity of cytochrome P450 isozymes. Concurrent use of other agents, which induce or inhibit drug metabolism, mandates dose adjustment as in younger patients. Many questions remain unanswered. For instance, limitations of in vitro studies prevent any firm conclusion about changes in hepatic drug metabolising enzyme activity in the elderly. With aging, some pathways of drug metabolism may be selectively affected, but this has not been adequately scrutinised. The possibility that metabolism of stereoisomers may be altered in the elderly has not been adequately tested. The effect of aging on the distribution of polymorphic drug metabolism phenotypes is still not established, despite potential implications for disease susceptibility and survival advantage.

Disposition kinetics of disopyramide in human healthy volunteers described by an open three compartment model

Disposition kinetics of disopyramide was examined in an open randomised cross-over study in 8 healthy volunteers. Disopyramide was randomly administered as a single bolus injection (150 mg) over a period of 5 min. and as an infusion (28.2) mg/h to steady state. Disposition kinetics of disopyramide were most precisely described by an open three compartment model according to Akaike's information criteria. Significant positive correlations (0.909 +/- 0.04, P less than 0.05 (injection study); 0.787 +/- 0.11, P less than 0.05 (infusion study] were observed between total serum concentrations of disopyramide and renal clearance while no significant correlation could be demonstrated between free serum concentrations and renal clearance. This implies a constant value of unbound renal clearance. The results are consistent with non linear kinetics (mainly caused by the variable free fraction of the drug), when based on total serum concentrations. The disposition of unbound disopyramide, however seems to be linear (i.e. the kinetic parameters are independent of dose) in the bolus injection study. Total elimination clearance (free and total), volume of distribution and elimination half-life were significantly higher in the steady state experiment than in the bolus injection study.

Disopyramide pharmacokinetics in the elderly after single oral administration

Disopyramide (D) kinetics were studied after single oral dose (200 mg) in ten elderly male patients (mean age: 75.5 yrs) without clinical or laboratory signs of hepatic, renal or cardiac disease, and in six healthy male subjects. They were all non smokers and had not taken alcohol for at least 10 days. Peak plasma concentration and area under the curve (AUCo-oo) were 54% and 51% respectively higher in the elderly group, whereas plasma half life was virtually the same in both groups (about 9 hrs). The major D metabolite, mono-N-desisopropyldisopyramide (MND), showed a tendency towards an increase of AUCo-24 h and T1/2 but did not reach the 5% significance level. Eight of the ten elderly patients but only two of the six young subjects complained of anticholinergic side effects. On the basis of the pharmacokinetic changes observed (and provided that plasma protein binding is unchanged), D oral dose should be reduced by 1/3, without modifying the dosage interval.

Elimination kinetics and urinary excretion of disopyramide in human healthy volunteers

Elimination kinetics and the renal handling of disopyramide was examined in 8 healthy volunteers. Approximately 50% of the administered disopyramide undergoes hepatic metabolism (metabolic clearance = 116.1 +/- 42.2 ml/min.), while the rest is excreted by the kidneys (renal clearance = 101.9 +/- 21.6 ml/min.). Total renal excretion rate of disopyramide was 0.676 +/- 0.188 mumol/min. and 0.258 +/- 0.029 mumol/min. was excreted by glomerular filtration leaving a net tubular secretion of 60% of the total renal elimination. A significant positive correlation was observed between total serum concentrations and renal clearance values of disopyramide while no significant correlation could be obtained between serum concentrations of the unbound drug and renal clearance values of disopyramide, implying a constant value of unbound renal clearance. Hepatic blood flow was significantly (P less than 0.005) decreased following disopyramide infusion.

Disopyramide pharmacokinetics and metabolism: effect of inducers

1. The disposition of orally administered disopyramide was studied in a population of smokers (n = 6) and non-smokers (n = 8) before and during phenobarbitone treatment (100 mg daily for 21 days; Cp 21st day = 13.9 +/- 2.0 micrograms ml-1). The comparative inducibility of these populations by phenobarbitone was assessed as was the inductive effect of cigarette smoking, per se. Furthermore, the determinants of the intensity of the inductive effect were examined, as well as the effect of the barbiturate on the binding of disopyramide to alpha 1-acid glycoprotein (AGP). 2. Smokers and non-smokers exhibited similar half-lives (6.48 +/- 1.49 vs 6.66 +/- 1.02 h), apparent total body clearances (0.100 +/- 0.020 vs 0.117 +/- 0.034 l h-1 kg-1), mean renal clearances (0.043 +/- 0.0093 vs 0.057 +/- 0.013 l h-1 kg-1) and apparent intrinsic metabolic clearances (0.057 +/- 0.015 vs 0.060 +/- 0.024 l h-1 kg-1) before phenobarbitone treatment. 3. Both populations responded comparably to barbiturate exposure in that apparent intrinsic metabolic clearance more than doubled. Interestingly, the magnitude of this increase was highly dependent on the observed baseline apparent intrinsic metabolic clearance, (r' = 0.81; P less than 0.001). 4. Phenobarbitone treatment of non-smokers resulted in an increase in the AUC of the active metabolite N-despropyl disopyramide (MND), but not significantly (3.8 +/- 1.6 vs 4.1 +/- 2.3 micrograms ml-1 h). Similar results were observed in smokers (3.5 +/- 1.4 vs 3.9 +/- 2.0 micrograms ml-1 h, respectively). 5. The percent of administered dose recovered in urine as disopyramide in non-smokers was significantly decreased upon phenobarbitone treatment (43 +/- 6% vs 25 +/- 5%), whereas the percent of dose recovered as MND increased significantly in this group (25 +/- 6% vs 31 +/- 5%). The population of smokers responded similarly. 6. At doses typically used to achieve hepatic microsomal enzyme induction in man, phenobarbitone treatment caused no significant change or trend towards a change in serum AGP concentrations as measured using the radial immunodiffusion method in nonsmokers (67.4 +/- 19.9 mg dl-1 vs 68.0 +/- 40.7 mg dl-1) or smokers (64.5 +/- 15.7 vs 67.9 +/- 14.9). Similarly, when AGP concentration was estimated in serum from non-smokers using a nephelometric method no effect attributable to phenobarbitone was observed (47.9 +/- 1.3 vs 47.9 +/- 16.8 mg dl-1). Consistent with this observation, disopyramide free fraction was not affected by barbiturate treatment.

Disopyramide. A reappraisal of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in cardiac arrhythmias

Disopyramide is a widely used class IA antiarrhythmic drug with a pharmacological profile of action similar to that of quinidine and procainamide. Over the past 10 years disopyramide has demonstrated its efficacy in ventricular and atrial arrhythmias. In therapeutic trials, usually involving small numbers of patients, the efficacy of disopyramide was comparable with that of mexiletine, perhexiline, tocainide, propafenone or prajmalium. Recent comparisons with quinidine have confirmed the similar efficacy and better tolerability of disopyramide. The suggestion from initial studies that disopyramide may be less effective than amiodarone or flecainide requires further investigation. In addition, studies have failed to demonstrate that the early administration of disopyramide after acute myocardial infarction decreases important arrhythmias or early mortality. Thus, disopyramide is now well established as an effective antiarrhythmic drug in ventricular and supraventricular arrhythmias although its role in therapy relative to that of recently introduced antiarrhythmic agents is not clear.

Haemodynamic effects of disopyramide using a new model of intravenous administration

Intravenous treatment with disopyramide is usually performed by administration of a bolus injection of 150 mg given over 5 min. followed by a continuous infusion of 18-24 mg hour-1. A decrease in cardiac output is associated with this rapid bolus injection. Seven patients with ischaemic heart disease entered an open randomised cross-over trial to elucidate if an extension of the bolus injection time to 20 min. resulted in a smaller decrease in cardiac output. Cardiac index decreased significantly (P less than 0.001) in both situations, with maximum decrease observed at time 5 and 20 min., respectively (equivalent to the ending of the administration of 150 mg disopyramide). The decrease in Cardiac index (mean +/- S.E.M.) was identical in the two situations (2.56 +/- 0.23 to 1.78 +/- 0.21 l/min. X m2 (30%) and 2.66 +/- 0.17 to 1.94 +/- 0.19 l/min. X m2 (27%], respectively. Blood pressure was unchanged, while heart-rate (P less than 0.025) and preejection period index (P less than 0.005) increased significantly and to the same extent in the two situations. Significant correlations between the log free and log total serum concentration of disopyramide and the relative change in preejection period index of r = 0.840 (P less than 0.01) and 0.919 (P less than 0.01), respectively, were observed giving disopyramide over 5 min. A significant anticlockwise hysteresis was observed extending the time of administration to 20 min. As no haemodynamic advantages are achieved by the slower way of administration we would still recommend the bolus injection to be given over 5 min.

Quantitative and qualitative binding characteristics of disopyramide in serum from patients with decreased renal and hepatic function

Protein binding of disopyramide, binding capacities, affinity constants and serum concentrations of alpha 1-acid glycoprotein (AAG) were studied in five groups of patients. A: young healthy volunteers (n = 8); B: elderly patients with minor symptoms of ischaemic heart disease (n = 9); C: patients with cirrhosis of the liver and normal values of coagulation factors (II, VII and X), albumin and immunoglobulin G (n = 8); D: patients with cirrhosis and at least two abnormal of the previously mentioned values (n = 9) and E: eleven patients with severely impaired renal function. Subfractions of AAG (Fr1, Fr2 and Fr3) were determined by affinoimmunoelectrophoresis. AAG concentration was significantly (P less than 0.005) elevated in group E patients and decreased (P less than 0.025) in group D patients. Fr2 is probably associated with the high affinity, first binding site of disopyramide to AAG. Earlier observations of a reduced qualitative binding of disopyramide in patients with cirrhosis can be explained by a significant decrease in Fr2 (P less than 0.001) in group D patients. The protein binding of disopyramide in patients with uraemia was significantly increased due to a significant (P less than 0.005) increase in AAG concentration in spite of a smaller (P less than 0.025) affinity constant. Suggestions for therapeutic drug monitoring based on total serum concentrations are given.

Plasma protein binding of drugs in the elderly

Binding to plasma proteins can affect the pharmacokinetics and pharmacodynamics of drugs. Age is one of many factors which can affect plasma protein binding of drugs. Unfortunately, very few generalities can be drawn from the studies of the effect of age on protein binding. Whether age has an effect on protein binding is dependent not only on the drug, but also on the manner in which the study is conducted. Several studies involve patients with various disease states making assessment of the effect of age alone on protein binding difficult. Results of different studies on the same drug do not always agree--in one case finding no change in protein binding with age and in another, a significant increase or decrease in protein binding. Most drugs which exhibit increased binding (decreased free fraction) in elderly subjects are basic and tend to have a greater affinity for alpha 1-acid glycoprotein than for albumin. The list of drugs exhibiting decreased binding (increased free fraction) in the elderly is longer and includes both acidic and basic drugs. The impact of changes in protein binding with age is dependent on the magnitude of the change, on the pharmacokinetic characteristics of the drug and on its therapeutic index. Some changes, although statistically significant, are not likely to be of importance clinically. From the studies reviewed, the free fraction is changed by greater than 50% in the elderly for only a few drugs, e.g. acetazolamide, diflunisal, etomidate, naproxen, salicylate, valproate and zimeldine.

A HPLC method for the simultaneous determination of disopyramide, lidocaine and their monodealkylated metabolites

This paper describes a simple high-performance liquid chromatographic method for the determination of disopyramide and lidocaine simultaneously with their dealkylated metabolites. After basic tert-butyl methyl ether extraction and back-extraction with phosphoric acid, the drugs and their metabolites were injected into a Supelcosil CN column and the absorbance of the eluate was measured at 215 nm. The sensitivity was 0.3 mumol/l and the obtained precision, selectivity and stability during storage were adequate for the performed clinical studies in patients therapeutically treated with disopyramide and/or lidocaine. Some results from the clinical studies are briefly presented.

The pharmacokinetics and protein binding of disopyramide in pigs

The pharmacokinetics of disopyramide were investigated in 5 pigs. Disopyramide was administered as intravenous bolus injections at different doses and as intravenous infusions at different rates. By measuring the free and total concentrations in plasma of parent compound and desisopropyldisopyramide (the main metabolite in humans) and the amounts excreted in urine it was found that disopyramide had a concentration dependent protein binding and that free and total concentrations could be described by a two-compartment model with a t1/2, beta of approximately 2 hours. The free concentrations were found to be more valuable for estimating the kinetic parameters. The total clearance of disopyramide in the pig was found to approximately 3 ml/min./kg which is about 3 times greater than in man. In contrast to humans the free clearance in the pig increased with declining concentration. Apart from this the kinetics of disopyramide in the pig were very similar to those in man. In conclusion the pig could be a relevant model for studying the pharmacokinetics in humans.

Haemodynamic effects and kinetics of concomitant intravenous disopyramide and atenolol in patients with ischaemic heart disease

The haemodynamic effects of concomitant intravenous administration of disopyramide (Norpace) and atenolol (Tenormin) were studied in a cross-over trial in 7 patients with ischaemic heart disease. Following 150 mg disopyramide i.v. the cardiac index (CI) and stroke volume index (SVI) decreased by 14% and 26%, respectively and the heart rate (HR) and preejection period index (PEPI) increased by 13% and 19%, respectively. A decrease in CI of 14% and HR of 21%, respectively were noted after intravenous administration of 7.5 mg atenolol; PEPI increased by 10% whereas SVI remained unchanged. The cardiac Index (CI) fell by 33% following the administration of both drugs. The effect on CI of the two drugs was additive. The effect of disopyramide and atenolol on HR, SVI and PEPI was not significantly modified by coadministration of the other drug. No change in blood pressure was observed after disopyramide or atenolol. A correlation (rho) of 0.540 and 0.387 was observed between the change in PEPI and the log free and total serum concentrations of disopyramide, respectively. Combined intravenous use of the two drugs in patients with incipient or overt heart failure is not recommended, unless it is due to the arrhythmia to be treated.

Kinetics of disopyramide in decreased hepatic function

The elimination kinetics of disopyramide was studied in 9 patients with decreased hepatic function (DHF) due to histologically verified cirrhosis of the liver, and in 11 patients with ischaemic heart disease (IHD). Disopyramide 100 and 150 mg was given intravenously as a bolus to the patients with IHD and DHF, respectively, followed by a continuous infusion of disopyramide 0.3 (DHF group) and 0.4 mg X min-1 (IHD group) until steady-state was achieved. A significant (p less than 0.001) positive correlation between the percentage unbound and total serum concentration of disopyramide was demonstrated in both groups. The percentage of unbound disopyramide at a total serum concentration of 5.9 mumol X l-1 was 45.5% and 19.4% in the DHF and IHD groups, respectively. A negative correlation (r = -0,751, p less than 0.05, and r = -0.827, p less than 0.01 in the IHD and DHF patients, respectively) between the free fraction of disopyramide and alpha 1-acid glycoprotein was observed. The serum concentration of alpha 1-acid glycoprotein, the major binding protein of disopyramide, was significantly lower in the patients with DHF. The clearance of unbound disopyramide and its total volume of distribution and half-life were significantly lower in the DHF patients. No difference in total elimination clearance could be demonstrated. The clinical implication of the present findings appear to be that the dosage of disopyramide should be reduced by 25% when it is given intravenously to patients with decreased hepatic function.