Drug absorption

Definition

Drug absorption is the process by which a drug enters the bloodstream after administration. This process is crucial because it affects the drug's bioavailability, which is the proportion of the drug that reaches systemic circulation and is available for therapeutic effect. Various factors, such as the drug's formulation, the route of administration, and physiological conditions of the body, can influence the rate and extent of absorption.

5 Must Know Facts For Your Next Test

1. The route of administration, such as oral, intravenous, or topical, plays a significant role in how quickly and effectively a drug is absorbed.
2. Factors like pH levels in the stomach and intestines can affect the solubility and stability of a drug, thus influencing its absorption.
3. Some drugs require specific transport mechanisms to be absorbed effectively, such as facilitated diffusion or active transport.
4. Lipid-soluble drugs tend to be absorbed more easily than water-soluble drugs because they can pass through cell membranes more readily.
5. The presence of food in the gastrointestinal tract can enhance or impede the absorption of certain drugs, leading to variations in their efficacy.

Review Questions

• How does the route of administration impact drug absorption?
  • The route of administration significantly influences how quickly and effectively a drug is absorbed into the bloodstream. For example, intravenous administration allows for immediate absorption and rapid onset of action since the drug is delivered directly into circulation. In contrast, oral administration requires the drug to be dissolved in the gastrointestinal tract before it can be absorbed, which can lead to delays in onset and reduced bioavailability due to factors like digestive enzymes and gastric pH.
• Discuss how first-pass metabolism affects the bioavailability of orally administered drugs.
  • First-pass metabolism refers to the reduction in concentration of a drug due to metabolic processes occurring in the liver before it enters systemic circulation. This phenomenon can significantly lower bioavailability, meaning that less of the active drug reaches its target site. For instance, many orally taken medications undergo extensive hepatic metabolism; therefore, dosages are often adjusted to ensure therapeutic effectiveness despite this loss during absorption.
• Evaluate the role of physiological factors on drug absorption and how this knowledge can inform clinical practice.
  • Physiological factors such as age, gender, and overall health can greatly influence drug absorption rates and effectiveness. For instance, older adults may have altered gastrointestinal function which could affect how well drugs are absorbed. Understanding these variations helps healthcare providers make informed decisions about dosing regimens and routes of administration. Tailoring treatments based on individual patient characteristics ensures optimal therapeutic outcomes while minimizing adverse effects.

Related terms

bioavailability: The measure of the extent and rate at which the active ingredient or active moiety is absorbed and becomes available at the site of action.

pharmacokinetics: The branch of pharmacology concerned with the movement of drugs within the body, encompassing absorption, distribution, metabolism, and excretion.

first-pass metabolism:

The phenomenon where a drug's concentration is significantly reduced before it reaches systemic circulation, often due to liver metabolism after oral administration.