Final answer:
To avoid the first pass effect, routes of drug administration such as sublingual, buccal, rectal (partially), transdermal, and inhalation are used, as these bypass the liver and allow direct entry into the systemic circulation.
Step-by-step explanation:
The question addresses the concept of the first pass effect, a pharmacokinetic phenomenon where the concentration of a drug is significantly reduced before it reaches the systemic circulation, primarily due to the liver's metabolic action. This effect is particularly notable for drugs administered orally, which pass through the liver via the hepatic portal system after absorption from the gastrointestinal tract. To avoid the first pass effect, alternative routes of administration that bypass the liver are used.
Sublingual and buccal absorption are two such routes where drugs are absorbed directly into the blood through the tissues under the tongue or inside the cheek, respectively, thereby entering the systemic circulation without passing through the liver first. Rectal administration of drugs, while it partially avoids the first pass effect, the lower rectal circulation bypasses the liver. Similarly, transdermal administration allows drugs to be absorbed through the skin and into the bloodstream, avoiding the gastrointestinal tract and the first pass through the liver. Inhalation is another route that avoids the first pass effect, as the drug is absorbed through the lungs' vast surface area and directly enters the systemic circulation.