Final answer:
The subcutaneous injection is designed for the slow absorption of drugs under the skin, typically used when drugs are not absorbed through the GI tract or when oral medication is not an option.
Step-by-step explanation:
The subcutaneous injection aims to deposit the drug just beneath the skin where it will slowly be absorbed into the animal's system. This route of administration is a method used for drugs that are not readily absorbed in the gastrointestinal (GI) tract or for patients who cannot take oral medications. When treating systemic infections, different routes like oral, intravenous, topical, or parenteral can be considered based on factors such as drug absorption rates, specificity of treatment, patient convenience, and whether immediate high plasma levels of the drug are needed. These methods, including controlled-release parenteral drug technologies, are essential in providing effective drug therapy while ensuring patient comfort and adherence to medication regimens. Oral administration is generally preferred for its convenience, but alternative methods are essential when the oral route is not viable or when rapid and high plasma drug levels are necessary.