Using a hand-held spirometer as a monitoring tool in chronic theophylline therapy

This study evaluates the use of a hand-held spirometer (pocket spirometer, Buhl type) in monitoring pulmonary function as a part of a homebased pharmacokinetic service for patients with respiratory disease. To calibrate the spirometer and determine its accuracy, six healthy volunteers were trained in its use by the pharmacist. Forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) were determined for each volunteer once a month for six months. The T test for the presence of outliers showed no statistical difference at p less than 0.05. Seven patients on chronic therapy with theophylline derivatives for respiratory problems were randomly referred by their physicians to the pharmacokinetic service. The pharmacist counseled each patient and measured FVC and FEV1 once a month for six months. The ratio, (FEV1:FVC) X 100, was calculated for each patient before and after steady-state serum level determination and dosage adjustment. The mean value for this ratio was 45.1 before pharmacokinetic intervention and 57.5 after intervention. Using the Student's t-test, these results were significant (p less than 0.05). The correlation coefficient was calculated to determine if a correlation existed between the increase in the ratio and the increase in serum theophylline levels. Serum levels were ordered before and after intervention for five of the seven patients receiving pharmacokinetic intervention. The change in serum levels vs. change in the ratio was associated with a correlation coefficient of 0.718. Monitoring pulmonary function may be a useful adjunct for the pharmacist who provides pharmacokinetic counseling to patients with respiratory disease, but expanded studies are needed to judge the value of routine spirometric measurements on homebased patients.