Pharmacokinetics Flashcards
What part of PK is excluded from IV drugs
Absorption
100% Bioavailability
What is first-past metabolism?
Extensively metabolized in the liver before reaching the systemic circulation
What is enterohepatic recycling
Drugs are transported through the bile back into the gut where they can be reabsorbed
What is the difference between active and passive transportation?
Passive: Drugs from higher concentrations move to an area of lower concentrations
Active: drugs are moved mechanically via transporter proteins
What is considered good or bad bioavailability?
High: >70%
Low: <10%
What is considered therapeutically interchangeable based on bioavailbity?
IV:PO is 1:1 is if PO is 100% F
Bioavailability Formula
Define absorption
Drug moving from site of administration into the bloodstream
Define distribution
Drug molecules move from the systemic circulation to various tissues and organs
What protein is most responsible for drug binding
Albumin
Phenytoin corrected
Two medications that must account for albumin for levels
Calcium and pheytoin
Vd formula
Define metabolism
Drug being converted into another form to facilitate elimination
Primary sits of metabolism
Gut, liver
Phase 1 reaction
Oxidation, reduction, hydrolysis
Phase 2 reactions
Conjugation or add-on constituents
Define excretion
Irreversible removal of drug from the body
Clearance formula
Cl = Rate of elimination/drug concentration
Cl = (F x dose)/AUC
What is first order elimination
Constant percentage of drug is removed per unit of time
Ex: 350 mg of a drug eliminates at the same rate as 650 mg of same drug
What is zero-order kinetics
A constant amount of drug is removed per unit of time
What drugs exhibit Michaelis-Menten kinetics
Phenytoin, theophilline, and voriconazole
What is Michaelis-Menten?
Saturable
First-order: low concentrations
Zero order: higher concentrations (↑ in dose leads to a disproportionate ↑ in drug concentration at steady state)
How do we adjust first-order drugs?
SS, doubling the dose → doubles the serum concnetration
