Effect of salbutamol on digoxin concentration in serum and skeletal muscle

Pharmacology and therapeutics of bronchodilators

Bronchodilators are central in the treatment of of airways disorders. They are the mainstay of the current management of chronic obstructive pulmonary disease (COPD) and are critical in the symptomatic management of asthma, although controversies around the use of these drugs remain. Bronchodilators work through their direct relaxation effect on airway smooth muscle cells. at present, three major classes of bronchodilators, β(2)-adrenoceptor (AR) agonists, muscarinic receptor antagonists, and xanthines are available and can be used individually or in combination. The use of the inhaled route is currently preferred to minimize systemic effects. Fast- and short-acting agents are best used for rescue of symptoms, whereas long-acting agents are best used for maintenance therapy. It has proven difficult to discover novel classes of bronchodilator drugs, although potential new targets are emerging. Consequently, the logical approach has been to improve the existing bronchodilators, although several novel broncholytic classes are under development. An important step in simplifying asthma and COPD management and improving adherence with prescribed therapy is to reduce the dose frequency to the minimum necessary to maintain disease control. Therefore, the incorporation of once-daily dose administration is an important strategy to improve adherence. Several once-daily β(2)-AR agonists or ultra-long-acting β(2)-AR-agonists (LABAs), such as indacaterol, olodaterol, and vilanterol, are already in the market or under development for the treatment of COPD and asthma, but current recommendations suggest the use of LABAs only in combination with an inhaled corticosteroid. In addition, some new potentially long-acting antimuscarinic agents, such as glycopyrronium bromide (NVA-237), aclidinium bromide, and umeclidinium bromide (GSK573719), are under development, as well as combinations of several classes of long-acting bronchodilator drugs, in an attempt to simplify treatment regimens as much as possible. This review will describe the pharmacology and therapeutics of old, new, and emerging classes of bronchodilator.

Effect of salbutamol on digoxin pharmacokinetics

A single dose of the beta 2-adrenoceptor agonist salbutamol has previously been shown to decrease serum digoxin concentration in healthy volunteers. A possible explanation of the phenomenon is a beta 2-adrenoceptor-mediated increase in the specific binding of digoxin to skeletal muscle. The present study was undertaken to further elucidate the effect of salbutamol on the pharmacokinetics of digoxin in man. Nine volunteers were studied on two occasions during salbutamol or placebo treatment. On test days salbutamol, 4 micrograms.kg-1.h-1 or saline was infused for 10 h, preceded and followed by four and three days, respectively, of oral administration. A single i.v. injection of digoxin 15 micrograms.kg-1, was given 20 min after starting the infusion. At the end of the infusion a muscle biopsy was taken from the vastus lateralis. Blood samples for the analysis of serum digoxin and potassium were repeatedly taken over 72 h. Urine was collected over a period of 24 h for determination of the renal excretion of digoxin and potassium. The serum digoxin concentration, expressed as the AUC 0-6 h was 15% lower during salbutamol infusion than during saline infusion. Salbutamol caused significantly faster elimination of digoxin from the central volume of distribution to deeper compartments. Salbutamol had no effect on the renal clearance of digoxin. The skeletal muscle digoxin concentration tended to be higher (48%) during salbutamol compared to placebo treatment. The serum potassium concentration was significantly lower after salbutamol compared to placebo, as was the rate of renal excretion of potassium.(ABSTRACT TRUNCATED AT 250 WORDS)

Digitalis enhances exercise-induced hyperkalaemia

In 9 patients with atrial fibrillation the effect of zero, low and high levels of serum digoxin on exercise-induced hyperkalemia was assessed by bicycle exercise tests. Exercise at each level of serum digoxin was associated with a significant (up to 20%) rise in plasma potassium. At a work load of 75 W the highest level of serum digoxin was associated with a significantly higher maximum plasma potassium concentration as compared to the maximum valueatazero serum digoxin. The enhancement of exercise-induced hyperkalemia may add to the arrhythmogenic effect of digitalis.

Oral salbutamol decreases serum digoxin concentration

The effect of a therapeutic dose of oral salbutamol on serum and skeletal muscle digoxin concentrations has been studied in volunteers digitalised with digoxin. On one occasion a biopsy was taken from the quadriceps after 2 h of supine rest and then 3-4 mg salbutamol was given orally. Blood samples were taken before and after that dose and another muscle biopsy specimen was taken from the same thigh 180 min after the medication. On another occasion control blood sampling, ECG and blood pressure recordings were made but without muscle biopsies or salbutamol administration. Compared to the control measurements, salbutamol decreased the serum digoxin concentration (0.30 nmol.l-1). It also reduced the serum potassium concentration (0.58 mmol.l-1). The digoxin concentration in skeletal muscle did not change significantly after the intake of salbutamol. Thus, even a therapeutic oral dose of salbutamol reduces the serum digoxin concentration in man.