Farmacocinética: Absorción de Fármacos

Farmacokinetics

• Farmacokinetics (PK) describes the movement of drugs within the body, encompassing absorption, distribution, metabolism, and excretion (ADME). This information is crucial for determining drug dosage, and timing for optimal therapeutic efficacy and minimizing adverse effects.

Absorption

• Absorption is the process by which a drug is transferred from the site of administration to the bloodstream.
• Factors influencing absorption include:
  • Drug formulation (e.g., tablet, capsule, solution)
  • Route of administration (e.g., oral, intravenous, intramuscular)
  • Physiochemical properties of the drug (e.g., lipid solubility, pKa)
  • Patient-specific factors (e.g., gastric emptying rate, blood flow to the absorption site, disease states)
• Oral administration is the most common route, but absorption can be influenced by factors such as the presence of food in the stomach, pH of the stomach, and membrane permeability.
• Bioavailability (F) represents the fraction of administered dose that reaches the systemic circulation in an unchanged form.

Distribution

• Distribution refers to the movement of the drug from the bloodstream to various tissues and organs throughout the body.
• Factors influencing distribution include:
  • Blood flow to tissues
  • Drug binding to plasma proteins (e.g., albumin)
  • Drug lipid solubility
  • Tissue barriers (e.g., blood-brain barrier)
• Drug distribution determines the drug concentration at the site of action, which influences its therapeutic effect.
• Drug partitioning between plasma and tissues is significant, affecting duration of action and potential accumulation in certain tissues.

Metabolism

• Metabolism, or biotransformation, is the process where the body chemically modifies the drug to make it more water-soluble and often less active.
• This process primarily occurs in the liver, but other organs such as the lungs, kidneys and intestines also play a role.
• Key enzymes in the liver, like cytochrome P450 enzymes, facilitate drug metabolism, often leading to metabolite formation.
• Metabolic pathways can be either phase I (e.g., oxidation, reduction, hydrolysis) or phase II (e.g., conjugation).
• Genetic variations in metabolic enzyme activity can significantly alter drug metabolism, leading to increased or decreased drug concentrations, impacting efficacy and toxicity.

Excretion

• Excretion is the removal of the drug and its metabolites from the body.
• The primary routes of excretion are through the kidneys (in urine) but also include the liver (bile), lungs, and sweat glands.
• Renal excretion can be affected by glomerular filtration, tubular secretion, and tubular reabsorption.
• Factors such as kidney function and pH can influence the rate of excretion.

Clinical Relevance

• Understanding the principles of pharmacokinetics allows for informed decision-making regarding drug selection and dosage regimens.
• Knowing these principles helps predict how and why drug concentrations change over time.
• It's crucial for optimizing therapeutic effectiveness while minimizing adverse effects.
• Personalized medicine increasingly relies on pharmacokinetic profiles to tailor drug treatments and dosages to individual patient characteristics.
• Clinical applications include determining appropriate dosing strategies, managing drug interactions (e.g., interactions between different drugs), and adjusting dosages for patients with compromised organ function.
• Therapeutic drug monitoring (TDM) is an important clinical application of pharmacokinetics, measuring drug concentrations in the blood to optimize drug efficacy and safety.

Este cuestionario explora los conceptos clave de la farmacocinética, especialmente el proceso de absorción de fármacos en el cuerpo. Aprenderás sobre los factores que influyen en la absorción y cómo afectan la eficacia terapéutica. Ideal para estudiantes de farmacología y medicina.