According to "The Pill Book Guide to Medication For Your Dog and Cat" (Kate Roby, VMD & Lenny Southam, DVM, 1998), due to the expense of getting a drug approved particularly for cats, there are very few drugs that have Food and Drug Administration approval for cats. However, there are times when human over-the-counter and prescription medications can work for cats. If one is not sure if the medication is safe, do not give it to a cat.
The use of human medications in cats is generally governed by how much the cat weighs. A cat gets a mush smaller dose than a person. Whenever a cat owner is not sure of the dosage level, it is imperative to contact a veterinarian. Too much medication can potentially kill a cat.
According to "Cat Owner's Home Veterinary Handbook" (Delbert G. Carlson, DVM, et. al., 1995), these are the dosages for several over-the-counter human medications that can help in cats. For milk of magnesia dosage: 1.2 tsp per 2.27kg. of cat will cure constipation. One teaspoon of Metamucil powder added to wet food once or twice a day will also cure constipation. For diarrhoea, use 1/2 tsp to 1 tsp of Kaopectate (bismuth subsalicylate) per 2.27kg. of cat every two to six hours.
"Cat Owner's Home Veterinary Handbook" recommends this formular for cleaning and disinfecting minor wounds: mix one part Bentadine and ten parts water. It also recommends using any triple antibiotic over-the-counter ointment for humans. "The Pill Book Guide To Dogs and Cats" get more specific by stating that hydrocortisone and neomyacin sulphate are the creams safe enough to use non-diluted on cats.
Many human antibiotics are also used for cats but in a much smaller dose than for people. These can usually only be acquired be prescription. These include penicillin, procaine, sulfa drugs (including sulfasalazine and sulfamethoxine), Neomycin and tetracycline drugs (including tetracycline hydrochloride and doxycycline hydrochloride).
Tiny amounts of narcotic painkillers like Demerol, codeine or morphine can only be used by a vet in emergencies and cannot be purchased, even with a prescription. Unfortunately, human narcotic drugs are the only safe human painkillers to give to a cat. Even child-sized aspirin is toxic enough to kill an adult cat.