What is a solution?

[Guest guest]

Dear All,

the reason Alligations can be used for solid or semisolid creams an

dointments is because they too are solutions. I had this conversation

with Wrap 4 U my student on Wed night. But here is some info from the

net to explain further.

http://www.mercksource.com/pp/us/cns/cns_hl_dorlands.jspzQzpgzEzzSzppdocszSzuszS\

zcommonzSzdorlandszSzdorlandzSzdmd_s_15zPzhtm

" " solution (so·lu·tion) (s & #601;-loo´sh & #601;n) [L. solutio] 1. a homogeneous

mixture of one or more substances (solutes) dispersed molecularly in a

sufficient quantity of dissolving medium (solvent). The solute may be

gas, liquid, or solid; the solvent is usually liquid, but may be

solid, as in a solid solution of copper in silver (sterling silver).

2. in pharmacology, a term used to denote a liquid preparation

containing one or several soluble chemical substances usually

dissolved in water and not, for various reasons, falling into another

category, (e.g., syrup, elixir). 3. the process of dissolving. 4. a

loosening or separation. " "

Chemically an ointment in which a powdered solid drug is incorporated

into Aquaphor is a solution. Alligation can be used to determine the

recipe.

For example how many grams of a 10 % Drug A and how many grams of

Aquaphor should be mixed together to make 1 pound of 7.5 % ointment?

Note: 1 lb = 454 grams

Note: 10% w/w means 10 grams in 100 grams not 10 grams in 100 ml.

10%-----------7.5/10 x 454 grams = 340.5 grams of 10% drug

------7.5%---------------------------AND

0--------------2.5/10 x 454 grams = 113.5 grams of Aquaphor base

----------------------------------= 454 grams of 7.5% Drug A ointment

Hope this helps someone.

Jeanetta Mastron CPhT BS

Pharm Tech Educator