What IV bolus loading dose would be required if you need to achieve 2mg/L and Vd is 50L?

LD=CssVd
so need 2 x 50 = 100mg

You are commencing an IV infusion to achieve Css=4mg/L. The clearance of the drug is 10L/h, what would be the required infusion rate?

Css=ko/CL
so ko= 4mg/L x 10L/h=40mg/h

If you commence an infusion at 40mg/h and the halflife of the drug is 4h, how long until steadystate plasma drug concentration is achieved?

it takes about 5 halflives to reach steady state therefore about 20h

The plasma drug concentration of a drug after an IV bolus is 10ng/mL 4h after dosing and it is 5ng/mL 8h after dosing. What is k? what is elimination halflife?

Cp2=Cp1e^kt
k= 0.174h1
t/12= 4h

If Vd=50L and k=0.1h1, what is CL?

CL=kVd
CL=50 x 0.1= 5L/h

If we administer an IV bolus dose of 500mg and collect urine so we collect all drug that is excreted unchanged and the amount collected = 300mg, what is the fraction excreted unchanged?

fe= amount in urine/dose reaching systemic circulation= 300/500=0.6

if we administer an oral dose of 500mg and F=0.8 and we collect all urine so that we determine that 100mg is excreted unchanged, what is fraction excreted unchanged (fe)?

100/(0.8 x 500)=0.25

A patient is receiving 250mcg digoxin daily and the bioavailability of tablet is 0.7. At steadystate the Cssav= 1ng/mL, what is the clearance of the drug in this patient?

1ng/mL=1mcg/L (matching units!!)
Cssav= (FxDose)/(CL.T)
1mcg/L=(0.7 x 250mcg)/CL x 24h
CL=7.3L/h

If patient is receiving 125mcg digoxin tablets orally daily and F=0.7 and CL=2L/h, what would be the Cssav achieved?

Cssav=FD/CL.T
=(0.7 x 125)/2 x 24
Cssav=1.8mcg/L=1.8ng/mL

If a patient is taking a 250mcg Digoxin tablet daily which has oral bioavailability of 0.6 and is now to be swapped to digoxin elixir (50mcg/mL) which has a bioavailability of 0.8, how many mL of digoxin elixir would be the appropriate dose?

250mcg x0.6=150mcg reaching systemic circulation from tablet
150mcg/0.8=187.5mcg as elixir
187.5/50=3.75mL
