BETA AGONISTS AND REGULAR USE

The regular use of beta agonists has been shown to be associated with an increase in tolerance in asthmatic airways, but this has been generally seen as a loss of protection against inhaled bronchoconstrictor stimuli (eg inhaled methacholine), rather than an increase in inflammatory responsiveness of the airway. However, a new study published in The Lancet (October 2) suggests evidence that inflammatory mechanisms of the airway can become tolerant to these drugs.

Researchers in Canada describe an experiment in which 13 mild atopic asthma patients received either regular inhaled salbutamol (Glaxo's Ventolin) four-times daily or placebo over a period of two weeks. The patients were assessed at baseline and at the end of the study period for bronchodilator response, responsiveness of the airway to methacholine and allergen and the acute protective effects of salbutamol against both stimuli.

The researchers note that "regular use of salbutamol increased airway responsiveness to allergen, and produced tolerance to the acute protective effect of salbutamol against bronchoconstriction induced by both methacholine and the allergen; this tolerance was greater for allergen-induced bronchoconstriction." They suggest that their approach is probably more representative of environmental exposure to asthma stimuli than other measures.