Pharmaceutical formulas

Question

Select the correct dose of a drug to be administered at a dosage of 10 mg/kg for a patient who weighs 44 pounds and is 6 years old. The drug is available as 500 mg in powder form, which will be mixed in enough water to make 100 ml of final solution (W/V).

Answer 1

Step 1:  Convert the weight in lbs to kg

 

1 kg = 2.2 lbs

 

44/2.2 = 20 kg

 

Step 2:  Calculate the dosage based upon the child's weight in kg

 

10 mg =  x mg

 1 kg        20 kg

 

Cross multiply

 

10 * 20 = 1x

 

X = 200 mg

 

Step 3: Based upon the concentration of the stock medication, determine how many ml will give a dose of 200 mg.  Remember liquid dosages have to measured in syringes, droppers, medicine spoons that are marked in ml.

 

According to the information, the drug, when mixed, will have a concentration of 500 mg/100 ml

 

Using ratio and proportion, we can solve for ml needed for a dose of 200 mg.

 

500 mg =  200 mg

100 ml       x ml

 

Cross multiply

 

100 * 200 = 500X

 

20000 = 500X

 

Divide both sides by 500 to find out X

 

X = 40 ml

 

You could have reduced 500mg/100 ml to 5 mg/1 mg and then cross multiplied. The answer will be the same!