Question

FORMULA SUPPLIES AVAILALBE Calamine 10% Lidocaine 0.5 % Zinc Oxide Ointment qs 200 g Calamine powder Lidocaine 2 % W/W Ointment 20 % w/w Zinc Oxide Ointment 5. Calculate how many grams of each ingredient should be weighed to compound the above ointment. (Include the extra 5 %.)

Answer 1

Calamine 10% means

10 gm of powder calamine is present in 100 ml of solution.

W/V of 10 % means 10 gm (amount of solute) is present in 100 ml of solution.

10 %= 10 gm of calamine powder .

Lidocaine availability is 2% W/W.

It means 2gm of lidocaine is present in 100 gm of solution.

W/W = weight of solute in grams/ weight of solution in gram

= 2 gm / 100 gm

So 2% means 2 gram lidocaine.

But we need 0.5% of lidocaine,

(In the same way 0.5% means 0.5 gm in 100 gm of solution f obtained from 2% w/w lidocaine).

To calculate the amount= desired dose/ hand dose * quantity.

= 0.5 gram / 2 gram *100 gms

= 25 grams. Lidocaine.

Zinc oxide is 20% W/W means ,

20 gm of solvent is present in 100 gm of solution.

Needed dose is 200 gm qs ( means 4 times)given

= 200 gm *4 ( qs)

= 800 grams.

W/ W = amount of solute in grams/ amount of solution in gm

W/ W = 20 gm / 100 gm

Available dose is 20 % = 20 gm solute is present in 100 gm soln

Needed dose= 800 grams.

To calculate the amount= Desired dose/ hand dose* quantity

=800 grams/ 20 gm *100 gm

= 4000 grams zinc oxide.

Individually,

10 gram calamine.

25 gm lidocaine.

4000 gm of zinc oxide.

Amount of ingredients should be weighed to compound above ointment.

As it is asked in the question to incude extra 5 % means,

After including extra 5 % extra 5gm will be added.