Wolfsbane potion

[Sarah]

Just a quickie

Can anyone tell me when and how often Lupin has to take Wolfsbane?  Is 
it something he has to take on a daily basis or just when a full moon 
approaches?  I had an idea that he had to take it for a fortnight 
running up to the full moon, but I'm not sure where I got that from and 
whether it's correct.

Its just for my fanfic - Snape is incapacitated (having lost his arm in 
an unfortunate altercation with Lucius Malfoy and his wand - Morsmorde 
amputare!)and I was wondering how long Remus would last without the 
potion.

Sarah xx