Formulae

Question 1

How do you calculate maintenance dose?

Answer 1

maintenance dose = (clearance x desired concentration) divided by volume of distribution

Question 2

How do you calculate loading dose?

Answer 2

LD = desired concentration x volume of distribution

Question 3

what is the unit of clearance?

Answer 3

Volume per unit time

Question 4

Total clearance is the sum of what?

Answer 4

hepatic + renal + other losses

Question 5

Clearance in L/min equals what?

Answer 5

(Volume of distribution x elimination constant which is 0.693)/ half life

Question 6

What does it mean when fraction excreted unchanged (FU) = 1?

Answer 6

Totally renally cleared

Question 7

What does it mean when fraction excreted unchanged (FU) = 0?

Answer 7

No renal clearance

Question 8

How to dose adjust in renal impairment?

Answer 8

How much of the renal function has changed, and how much of the excretion is due to renal function.

Question 9

Examples of zero order kinetic drugs

Answer 9

PHENYTOIN (need careful small increments when changing dose)
Alcohol
Theophylline
Aspirin
Perhexilline in CYP2D6 poor metabolisers

Question 10

If fraction excreted unchanged is one, how do you calculate the dose of your drug?

Answer 10

Dosing regimen patient/dosing regimen normal = CrCl patient/CrCl normal

CrCL normal is 1.5 ml/sec

Question 11

If fraction excreted unchanged is less than one, how do you calculate the dose of your drug?

Answer 11

Dosing regimen patient/dosing regimen normal = (1-Fu) + fu (Cr Cl patient/CrCl normal)

Question 12

Does Vd go up or down in the elderly?

Answer 12

Down

Reduced lean body mass, reduced water, increased fat

Question 13

plasma concentration at steady state equals

Answer 13

(BIOAVAILABILTY X DOSE)/DOSING INTERVAL

Question 14

elimination rate

Answer 14

elimination rate = clearance x plasma concentration

Question 15

bioavailability equals

Answer 15

fraction absorbed x fraction escaping first pass metabolism

Question 16

hepatic extraction ratio

Answer 16

hepatic clearance/hepatic blood flow

Question 17

IV and oral dosing: estimating

Answer 17

IV: desired concentration = maintenance dose rate in mg/hr /clearance

Oral: same but x bioavailability

Question 18

oral dose rate

Answer 18

is IV dose rate/bioavailability

Question 19

effect of doublind the dose?

Answer 19

increase duration of action by one half life

Question 20

What does level of enzyme activity have to do with hepatic clearance

Answer 20

if very high enzyme activity, then clearance is limited by blood flow

if low enzyme activity, then clearance is not limited by blood flow, but but

Question 21

AUC equals

Answer 21

dose/clearance

or if oral AUC then (bioavail x dose)/clearance