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 micrograms 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.