Question

The doctor ordered Aminophylline oral liquid 2.5mg per lb per dose PO. Aminophylline oral liquid comes as 105mg per tsp. The child's weight is 18kg. How many ml should the child receive per dose?

Please show me step by step. I did it but i dont get it why 4.7ml is the answer for this. thanks!

Answer 1

No. of mL the child should recieve per dose = 4.7 mL

Solution:

Ordered dose = 2.5 mg/lb

Available dose = 105 mg/tsp

Weight of the child = 18 kg

Method 1:

By using Dimensional analysis method: In this method, the given terms are arranged in a manner that only required units are obtained (i.e mL in this case) while all the other units are cancelled off using appropriate conversion factors (i.e lb to kg, tsp to mL etc)

No. of mL the child should receive per dose =

= (since, 1 tsp = 5 mL and 1lb = 0.454kg)

=( ) mL (all the other units are cancelled off, except mL)

= 4.7199 mL or

= 4.7 mL (approximately)

Method 2: By using proportionality:

Ordered dose = 2.5 mg/lb

Available dose = 105 mg/tsp

Weight of the child = 18 kg or 18 kg x   = 39.64 lb.

1 lb of body weight requires 2.5 mg

Let, 39.64 lbs require x mg of drug

By using cross multiplication =>

x = = 99.1 mg

Available dose = 105 mg/1 tsp i.e 105 mg/ 5mL (since, 1 tsp = 5 mL)

So 5 mL contains 105 mg

Let x mL contains 99.1 mg,

Then x =

=

= 4.719 mL or

= 4.7 mL

Hence, the child shall receive 4.7 mL for each dose.