Effect of inhaled terbutaline sulphate in relation to its deposition in the lungs

Abstract

We studied the effects of inhaled terbutaline on FEV 1 and gas exchange, and the pattern of deposition within the lungs. To document this and to estimate the dose of terbutaline administered to the lungs, [ 99mTc]DTPA was added to nebulised terbutaline solution. The aerosol was deposited preferentially in large or small airways by using aerosols with different particle mass median diameters (1.5 and 4.8 μm) and different inhalation flow rates (0.25 and 1.01/s). The patients inhaled placebo and then three increasing doses of terbutaline (0.006, 0.02 and 0.08 mg to the lungs). Finally, 2 mg terbutaline was inhaled from a metered dose inhaler via a spacer. After each inhalation FEV 1, PaO 2 and PaCO 2 was measured. The inhalation of small particles at a low flow resulted in a fairly uniform lung deposition, while larger particles at a higher flow resulted in heavy central deposition. Penetration index for small and large particles were 1.3 ± 0.2 and 0.8 ± 0.3 ( P < 0.001), respectively. In both groups FEV 1 increased similarly with each dose, and at 0.02 and 0.08 mg the increase was significant ( P < 0.01). After eight metered doses of terbutaline sulphate (0.25 mg per dose) inhaled via a spacer, there was a further increase in FEV 1 ( P < 0.001). Gas exchange did not differ between the two groups but if they were combined the D a-aO 2 was significantly lower after metered doses than control ( P < 0.05). Thus, it appears that the site of deposition is not important for the bronchodilator effect of terbutaline, and gas exchange tended to improve with both modes of administration.