pharmacokinetics Flashcards
what is the therapeutic effect proportional to
the concentration of drug in the plasma
what do membrane pores allow to diffuse through
low molecular weights (<200Da) or small ions (Li+)
what drugs are able to diffuse directly across the membrane
lipid soluble molecules
what is the condition for carrier mediated absorption of a drug
the drug must resemble a natural ligand/substrate
what are the factors affecting absorption
lipid solubility
ionisation
formulation
gastro-intestinal function
first-pass metabolism
what does it mean when ionisation is at 50%
pH=pKa
what is the Henderson-Hasselbach equation
pH – pKa = log [conjugate base]
[conjugate acid]
for acids: what is the difference in absorption between a conjugate acid (COOH) and a conjugate base (COO-)
conjugate acid (COOH) - lipid soluble, crosses membranes
conjugate base (COO-) - water soluble, doesn’t cross membranes
for bases what is the difference in absorption between a conjugate acid (NH3+) and a conjugate base (NH2)
conjugate acid (NH3+) - water soluble, doesn’t cross membranes
conjugate base (NH2) - lipid soluble, crosses membranes
when are acids most ionised
most ionised at high pH
strong acids have pKa of 3 or lower
very poorly absorbed
when are bases most ionised
most ionised at low pH
strong bases have a pKa of 10+
strong bases are poorly absorbed
