COMPARISON OF GAMMA-SCINTIGRAPHY AND A PHARMACOKINETIC TECHNIQUE FOR ASSESSING PULMONARY DEPOSITION OF TERBUTALINE SULFATE DELIVERED BY PRESSURIZED METERED-DOSE INHALER

A comparison has been made of pulmonary deposition of terbutaline sulp hate from a pressurized metered dose inhaler (pMDI), measured in 8 hea lthy male subjects by gamma scintigraphy and by a pharmacokinetic (cha rcoal-block) method, involving drug recovery in urine. Measurements we re carried out with a pMDI at slow (27 l/min) and fast (151 l/min) inh aled flows and with Nebuhaler(R) large volume spacer device (average i nhaled flow 17 l/min). Overall, the two methods did not differ signifi cantly in their estimates of whole lung deposition, although values ob tained by gamma scintigraphy exceeded those from the charcoal-block me thod for the pMDI with fast inhalation. The regional distribution of d rug within the lungs and deposition in the oropharynx could be assesse d by gamma scintigraphy, but not by the charcoal-block method. It is c oncluded that either method may be used to assess whole lung depositio n of terbutaline sulphate from pMDIs, both with and without a spacer, although each method has its own inherent advantages and disadvantages .