Good morning Bill
I take Marevan, and I had an issue with being not able to obtain the 1mg tablets at one stage which I needed to make my dose up conveniently to 6.5mg daily without engaging in too much giggery pokery.
For us as the PBS makes these all about the same price (1, 3 and 5mg in my case) it no more or less costly for me to have needed extra bottles to make my dose (PBS).
I believe this is a temporary situation caused by the various global supply issues, but as the War (not special operation) waged by Russia in Ukraine is driving the next round of "the system hits its just in time
It is unwise without testing to change brands, this has been discussed before here many times. The short answer however is that the Australian government recognises this (even if a member or two here doesn't) and that is why your script is not for "any coumarin" but for your brand. So a doctor will be needed for you to change brands.
In theory this should not be needed, but actual evidence does not support the theory (I have my own theory on why that is so), but this article makes clear why (Note the source is the Australian pharmacy organisation hosted by the Australian Commission on Safety and Quality in Health Care, not just some random poster on the internet).
Key point in that is this paragaraph segment
Our experience with a single patient indicates that the brands are not bioequivalent. The patient was on a dose of 4 mg of warfarin, initially provided by 1 x 1 mg, 1 x 3 mg Marevan, and had an INR = 2.7. Upon completion of that supply, the patient was given Coumadin (2 x 2 mg) and subsequently presented with an INR = 4.4. After questioning, we established that the patient was well and that brand substitution had occurred. The Coumadin was stopped and replaced with Marevan and the INR returned to an acceptable level. It was fortunate that the initial INR was not higher as the brand substitution could easily have placed the patient at risk of haemorrhage. It is reasonable to suggest from this patient that the brands are not bioequivalent. There is a report of similar instability in 15 patients who had their brand of warfarin substituted.4
So I strongly advise you to "work around this" not just "mix n match"
My theory is that the racemic mix isn't always perfectly racemic and that the factors of S and R entaniomers of warfarin are key to understanding of this. S is approximately 5 times more potent than R but R has about double the half life, which drastically changes what the outcomes are in obtaining a steady state. I am discussing this exact point in my book on managing INR but that's not yet completed (watch this space).
Enantiomers is a chemistry term for mirror images of compounds but like gloves they only fit one hand, they have therefore entirely different actions within the body.
S is so named after the latin for Left as is R for Right