Bromocriptine treatment of digitalis-induced ventricular tachyarrhythmias: studies in a canine model

Comparison of digitalis-related adverse events in hospitalized men and women in Italy: An observational study

BACKGROUND

A higher mortality rate in women than in men treated with digitalis has been described. We hypothesized that this result could be due in part to an increased susceptibility of women to adverse events (AEs) from digitalis.

OBJECTIVE

The aim of this study was to compare the incidence of AEs related to digitalis in women and men.

METHODS

This was an observational study conducted in geriatrics and internal medicine acute-care wards located throughout Italy. We used the data of the Gruppo Italiano di Farmacoepidemiologia nell'Anziano (Italian Group of Pharmacoepidemiology in the Elderly), a collaborative study group on drug use and adverse drug reactions in hospitalized adults that performed 6 different surveys between 1988 and 1998. Adults who were taking digitalis at the time of admission or during the hospital stay were studied, with no other inclusion or exclusion criteria. The proportion of AEs to digitalis diagnosed at the time of admission or during the hospital stay was compared in men and women. Information on AEs was collected using a structured questionnaire at admission and during the hospital stay. A logistic regression model was used to evaluate the association between sex and AE(s) to digitalis, corrected for potential confounding variables.

RESULTS

The total sample size was 9626 patients. Women received a higher weight-adjusted dose of digitalis compared with men (0.0027 mg/kg per day vs 0.0025 mg/kg per day; P < 0.001). Overall, 199 AEs to digitalis were diagnosed. Women were more likely than men to suffer from an AE to digitalis (odds ratio, 1.51; 95% CI, 1.12-2.02). This finding was confirmed after correction for dose of digitalis, age, physical and cognitive impairment, atrial fibrillation, chronic obstructive pulmonary disease, glomerular filtration rate, and use of amiodarone, beta-blockers, nondihydropyridine calcium channel blockers, and potassium-sparing diuretics (odds ratio, 1.58; 95% CI, 1.01-2.48).

CONCLUSIONS

In this sample of hospitalized adults in Italy, we found a higher incidence of AEs to digitalis in women than in men.

Absence of interactive effects of trans-1,2-cyclohexanediol, a major metabolite of the side-chain of candesartan cilexetil, on digoxin-induced arrhythmias in dogs

trans-1,2-Cyclohexanediol, the major metabolite of the cilexetil moiety of candesartan cilexetil (CC), has been reported to have potent pro-arrhythmic effects in dogs with congestive heart failure (CHF), especially when co-administered with digoxin. To verify this and to clarify the clinical relevance and the underlying mechanisms, a series of in vivo and in vitro experiments was conducted. When CC up to 300 mg/kg was administered orally to intact dogs, no changes in the electrocardiograms (ECG) or the required cumulative doses of ouabain to induce ventricular arrhythmias were observed. In dogs with CHF, intravenous bolus administration of trans-1,2-cyclohexanediol at 4 mg/kg followed by continuous infusion at 0.1 mg x kg(-)(1) x min(-)(1) had no effects on the ECG parameters, the type, incidence, and onset time of digoxin-induced arrhythmias or the metabolism of digoxin. In an in vitro experiment using isolated guinea pig papillary muscle, trans-1,2-cyclohexanediol (1 - 100 micromol/L) showed no effects on any parameter of the action potentials. Because no effects were observed in these experiments where the exposure levels of trans-1,2-cyclohexanediol were extremely high compared to those in humans given the maximum therapeutic dose of CC, it is unlikely that CC would induce arrhythmias in clinical use even in patients treated with cardiac glycosides.

Early institution of bromocriptine in Parkinson's disease inhibits the emergence of levodopa-associated motor side effects. Long-term results of the PRADO study

Long-term levodopa treatment in Parkinson's disease is typically associated with "motor side effects" consisting in dyskinesias and/or fluctuations in motility referred to as the on-off phenomena. The main objective of this prospective, randomized, multi-centre study was to determine to what extent the development of such complications could be prevented by partial substitution of levodopa monotherapy (L-DOPA/benserazide) by bromocriptine in patients with early symptoms of the disease. The basic trial population included 674 newly diagnosed Parkinsonian patients that were randomly allocated to monotherapy with levodopa or a combination therapy based upon a nearly 40% replacement of levodopa by bromocriptine. The two target regimens had to be consistently maintained for 42 months. Parkinsonian symptoms were assessed by means of the Webster rating scale, the Hoehn and Yahr scale, and the Zung Self-Rating Depression scale. Motor side effects and adverse events were recorded at each regular clinic visit. Neurological symptoms improved and stabilized in a similar manner during treatment with both regimens throughout the study period. Motor side effects were observed in more patients on levodopa alone than on combination therapy (28.8 vs 20%; p = 0.008). According to Kaplan-Meier estimates the cumulative probability of experiencing motor side effects was 0.43 on monotherapy, compared to 0.28 on combination therapy, which was equal to a one third reduction of risk (p = 0.025). In regard to motor side effects, the degree of substitution of levodopa proved relevant: patients with > 50% substitution by bromocriptine exhibited half the risk observed in those with < 30% (p = 0.045). The overall burden of motor side effects, as reflected by a sum score based upon the relevance, the severity and the extent of motor dysfunction, was also significantly less on combination therapy (p = 0.046). In conclusion, partial substitution of levodopa by bromocriptine (> 30%) as first-line treatment of Parkinson's disease proves active in the prophylaxis of levodopa associated motor side effects. Early combination therapy therefore extends the period of optimal disease control.

Is stimulation of prejunctional dopamine receptors an antihypertensive principle?

Bromocriptine and co-dergocrine (Hydergine R) reduce blood pressure and heart rate in experimental animals largely by stimulating DA2 receptors. A stimulant effect on DA1 receptors can be demonstrated in isolated tissues, but this action does not appear to make an important contribution to the depressor response to the two compounds, since effects are abolished by DA2 receptor blockade. Although both compounds are known to penetrate the brain, their antihypertensive effects, and the concomitant reductions in plasma noradrenaline levels produced in hypertensive patients can be prevented by domperidone, confirming a peripheral site of action. A review of the data available concerning the cardiovascular effects of bromocriptine and co-dergocrine in animals and man suggests that a DA2 receptor stimulant is effective in the treatment of hypertension.

Flecainide: a new prototype antiarrhythmic agent

Flecainide acetate is the first class IC antiarrhythmic agent marketed in the United States. In vitro, animal and human studies have shown that the drug markedly prolongs conduction and has minimal effect on repolarization. Efficacy trials have shown flecainide to be effective in a wide range of ventricular and selected atrial arrhythmias. The drug is generally well tolerated, although minor adverse effects are common. These generally are related to the central nervous system and respond to a reduction in dosage. Like other antiarrhythmic agents, flecainide may demonstrate proarrhythmic effects. It is excreted in the urine as the parent compound and inactive metabolites. The elimination half-life ranges from 12-27 hours in patients with normal renal function, allowing convenient dosing regimens of 100-200 mg twice daily in most patients. Flecainide has the potential for widespread use.