Pharmacology - Pharmokinetic Flashcards
What is pharmokinetic?
Absorption, distribution, excretion
Describe differences between administration route?
IV - more rapid
IM - more prolonged effect (compared SC)
Effect of gastric emptying on absorption?
Critical to drug absorption
SA intestine > stomach - most drugs absorbed via intestine
Fed vs fasting state - affect drug availability
What is bioavailability?
Fraction of unchanged drug reaching circulation following route admin
What can affect bioavailability?
Absorption, first pass metabolism, food
How can physiochemical and physiological factors affect distribution?
Physiochemical: size of molecule, degree of ionisation, protein binding
Physiological factors: organ/ tissue size and blood flow
Where do acid and basic drugs bind?
Acidic drugs bind to albumin
Basic drugs bind alpha1-acid-glycoprotein
Relationship between free drug and clearance?
Increased amount of free drug - increased clearance from circulation
What factors can affect drug distribution?
- Perfusion - blood flow
2. Permeability - membrane barrier limitation (BBB, placenta)
Where are polar and non-polar drugs excreted?
Polar drugs are excreted renally - urine
Non-polar are excreted billiary - faeces
Explain phase I reaction
Produce active metabolites - polar
- Introduction of polar group by oxidation, reduction or hydrolysis
- If sufficiently polar can be renally excreted
- Can produce toxic components
- Catalysed by cytochrome P450
Explain phase II reaction
Attachment of endogenous molecule to drug or phase I reaction to produce metabolite
- often use sulphur, acetyl
- Produce heavier molecule - less effective
What enzyme is used in phase I reaction
Cytochrome P450
Explain cytochrome 3A4 and inducers/ inhibitors
Inducers - increase clearance - decrease levels of drug in blood (E.g phenytoin)
Inhibitors - decrease clearance - increase level of drug in blood (e.g erythromycin)
Factors affecting metabolism? (both increase and decrease)
Increasing drug level - excessive dose or decreased clearance - liver failure, age
Decrease drug level - low dose or increased clearance
- enzyme induction, first pass metabolism
