[SallyintNorth]

You may find that one of your local agri merchants has an animal health division and dispensary where they make up their own meds; hereabouts Carrs has one in Penrith and I think Jobsons has one. 

You could then explore buying the amount you need dispensed for yourself - no doubt way more expensive per ml than the commercial packs, but cheaper overall than wasting loads.

Carrs Penrith usually put a 180 day expiry date on wormers and flukers, but have told me that the active ingredients are probably safe and effective to use long after that; the ones we were buying included minerals and vitamins, which latter would have started to become inactive after six months.  (And they never said it made a difference whether the pack was opened or not; I've only come across that in packs of vaccine.)

Worming sheep is often a drench too, PA, although there are some injectables you can use.

[Anke]

The only thing to be careful with keeping wormer/flukicides/flystrike stuff/Veccoxan etc bottles is that they don't freeze, as mine normally live in the garage (unheated) they move to an inside cupboard for the winter.