a) A child weighing 33 pounds requires a dose of 8 mg/kg of drug X. Given that a 5 mL dose is to be given each time, what volume of water must be added when the drug X powder is reconstituted? Instruction on the label indicates that dilution to 120 mL (by adding 100 mL of water) gives 125 mg drug X per 5 mL. 

(4 marks) 

1kg = 2.2 lbs (Memorize)

Weight of child: 33 lbs

Convert to kg: 33/2.2 = 15 kg

Dose of drug X: 8 mg/kg -> 8*15 = 120 mg

120 mg/ 5 ml requested = 24 mg/ml

When reconstituted with 100 ml of water you get 120 ml of 125 mg/5 ml

Total amount of X in the bottle:

125/5 = 25 mg/ml

25 * 120 = 3000 mg

Volume for 3000 mg of 24 mg/ml solution:

Concentration = mass/volume

3000/24 = 125 ml

Volume of water to be added to reconstituted solution

125 - 120 = 5 ml