Nebulized fenoterol in severe asthma: determinants of the dose response

We assessed the bronchodilator response to cumulative doses of nebulised fenoterol in 16 patients with severe asthma to determine (1) the magnitude of the bronchodilator response, (2) the factors determining this response, and (3) the dose producing maximum bronchodilation. To reflect the degree to which ventilatory function returned to normal, individual bronchodilator responses were assessed as the change in FEV1 (post-fenoterol FEV1 - initial FEV1) and expressed as a percentage of the predicted maximum response (predicted FEV1 - initial FEV1). The bronchodilator response was extremely varied (about 55% of predicted maximum in six patients, 40% in three patients, and 20% in seven patients), as was the dose producing maximal bronchodilation (1 mg in three patients, 2 mg in six patients, and 2.5 or 3 mg in seven patients). In individual patients the maximum response could be predicted by the response to the initial dose of fenoterol and by the duration of the episode of severe asthma. The maximum response was not predicted by the initial severity of obstruction or the patient's usual treatment.