Polymorphic acetylation procainamide in man

Procainamide pharmacokinetics during extracorporeal membrane oxygenation

Procainamide is a useful agent for management of ventricular arrhythmia, however its disposition and appropriate dosing during extracorporeal membrane oxygenation (ECMO) is unknown. We report experience with continuous procainamide infusion in a critically ill adult requiring venoarterial ECMO for incessant ventricular tachycardia. Pharmacokinetic analysis of procainamide and its metabolite, N-acetylprocainamide (NAPA), was performed using serum and urine specimens. Kidney function was preserved, and sequencing of the N-acetyltransferase 2 gene revealed the patient was a phenotypic slow acetylator. Procainamide volume of distribution and half-life were calculated and found to be similar to healthy individuals. However, despite elevated serum procainamide concentrations, NAPA concentrations remained far lower in the serum and urine. The magnitude of procainamide and NAPA discordance suggested alternative contributors to the deranged pharmacokinetic profile, and we hypothesized NAPA sequestration by the ECMO circuit. Ultimately, the patient received orthotopic cardiac transplantation and was discharged home in stable condition. Procainamide should be used cautiously during ECMO, with close therapeutic drug monitoring of serum procainamide and NAPA concentrations. The achievement of therapeutic NAPA concentrations while maintaining safe serum procainamide concentrations during ECMO support may be challenging.

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.

Determination of Arylamine N-Acetyltransferase 2 Acetylation Genotype by PCR and Phenotyping Using Dapsone Through High-Pressure Liquid Chromatography Assay: A Gender Wise Study

The main aim of the study was to establish the acetylation status of local population of Pakistan by N-acetyltransferase 2 (NAT2) enzyme and to find out the concordance between phenotypic and genotypic methods for the determination of NAT2 acetylation. Gender-wise comparison of selected healthy male and female volunteers aged greater than 18 years was also conducted to see the effect of sex on NAT2 acetylation. Phenotypically, the rate of acetylation was determined by high-pressure liquid chromatography with dapsone (DDS) probe drug, while genotypically, NAT2 acetylation was determined by using specific primers for NAT2 variant alleles (M1, M2, and M3) amplified in separate polymerase chain reactions. High-pressure liquid chromatography results indicated 64% of the male volunteers to be fast acetylators while 36% were slow acetylators, while ratio of fast and slow acetylators for female was found to be 66% and 34%, respectively. Genotypically, the ratio of fast and slow for male was 60% and 40% and for female was 66% and 34%, respectively. The distribution of 3 NAT2 variant alleles was found in invariable number. For male volunteers, the highest frequency distribution showed by M2 allele was 56%, while for M1 and M3 the frequency was 32% and 12%, respectively, and for female volunteers highest frequency (51%) was shown by the M2 variant allele while lowest frequency (18%) was shown by M3 allele. There was the 94% concordance between the DDS phenotype and genotype. Gender effect on the acetylation was found to be nonsignificant (P > .05). Therefore, it is concluded that NAT2 acetylation rate can be used to check in vivo acetylation status with dapsone as probe drug. It is concluded that NAT2 acetylation rate was unaffected by gender and can be used to check in vivo acetylation status with dapsone as probe drug, which is inexpensive and less time-consuming.

Drug Therapy in Adult Congenital Heart Disease

Adults with congenital heart disease are at risk for atrial and ventricular arrhythmias that can lead to an increased morbidity as well as mortality. When catheter ablation is not an option or unsuccessful, antiarrhythmic drugs are the mainstay of treatment. There is limited data on the use of antiarrhythmics in this population. The purpose of this article is to discuss the practical aspects of the use of antiarrhythmics in adults with congenital heart disease. Several tables have been provided to provide clinicians a reference for daily use.

The Clinical Significance of the Pharmacogenetics of Cardiovascular Medications

Inter-individual variability in the response to numerous drugs can be traced to a number of sources. One source of variability in drug response is the variability associated with the metabolic capacity of an individual. The component of metabolic capacity that will be the focus of this article is that determined by heredity. Pharmacogenetics is frequently referred to as the study of the effects of heredity on the disposition and response to medications. This article will review the pharmacokinetic and pharmacodynamic significance of pharmacogenetics as it pertains to a select number of cardiovascular agents. The enzyme systems responsible for drug metabolism discussed in this article will be limited to the P-450IID6 and N-acetylation pathways. Given the extensive use of cardiovascular agents in clinical practice that are affected by this genetic polymorphism, it is important for the practicing pharmacist to be aware of this phenomenon and its implications. Hopefully, the knowledge gained from this article will help practicing pharmacists to appreciate the clinical significance of polymorphic drug metabolism and provide a basis for the application of this knowledge to a variety of practice settings.

Pharmacokinetic and pharmacodynamic drug interactions with ethanol (alcohol)

Ethanol (alcohol) is one of the most widely used legal drugs in the world. Ethanol is metabolized by alcohol dehydrogenase (ADH) and the cytochrome P450 (CYP) 2E1 drug-metabolizing enzyme that is also responsible for the biotransformation of xenobiotics and fatty acids. Drugs that inhibit ADH or CYP2E1 are the most likely theoretical compounds that would lead to a clinically significant pharmacokinetic interaction with ethanol, which include only a limited number of drugs. Acute ethanol primarily alters the pharmacokinetics of other drugs by changing the rate and extent of absorption, with more limited effects on clearance. Both acute and chronic ethanol use can cause transient changes to many physiologic responses in different organ systems such as hypotension and impairment of motor and cognitive functions, resulting in both pharmacokinetic and pharmacodynamic interactions. Evaluating drug interactions with long-term use of ethanol is uniquely challenging. Specifically, it is difficult to distinguish between the effects of long-term ethanol use on liver pathology and chronic malnutrition. Ethanol-induced liver disease results in decreased activity of hepatic metabolic enzymes and changes in protein binding. Clinical studies that include patients with chronic alcohol use may be evaluating the effects of mild cirrhosis on liver metabolism, and not just ethanol itself. The definition of chronic alcohol use is very inconsistent, which greatly affects the quality of the data and clinical application of the results. Our study of the literature has shown that a significantly higher volume of clinical studies have focused on the pharmacokinetic interactions of ethanol and other drugs. The data on pharmacodynamic interactions are more limited and future research addressing pharmacodynamic interactions with ethanol, especially regarding the non-central nervous system effects, is much needed.

Pharmacologically active drug metabolites: impact on drug discovery and pharmacotherapy

Metabolism represents the most prevalent mechanism for drug clearance. Many drugs are converted to metabolites that can retain the intrinsic affinity of the parent drug for the pharmacological target. Drug metabolism redox reactions such as heteroatom dealkylations, hydroxylations, heteroatom oxygenations, reductions, and dehydrogenations can yield active metabolites, and in rare cases even conjugation reactions can yield an active metabolite. To understand the contribution of an active metabolite to efficacy relative to the contribution of the parent drug, the target affinity, functional activity, plasma protein binding, membrane permeability, and pharmacokinetics of the active metabolite and parent drug must be known. Underlying pharmacokinetic principles and clearance concepts are used to describe the dispositional behavior of metabolites in vivo. A method to rapidly identify active metabolites in drug research is described. Finally, over 100 examples of drugs with active metabolites are discussed with regard to the importance of the metabolite(s) in efficacy and safety.

Acetylator phenotype and the clinical pharmacology of slow-release procainamide

Slow-release procainamide given 8-hourly is shown to produce plasma levels generally accepted as giving effective prophylaxis against ventricular dysrhythmias occurring after recent myocardial infarction. Patients can be classified into 'slow' and 'fast' acetylators of procainamide. Knowledge of acetylator status is helpful in determining the dose of procainamide necessary to attain effective steady-state plasma levels while avoiding toxic ones. Acetylator status cannot be assessed accurately using sulphadimidine when the patients are also taking procainamide.

Genetic polymorphisms of drug-metabolizing phase I enzymes CYP2E1, CYP2A6 and CYP3A5 in South Indian population

CYP2E1, CYP2A6 and CYP3A5 enzymes belong to phase I group of drug-metabolizing enzymes, which are involved in the metabolism of various compounds and xenobiotics. Presence of polymorphisms in the genes coding for these enzymes results in interindividual variations in drug metabolism, therapeutic response and susceptibility towards various diseases. The frequencies of these variants in genes differ considerably between ethnic groups. This study was carried out to estimate the allele and genotype frequencies of common variants in CYP2E1, CYP2A6 and CYP3A5 in South Indian population. Six hundred and fifty-two unrelated healthy volunteers of South Indian origin (Andhra Pradesh, Karnataka, Kerala and Tamil Nadu) were included in this study. Polymerase chain reaction-restriction fragment length polymorphism, allele-specific PCR, real-time PCR, SNaPshot and gene sequencing methods were used for the identification of gene polymorphisms. The frequencies of CYP2E1*1B, CYP2E1*5B and CYP2E1*6 alleles in South Indian population were 14.3, 1.3 and 22.4%, respectively. The frequencies of CYP2A6*2, CYP2A6*4A and CYP2A6*5 alleles were found to be 1, 8.9 and 0.7%, respectively. The distribution of CYP3A5*3 allele was 63.5%. There were no variant alleles of CYP3A5*2, CYP3A5*4 and CYP3A5*6 in South Indian population. The frequencies of CYP2E1, CYP2A6 and CYP3A5 in the South Indian population are distinct from Caucasians, Chinese, Japanese, African Americans and other compared populations. This is the first study conducted in the South Indian population with a larger sample size. The findings of our study provide the basic genetic information for further pharmacogenomic investigations in the population.

Pharmacogenomics: a systems approach

Pharmacogenetics and pharmacogenomics involve the study of the role of inheritance in individual variation in drug response, a phenotype that varies from potentially life-threatening adverse drug reactions to equally serious lack of therapeutic efficacy. Pharmacogenetics-pharmacogenomics represents a major component of the movement to 'individualized medicine'. Pharmacogenetic studies originally focused on monogenic traits, often involving genetic variation in drug metabolism. However, contemporary studies increasingly involve entire 'pathways' that include both pharmacokinetics (PKs)--factors that influence the concentration of a drug reaching its target(s)--and pharmacodynamics (PDs), factors associated with the drug target(s), as well as genome-wide approaches. The convergence of advances in pharmacogenetics with rapid developments in human genomics has resulted in the evolution of pharmacogenetics into pharmacogenomics. At the same time, studies of drug response are expanding beyond genomics to encompass pharmacotranscriptomics and pharmacometabolomics to become a systems-based discipline. This discipline is also increasingly moving across the 'translational interface' into the clinic and is being incorporated into the drug development process and governmental regulation of that process. The article will provide an overview of the development of pharmacogenetics-pharmacogenomics, the scientific advances that have contributed to the continuing evolution of this discipline, the incorporation of transcriptomic and metabolomic data into attempts to understand and predict variation in drug response phenotypes as well as challenges associated with the 'translation' of this important aspect of biomedical science into the clinic.

Pharmacogenomics: a new paradigm to personalize treatments in nephrology patients

Although notable progress has been made in the therapeutic management of patients with chronic kidney disease in both conservative and renal replacement treatments (dialysis and transplantation), the occurrence of medication-related problems (lack of efficacy, adverse drug reactions) still represents a key clinical issue. Recent evidence suggests that adverse drug reactions are major causes of death and hospital admission in Europe and the United States. The reasons for these conditions are represented by environmental/non-genetic and genetic factors responsible for the great inter-patient variability in drugs metabolism, disposition and therapeutic targets. Over the years several genetic settings have been linked, using pharmacogenetic approaches, to the effects and toxicity of many agents used in clinical nephrology. However, these strategies, analysing single gene or candidate pathways, do not represent the gold standard, being the overall pharmacological effects of medications and not typically monogenic traits. Therefore, to identify multi-genetic influence on drug response, researchers and clinicians from different fields of medicine and pharmacology have started to perform pharmacogenomic studies employing innovative whole genomic high-throughput technologies. However, to date, only few pharmacogenomics reports have been published in nephrology underlying the need to enhance the number of projects and to increase the research budget for this important research field. In the future we would expect that, applying the knowledge about an individual's inherited response to drugs, nephrologists will be able to prescribe medications based on each person's genetic make-up, to monitor carefully the efficacy/toxicity of a given drug and to modify the dosage or number of medications to obtain predefined clinical outcomes.

Cardiovascular pharmacogenomics and individualized drug therapy

The goal of individualized drug therapy requires physicians to be able to accurately predict an individual's response to a drug. Both genetic and environmental factors are known to influence drug response. 'Pharmacogenetics' is the study of the role of inheritance in variation in drug response phenotypes. Pharmacogenetics is now moving genome-wide to become 'pharmacogenomics', resulting in the recognition of novel biomarkers for individual variation in drug response. This article reviews the development, promise and challenges facing pharmacogenomics, using examples of drugs used to treat or prevent cardiovascular disease.

Procainamide-induced lupus erythematosus-like syndrome in relation to acetylator phenotype and plasma levels of procainamide

To investigate the relationship between acetylator phenotype and the development of procainamide (PA)-induced systemic lupus erythematosus (SLE-like syndrome, 28 patients with chronic ventricular arrhythmias treated with PA were followed for one year. The therapy was guided by plasma monitoring in all patients in order to obtain the proposed therapeutic plasma level of PA. Nine patients (30%), both slow and rapid acetylators, developed the SLE-like syndrome within one year. PA plasma levels were similar in both slow and rapid acetylators and there was no difference in total dose or duration of therapy before development of the syndrome. Thus, the acetylator phenotype is probably of no or minor predictive importance when PA therapy is guided by plasma monitoring. On the other hand, the antinuclear antibodies appeared significantly more rapidly in patients developing the syndrome and could possible be used as an indicator of the risk. The results support the hypothesis that the primary amino group structure of PA may be of importance in the induction of the SLE-like syndrome.

Acetylator phenotype in patients with hydralazine-induced lupoid syndrome

The acteylator phenotype has been determined (isoniazid half-life) in 31 patients, 25 of them women, who had exhibited a lupus erythematosus-like syndrome during treatment with hydralazine. Twenty-nine patients were slow acetylators, one was rapid (probably spontaneous SLE) and one uncertain. Only two patients had been given more than 200 mg of hydralazine daily. The mean duration of therapy was 32 months at the onset of symtoms. These were not serious but rather long-standing. Our study confirms that patients who risk developing hydralazine lupus are slow acetylators, especially females, treated with more than 100 mg daily. Rapid acetylators seem to develop this side-effect rarely, if at all.

Primer on the human genome

The study of the expression patterns of many genes, or even the entire genome, is now routinely possible. Such powerful tools have enabled hypothesis-generating research at a scale never before possible. Moreover, spatially or temporally linked gene and protein expression, implying co-regulation and functional relatedness, has led to the identification of particular clusters of genes important for fundamental biologic processes, such as development and cancer. Not only is this expected to yield further mechanistic insights into disease processes, but perhaps most exciting, it will likely establish the foundation of predictive medicine, in which understanding of individual genomic signatures leads to the use of appropriately targeted therapy.

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should be able to understand the fundamental tenets of molecular biology as they relate to the field of genomics.

Therapeutic Levels of Intravenous Procainamide in Neonates: A Retrospective Assessment

STUDY OBJECTIVES

To evaluate dosing and pharmacokinetic parameters of intravenous continuous-infusion procainamide in neonates, and to identify dosage regimens and factors leading to therapeutic procainamide levels and minimal adverse events.

DESIGN

Retrospective, observational study.

SETTING

Pediatric hospital.

PATIENTS

. Twenty-one patients (seven preterm, 14 full term) younger than 30 days who received continuous-infusion procainamide therapy for more than 15 hours or had two consecutive therapeutic procainamide levels obtained while receiving therapy between June 1, 2002, and December 31, 2005.

MEASUREMENTS AND MAIN RESULTS

Data on demographics, dosing, drug levels, and adverse effects were collected. Doses that achieved therapeutic levels were documented, and procainamide clearance was calculated and evaluated with regard to renal function and gestational age in patients who were at steady state. Mean clearance and mean N-acetylprocainamide (NAPA):procainamide ratios were compared between preterm and term neonates. No patients experienced hemodynamic instability or other adverse effects due to procainamide. Procainamide was given as a mean +/- SD 9.6 +/- 1.5-mg/kg bolus in 20 of 21 patients before continuous infusion. The mean +/- SD dose at which two therapeutic levels were achieved was 37.56 +/- 13.52 microg/kg/minute. Procainamide clearance was 6.36 +/- 8.85 ml/kg/minute and correlated with creatinine clearance (r=0.78, p<0.00001) and age at day of sampling (r=0.49, p<0.00001). The NAPA:procainamide ratio at steady state was 0.84 +/- 0.53; two patients were determined to be fast acetylators (ratio > 1). Preterm infants had lower mean clearance rates (p<0.001) but higher NAPA:procainamide ratios (p<0.01) than those of term infants. Five patients experienced seven supratherapeutic levels while receiving therapy; four of these patients were preterm, and all had creatinine clearances less than 30 ml/minute/1.73 m(2). Three patients had four pairs of levels obtained after discontinuation of procainamide, and elimination rate constant and half-life were calculated.

CONCLUSION

Procainamide can be safely used in neonates, with no short-term adverse effects. The dosage regimen for intravenous procainamide required to achieve therapeutic levels in neonates is similar to that of older infants and children. Doses may need to be reduced in premature infants and in those with renal dysfunction.

Pharmacogenetics and Pharmacogenomics: Development, Science, and Translation

Pharmacogenetics and pharmacogenomics involve the study of the role of inheritance in individual variation in drug response, a phenotype that varies from potentially life-threatening adverse drug reactions to equally serious lack of therapeutic efficacy. This discipline evolved from the convergence of rapid advances in molecular pharmacology and genomics. Originally, pharmacogenetic studies focused on monogenic traits, often involving genetic variation in drug metabolism. However, contemporary studies increasingly involve entire "pathways" encoding proteins that influence both pharmacokinetics--factors that influence the concentration of a drug reaching its target(s)--and pharmacodynamics, the drug target itself, as well as genome-wide approaches. Pharmacogenomics is also increasingly moving across the "translational interface" into the clinic and is being incorporated into the drug development process and the governmental regulation of that process. However, significant challenges remain to be overcome if pharmacogenetics-pharmacogenomics is to achieve its full potential as a major medical application of genomic science.

Cardiovascular drugs for the newborn

This article reviews the various cardiovascular drugs for newborns, including antiarrhythmics, antihypertensives, inotropes, and pulmonary vasodilators. Antiarrhythmic drugs are classified according to their mechanisms of action, such as effects on ion channels, duration of repolarization, and receptor interaction, which help with understanding the effects of individual antiarrhythmic drugs and selection of drugs for specific arrhythmias. Drug treatment for hypertension should start with a single drug from one of the following classes: ACE inhibitors, angiotensin-receptor antagonists, beta-receptor antagonists, calcium channel blockers, or diuretics. The inotropic drug should be selected according to its specific pharmacologic properties and the specific cardiovascular abnormality to be corrected. An effective pulmonary vasodilator must dilate the pulmonary vasculature more than the systemic vasculature.

Pharmacogenomic Discovery Approaches: Will the Real Genes Please Stand Up?

Genetic inheritance plays a significant role in the interindividual variability of drug response. The field of pharmacogenomics seeks to identify genetic factors that influence drug response, including both those that are inherited and those that arise within tumors, and use this information to improve drug therapy. Candidate gene approaches have led to clinical tests for toxicity avoidance (eg, TPMT, UGT1A1) and efficacy prediction (eg, epidermal growth factor receptor–activating mutations). However, the “right” genes are not known for most anticancer drugs. Strategies for uncovering pharmacogenomic associations vary widely from monogenic candidate gene approaches to polygenic genome-wide approaches. This review will place in context clinically relevant pharmacogenomic discovery approaches, including the relative strengths and weaknesses and the challenges inherent with achieving the goal of individualized therapy.

Levofloxacin and ciprofloxacin decrease procainamide and N-acetylprocainamide renal clearances

Ten healthy adults participated in a randomized, crossover drug interaction study testing procainamide only, procainamide plus levofloxacin, and procainamide plus ciprofloxacin. During levofloxacin therapy, most procainamide and N-acetylprocainamide (NAPA) pharmacokinetic parameters, including decreased renal clearances and renal clearance/creatinine clearance ratios, changed (P < 0.05). During ciprofloxacin treatment, only procainamide and NAPA renal clearances decreased significantly.

Pharmacogenomics: bench to bedside

Pharmacogenetics is the study of the role of inheritance in inter-individual variation in drug response. Since its origins in the mid-twentieth century, a major driving force in pharmacogenetics research has been the promise of individualized drug therapy to maximize drug efficacy and minimize drug toxicity. In recent years, the convergence of advances in pharmacogenetics with rapid developments in human genomics has resulted in the evolution of pharmacogenetics into pharmacogenomics, and led to increasing enthusiasm for the 'translation' of this evolving discipline into clinical practice. Here, we briefly summarize the development of pharmacogenetics and pharmacogenomics, and then discuss the key factors that have had an influence on - and will continue to affect - the translation of pharmacogenomics from the research bench to the bedside, highlighting the challenges that need to be addressed to achieve this goal.

THEINTEGRATION OFPHARMACOKINETICS ANDPHARMACODYNAMICS: Understanding Dose-Response

Pharmacokinetic (PK) and pharmacodynamic (PD) studies have proven to be powerful and instructive tools, particularly in elucidating important aspects of human pharmacology. Nevertheless, they remain imperfect tools in that they only allow researchers to indirectly extrapolate, through computational modeling, the dynamic processes of drug action. Furthermore, neither tool alone provides a complete nor necessarily relevant picture of drug action. This review explores the utility and applications of PK and PD in the study of drugs, provides examples of lessons learned from their application to studies of human pharmacology, points out some of their limitations, and advances the thesis that these tools ideally should be employed together in an integrated approach. As we continue to apply these tools across the continuum of age and disease, they provide a powerful means to enhance our understanding of drug action, drug interactions, and intrinsic host factors that influence pharmacologic response.

Therapeutic drug monitoring of antiarrhythmic drugs

Most antiarrhythmic drugs fulfil the formal requirements for rational use of therapeutic drug monitoring, as they show highly variable plasma concentration profiles at a given dose and a direct concentration-effect relationship. Therapeutic ranges for antiarrhythmic drugs are, however, often very poorly defined. Effective drug concentrations are based on small studies or studies not designed to establish a therapeutic range, with varying dosage regimens and unstandardised sampling procedures. There are large numbers of nonresponders and considerable overlap between therapeutic and toxic concentrations. Furthermore, no study has ever shown that therapeutic drug monitoring makes a significant difference in clinical outcome. Therapeutic concentration ranges for antiarrhythmic drugs as they exist today can give an overall impression about the drug concentrations required in the majority of patients. They may also be helpful for dosage adjustment in patients with renal or hepatic failure or in patients with possible toxicological or compliance problems. Their use in optimising individual antiarrhythmic therapy, however, is very limited.

Pharmacogenetic screening and therapeutic drugs

BACKGROUND

Pharmacogenetics is the science of the influence of heredity on pharmacological response.

ISSUES

The cost of severe adverse drug reactions in individuals has been estimated in the US alone to be in excess of US$4 billion. It has been argued that in a significant proportion of cases, the efficacy and toxicity profiles of drug therapy would be substantially improved in individuals if characteristics due to genetic variation were taken into account. Methods are now available, which make screening for susceptibility feasible.

CONCLUSIONS

There are several therapeutic areas in which screening may give rise to significant improvements in outcome with cost-benefits to both the individual and the community. However, there is currently a lack of data on which cost-benefit analysis can be based. The challenge is to provide this information for new drugs, and for drugs with established therapeutic roles.

Role of K+ channels in N-acetylprocainamide-induced relaxation of bovine tracheal smooth muscle

We examined the relaxant effects of N-acetylprocainamide, the major hepatic metabolite of procainamide, on bovine tracheal smooth muscle, focusing on the possible involvement of K+ channels. N-acetylprocainamide produced a concentration-dependent and full inhibition of the tension development elicited by methacholine (0.3 or 1 microM). The potency of N-acetylprocainamide in diminishing methacholine-elicited tension development was one-half of that of procainamide. By comparison, N-acetylprocainamide inhibited high-K+ (40 mM)-induced contraction more potently than procainamide though both inhibitions were largely reduced when compared to those against methacholine-induced contraction. Iberiotoxin (30 nM), Ba(2+) (1 mM) or a combination of both agents significantly attenuated the relaxant effect of N-acetylprocainamide on methacholine-induced contraction, whereas apamin (100 nM), 4-aminopyridine (300 microM), and glibenclamide (10 microM) did not affect it. These results suggest that N-acetylprocainamide, similar to procainamide, elicits tracheal smooth muscle relaxation mainly through the activation of plasma membrane K+ channels.

Classification and pharmacology of antiarrhythmic drugs

Despite the emergence of several forms of nonpharmacologic therapy for cardiac arrhythmias, antiarrhythmic drugs continue to play an important role in the management of patients with this common clinical problem. The key to the proper use of antiarrhythmic drugs is a thorough knowledge of their mode of action and pharmacology. The pharmacology of antiarrhythmic drugs is particularly important because patients with cardiac arrhythmias frequently have multiorgan disease, which may influence the metabolism and elimination of antiarrhythmic drugs. The accumulation of toxic amounts of these agents can lead to dire effects including, but not limited to, ventricular proarrhythmia and malignant bradycardia. The goals of pharmacologic therapy of cardiac arrhythmia are to provide the maximum benefit in terms of arrhythmia suppression while maintaining patient safety. To accomplish these goals, a knowledge of the pharmacology of several antiarrhythmic drugs is mandatory.

Therapeutic drug monitoring: antiarrhythmic drugs

Antiarrhythmic agents are traditionally classified according to Vaughan Williams into four classes of action. Class I antiarrhythmic agents include most of the drugs traditionally thought of as antiarrhythmics, and have as a common action, blockade of the fast-inward sodium channel on myocardium. These agents have a very significant toxicity, and while they are being used less, therapeutic drug monitoring (TDM) does significantly increase the safety with which they can be administered. Class II agents are antisympathetic drugs, particularly the beta-adrenoceptor blockers. These are generally safe agents which do not normally require TDM. Class III antiarrhythmic agents include sotalol and amiodarone. TDM can be useful in the case of amiodarone to monitor compliance and toxicity but is generally of little value for sotalol. Class IV antiarrhythmic drugs are the calcium channel blockers verapamil and diltiazem. These are normally monitored by haemodynamic effects, rather than using TDM. Other agents which do not fall neatly into the Vaughan Williams classification include digoxin and perhexiline. TDM is very useful for monitoring the administration (and particularly the safety) of both of these agents.

Genotyping of N-acetylation polymorphism and correlation with procainamide metabolism

We studied the genotypes of polymorphic N-acetyltransferase (NAT2) in 145 Japanese subjects by the polymerase chain reaction-restriction fragment length polymorphism method. The rapid-type NAT2*4 was expressed at a higher frequency (68.6%) than the slow-type genes with specific point mutations (NAT2*6A, 19.3%; NAT2*7B, 9.7%; NAT2*5B, 2.4%). The frequency of NAT2* genotypes consisted of 44% of a homozygote of NAT2*4, 49% of a heterozygote of NAT2*4 and mutant genes, and 7% of a combination of mutant genes. The metabolic activity for procainamide to N-acetylprocainamide was measured in 11 healthy subjects whose genotype had been determined. Although the acetylation activity substantially varied interindividually, the variability was considerably reduced after classification according to the genotype. The N-acetylprocainamide/procainamide ratio in urinary excretion was 0.60 +/- 0.17 (mean +/- SD) for those with NAT2*4/*4, 0.37 +/- 0.06 for NAT2*4/*6A, 0.40 +/- 0.03 for NAT2*4/*7B, and 0.17 for NAT2*6A/*7B. The results indicated that the NAT2* genotype correlates with acetylation of procainamide.

Efficacy and safety of procainamide in preventing arrhythmias after coronary artery bypass surgery

Arrhythmias are common after cardiac surgery and are associated with hemodynamic compromise, stroke, and prolonged hospitalization. Beta blockers prevent atrial fibrillation postoperatively, but there are few data regarding the prophylactic use of type 1 antiarrhythmic agents or the prevention of ventricular arrhythmias. Accordingly, we performed a randomized, double-blind, placebo-controlled study of the effects of oral procainamide on 100 patients undergoing elective coronary artery bypass surgery. Procainamide was received for 4 days; the dosage was adjusted for body weight. Patients receiving procainamide had a significant reduction in atrial fibrillation (16 vs 29 patient-days, p < 0.05) and ventricular tachycardia (2% vs 20%, p < 0.01). However, the incidence of atrial fibrillation was not significantly reduced (38% vas 26%). In the group achieving therapeutic serum procainamide levels, there was reduction in all measured postoperative arrhythmias. No serious cardiac or noncardiac adverse events were noted during procainamide therapy, although there was a significant increase in the incidence of nausea. We conclude that procainamide reduces arrhythmias in the early postoperative period after coronary artery bypass surgery, most prominently in patients who achieve therapeutic serum levels. This was associated with no serious cardiac adverse reactions.

Role of genetic factors in drug-related autoimmunity

Although there is evidence to suggest that genetic factors play a major role in the pathogenesis of many of the rheumatic diseases, far less is known of their role in the induction and expression of human autoimmunity resulting from long-term exposure to drugs, chemicals and environmental agents. Pharmacogenetic factors represent an important source of interindividual variation in response to drugs; most research to date has focused on genetic polymorphism of drug metabolism via N-acetylation, S-methylation or cytochrome P-450-catalyzed oxidation. In drug-related autoimmunity, there is limited evidence that the host's genetic background plays a major role beyond the expression of autoantibodies. More recent prospective studies have concentrated on the association of MHC-genes in the expression of autoimmunity and the susceptibility of patients to develop drug-related clinical syndromes.

Genetic, immunologic and biotransformation studies of patients on procainamide

This report represents follow-up observations of a unique long-term study of patients on procainamide (PA) for various cardiac arrhythmias. Serologic and clinical evaluations associated with drug-related autoimmunity were assessed and patients were characterized for factors postulated to influence susceptibility to autoimmunity, including acetylator phenotype, oxidative metabolism of PA, HLA class profile, and production of interleukin-1 (IL-1) and tumor necrosis factor (TNF). Fifty-two percent had IgM and 70% IgG antibodies to total histones; 67% had IgG antibodies to histone H2A/H2B. Patients were equally divided between fast and slow acetylators. N-oxidative metabolism of PA was indicated by the presence of urinary nitroprocainamide, which correlated with elevated titers of antihistone antibodies. There was a significant incidence of the DQw7 split of DQw3 in PA patients when compared to controls, and the frequency of antibodies to total histones and H2A/H2B was significantly increased in the DQw7 patients. C4A*QO and C4B*QO alleles were more frequent in the PA patients than in controls. IL-1 and TNF production was not different in patients compared to controls. These data suggest that certain genetic factors may serve as markers for PA-related autoimmunity.

Combined high-efficiency hemodialysis and charcoal hemoperfusion in severe N-acetylprocainamide intoxication

Several extracorporeal techniques have been used to remove N-acetylprocainamide (NAPA), the major metabolite of procainamide, in patients intoxicated with this substance. We report a patient with life-threatening NAPA intoxication who was rapidly and successfully treated with combined high-efficiency hemodialysis and charcoal hemoperfusion. The hemodialyzer and hemoperfusion cartridge were placed in series such that the patient's blood was dialyzed before reaching the cartridge. Overall clearance of NAPA was 153 mL/min, with clearance due to hemodialysis averaging 102 mL/min and that due to hemoperfusion averaging 88 mL/min. Thus, addition of the hemoperfusion cartridge into the extracorporeal circuit resulted in a 50% increase in clearance over that obtainable by high-efficiency hemodialysis alone. In comparison to other modalities, this technique is more effective than either hemodialysis or charcoal hemoperfusion alone and can achieve a more rapid reduction of serum NAPA levels than that observed with slow continuous hemofiltration or hemodiafiltration.

Acecainide pharmacokinetics in normal subjects of known acetylator phenotype

The purpose of this study was to determine the pharmacokinetics of acecainide (formerly N-acetylprocainamide) in six normal subjects of known acetylator phenotype. Three subjects were fast acetylators and three slow acetylators by sulfapyridine phenotyping criteria. Each subject received a 20-min, 3 mg kg-1 intravenous acecainide infusion. Concentrations of acecainide, procainamide, and their deethylated metabolites were measured in serum and urine samples using HPLC. Acecainide renal clearance, nonrenal clearance, steady-state volume of distribution, and other pharmacokinetic parameters were estimated using standard approaches. Acecainide renal clearance and steady-state volume of distribution were (mean +/- SD) 13.6 +/- 1.581 h-1 and 135 +/- 20.31, respectively, and were not significantly different in fast and slow acetylators. Acecainide nonrenal clearance in the six subjects was 3.0 +/- 1.01 h-1; however, nonrenal clearance in slow acetylators was 1.8 times that in fast acetylators (3.9 vs 2.21 h-1, p = 0.012) with clear separation of the subjects into two groups when the data were grouped by acetylator phenotype. The nonrenal clearance of acecainide was inversely correlated with percentage sulfapyridine acetylation. Computer simulations were conducted to explore possible explanations for the observed difference in nonrenal clearance.

Poisoning due to class IA antiarrhythmic drugs. Quinidine, procainamide and disopyramide

Quinidine, procainamide and disopyramide are antiarrhythmic drugs in the class 1A category. These drugs have a low toxic to therapeutic ratio, and their use is associated with a number of serious adverse effects during long term therapy and life-threatening sequelae following acute overdose. Class 1A agents inhibit the fast inward sodium current and decrease the maximum rate of rise and amplitude of the cardiac action potential. Prolonged Q-T interval and, to a lesser extent, QRS duration may be observed at therapeutic concentrations of quinidine. With increasing plasma concentrations, progressive depression of automaticity and conduction velocity occur. 'Quinidine syncope' (a transient loss of consciousness due to paroxysmal ventricular tachycardia, frequently of the torsade de pointes type) occurs with therapeutic dosing, often in the first few days of therapy. Extracardiac adverse effects of quinidine include potentially intolerable gastrointestinal effects and hypersensitivity reactions such as fever, rash, blood dyscrasias and hepatitis. Procainamide produces electrophysiological changes that are similar to those of quinidine, although Q-T interval prolongation with the former is less pronounced at therapeutic concentrations. Hypersensitivity reactions including fever, rash and (more seriously) agranulocytosis are associated with procainamide, and a frequent adverse effect requiring cessation of therapy is the development of systemic lupus erythematosus. Of the 3 drugs, disopyramide has the most pronounced negative inotropic effects, which are especially significant in patients with pre-existing left ventricular dysfunction. As with quinidine, unexpected 'disopyramide syncope' at therapeutic concentrations has been described. Anticholinergic side effects are common with this drug and may require cessation of therapy. Disopyramide therapy may unpredictably induce severe hypoglycaemia. Severe intoxication with the class 1A agents may result from acute accidental or intentional overdose, or from accumulation of the drugs during long term therapy. Acute overdose can result in severe disturbances of cardiac conduction and hypotension, frequently accompanied by central nervous system toxicity. Decreased renal function can cause significant accumulation of procainamide and its active metabolite acecainide (N-acetyl-procainamide), resulting in severe intoxication. Mild to moderate renal dysfunction is less likely to lead to quinidine or disopyramide intoxication, unless renal failure is severe or concurrent hepatic dysfunction is present. Management of acute intoxication with class 1A drugs includes gut decontamination with provision of respiratory support and treatment of seizures as needed. Hypertonic sodium bicarbonate, by antagonising the inhibitory effect of quinidine on sodium conductance, may reverse many or all manifestations of cardiovascular toxicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Species differences in the pharmacokinetics of recainam, a new anti-arrhythmic drug

The pharmacokinetics of recainam, an anti-arrhythmic drug, were compared in mice, rats, rabbits, dogs, rhesus monkeys, and man. Bioavailability was virtually complete in monkeys and dogs, 67 per cent in man and 51 per cent in rats. Non-linear kinetics between the oral and i.v. dose in rabbits precluded estimation of bioavailability. Linear plasma dose proportionality occurred in dogs between 6 and 60 mg kg-1 oral doses and rhesus monkeys between 1 and 15 mg kg-1 i.v. doses. A greater than proportional increase in the plasma AUC of recainam occurred between oral doses ranging from 54-208 mg kg-1 in mice, 25-110 mg kg-1 in rats, and 50-100 mg kg-1 in rabbits. In human subjects, the AUC/unit dose was linear between 400 and 800 mg. The terminal elimination t1/2 of recainam ranged from 1-5h in laboratory animals and man. The plasma Cmax and AUC of recainam were virtually identical after single or multiple (21 day) oral doses in dogs. After an i.v. dose, plasma clearance of recainam (l kg-1 .h) was 4.9-5.2 in rats and rabbits and 0.4-1.9 in dogs, rhesus monkeys, and man. The steady state volume of distribution was 2-5 times larger than the total body water of laboratory animals and man. Recainam was very poorly bound (10-45 per cent) to the serum proteins of rodents, rabbits, dogs, rhesus monkeys and man. In rhesus monkeys and man, recainam accounted for 10 per cent and 70 per cent, respectively, of the plasma radioactivity at 6 h post-dose. The pharmacokinetic profile of recainam in dogs most closely resembled that of man.

Genetically determined N-acetylation and oxidation capacities in Japanese patients with non-occupational urinary bladder cancer

Genetically determined polymorphisms of N-acetylation and oxidative capacity have been studied using dapsone and metoprolol in 51 Japanese patients with spontaneous bladder cancer and 203 healthy control subjects. The results for N-acetylation pharmacogenetics were against the initial expectation that there would be a preponderance of slow acetylators in the cancer group, as 3 such patients (5.9%) were found as compared to 13 (6.4%) in the healthy group. There was no poor metabolizer (PM) of metoprolol in the cancer group, whereas in the healthy group one (0.5%) was a PM. There were no significant differences between the groups in the frequency of slow acetylator and poor oxidiser phenotypes, or in the frequency distribution profiles of acetylation (monoacetyldapsone/dapsone) and oxidative metabolic ratio (log metoprolol/alpha-hydroxymetoprolol). The results indicate that neither N-acetylation nor the debrisoquine/sparteine-type oxidative phenotype and/or capacity represent a genetic predisposition to spontaneous bladder carcinogenesis in Japanese patients. In the normal Japanese population there is a great predominance of rapid acetylators and extensive oxidisers.

Effects of salbutamol on the absorption and disposition of sulphamethoxazole in adult volunteers

On the basis of the reports that beta-adrenergic stimulation affects gastrointestinal motility in man as well as induces N-acetyltransferase in rat pineal gland, we decided to assess the effects of salbutamol pretreatment on the absorption as well as disposition of sulphamethoxazole (SMZ). After a control pharmacokinetic study of SMZ, each of six healthy volunteers took salbutamol at a dose of 4 mg four times daily for two weeks, and the kinetic study of SMZ was repeated after the morning dose on the fifteenth day. None of SMZ half-life, volume of distribution, renal and hepatic clearance rates was significantly altered. However, salbutamol pretreatment resulted in significant reduction in the absorption rate constant of SMZ from 1.168 +/- 0.509 h-1 (mean +/- S.D.) to 0.688 +/- 0.348 h-1 (P less than 0.025), and this was associated with prolongation of tmax from 3.00 +/- 1.69 h to 4.33 +/- 1.51 h (P less than 0.025). Cmax, however, was not correspondingly reduced probably as a result of significant increase in the extent of SMZ absorption from 611 +/- 108 mg to 749 +/- 78 mg (P less than 0.025). Our findings suggest that beta-adrenergic stimulation does not significantly induce human hepatic N-acetyltransferase enzyme. However, it does reduce the absorption rate as well as increase the extent of absorption of SMZ.

Determination of acetylator phenotype in Caucasians with caffeine

Acetylator status in 595 healthy Caucasian volunteers was determined with caffeine. The test group consisted of 372 males and 223 females, 18 to 78 years of age. 312 volunteers were smokers. Caffeine was taken orally as Coffein Comprette (200 mg caffeine x H2O) and urine was collected for 8 h. The metabolic ratio (MR) of 5-acetylamino-6-formylamino-1-methyluracil (AFMU) to 1-methylxanthine (MX) was determined by HPLC. In total 61.7% of the group had a MR less than 0.48 and were classified as slow acetylators. MR varied from 0.01 to 0.47 in the slow acetylators and from 0.48 to 4.7 in the fast acetylator group. Clear dependence of acetylator type upon age, sex or smoking behaviour was not observed. The present study has confirmed the caffeine test as a feasible tool to determine acetylation capacity.

Effect of amiodarone on the disposition of procainamide in the rat

We examined the effect of amiodarone on the disposition of procainamide in the rat to determine the mechanism of a reported interaction between amiodarone and procainamide and to determine the effect of amiodarone on drug acetylation. Animals received a 5-d pretreatment with amiodarone hydrochloride (100 mg/kg) or diluent prior to the intravenous administration of 50 mg/kg of procainamide hydrochloride. The plasma clearance, volume of distribution, and half-life of procainamide did not significantly differ between the two groups. The urinary recovery of N-acetylprocainamide was increased by 31% (p less than 0.01) in amiodarone pretreated animals. However, there was no change in the partial clearance of procainamide to N-acetylprocainamide. Neither the renal clearance of procainamide nor N-acetylprocainamide was altered by amiodarone pretreatment. These data suggest that amiodarone interacts with procainamide by reduction of an alternate pathway of elimination, possibly oxidative metabolism.

N-acetylation and serotonergic measures in a group of psychiatric patients

Serotonin is N-acetylated to melatonin. The purpose of this study was to explore the possibility of N-acetylation of dapsone reflecting serotonergic activity. The ratio of monoacetyldapsone/dapsone (MAD/DDS) in plasma, 5-HIAA in CSF, and imipramine-binding to platelets were investigated in a group of psychiatric patients, diagnosed according to the DSM-III as affective disorders, schizophrenia, and personality disorders. There was no significant correlation between either of the serotonergic estimates and N-acetylation in the whole patient group or in diagnostic subgroups of patients. Sixty-four percent of the patients were slow N-acetylators (MAD/DDS less than 0.4), which is a ratio in line with several other studies of psychiatric patients. Among patients with affective disorders, all unipolar patients were slow N-acetylators, while five out of six bipolar patients were fast N-acetylators. The N-acetylation of patients with a history of suicide attempt did not differ from those without. The discrepancy in N-acetylation between uni- and bipolar patients might again address the issue of them representing two different biochemical and genetic disorders.