Session 2 Flashcards
What is bioavailability?
First pass metabolism?
Benefits of extended release medication?
The fraction of a dose of a drug that is absorbed
Metabolism of the drug before it reaches the systemic circulation (gut lumen/liver)
Spends majority of time in the therapeutic window as opposed to immediate release more frequent doses which can fluctuate levels of drug too high and low.
What is distribution?
Factors affecting therapeutic agents?
Adequate plasma levels and reaching target organs
Blood flow, lipophilicity, hydrophilicity, protein binding (albumin to acidic drugs), vd
When can a drug bind to a receptor and/or be eliminated?
How to increase free drug of a class 1?
Issue with this?
Only when it is free
Lower dose of 1 compared to protein binding,sites with class 2 with higher dose than binding sites so class 2 displaces class 1 from the proteins.
If first drug is now too high it can cause harm
What is Vd?
What does a small vd indicate?
Dose/plasma conc
Drug is confined to plasma and extracellular tissues and not spreading through tissues
Describe drug metabolism in the liver?
Problem with smoking alcohol age poor blood flow?
Phase 1 with cytochrome p450 converts drugs to lipophillic metabolites. Phase 2 conjugated them making even more lipophillic for excretion.
They can induce/inhibit cyp’s causing problems as metabolism affected
What kind of drugs are metabolised by the kidney?
Liver?
How conjugated leave the liver?
Low molecular weight polar metabolites
High molecular weight conjugated with glucoronic acid
Via bile
What is true about clearance?
What is clearance?
Equation?
Why does a higher drug concentration increase clearance?
The proportion remains constant
Volume of blood cleared per unit time, ml/min
Rate of elimination/plasma conc of drug
Greater amount in same volume of blood cleared
Important equation involving half life vd and clearance?
Key issue to zero order reaction?
Half life= (0.693)(Vd)/CL
Reaction rate independent of conc or reactants therefore dose change can produce an unpredictable change in plasma conc. alcohol and salicylic acid are examples. Therefore you can’t calculate half life.
When is steady state concentration reached?
What is steady state?
Equation for steady state?
After 5 Half lives
When plasma conc of drug is in therapeutic window
CSS=rate of infusion/Cl
When loading dose?
Equation?
Urgent requirement or long half life
Steady state x vd
Therapeutic index equation?
Td50%ED50
