The route of administration plays a significant role in determining the pharmacokinetics of a drug in the body. Pharmacokinetics refers to the study of how a drug is absorbed, distributed, metabolized, and excreted by the body. The two most common routes of administration are oral through the mouth and intravenous directly into the bloodstream . Here is a comparison of the pharmacokinetic parameters for drugs administered orally and intravenously:1. Absorption:Oral administration: When a drug is administered orally, it must first pass through the gastrointestinal GI tract. The drug is absorbed through the stomach and intestinal lining, and then enters the hepatic portal system, which transports it to the liver. The rate and extent of absorption depend on factors such as the drug's solubility, stability in the GI tract, and the presence of food or other drugs. The first-pass metabolism in the liver may also significantly reduce the bioavailability of the drug before it reaches systemic circulation.Intravenous administration: In contrast, intravenous administration bypasses the GI tract and first-pass metabolism, delivering the drug directly into the bloodstream. This results in 100% bioavailability, meaning the entire dose of the drug is available to exert its therapeutic effect. The onset of action is also faster with intravenous administration compared to oral administration.2. Distribution:Oral administration: After absorption, the drug enters the systemic circulation and is distributed throughout the body. The distribution of the drug depends on factors such as blood flow, tissue permeability, and protein binding. Oral administration may result in uneven distribution due to variations in absorption and first-pass metabolism.Intravenous administration: Intravenous administration allows for more rapid and even distribution of the drug throughout the body. Since the drug is directly introduced into the bloodstream, it can quickly reach its target site and exert its therapeutic effect.3. Metabolism:Oral administration: Drugs administered orally undergo first-pass metabolism in the liver, which can significantly alter the drug's concentration and activity. Some drugs may be extensively metabolized, reducing their bioavailability and efficacy, while others may be converted into active metabolites that can have different pharmacological effects.Intravenous administration: Intravenous administration bypasses first-pass metabolism, allowing the drug to maintain its original structure and activity. However, the drug will still be metabolized by the liver and other tissues once it has been distributed throughout the body.4. Excretion:Oral administration: Drugs and their metabolites are primarily excreted through the kidneys in the urine, although some may also be eliminated through the GI tract in the feces. The rate of excretion depends on factors such as renal function, drug solubility, and the presence of transporters that facilitate drug elimination.Intravenous administration: The excretion of drugs administered intravenously follows a similar pattern to those administered orally, with the primary route of elimination being through the kidneys. However, the rate of excretion may be different due to the higher initial concentration of the drug in the bloodstream.In summary, the route of administration significantly affects the pharmacokinetics of a drug in the body. Oral administration involves absorption through the GI tract and first-pass metabolism, which can lead to variable bioavailability and distribution. Intravenous administration bypasses these barriers, resulting in rapid onset, 100% bioavailability, and more even distribution of the drug. However, both routes ultimately involve metabolism and excretion through similar pathways.