GPhC Exam Calculations Question

A Dr rings and asks for the approximate equivalent dose of ferrous gluconate which should be given for 600mg of ferrous sulphate.

Choose one
a. 1.6g
b. 0.8g
c. 0.6g
d. 1.2g
e. 0.2g

Refer to the ferrous equivalence table in the BNF.

Ferrous gluconate 300mg 35mg iron
Ferrous sulfate 300mg 60mg iron
A prescription with 600mg ferrous sulphate and it is not available , therefore I need to give ferrous gluconate instead!!!
So:
600mg Ferrous Sulphate contains 120mg iron
Then you ask yourself how much gluconate is contains 120mg of iron. So algebraically it is 120/35 x 300 = which is about 1000. You cannot give 900mg ie 3 tabs as this would be too little, so the only other option is C 1.2g 4 tablets!