Role of plasma concentration monitoring in the evaluation of response to antiarrhythmic drugs

Suggested Transition from Oral to Intravenous Amiodarone Therapy

Objective:

To provide clinicians with a basis from which to decide the appropriate intravenous dosage of amiodarone in patients who are currently taking oral amiodarone.

Data Sources:

English-language articles describing the pharmacokinetics of amiodarone were collected through literature searches of the Index Medicus database over a period of approximately 4 years. Reference lists from the publications were reviewed to search further for original articles.

Study Selection:

Data were rejected only if there was reason to doubt the validity of the pharmacokinetic parameters reported. For example, dose administration, sample collection times, and pharmacokinetic analysis procedures had to be clearly stated.

Data Extraction:

Data describing the pharmacokinetics, particularly the half-life, of amiodarone after discontinuation of long-term oral treatment were extracted from the articles.

Data Synthesis:

No formal methods were used to combine the data.

Conclusions:

Based on pharmacokinetic considerations, no intravenous replacement treatment is necessary in patients for whom oral administration is contraindicated for less than 2 weeks and who have received adequate loading doses of amiodarone. Intravenous amiodarone may be administered at half the dosage of oral amiodarone, assuming a bioavailability of 50%, to patients for whom oral administration is contraindicated for an undetermined time or in whom a steady-state concentration is unlikely to have been reached.

Day-night variations in the renal excretion of the antiarrhythmic agent tiracizine and its metabolites

Daytime and nighttime urinary recovery as well as morning and evening trough serum levels of the antiarrhythmic agent tiracizine and three of its metabolites (M1, M2, and M3) were assessed during a 7-day multiple-dose study period (50 mg tiracizine twice daily) in eight healthy volunteers. A significantly lower mean steady-state urinary recovery was observed during the daytime as compared with during the nighttime (Ae (tot tau d)=42.0 +/- 15.7% vs. Ae (tot tau n)=51.2 +/- 19.6%). This difference is mainly due to a substantial increase of M1 and a smaller increase of M2 urinary recovery by night. Results of additional in vitro investigations showed the ratio of the nonionic/ionic forms of M1 and M2 to be highly dependent on pH in the range of pH 5-pH 7. Therefore, the observed day-night variations might be attributed to alterations of ionization, i.e., nonionic tubular reabsorption of the metabolites due to circadian differences in urinary pH. Trough serum levels of M1 and M2 tended to be higher at 7 P.M. as compared with 7 A.M. Due to the narrow therapeutic index of class I antiarrhythmics, the present results indicate the need for further investigations concerning the effect of urinary pH on the pharmacokinetics of tiracizine and its metabolites.

Effectiveness of amiodarone and electrical cardioversion for chronic rheumatic atrial fibrillation after mitral valve surgery

Thirty consecutive patients with chronic rheumatic atrial fibrillation (AF) > or = 3 months after successful mitral valve surgery and left atrial diameter < or = 60 mm were treated with oral amiodarone. Protocol included high loading dosages of amiodarone for 4 weeks, and if conversion to sinus rhythm (SR) was not achieved then electrical cardioversion was performed. Patients converted to SR were maintained on low-dose amiodarone for another 4 weeks when treatment was discontinued. Overall, 23 patients (77%) converted to SR after 4 weeks of therapy: 12 (40%) taking amiodarone alone and 11 (37%) with the addition of electrical cardioversion. The duration of AF > 48 months was an adverse factor in the ability to restore SR. Sixteen patients (70%) remained in SR at a mean follow-up of 17 months. The duration of AF < or = 48 months alone or in combination with left atrial diameter < or = 45 mm were the best predictors for long-term maintenance of SR. Thus, short-term amiodarone with or without electrical cardioversion is effective and safe in the treatment of chronic rheumatic AF after mitral valve surgery. The duration of AF and left atrial size can be used to identify patients with successful outcome.

Factors determining maintenance of sinus rhythm after chronic atrial fibrillation with left atrial dilatation

Successful therapy of atrial fibrillation (AF) has been reportedly influenced by a variety of factors including patient age, type of underlying heart disease, duration of arrhythmia, left ventricular function and left atrial (LA) size. To determine which of these factors are associated with maintenance of sinus rhythm after conversion, 43 patients with symptomatic chronic AF in the setting of a dilated left atrium (greater than or equal to 45 mm, range 45 to 78) were followed for at least 6 months after the return of sinus rhythm. Class IA drugs, IC drugs or amiodarone were used for therapy. Life table analysis showed sinus rhythm to be maintained in 81% for 6 months, 79% for 12 months and 60% for 24 months. Factors positively associated with success were conversion with drug therapy alone, duration of chronic AF less than or equal to 1 year, absence of mitral valve disease and LA dimension less than or equal to 60 mm (all p less than 0.05). Patient age, left ventricular function and presence of coronary disease were not associated with outcome. Thus, patients with moderate LA dilatation (45 to 60 mm) and a short duration of chronic AF can often be maintained in sinus rhythm, especially if they convert with pharmacologic intervention alone.