Pharmacokinetics Flashcards
Define oral bioavailability
Proportion of the drug given orally, that reaches the circulation unchanged.
Define therapeutic ratio.
How do you work it out?
The amount of drug to reach a therapeutic dose, without going too far and becoming toxic. Shows safety window for a patient to take the drug.
Max tolerated drug/ min effective drug
Define the first pass effect
Drugs given orally our first exposed metabolised before reaching the rest of the body. You can avoid this by having parental, rectal or sublingual drugs
Define the volume of distribution
The theoretical volume of a drug if it were instantaneous.
Work out by amount given/concentration at T0
What’s the difference between Class 1 and Class 2 drugs?
Class one is a drug used at a dose lower than the number of albumin binding sites available (Object Drug) 2 (Precipitant Drug) is used at the dose larger than the number of binding sites, it displaces class one drugs. It raises the level of Class 1 drugs, so it has a higher risk of toxicity.
Give an example of Class I and II drugs
I: warfarin, tolbutamide
II: aspirin
What is Zero Order?
What does the graph look like?
When the rate of drug elimination is constant and saturated.
Concentration vs Time gives straight diagonal line
Rate vs Concentration gives a straight line
What is first order?
Graph?
Linear relationship, half life can be defined
Rate of elimination is proportional to drug level
Predictable response, most drugs behave like this
Concentration vs Time gives curve
Log Concentration vs Time gives a straight diagonal line
What is the Steady State?
Reached within 5 half lives
Use a loading dose if emergency
The state in which the overall intake of a drug is fairly in dynamic equilibrium with its elimination
Describe Drug Metabolism in the Liver
Phase I- hydrolysis, oxidation, reduction. A reactive group is exposed or added to the stable drug ➡️ reactive intermediate
Requires cytochrome P450 and NADPH
Some drugs bypass phase one
Phase II- Conjugation of reactive intermediate with a polar molecule ➡️ water soluble complex
E.g glucoronic acid/glutathione/sulphate ions
Requires UDPGA and enzymes
Describe Alcohol and Paracetamol Metabolism
Look at Semester One
Describe the excretion of drugs
In kidneys
Free drug can be filtered in Glomerulus. Can be actively secreted in PCT
Non polar or lipid soluble can be reabsorbed in the DCT ➡️
Passive Reabsorption is dependent on pH, if acidic urine then it’s lowered and vice versa
