Compounding Hotline

Martin A. Erickson III, RPh
Published Online: Monday, August 1, 2005

Q: To make 250 g of 1:1000 triiodothyronine (T-3) trituration, we need to use 250 mg (0.25 g) of T-3 and 249.4 g of Avicel (or lactulose). This formula also calls for some food coloring (blue, 0.35 g), making a total of 250 g. Please verify that 250 mg (or 0.25 g) is the appropriate amount of T-3 to use when making 250 g of 1:1000 T-3 trituration. Additionally, please verify that, if we were to make 100 g of the 1:1000 trituration, only 0.1 g (or 100 mg) of T-3 would be used with 99.55 g of Avicel (or lactulose) and 0.35 g of food coloring.

A: Proportionalities and nomenclature are subjects of frequent and great confusion. Sometimes analogies are helpful when describing approaches to problems. Here, a trituration is similar to a solution. For solutions, the United States Pharmacopeia/ National Formulary gives solubility ratios as "x:y" and "x in y" (1:4 and 1 in 4, respectively, for example). The statements mean x part(s) of solute plus y parts of solvent to make the solution, and the final product is an "x:(x+y) solution," which contains x part(s) in (x+y) parts of solution. For example, if the solubility is 1:3, then the solution described is a "1:4 solution."

In your example, the final product is described as a "1:1000 T-3 trituration," analogous to the 1:4 solution in the answer above. Therefore, the final trituration contains 1 in (1+y) of trituration, but the relationship of the active ingredient to the diluent can be described as x in (1000-x) or 1 in (1000-1) trituration.

If your dilution is to be 250 g trituration, then, from the above, 1:1000:x:250, x = 250/1000 = 0.25. Therefore the trituration is 0.25:250, but the ratio of the T-3 ("solute") to the diluent ("solvent") is 0.25 in 250-0.25, or 249.75.

Another method is to use a simple proportionality:

You require 250 g of a 1:1000 trituration.

1:1000:x:250

x = 250/1000 = 0.25

Diluent = 250-0.25 = 249.75

Any minor additional ingredients, such as aluminum lake (insoluble) powder FD&C or D&C dye, are subtracted from the total diluent, 249.75-z = diluent, z = amount of dye.

Mr. Erickson is director of professional affairs at Gallipot Inc.

E-mail your compounding questions to compounding@pharmacytimes.com



Latest Articles
This weekly video program provides our readers with an in-depth review of the latest news, product approvals, FDA rulings and more.
Chronic kidney disease incidence has grown faster than many of its common comorbidities such as diabetes and hypertension, and medications may be an underappreciated driver of this growth.
President Barack Obama’s fiscal year 2017 budget proposal calls for an additional $1.1 billion to combat the nation’s spiraling opioid epidemic.
Baxter International is voluntarily recalling intravenous solution due to leaking containers and the potential for particulate matter.
Latest Issues
$auto_registration$
VSEO N/A