What is the process of delivering drugs via a needle into various layers of the body called?

The process of delivering drugs via a needle into various layers of the body is referred to as parenteral drug administration. This method encompasses delivering medications through routes other than the digestive tract, and it usually involves injections directly into tissues, muscles, or veins. Parenteral administration allows for rapid absorption and action of the medication, making it particularly suitable in emergency situations where immediate effect is required.

In contrast, inhalation would involve delivering medication through the respiratory system, typically using inhalers or nebulizers, which is not applicable in this context. Topical application refers to delivering medications directly onto the skin or mucous membranes, which does not involve a needle or injections. Intranasal administration involves delivering medications into the nasal cavity, bypassing the gastrointestinal tract but again, does not utilize a needle or involve deeper layers of tissue.

Thus, parenteral drug administration is the only choice that accurately describes the method of using a needle to inject drugs into the body.