6 - Introduction to ADME Flashcards
What does ADME stand for
Absorption, Distribution, Metabolism, and Excretion — the processes that determine how a drug moves through the body
Why is oral administration the most common route
It’s easy to use and offers high patient compliance
Name three other routes of drug administration besides oral
Intravenous (IV), Inhalation, Sublingual (also: Intramuscular, Rectal, Dermal, Ocular)
What is drug absorption
The process by which drugs move from the site of administration into the bloodstream
Two types of drug transporters involved in absorption
SLC transporters (passive) and ABC transporters (ATP-dependent, genetically variable)
Physiological factors affecting GI absorption
pH
Gut motility
Blood flow
Gut flora
Bile flow
Example of a food-drug interaction
Tetracycline and calcium — calcium reduces drug absorption
Order of absorption rate based on drug formulation
Solution → Emulsion → Suspension → Capsule → Tablet
What is drug distribution
How a drug moves from the bloodstream into tissues
Why is lipophilicity important in distribution
High lipophilicity allows fast membrane crossing and quicker brain distribution (e.g. thiopental)
Which plasma proteins binds to drugs
Albumin (acidic drugs) and globulins (basic drugs)
What part of a drug exerts pharmacological effect
The unbound (free) portion — not protein-bound
What’s the partition coefficient (Log P)
A measure of drug lipophilicity, indicating how well it crosses membranes
Why is extreme lipophilicity bad for absorption
Too lipophilic → poor water solubility
Too hydrophilic → poor membrane diffusion
What does Henderson-Hasselbalch equation explains
It defines how weak acids and bases dissociate, affecting absorption
Why is PKa important in absorption
Weak acids and bases are better absorbed; strong acids/bases are poorly absorbed
What is drug metabolism
The chemical alteration of a drug, mostly by liver enzymes
Two phases of drug metabolism
Phase I: oxidation, reduction, hydrolysis
Phase II: conjugation (e.g. glucuronidation)
Paracetamol metabolism in therapeutic doses
Mainly converted into glucuronides and sulfates
Paracetamol metabolism in overdose
Processed by CYP450 into NAPQI (toxic), leading to liver damage
Main routes of drug excretion
Kidneys (urine), liver (bile/faeces), lungs (breath), others include sweat, milk, semen
What does drug half-life mean
The time it takes for the drug concentration in the blood to decrease by half
What does drug clearance refers to
The efficiency at which a drug is removed from the body
