Pharmacology- drug disposition/elimination

Question 1

how is volume of distribution equated in IV drugs

Answer 1

Vd = dose/plasma concentration

Question 2

clearance is the volume of plasma cleared of drug in unit time. With regard to this, state the equation for the rate of elimination

Answer 2

clearance x plasma conc.

Question 3

what does css stand for

Answer 3

steady state concentration for IV dosing

Question 4

when is css reached

Answer 4

after approx 5 half lives

Question 5

highlight the difference in drug dosing betwee IV and oral

Answer 5

IV - steady state found after approx 5 half lives

oral - plasma conc. fluctuates about an avg steady state

Question 6

a loading dose is one which is a higher dose given initially, before stepping down to a maintenance dose. why si this, what type of drugs is this for

Answer 6

so that a steady state conc. is found faster

drugs with a long half life

Question 7

first order kinetics (3)

Answer 7

rate of elimination is directly proportional to drug concentration , and so plasma conc. falls exponentially.
half life inversely proportional to elimination rate constant

T(half) = 0.68/Kel

Question 8

2 factors which affect half-life of drug

Answer 8

Volume of distribution

Clearance

Question 9

zero order kinetics is when

Answer 9

a drug is initially eliminated at a constant rate, then when it reaches a low dosage it goes back to 1st order

Question 10

factors which influence drug disposition (ADME)

Answer 10

absorption
distribution
metabolism
excretion

Question 11

drug metabolism can convert the drug into an either …(2)

Answer 11

more polar metabolites that are not readily absorbed (therefore excreted)
metabolites that are usually pharmacologically less active than their parent compound

Question 12

define conjugation

Answer 12

addition of sulphuric/glucuronic acid, deactivating the drug

Question 13

drug metabolism is broken into 2 phases, the first takes place in the RHS of liver, 2nd in LHS. Outline each

Answer 13

1 - oxidation, reduction and hydrolysis, makes drug more polar, able to conjugate
2-conjugation (addition of endogenous compounds, incr polarity)

Question 14

CYP450 monooxygenase cycle

Answer 14

enters as substrate
oxygen added to form hydroxyl group, leaves
second oxygen combines to form H20
can then be excreted

Question 15

drugs can only enter filtrate via glomerular if (2)

Answer 15

Molecular weight < 20000 (most are)
if unbound
(equilibrium in blood exists of drugs bound to large proteins, and unbound

Question 16

3 phases of drug excretion

Answer 16

glomerular filtration
active tubular secretion
passive reabsorption across tubular epithelium

Question 17

percentages of rena blood flow through glomerulus and peritubular capillaries

Answer 17

20%

80%

Question 18

purpose of tubular secretion

Answer 18

to secrete drugs via transpoters to lumen of the nephron

Question 19

transporters of tubular secretion are either anion or cation, type of drug that each handles, example of each

Answer 19

anion - acidic (penicillins) (also uric acid)

cation- basic drugs (morphine)

Question 20

t/f tubular secretion can secrete drugs that are highly protein bound

Answer 20

true

Question 21

function of tubular secretion which is important for tubular reabsorption

Answer 21

can concentrate drugs in tubular fluid against electrochemical gradient

for reabsorption, concentration of uurine favours passive reabsorption of drugs across distal tubue by diffusion

therefore maintains drugs in tubule, so that they can b reabsorbed

Question 22

4 factors which influence reabsorption

Answer 22

lipid solubility
polarity
urinary flow rate 
urinary pH
(alkaline - incr excretion of acids
acidic - incr excretion of bases)