Rabbits housed indoors rarely suffer from internal parasites or worms. However, bunnies kept in outdoor hutches are prone to a variety of internal, parasitic worms including flatworms, roundworms, pinworms and tapeworms. Luckily, rabbits are not susceptible to heartworms. Before giving any medication to your rabbit, consult a rabbit-savvy veterinarian. If you have found worms in your rabbit's poop, bring a sample to your vet for positive identification. The best medication for the job will depend on the exact species of worm infesting your pet.
Selamectin and Ivermectin
In the past, ivermectin was the chosen medication for controlling a variety of worms and mites in rabbits. More recently, a "cousin" called selamectin has usurped ivermectin. Selamectin is sold under the brand name Revolution, which is often available over the counter. Ivermectin is most effective when injected, while selamectin can be given topically with equal results. In addition, selamectin treats a broader range of worms and mites than ivermectin. Either medication will treat many species of roundworm and pinworm with little risk of side effects, and can be used as a preventive medication for outdoor rabbits; however, the 'mectins will not rid your rabbit of tapeworms.
Panacur or Fenbendazole
Fenbendazole, most often sold under the brand name Panacur, can be given orally. Of the deworming medications safe for rabbits, Panacur treats the most species of roundworm and pinworm. It will also eliminate some species of tapeworm. In rabbits, Panacur is most often prescribed to treat Encephalitozoon cuniculi, a common protozoal brain parasite that causes paralysis and seizures in rabbits. A "cousin" of fenbendazole, namely thiabendazole, is also sometimes used to treat nematode worms in rabbits.
Praziquantel, sold under the brand named Droncit or Drontal, is the most effective drug for treating tapeworm infestation in rabbits. Most rabbit-savvy veterinarians agree that Droncit is safe for rabbits, although it is not licensed in the U.S. for use in this species.
Two forms of piperazine are generally used in veterinary medicine: piperazine adipate or piperazine citrate. "Adipate" and "citrate" simply refer to the salt in the compound. Piperazine kills some roundworms, but is singularly effective against the most common pinworm found in rabbits, Passalurus abiguus.