Pharmacokinetics Flashcards
Define T max
Time the drug takes to reach its max conc
Define C max
Max conc of drug in the plasma
Define bioavailability
Fraction of a dose which finds its way into a body compartment (usually circulation
IV = 100%
Other routes compare against IV)
How is bioavailability (F) calculated?
F = AUC oral / AUC IV
What factors affect bioavailability?
Drug formulation
Age
Food: lipid-soluble > water-soluble
Vomiting/malabsorption
First pass metabolism
Define first pass metabolism
Any metabolism occurring before the drug enters the systemic circulation
Occur in = gut lumen, gut wall, liver
Recognise the main routes of drug administration in to the body
Oral
IV
IM
PR
SL
Dermal
What key factors effect drug distribution?
Protein binding
Volume of distribution
Briefly outline the factors affecting drug-protein binding
Hypoalbuminaemia
Pregnancy
Renal failure
Displacement by other drugs
How can adding another drug affect protein binding?
Drug B may bind more highly = displaced drug A = higher [free drug A]
What is volume of distribution?
measure of how widely a drug is distributed in body tissues
Vd = dose / [drug]t0
Describe CYPs
Genetically dependent
Role = oxidation, dealkylation, reduction, hydrolysis
Can be influenced by enzymes inducing/inhibiting drugs
CYP450 - mainly present in liver
Outline the factors affecting drug Metabolism
Race – CYP 2D6 absent in 7% caucasians
Age – reduced in older/children
Sex
Species
Clinical or physiological condition
What are the phases of drug metabolism?
Phase 1 = chemical changes, CYP450
Phase 2 = conjugation, increased solubility, allows excretion
What factors effect drug excretion
Age
Glomerular filtration
Passive tubular reabsorption
Active tubular secretion