Investigations of an optimal inhaler technique with the use of urinary salbutamol excretion as a measure of relative bioavailability to the lung.

Abstract

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 ug 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 imin) compared with fast inhalation (50 1min); (3) breath holding for 10 seconds after inhalation compared with no breath holding.Conclusions-AU patient information leaflets and healthcare personnel should standardise the instructions given to patients and should adopt the inhalation method proposed. (Thorax 1993;48:607-610)

Clarifying the dilemmas about inhalation techniques for dry powder inhalers: integrating science with clinical practice

“…31 Since failing to exhale before an inhalation through a DPI is a common mistake [3][4][5] and lung deposition is related to the extent of the exhalation, 32 patients should be trained to exhale gently before they start to inhale. The increased volume will ensure better drug penetration into their airways and deposition onto the therapeutic targets in the lungs.…”

Relative bioavailability of salbutamol to the lung following inhalation using metered dose inhalation methods and spacer devices.

“…Compared with the MDI the inhalation aid increases were much greater than the intra-individual variability of the urinary excretion method. In 11 individuals who each repeated the same inhalation procedure on four separate occasions, the mean (SD) coefficient of variation was [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] (2-36)%. The mean (SD) 24 hour urinary excretion of salbutamol and its metabolites was 26-6 (6 79), 27'0 (7 95), and 55-6 (9- Inhalation from a static aerosol cloud, from within these devices, reduces particle velocity during inspiration thereby limiting oropharyngeal impaction and systemic absorption.…”

Assessment of inhalation technique and predictors of incorrect performance among patients of chronic obstructive pulmonary disease and asthma

“…5 Correct pMDI technique involves firing the pMDI, while breathing in deeply and slowly, and then following inhalation with a breath-holding pause to allow particles to sediment on the airway surfaces. 6,7 Most importantly, the pMDI must not be fired after the inhalation is completed, as then there is no air-stream to carry the aerosol into the lungs. Some aerosol will probably still reach the lungs if the pMDI is fired shortly before inhalation starts.…”