What is the primary disadvantage of oral drug administration compared to other routes?

The primary disadvantage of oral drug administration is first pass metabolism. This phenomenon occurs when a drug is absorbed from the gastrointestinal tract and then travels to the liver via the portal vein before it enters systemic circulation. During this journey, a portion of the drug can be metabolized and become inactive, which reduces the overall bioavailability of the medication. This is particularly relevant for drugs that have a high first pass effect, meaning that a significant amount is metabolized before it can exert its intended therapeutic effect in the body.

In contrast to other routes of administration, such as intravenous or sublingual, where drugs can enter the systemic circulation directly, oral administration can lead to substantial losses in the active drug concentration. Understanding this disadvantage is crucial in pharmacology, as it influences dosage forms and routes chosen for effective drug therapy.