Question

A patient is taking a commercial lithium carbonate capsule that contains 600 mg of lithium carbonate. They have developed a sensitivity to one of the inactive ingredients in the commercial capsule, and their doctor has prescribed lithium citrate instead. You have been asked to compound lithium citrate capsules such that each capsule has the same strength, expressed as milliequivalents of lithium, as the commercial tablet. How many milligrams of lithium citrate should each capsule contain? Round your final answer to the nearest milligram. MW Lithium carbonate = 74; MW Lithium citrate = 210.

Answer 1

Lithium Carbonate: Molecular formula: Li₂CO_3; molecular weight is 74

Lithium Citrate: Molecular formula: C₆H₅Li₃O_7; molecular weight is 210

Lithium atomic mass is 6.94 u

Since, there is 2 atoms of Li in lithium carbonate

It means 74 mg of lithium carbonate contains 2 x 6.94 = 13.88 mg of lithium.

Therefore in a capsule containing 600 mg of Lithium carbonate contains the amount of Lithium can be calculated as:

For 74 mg of Lithium carbonate = 13.88 mg of Li

So for 600 mg of Lithium carbonate = (13.88 x 600)/74

= 112.5 mg of Li

Now, Lithium citrate contains 3 atoms of Lithium in its formula

Its means 210 mg of Lithium citrate contains = 3 x 6.94 mg of lithium

= 20.82 mg of Li.

Therefore for equivalent weight of Li to the 600 mg of lithium carbonate, the amount of Lithium citrate can be calculated as:

20.82 mg of Li = 210 mg of Lithium citrate

112.5 mg of Li = (112.5 x 210)/20.82 mg of Lithium citrate

= 1134.7 mg

or 1135 mg (approx.) of the Lithium citrate is to be present in each capsule that contains Li milliequivalent to 600 mg of Lithium carbonate.

Hence, the answer is 1135 mg approx.