There are many reasons for cats to vomit. If the vomiting is caused by gastroenteritis and other diseases, you can take gentamicin. If the vomiting is caused by parasites or hairball disease, taking gentamicin will have no effect. of. When giving gentamicin to cats, you need to pay attention to the dosage. It is best to take your cat to a pet hospital to seek professional medical advice. Cats should be dewormed regularly, eat cat grass or use hair removal cream. If there are parasites or hair balls in the intestines and stomach, it will also cause vomiting.