Becker RHA et al. (2006) The effect of smoking cessation and subsequent resumption on absorption of inhaled insulin. Diabetes Care 29: 277–282

Smoking has been shown to increase pulmonary permeability, and thereby to increase the absorption of inhaled insulin. To determine the effect of cessation and resumption of smoking on the time course of inhaled insulin absorption, researchers in Germany conducted a case–control study that enrolled 20 nondiabetic male smokers and 10 matched nonsmokers. They compared the pharmacokinetics of inhaled and subcutaneously injected insulin before smoking cessation, after smoking cessation, and after resumption.

Baseline systemic insulin exposure and maximum insulin concentration were substantially higher in smokers than in nonsmokers after inhalation of insulin, and the time required to reach maximum insulin concentration was considerably reduced in smokers. By contrast, smoking had no effect on the pharmacokinetics of subcutaneously administered insulin. Although cessation of smoking initially led to an increase in inhaled insulin absorption, after 7 days without smoking, absorption of inhaled insulin fell to levels approaching those for nonsmokers. Resumption of smoking restored insulin exposure and maximum concentration to baseline levels within 3 days, completely reversing the effect of smoking cessation. Importantly, two hypoglycemic episodes were reported among the smokers.

This is the first study to show the immediate effects of both smoking and smoking cessation on absorption of inhaled insulin. The authors recommend that smokers with diabetes should not be prescribed inhaled insulin, because of the increased risk of hypoglycemia associated with its absorption profile.