Absorption of Rapid-Acting Insulin in Obese and Nonobese NIDDM Patients

OBJECTIVE To study the absorption rate of rapid-acting insulin from subcutaneous injection sites in nonobese and obese non-insulin-dependent diabetes mellitus (NIDDM) patients.

RESEARCH DESIGN AND METHODS Ten nonobese and 10 obese NIDDM patients (body mass indexes 24.1 ± 0.4 and 31.4 ± 0.8 kg/m², respectively) received four subcutaneous injections of 125I-labeled rapid-acting insulin (Actrapid Human, 5 U): three in the abdominal wall above, lateral to, and below the umbilicus; and one in the thigh. The depth of the subcutaneous fat layer was measured using ultrasound techniques. The residual radioactivity was monitored externally for 270 min.

RESULTS The disappearance half-life of ¹²⁵I-insulin was between 4 and 6 h from all injection sites, with the exception of the upper abdominal area in the nonobese subjects, where it measured ∼ 3 h. The residual radioactivity did not differ between nonobese and obese patients measured from any of the sites. In the nonobese group, the most rapid absorption of ¹²⁵I-insulin was found from the upper abdominal area and the slowest from the thigh. In the obese group, the absorption rates did not differ between sites. No correlation was found between the depth of the fat layer and the residual radioactivity when measured at any site.

CONCLUSIONS Our results indicate that the absorption of rapid-acting insulin is markedly slow in both obese and nonobese NIDDM patients compared with IDDM patients and healthy subjects studied previously. In the nonobese group, the most rapid absorption of ¹²⁵I-insulin is obtained after injection into the upper abdominal area. Inter- and intraregional differences are small in the obese patients. Consequently the choice of injection site is of little importance in this group.