**5. IM insulin**

The skin in children is slightly thinner than in adults, but these differences are largely irrelevant for insulin infusions and injections. Skin thickness increases during adolescence and

The SC tissue is the target for insulin. Injections must reach the SC tissue, but not go deeper into the muscle fascia or the muscle itself. Therefore, the thickness of the SC is critical in determining the desired length of the needle as well as the injection technique (e.g., lifting a skin fold or not). SC tissue thickness varies widely depending on gender, site of injection, and BMI. Women, on average, have approximately 5-mm thicker SC fat than men, when one controls for BMI and body site. Truncal sites (abdomen and buttocks) have more SC fat than limbs (arm and thigh), in the same patient. The higher the BMI, the thicker the SC fat. Studies within the last decade have used precision US to determine the SC tissue thickness in

**Marran, 2014 [13] Lo Presti, 2014 (pooled) [14]**

.

With kind permission from Hirsch L et al. [16]. Intramuscular risk at insulin injection sites—measurement of the distance

**Table 2.** Calculated risk of IM injection in children and adolescents as a function of injection site, age, and needle length\*

 mm 27.5% 12.5% 12.5% 0% 20.2% 4.6% 2.4% mm 47.5% 22.5% 30.0% 0% 46.0% 18.4% 16.1% mm 62.5% 30.0% 37.5% 5.0% 66.5% 38.0% 34.5% mm 87.5% 62.5% 50.0% 15.0% 83.9% 65.3% 66.1% 12.7 mm 100% 90.0% 85.0% 35.0% 97.2% 93.9% 96.4%

**2–6**

**Ages 7–13**

**Ages 14–17**

.

**Arm Thigh Abdomen Buttock Ages**

from the skin to the muscle and rationale for shorter-length needles for subcutaneous insulin therapy.

Assumes injection straight at 90° without pinch-up (the table adapted from Hirsch [16]).

Assumes that injections are into flat skin and not into lifted skin fold.

**Table 1.** Estimated IM injection risk in adults, by body site\*

a diverse group of adults [7, 9, 15, 16], adolescents, and children [13, 14].

**Needle length Combined Thigh Arm Abdomen Buttock** mm 0.4% 1.6% 1.0% 0.3% 0.1% mm 1.8% 4.7% 3.1% 1.1% 0.5% mm 5.7% 10.0% 7.0% 2.8% 1.3% mm 15.3% 25.0% 19.5% 9.7% 5.5% 12.7 mm 45.0% 63.0% 55.0% 38.0% 26.9%

reaches adult size in the late teens.

**4. SC thickness**

60 Ultimate Guide to Insulin

\*

\*

IM-injected insulins have a much greater variability in absorption and effect (PK and PD) compared to SC-injected. This variability is influenced by both exercise and the properties of the individual insulins. Human insulins and the new analogs also differ as to their PK when injected IM. In general, IM insulin is often associated with a more rapid absorption and unexplained hypoglycemia [17–19]. Because of the difficulty of predicting the impact of IM injections on PK and PD, various measures can be taken to avoid injecting IM: using of shorter needles, lifting of a skin fold into which one injects the insulin, or choosing injection sites with thicker layers of SC fat. A combination of the above techniques can also be used [20].
