Pharmacokinetics Quiz

Liberation and Absorption

• Active Pharmaceutical Ingredient (API) release from formulation marks the start of pharmacokinetic action.
• Drug action varies by route of administration and formulation type.
• Absorption refers to the drug entry into plasma, initiated at the administration site; differs between oral and IV routes.
• IV administration leads to complete absorption into circulation, while oral offers only partial absorption.
• Other factors influencing absorption include:
  • Dissolution of the API into solution.

Route of Administration

• Different routes impact the pharmacokinetics of a drug and its formulation.

Distribution of API

• Distribution involves drug transport from the gastrointestinal (GI) tract to the bloodstream.
• Mechanisms include:
  • Passive diffusion based on concentration gradients.
  • Active transport utilizing ATP.
  • Endocytosis and exocytosis.

Bioavailability

• Defined as the fraction of administered drug reaching systemic circulation.
• Depends on drug dissolution and first-pass metabolism.

Distribution Factors

• Transition of drug from blood plasma to tissue influenced by:
  • Blood flow to tissues.
  • Capillary permeability (e.g., blood-brain barrier).
  • Binding affinity to plasma and tissue proteins.
  • Drug hydrophobicity.

Metabolism (Biotransformation)

• Phase I: Drug modification via oxidation, reduction, or hydrolysis, predominantly through cytochrome P450 isoenzymes; crucial for understanding drug interactions.
• Phase II: Conjugation with substances to enhance solubility for urine excretion.

Excretion Pathways

• Major excretion routes involve:
  • Urinary system (e.g., glomerular filtration rate, proximal and distal tubules).
  • Gastrointestinal system (feces).
  • Respiratory system (exhalation).
  • Mammary glands (milk in nursing mothers).

Pharmacodynamics

• Pharmacodynamics concerns how drugs affect the body and the relationship between drug concentration and response magnitude.
• Drug effects on target sites categorized as:
  • Activation: Stimulates processes (e.g., caffeine enhances CNS stimulation).
  • Inhibition: Suppresses processes (e.g., aspirin inhibits COX enzyme, reducing prostaglandins).
  • Complexation: Forms inactive complexes, e.g., deferoxamine chelating ions.
  • Neutralization: Binds to target sites, neutralizing existing actions (e.g., antacids).

Common Target Sites

• Drug molecules can act on various biological targets:
  • Receptors
  • Enzymes
  • Structural proteins
  • Nucleic acids
  • Ion channels

Major Receptor Families

• Include:
  • Ligand-gated ion channels.
  • G protein–coupled receptors.
  • Enzyme-linked receptors.
  • Intracellular receptors.

Drug Response Relationship

• Graphical representation of drug effect percentage (%Emax) against concentration illustrates:
  • Full agonist response.
  • Inverse agonist dynamics.
• Maximal efficacy peaks at 100%, indicating complete drug response capability.