Evaluation of tolerance after continuous and prolonged oral administration of salbutamol to asthmatic patients

Inhaled short acting beta2-agonist use in asthma: regular vs as needed treatment

BACKGROUND

Inhaled beta2-adrenergic agonists delivered by inhalation are very widely used in asthma. There has been much controversy of the use and possible consequences of the use of these agents for regular, as opposed as-needed use in asthma.

OBJECTIVES

This review to assessed the clinical trial evidence to test whether using regular use of short-acting beta2-agonists reduced asthma control and pulmonary function; worsened symptoms, airway reactivity and quality of life; and increased the rate of exacerbations.

SEARCH STRATEGY

A search was carried out of the Cochrane Airways Group "Asthma and Wheez* RCT" register using the terms: regular AND [beta agonist OR bronchodilator OR salbutamol OR albuterol Or terbutaline OR isoproterenol OR reproterol OR fenoterol]. Bibliographies of existing trials were searched and primary trial authors and pharmaceutical companies were approached for additional trials.

SELECTION CRITERIA

Randomised controlled trials in which the short-acting beta2-agonist was given regularly in the experimental group, together with an inhaled bronchodilator for relief of symptoms ('rescue use'). The control group consisted of matching placebo inhaled regularly, with an inhaled bronchodilator for as-needed 'rescue use'.

DATA COLLECTION AND ANALYSIS

Data were extracted and quality assessments were made by both reviewers. Parallel group and cross-over trials were analysed separately. Where possible data were pooled using a fixed effects model.

MAIN RESULTS

Over 800 abstracts were identified, following a review, 60 papers were requested for full assessment by both reviewers. 34 trials from 30 papers met the entry criteria. Data from 31 outcomes were analyzable. There was little difference between the treatments for nearly all outcomes. In cross-over studies, evening peak flow was better with regular treatment, weighted mean difference (WMD) 13.1 l/min (95% confidence interval 24.3, 1.9). In contrast, the FEV1 was better with as-needed treatment (WMD 157 ml (95% CI: 123, 192). Bronchial hyper reactivity was slightly better in the as-needed group, standardised mean difference 0.23, 95% CI: 0.52, 1.12.

REVIEWER'S CONCLUSIONS

These results support current guidelines. There is little advantage in using short-acting beta2-agonists regularly, and potentially some small clinical disadvantage.

Plasma concentrations of salbutamol after an oral slow-release preparation

Studies were carried out to investigate the plasma concentrations of salbutamol after administration of a slow-release formulation (8 mg) compared with those after 1 and after 2 standard 4 mg tablets. In the first study, 9 subjects received, at random, either the slow-release tablet or a single standard tablet. Blood samples were taken and histamine challenge tests were carried out before and at fixed time intervals after drug administration. The procedures were repeated after an interval of at least 5 days with the alternative treatment. In the second study, plasma concentrations were measured in 5 of the subjects before and after taking 2 standard 4 mg tablets. The results showed that there was slower attainment of peak plasma concentrations after the slow-release formulation compared to those after one 4 mg and two 4 mg standard tablets. In addition, the 8 mg slow-release formulation produced lower peak plasma concentrations than did two 4 mg standard tablets. Protection against a bronchoconstricting histamine challenge lasted at least twice as long after the slow-release compared with after a single 4 mg standard tablet.