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Is 22.5mg/0.45ml MXT the same as 25 mg/0.5ml MXT?


I'm on 22.5mg MXT which I have as a Metoject pen.

When I picked up my prescription today I had 25 mg/0.5ml. I was pretty sure this wasn't right so popped back into town to the pharmacy to check.

The pharmacist said they were the same thing, and I said 'really?'. She said 25/.5 is the same as 22.5/.45. Then changed her mind and said she would have to check.

Can anyone explain the finer points of the above.

I seem to remember I was told the .45 is the solution the MXT is suspended in, but I have no idea really!

Grateful for any help!

Thank you xx

9 Replies

I doubt that they're correct but best to get it checked.

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I would have said it's 25 and not 22.5

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Thanks for your replies Moomin and Matilda.

Looking more on the internet I think it probably is 25 not 22.5 that I have been given.

I think the .5 and .45 ml also relate to the dosage, but in millilitres rather than milligrams?

Not sure that's right though.

How confusing!

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The liquid in the pens of different doses is the same stuff, at the same concentration. So if you are only on say 10mg then your pen only contains 0.2ml, and you are on 22.5mg so you should have 0.45ml of liquid. So the bigger the doses you are on the more liquid you have to inject - although even 25mg is hardly a teaspoon full!

Your pharmacist was perhaps a trainee?


Thank you Helixhelix. I think she was a trained one, but when I said 'really?' She seemed less sure of her answer.

We left it she is going to talk to the supplier, luckily I have a pen for tonight's dose.

I doubt another 2.5mg would have made much difference - although my liver is very unhappy at 22.5!


Definitely check it out if your liver is already rebelling!


with my understanding its the amount of methotrexate over the volume of liquid it is in. they are not the same thing the 25mg has 25 mg equivalent in at and the 22.5 as 22.5 in it. I assume the pen only works within a small range of liquid volumes or it is cheaper to vary the concentration of the liquid to get different amounts of MTX into the body.

Clear as mud lol



It is wrong what she's saying & actually it needs to be reported by her as an incident of error. Which is probably why she said what she had said to you. As she didn't want to do that. It's completely unprofessional by her. Maybe go to another pharmacy to see what the pharmacist there says to double check the dosage then take it from there.


25mg /0.5ml is the same concentration as 22.5mg /0.45 ml ie the same number of grams per millilitre.

If you were using an old fashioned syringe you could decide what volume to inject. And you could then have injected only 0.45ml and then you would have injected a dose of 22.5mg.

However as you are using a pen you will have to inject all the liquid ie 0.5ml, so you will get a dose of 25mg if you use a pen which says it has 25mg/ 0.5ml.

If you need a dose of 22.5mg then you need a pen which has the smaller volume of solution ie 0.45 ml.

Hope this helps!


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