Maths dosing calculation

As.1997

Can someone please help breakdown how to solve this:

An 83year old female patient is admitted following a suspected stroke. She is known to suffer with an irregular heart rate (Atrial Fibrillation) and whilst she is nil by mouth requires 125mcg Digoxin intravenously once per day (OD). Digoxin is available in 2mL ampoules containing 250mcg / mL and should be administered as an infusion in 50mL of Sodium Chloride 0.9%. How many mL of Digoxin should therefore be added to the bag of sodium Chloride?

Answer is 0.5mL

My working out so far:
250mcg/mL but only 125mcg is needed so 0.5mL is required but how do we deal with the 50mL of sodium chloride????

(edited 7 months ago)

Reply 1

mqb2766

A very naive answer is that the only thing that matters is the total amount of Digoxin and as you say, its 1/4 of the 2mL ampoule so 0.5 mL. Cant see that the sodium chloride affects things at all.

Reply 2

As.1997

Original post by mqb2766

A very naive answer is that the only thing that matters is the total amount of Digoxin and as you say, its 1/4 of the 2mL ampoule so 0.5 mL. Cant see that the sodium chloride affects things at all.

One thing I've just realised is 0.5mL will still give 125mcg of digoxin - this remains true regardless of how much fluid it is diluted in, provided the entire 50mL + the extra bit with digoxin enters the blood.