Session 11.3 Pharmacokinetics 6

Question 1

what does plasma concentration curve look like

Answer 1

decreases exponentially unless y axis is exponentia then becomes linear

Question 2

why si the rate of metabolism or excretion linear

Answer 2

rate is proportional to plasma conc of drug

Question 3

what is a large functional reserve

Answer 3

plenty of phase 1 and 2 enzyme sites

plenty of OAT/OCT transporters

Question 4

what happens if there is a large functional reserve

Answer 4

rate of metabolism proportional to number of molecules occuping a catalytic/carrier site per unit time

Question 5

if plasma conc of drug doubles

Answer 5

rate doubles

Question 6

when processes are saturated

Answer 6

at high doses, drug metablism is constant and independent of drug dose, cannot go any faster as enzymes and carriers working at capacity= zero order = linear straight inversed line for drug conc and time or levels out for dose of drug v rate

Question 7

what is first order

Answer 7

at low doses, drug metabolism is proportional to drug dose

Question 8

why do relatively few drugs in adults with zero order kinetics at therapeutic dose

Answer 8

fixed rate of elimination per unit time so small changes in dose can produce large increase in plasma concentration of drug as elimination doesnt increase..occurs at same rate = toxicity
and can not calculate half life so can not predict dosage regimes
also narrow therapeutic window
and greater risk of drug drug interactions due to taking up site

Question 9

who is most at risk with zero order kinetics

Answer 9

elderly/infants = decreased capacity

in seriously ill - reduced hepatic and renal capacity means easier to saturate

Question 10

what are some drugs that operate at zero order kinetics at therapeutic dose

Answer 10

alcohol or paracetamol at a high dose