Why do they have to give certain injections in different spots/kinds of tissue?

The question:
Why do they have to give certain injections in different spots/kinds of tissue?

The Pediatrician Answers:
Each injection is made to be given in the type of tissue it is best absorbed from. Some injections are given into muscle (IM), some into subcutaneous tissue (SC) and some intravenously (IV).

In children, the MMR (measles, mumps, rubella) and Varivax (chicken pox) are given SC. The DTaP (diphtheria and tetanus toxoids and acellular pertussis vaccine), HIB (Haemophilus influenzae type b), HepB (hepatitis B), IPV (inactivated polio), and Prevnar (pneumococcal) are all given IM.

In infants, we use the anterior (front) thigh muscle for IM injections because it is a large muscle and a safe area to give the injection.