Percentage dilution question

[SeattleDan]

My mother is taking an antihistamine preparation containing Ketotifen. I am trying to determine how many milligrams of Ketotifen are contained in each milliliter of the preparation. Here is a pic of the package, showing the concentrations:

 

 

Using the Ketotifen Fumarate concentration of 0.035%, my calculations say there are 3.5 milligrams in each milliliter of the preparation. Can someone verify this, or give me the correct level? I know this is pretty basic, sorry for that, but it's been a long time since I studied chemistry! This is related to a serious health matter, so if someone could check this for me, I sure would appreciate it!

TIA

Dan

[studiot]

 

Can someone verify this, or give me the correct level

 

 

According to the BNF (British National Formulary) the standard dose for eye drops is 250 microgrms per mL = 0.25 milligrams per mL

[SeattleDan]

Thanks for the reply, but that doesn't really address my question. Based on the label for this particular preparation, how many milligrams of Ketotifen Fumarate are contained in each milliliter?

[studiot]

The label states the standard dose.

 

Your maths is adrift.

 

0.025%

 

[math] = \frac{{.025}}{{100}}g/L[/math]

[math] = .00025g/L[/math]

[math] = 0.250mg/L[/math]

[math] = 250\mu g/L[/math]

 

If you want to know why the 0.025% and 0.035%, fumaric acid is diprotic and the salt is some mixture of ketotifen hydrogen fumarate and ketotifen fumarate that makes 250 microgrms of it equivalent to 350 micrograms of pure fumarate.

You will need to ask pharmacist for more details than that.

Edited June 14, 2014 by studiot

[SeattleDan]

So, how many milligrams of the fumarate equivalent is contained in each milliliter of the solution? That's all I'm trying to determine.

 

Thanks

[John Cuthber]

Well, each ml will contain 0.35 mg of the fumarate.

The maths is the same as in studiot's post, but with all the 3s replaced by 2s.

 

However I rather doubt this bit "If you want to know why the 0.025% and 0.035%, fumaric acid is diprotic and the salt is some mixture of ketotifen hydrogen fumarate and ketotifen fumarate that makes 250 microgrms of it equivalent to 350 micrograms of pure fumarate."

The molar mass of the ketotifen is 309.4

The molar mass of the fumaric acid is 116

So the mass of the salt is 425.4

So each gram of the salt contains the equivalent of 309.4/425.4 =0.727 grams of ketotifen.

So 0.35 mg of the salt contains 0.254 mg of the actual ketotifen and someone has rounded that off to 0.25mg.

 

The difference between the numbers is that one is the mass of the active part of the drug and the other includes that fumarate which is there because it makes the stuff easier to work with.

(for example, the fumarate salt might be more readily soluble in water or it might be easier to purify by recrystallisation or something like that)

[studiot]

 

However I rather doubt this bit "If you want to know why the 0.025% and 0.035%, fumaric acid is diprotic and the salt is some mixture of ketotifen hydrogen fumarate and ketotifen fumarate that makes 250 microgrms of it equivalent to 350 micrograms of pure fumarate."

The molar mass of the ketotifen is 309.4

The molar mass of the fumaric acid is 116

So the mass of the salt is 425.4

So each gram of the salt contains the equivalent of 309.4/425.4 =0.727 grams of ketotifen.

So 0.35 mg of the salt contains 0.254 mg of the actual ketotifen and someone has rounded that off to 0.25mg.

 

Thank you for a better viewpoint JC, your numbers certainly stack up.

I didn't think of that explanation, but it's so obvious when you put it like that, and really helps the thread along.

Edited June 15, 2014 by studiot