INVESTIGATIONS OF AN OPTIMAL INHALER TECHNIQUE WITH THE USE OF URINARY SALBUTAMOL EXCRETION AS A MEASURE OF RELATIVE BIOAVAILABILITY TO THELUNG

Background-A simple non-invasive method, in which a urine sample is ta ken 30 minutes after drug administration, has previously been shown to be a measure of the relative bioavailability of salbutamol to the lun gs. This technique has been used to determine an optimal inhaler techn ique with commercially available metered dose inhalers (MDI). Methods- Ten healthy subjects were trained in the use of MDIs. Each inhaled 4 x 100 mug salbutamol in a series of experiments to examine the relative bioavailability to the lung after different respiratory manoeuvres. U rine collection intervals were 0-0.5 hours and 0.5-24 hours after admi nistration. Results-There was significantly greater elimination of unc hanged salbutamol 30 minutes after administration, indicating a greate r relative bioavailability of salbutamol to the lungs after (1) exhali ng gently to residual volume rather than to functional residual capaci ty before inhalation; (2) slow inhalation (10 l/min) compared with fas t inhalation (50 l/min); (3) breath holding for 10 seconds after inhal ation compared with no breath holding. Conclusions-All patient informa tion leaflets and healthcare personnel should standardise the instruct ions given to patients and should adopt the inhalation method proposed .