Key Factor in Drug Absorption
A rich blood supply to the area of absorption leads to better absorption is the correct answer among the options provided.
Understanding Drug Absorption Factors
The absorption of drugs depends on multiple physiological and physicochemical factors that determine how effectively a drug enters systemic circulation. Let me explain why each option is correct or incorrect:
Blood Supply and Absorption (CORRECT)
- Rich blood supply enhances drug absorption by maintaining concentration gradients that favor drug movement from the absorption site into circulation 1
- Decreased splanchnic blood flow and tissue perfusion (as seen in elderly patients) leads to delayed absorption, demonstrating the importance of adequate blood supply 1
- Hepatic blood flow is a critical determinant for drugs with high hepatic extraction ratios, affecting their clearance and bioavailability 1
Ionization Status (INCORRECT)
- Non-ionized (unionized) drugs are easily absorbed across cell membranes, NOT ionized drugs 1
- Drugs are absorbed in their unionized state, which depends on gastrointestinal pH 1
- The ionization state affects lipid solubility and membrane permeability—only the unionized form can passively diffuse across lipid membranes 2
Surface Area (INCORRECT)
- Larger surface area leads to MORE rapid absorption, not smaller surface area 1
- Decreased absorption surface area (as occurs with aging or gastrointestinal disease) reduces drug absorption 1
- The small intestine's extensive surface area is specifically designed to maximize absorption of nutrients and drugs 3
Drug Solubility (INCORRECT)
- More soluble drugs are generally MORE easily absorbed, not less soluble drugs 2, 3
- Drug solubility is a critical factor determining bioavailability—poorly soluble drugs often have absorption problems 2, 3
- Securing adequate solubility prior to reaching absorption sites is essential for effective pharmacotherapy 3
Clinical Implications
Common pitfall: Assuming all drugs absorb equally regardless of site characteristics. In reality, blood flow, surface area, pH, and drug properties all interact to determine absorption efficiency 2, 4, 5.
The absorption process is complex and influenced by drug-related factors (solubility, lipophilicity, molecular size), patient-related factors (gastrointestinal pH, motility, blood flow), and environmental factors (food, drug interactions) 2, 4.