Injected drugs are often erratically absorbed because of Variability in their chemical characteristics Differences in absorption by site of injection (intramuscular or subcutaneous) Variability in muscle mass among children Illness (eg, compromised circulatory status) Variability in depth of injection (too deep or too shallow) Intramuscular injections are generally avoided in children because of pain and the possibility of tissue damage, but, when needed, water-soluble drugs are best because they do not precipitate at the injection site.