Biopharmaceutics and ADME Flashcards
(27 cards)
What does biopharmaceutics study?
The relationship between a drug’s physicochemical properties, dosage form, and route of administration, affecting the rate and extent of absorption (bioavailability).
What is bioavailability?
The rate and extent to which an active drug is absorbed and becomes available at its site of action, leading to a clinical response.
Name four factors that affect bioavailability.
- Drug release from dosage form
- Stability in biological fluids (can be degraded in biological fluid)
- Permeability through intestinal epithelial cells
- Pre-systemic metabolism (only after passing through the liver is bioavailability considered)
What are the methods to assess bioavailability?
- Quantitative clinical response (lowering blood pressure)
- Detection at site of action (e.g., molecular imaging)
- Measurement of plasma drug concentration (most common)
What is the primary method used to assess bioavailability in practice?
Measurement of drug concentration in plasma.
What is the significance of protein binding in blood?
Only unbound drug can diffuse across membranes and be pharmacologically active. Bound drug acts as an inactive reservoir.
What is ADME?
The pharmacokinetic processes of Absorption, Distribution, Metabolism, and Elimination.
What is first-pass metabolism and why is it significant?
Metabolism that occurs in the liver before a drug reaches systemic circulation, significant for orally administered drugs.
What are the main phases on a plasma concentration-time curve?
Absorption phase: Drug concentration increases
Peak (Cmax)
Elimination phase: Drug concentration decreases
What is Cmax and Tmax on a plasma concentration-time curve?
Cmax: Maximum drug concentration in plasma
Tmax: Time to reach Cmax
What does AUC represent?
Area Under the Curve; represents the extent of drug absorption.
Define absolute bioavailability and its formula.
Fraction of an oral dose that reaches systemic circulation compared to IV.
Formula: (AUC oral / AUC IV) × 100
Define relative bioavailability.
Comparison of bioavailability between different formulations of the same drug.
Formula: (AUC test / AUC standard) × 100
What are the criteria for bioequivalence?
No significant differences in Cmax, Tmax, and AUC between formulations.
What physicochemical properties influence drug absorption and distribution?
Lipid solubility, Degree of ionization, Molecular weight
What is the primary mechanism of drug absorption?
Passive diffusion driven by concentration gradients.
What is the role of albumin in drug distribution?
Binds drugs in plasma, making them inactive but acting as a reservoir; binding is reversible and saturable.
Name a drug interaction due to protein binding.
Naproxen (99% bound) can displace warfarin (97% bound), increasing free warfarin levels.
What are common sites of drug metabolism?
Lumen of the GI tract, Gut wall, Liver (first-pass and systemic)
Name the four main pathways of drug metabolism.
- Oxidation - via oxidases in liver
- Reduction - via GIT and liver
- Hydrolysis esterases in liver
- Conjugation (e.g., glucuronidation)
What are characteristics of metabolites formed from drug metabolism?
More water-soluble, More ionized, Less active, Easier to excrete
What are the primary routes of drug excretion?
Urine (kidneys), Faeces (GI tract), Bile, Lungs (for volatile substances), Sweat, saliva, breast milk
What is drug half-life (t½)?
Time required for plasma concentration to decrease by half; impacts dosing interval and reflects metabolism/excretion rates.
How does kidney function affect drug half-life?
Impaired kidney function prolongs half-life; dosing must be adjusted to avoid toxicity.
