For pet owners wanting to go it alone and explore the use of over-the-counter medication in their pet, antihistamines are a good place to start. A broad and diverse family of drugs, their effects range from anti-allergy and cough suppression, through to anti-nausea, and appetite stimulation. Sedation is the most common side effect, which is sometimes exactly what’s desired. Just like in man, your dog shouldn’t drive nor your cat use heavy machinery when taking antihistamines..
Antihistamines are one of the treatment options for dogs and cats that suffer with atopy (skin, paw and ear problems due to airborne allergens), and are useful in a couple of other situations. They are of no use for treating contact, flea or food allergies. Rather than completely eliminating symptoms, these drugs may decrease severity, improve quality of life, and reduce dependency on cortisones and/or cyclosporine.
.They are appealing to many pet owners who:
- have personal experience of the effectiveness of such drugs in man;
- like the over-the-counter availability of many antihistamines in chemists;
- are dissatisfied with cortisones, and unable to afford cyclosporine or desensitisation.
- Antihistamines are no cure and, like cortisones and cyclosporine, only suppress allergic reactions. They are only effective in up to 33% of dogs, and up to 73% of cats with atopy, but may not eliminate all itchiness and the need for other treatments.
- An animal may be responsive to one antihistamine but not another, so a 3-6 week cycle of experimentation is required. By testing at least 3-4 different drugs, pet owners can work-out which agent works best.
- While this family of drugs is safe enough to be available without script in many cases, they are not without side effects. Described below, they are uncommon, usually mild, and resolve on discontinuation of treatment.
.The antihistamine drug trial protocol for atopy:j
When doing the trial:
- It is easiest to be confident a drug is effective if the trial is done during the times of year when your pet’s allergies are known to be unrelentingly bad; if you start treating with a drug and coincidentally the wattle stops flowering, you may be lead to believe the antihistamine worked well. Spring and summer are usually the worst seasons, but get your vet to check your pet’s medical history for more accurate patterns.
- To firm-up our certainty an improvement is really a drug effect, it is best to rechallenge: stop the antihistamine after a month of use and watch for the symptoms to return. If they do, you win; if not, back to square-one.
- Put your dog on an Essential Fatty Acid Supplement or fish-based diet, as such diets seem to make antihistamines more potently effective.
- If you find a drug that works, continue to try a few more, as others may be even more effective.
.Here is a link to a paper which desribes the use of Telfast, an over-the-counter, once daily antihistamine for atopy in dogs, and it’s effectiveness equivalent to cortisone after 6 weeks of treatment.
Insect bite reactions:
Vets commonly see dogs affected by acute allergic reactions to insect bites (bees, ants, wasps) with symptoms of local swelling and itchiness, often facial, and lumps or hives erupting suddenly all over the body. Very rarely more dramatic symptoms are collapse, vomiting, breathing difficulty, and heart rhythm disturbances. Vaccination reactions rarely manifest similarly. For more detail, see Insect Bite Reactions: from Itch to Anaphylaxis.
While antihistamines are only really effective when given before exposure to an allergen, they are often given by vets as an injection to treat such reactions. An antihistamine tablet given as first-aid by an owner who cannot get to a veterinarian may be of use, and such advice is often given over the phone by after-hours veterinarians. If given early, it may slow or limit the progression of the reaction, or at least have some sedative effect, calming an agitated dog driven mad by their bee sting.
Notes on diphenhydramine:
This drug has a variety of actions, beyond just treating itchy skin, and is worth keeping on hand in your doggy first aid kit. Branded as ‘Benadryl Original Formula’ syrup or Snuzaid® in Australia, it has mild cough suppressant, sedative and antinausea actions. It’s unpalatable in liquid form and doesn’t really touch-the-sides with severe Kennel Cough, but can be useful for car sickness, mild tracheitis, and acute allergies..
Notes on Periactin® in cats:
This over-the-counter antihistamine for man is often used by vets trying to stimulate appetite in cats. While not wanting to mask loss-of-appetite due to disease, this agent can be useful in cats whose eating habits may have been disrupted by the stress of hospitalisation, cattery, house guest or other diseases (syntax intended)..
There are several antihistamines that are also antidepressants and yes, Clomicalm® has the same active as Placil®, a product for man. In these drugs the psychotropic/sedative effects are the desired treatment goals, and the antihistamine effect coincidental. If lucky you can resolve your terrier’s skin and separation anxiety in one hit..
These depend on which drug is used, and are reported to occur in up to 25% of dogs and 10-40% of cats. Don’t be too put off by these as they are usually mild sedation or tummy upsets, which resolve when treatment is stopped.
- Drowsiness, which may abate after 3-7 days of use, so do persist if not severe. Speak with your vet before giving antihistamines to dogs on anti-seizure medication as they may increase sedative side effects.
- Stimulatory: excitement, vocalising, hunger, or thirst.
- Gastrointestinal: salivation, vomiting, diarrhoea, off food.
- Haematologic side effects are rare and detected by blood test if using some agents in the longer-term.
- Blood pressure and rhythm effects are rare but demand care when using is animals with heart disease, hypertension, glaucoma and hyperthyroidism.
- Don’t use combination cold and flu medications that also have other ingredients like paracetamol – speak with your pharmacist or vet if confused. Be careful not to confuse Benadryl Original Formula, with other Benadryl combination products.
While all these dose rates are correct as of 2009, I don’t wish to be held responsible for incorrect dose calculations or misuse of this information. If you’re uncertain if your pet is atopic, or your math is poor, you should speak with your vet to make sure the exercise is safe and worthwhile.
Tags: allergies, antidepressant, antihistamines, appetite stimulant, atopy, canine, cat, cortisone, cyclosporine, diphenhydramine, DIY, dog, drug trial, feline, fish-based diets, hayfever, hyperthyroidism, insect, insect bite, motion-sickness, Omega-3's, OTC, over-the-counter, periactin, seasonal, sedation, skin, vet, veterinary