I would urge a HUGE CAUTION here. Most of the deworming products you can buy at different stores for dogs and cats aren't even safe for dogs and cats...much less a rabbit. I have seen so many animals, especially cats, come into the E Clinic due to severe reactions to the "dime store" variety products. I have seen horrible seizures....and have watched many die.
Another issue is that if there are a lot of worms and they all die at once...they will decay and that can be deadly.
Not one wormer covers all possibilities. And coccidia, which is apossibility, brings on more conversation.
And loss of weight is not necessarily an indication that worms are your problem. While I generally have no problem deworming as a matter of course, don't assume it is the concern.
Randy