dosage calculations: help

hello everyone,

it's my first time in this forum, which i must say is very interactive.

i'm a first year student nurse in france having difficulties with dosage calculations. my calculations book confuses me and we don't have a dosage calculations class.

so if anyone could help me solve these problems i'd be grateful.

exercise 1

order: 120mg of gentamicin im

supply: ampoules of 10mg, 40mg, 80mg of 2ml each

choose the ampoules to be used and the volume in ml to be injected

i answered as follows:

volume to inject choosing the more concentrated solution: 120mg x 2ml /80mg= 3ml,

now i will be short 1ml since there is 2ml by ampoule

so i'll adjust by adding 1ml from the 10mg/2ml solution

i'm not quite sure what you are doing here. you are correct that if you use ampules with a concentration of 80 mg/ 2ml, you'd need 3 ml. however, this means you need 1 ml from a second 80 mg/ 2 ml ampule. if you were to use the 10 mg / 2 ml ampule as you intended, you'd only be giving 85 mg total.

exercise 2

order: zofran 6mg in 20 minutes with 100ml of 0.9%nacl

supply: 8mg/4ml

what's the volume to be injected?

calculate the flow rate in gouttes/min and in ml/h

volume to inject: 6mg x 4ml/8mg = 3ml

flow rate in ml/h= total ml/total hours, here the total hours is 1/3(20minutes), so 100ml/1/3h = 300ml/h

flow rate in gttes/min= v ml/ t min x c (gttes/ml), here the gttes/ml will be 20, so 300ml/60min x 20gttes/ml = 100gttes/min:confused:

am i doing it right:confused:

you did this correctly. however, if you want to get technical, remember that you added 3 ml to the 100 ml bag, giving you a total volume of 103 ml, not 100 ml.