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

Background-A simple non-invasive method, in which a urine sample is taken 30 minutes after drug administration, has previously been shown to be a measure of the relative bioavailability of salbutamol to the lungs. This technique has been used to determine an optimal inhaler technique 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. Urine collection intervals were 0-0.5 hours and 0.5-24 hours after administration. Results-There was significantly greater elimination of unchanged salbutamol 30 minutes after administration, indicating a greater relative bioavailability of salbutamol to the lungs after (1) exhaling gently to residual volume rather than to functional residual capacity before inhalation; (2) slow inhalation (10 l/min) compared with fast inhalation (50 l/min); (3) breath holding for 10 seconds after inhalation compared with no breath holding. Conclusions-All patient information leaflets and healthcare personnel should standardise the instructions given to patients and should adopt the inhalation method proposed.