Vet Veterinary Dosage calculator is a drug formulary with more than 500 drugs for dogs and cats, where you put the weight of the animal and the app gives you the dose.
You can search by drug name or just type a word like antibiotic or anti inflammatory and the app show you the drugs that meet that criteria.
Every drug has the indication and the dosage.

Check out other veterinary apps, available in the AppStore:
VetPro, the most complete veterinary app in the AppStore
VetPlus
Vet Anesthesia Guide
Vet Cardiology
Vet Therapeutic Guide
VetECG
Vet Medicamentos e Pacientes em português