Is too much antihistamine bad for dogs

Is It Possible to Overdose on Antihistamines?

An antihistamine overdose, also called antihistamine poisoning, occurs when theres too much of the medication in your body. This can be life-threatening.

Antihistamines, or allergy pills, are medications that reduce or block the effects of histamine, a chemical the body produces in response to an allergen.

Whether you have seasonal allergies, indoor allergies, pet allergies, food allergies, or a chemical sensitivity, an allergic response can trigger multiple symptoms, such as:

• sneezing
• coughing
• sore throat
• runny nose
• skin rash
• ear congestion
• red, itchy, watery eyes

Allergy medication is considered safe when used correctly and can provide quick relief from symptoms, but its possible to take too much. Its important that you understand proper dosing to avoid toxicity.

Antihistamines include first-generation medications that have a sedating effect and newer non-sedating types.

Examples of sedating antihistamines include:

Examples of non-sedating antihistamines include:

Its possible to overdose on both types of antihistamines. Symptoms of an overdose when taking sedating medication can vary but may include:

• increased drowsiness
• blurred vision
• nausea
• vomiting
• increased heart rate
• confusion
• loss of balance

More serious complications of first-generation antihistamine overdose include seizures and coma.

Non-sedating antihistamine overdoses tend to be less toxic and less severe. Symptoms may include:

Sometimes, however, tachycardia can occur. This is when your resting heart rate is more than 100 beats per minute.

Symptoms of an overdose usually appear within six hours of taking too much antihistamine. Your symptoms may start off mild and then gradually worsen over time.

Deaths from antihistamine overdose

There have been reports of death due to antihistamine toxicity. These include accidental overdoses and intentional misuse.

Death can occur when an overdose causes severe complications such as respiratory distress, cardiac arrest, or seizures. Each persons tolerance to medication can vary. However, toxicity usually occurs when a person ingests three to five times the recommended dosage.

Medical emergency

To avoid life-threatening complications, call 911 or go to the emergency room if you have any symptom of an overdose. You can also call the Poison Control Help Line at 800-222-1222.

Antihistamine overdose treatment focuses on stabilizing your health and providing supportive care.

Youll likely receive activated charcoal in the hospital. This product is used in emergency situations to help reverse the effects of poisoning. It works as an antidote, stopping the absorption of toxins and chemicals from your stomach into the body. Toxins then bind to the charcoal and exit the body through bowel movements.

In addition to activated charcoal, general support may include cardiac and respiratory monitoring.

The prognosis depends on the amount of antihistamine ingested and the extent of an overdose, but a full recovery is possible with immediate medical treatment.

Some side effects of taking antihistamines can mimic symptoms of an overdose. These include mild nausea, dizziness, vomiting, diarrhea, and stomach pain.

These symptoms dont usually require medical treatment, and may subside as your body adjusts to the medication. Even so, check with a doctor if you have side effects. You may need to reduce your dosage or take a different medication.

The difference between a side effect and an overdose is the severity of symptoms. Severe symptoms like rapid heart rate, tightness in the chest, or convulsions require a visit to the emergency room.

Antihistamines are safe when used properly. Here are some tips to avoid ingesting too much:

• Dont take two different types of antihistamines simultaneously.
• Dont take more than the recommended dosage.
• Dont double up on doses.
• Keep drugs out of reach of children.
• Dont take two doses too close together.

Make sure you read labels carefully. Some antihistamines can interact with other drugs you take. If you dont know whether its safe to combine an antihistamine with another medication, speak with a doctor or pharmacist.

Be mindful that some antihistamines include other ingredients like a decongestant. If you take these types of antihistamines, its important that you dont take a separate decongestant.

Antihistamines can also relieve allergy symptoms in children, but they arent right for all children. Generally speaking, you shouldnt give an antihistamine to a child under the age of 2.

Dosage recommendations for children ages 2 and up vary depending on the type of antihistamine, and its sometimes based on a childs weight.

Talk to your childs pediatrician or pharmacist if you have questions about the proper dosage.

Whether you have seasonal or indoor allergies, an antihistamine can help relieve symptoms like sneezing, a runny nose, sore throat, and watery eyes.

However, taking too much of an antihistamine can lead to an overdose or poisoning. Be sure to read medicine labels carefully and dont take more than directed.

Benadryl For Dogs

The temptation to reach into our medicine cabinets to treat our pets can be dangerous. Humans and dogs react very differently to medications, which is why veterinarians caution dog owners against making independent decisions about how to medicate their animals. However, some human medications are safe for use with dogs, as long as they are used appropriately.

Veterinarians use diphenhydramine for dogs, commonly known by the over-the-counter human medication brand name Benadryl, for dogs on a regular basis to treat allergies, travel anxiety, and motion sickness. While you should always consult with your veterinarian before giving your dog human medication, here is what you need to know about using diphenhydramine or Benadryl for dogs.

What Is Benadryl?

Benadryl is the brand name for the active ingredient diphenhydramine HCl. Diphenhydramine is a first-generation ethanolamine-derivative antihistamine, which is the scientific way of classifying antihistamines that can cross the blood-brain barrier making them very effective but also increasing risks of adverse side effects. While Benadryl is not yet FDA-approved for veterinary use, it is considered safe for use in dogs and cats and is commonly used in veterinary practices across the U.S.

Diphenhydramine works by blocking the receptors that receive histamines in the body. This relieves many of the symptoms associated with allergies, like itching, sneezing, and hives. The body still produces histamines, but the receptor antagonist blocks the receptors from registering the histamines.

What Does Benadryl Treat in Dogs?

Benadryl is a great medication for use in dogs with mild-to-moderate allergies. Seasonal allergies, food allergies, environmental allergies, and allergic reactions to bites from snakes and insectsall respond to Benadryl in most cases. Benadryl is commonly used to treat itchiness in dogs caused by skin allergies, and it also reduces many of the other symptoms of allergies, including:

• Hives
• Swelling and inflammation
• Redness
• Runny nose and eyes
• Coughing
• Sneezing
• Anaphylactic reaction

One of the side effects of Benadryl is drowsiness, which can help to calm anxious dogs. Diphenhydramine may help relieve symptoms of mild-to-moderate travel anxiety in pets. It also may help relieve motion sickness. Although Benadryl may sometimes relieve anxiety, its best to talk to your veterinarian or an animal behaviorist to determine and treat whats causing the anxiety.

Veterinarians prescribe Benadryl for dogs with mast cell tumors to help mitigate the effects of the massive histamine release caused by mast cell degranulation. Veterinarians sometimes prescribe diphenhydramine during heartworm treatment, as it helps reduce the risk of an allergic reaction to heartworm treatment therapy. Benadryl makes an excellent addition to your diphenhydramine for dogs.

When to Ask Your Vet About Benadryl For Dogs

Before you reach for Benadryl, consult your veterinarian about your dogs symptoms. Allergy symptoms like itching and red eyes may also be signs of more serious conditions. In some cases, giving your dog Benadryl can actually worsen your dogs condition.

Red, goopy eyes could be a symptom of allergies, or it could also be a sign of glaucoma or dry eye, which Benadryl will not help treat. Similarly, itching is frequently associated with allergies and other skin conditions. Your vet will also be able to tell you whether Benadryl will interact with any other medications that your dog is taking.

Side Effects of Benadryl

There are side effects associated with using Benadryl for dogs that all owners should be aware of. Most side effects occur within the first hour of exposure, so monitor your dog carefully during this time.

If your dog has any of the following conditions, only use Benadryl after consulting your veterinarian:

Common side effects associated with using Benadryl for dogs include:

• Drowsiness
• Dry mouth
• Urinary retention
• Hypersalivation
• Increased heart rate
• Rapid breathing

Rare side effects include:

Benadryl Overdose

Its possible to overdose on Benadryl. Signs of an overdose include hyper-excitability of the central nervous system, which can be fatal. Other warning signs to watch for are:

If you suspect your dog has overdosed on Benadryl, contact your veterinarian or emergency veterinary hospital immediately. Some dogs develop an allergic reaction to Benadryl. If your dog starts having symptoms of an allergic reaction, seek veterinary care immediately.

How Much Benadryl Can I Give My Dog?

The best way to determine the correct Benadryl dosage for dogs is to consult your veterinarian. The Merck Veterinary Manual recommends administering 2-4 milligrams of Benadryl per kilogram of body weight, two to three times a day. However, this dosage can vary depending on your dogs medical conditions.

Dr. Jerry Klein, Chief Veterinary Officer for the AKC, warns that you should always consult with a veterinarian before giving Benadryl to a puppy because young puppies can be very sensitive to certain medications. The drug is also not recommended for pregnant or nursing dogs.

Never use time-release capsules for dogs, as capsules are absorbed differently in dogs than in humans and may affect your dogs dosage. They may also break open when chewed and deliver too much medication at one time, putting your dog at risk of an overdose. Your veterinarian can prescribe diphenhydramine capsules for dogs.

Its best to avoid using liquid Benadryl if it contains sodium, which can cause other side effects. Also, avoid any form of Benadryl that contains alcohol. Your vet can prescribe diphenhydramine liquid for dogs.

Childrens Benadryl pills or tablets can be used safely if you ask your veterinarian for the appropriate dosage. Your vet can even prescribe diphenhydramine flavored chews if your dog refuses to take pills or liquids.

Is Benadryl Safe For Your Dog?

Benadryl is a relatively safe and effective medication for dogs when used according to the instructions of a veterinarian. As with any new medication, always observe your dog closely after administration to make sure there arent any adverse reactions. If you have any further questions about diphenhydramine or Benadryl for dogs, contact your veterinarian for more information. And remember to keep all medicineshuman and canineout of reach of your curious dog.

What Human Drugs Are Safe For Dogs?

Updated April 25, 2023

Youve got a dog needing treatment and youve even got some of your own meds nearby. Can you use them?

The use of non-veterinary drugs is a common question from pet owners. When is it a good idea to give your dog human medications? Sometimes, surprisingly, it is. Just not that often.*

Here are the top over the counter (OTC) drugs you can give, and a few you definitely cant! Plus some guidelines for safe and appropriate use. See full disclaimer below.

Dog Antihistamine Dose Chart

Antihistamines can be used in dogs to reduce the signs of allergy. The following antihistamines appear safe in dogs (note that Benadryl is no longer sold in Australia as diphenhydramine tablets).

These doses have essentially been worked out by trial and error and often scaled down from human doses.

Bad stuff: We dont know why, but dog allergies respond very poorly to antihistamines. Even the best (cetirizine) only helps 20% of dogs. The response may improve if combined with EFAs (see below) and its worth trying a few before giving up.

Aspirin, ibuprofen, Naproxen for Dogs

Non-steroidal anti-inflammatory drugs like these work well in humans with minimal side-effects. This means we get a lot of questions about using them in dogs.

Bad Stuff: Please dont use these drugs at all. Human anti-inflammatory medications are almost universally toxic to dogs. A single dose of Nurofen or Voltaren can be fatal, and survivors are left with permanent organ damage. Even aspirin, although used in the past as a blood thinner, is not recommended.

The veterinary pain medications are the only safe option. Read about effective treatments for arthritis in dogs here. If your dog has taken any human anti-inflammatory, contact a vet immediately. See also paracetamol below.

Carsickness Treatments

Mild motion sickness in dogs can be treated with Phenergan or Benadryl antihistamine tablets (see doses above) which may also cause mild drowsiness. Ginger products used for people also appear safe.

Bad Stuff: Most dog owners dont see much success. Nowadays the only good drugs for car sickness are prescribed at the vet. Dramamine was great but was taken off the market due to problems with human abuse.

Read a lot more about stopping car sickness in dogs here.

Cough Suppressants

Dextromethorphan is an ingredient found in many human dry cough treatments. We often use it to comfort dogs with kennel cough at a dose of 5, 10 or 20mg depending on the dogs size (usual dose 0.5-1 mg/kg twice daily). Just make sure that the product you use contains no other drugs.

Bad Stuff: You need to be 100% sure that the cough can be safely suppressed. Click here for the common causes of coughs in dogs. If it is caused by lower airway infection, heart disease or a foreign body then suppressing it is very dangerous. Even when the diagnosis is confirmed to be kennel cough, antibiotics usually work faster so please see your vet first.

Diarrhoea Meds

PAW Digesticare is an OTC veterinary probiotic and prebiotic food supplement. Combined with a bland diet, it helps restore the normal gut bacterial flora and can assist with some diarrhoeas. We supply either sachets or you can purchase a whole tub.

Vets use binding products to help reduce the unpleasant symptoms of diarrhoea. These include bismuth sub-salicylate, kaolin or montmorillonite. All are fairly harmless but you might have trouble finding them as they arent used much in people.

Bad Stuff:Home treatment is only appropriate for bright and happy, fully vaccinated adult dogs with mild diarrhoea of no more than a few days duration. They need to also have a good appetite and no blood in the stool. Although I understand why frustrated owners may resort to it, there is no place for Imodium in canine medicine. If symptomatic treatment doesnt work, its off to the vet.

Ear Drops for Dogs

Epi-otic and similar veterinary ear cleaners are an essential part of good preventive management of problem ears. Aqua ear can be used to dry the ears of frequent swimmers and prevent infection. Except for these, there isnt much.

Bad Stuff:OTC ear drops are over-used and frequently abused. They are only appropriate for prevention, not treatment. None will fix even the mildest problem so dont be fooled by your dogs improvement. They are just learning to live with the pain. Most ear drops permanently damage hearing if the eardrum is ruptured, and are always painful in diseased ears.

Read a review of over-the-counter ear cleaning solutions here.

Eye Drops for Dogs

Human artificial tears and OTC antibiotic eye ointment can be used in dogs.

Bad Stuff: The use of these products without a diagnosis masks serious disease and could lead to loss of the eye or loss of sight. Glaucoma, dry eye or corneal ulcers look the same as conjunctivitis without testing.

Glucosamine for Dogs

Glucosamine and chondroitin supplements for arthritis can be given to dogs with a very low risk of side effects. Doses are assumed to be similar to that of a human of the same size.

Bad Stuff: There is next to no evidence that glucosamine works in pets. Read here about the caregiver placebo effect and more effective arthritis treatments for dogs.

Laxatives for Dogs

Lactulose is a safe and effective laxative suitable for prolonged use in most dogs. It is sold as a liquid in pharmacies and given at approximately one teaspoon per 5kg body weight. The dose is then adjusted to give a faecal consistency neither firm or sloppy.

Paraffin oil can also be used at similar doses but must be mixed with food, and is much less suitable for long-term use.

Bad Stuff: For every five dogs that owners think are constipated, only one really is. Unless youre certain (e.g. your dog always gets bound up after chewing a bone) its best to confirm the diagnosis first and rule out more serious problems. Severely bound up animals will need a proper enema, and I dont mean Microlax.

Melatonin for Dogs

Melatonin is commonly advocated as a mild and safe sedative for dogs.

Bad Stuff: Evidence is sorely lacking for its efficacy, and the only melatonin sold without prescription in Australia is homeopathic. How they can even claim its really melatonin is beyond me.

Omega 3 Essential Fatty Acids

Theres very solid evidence for the benefit of omega 3s in dogs. They are proven to reduce signs of dermatitis and may play a role in reducing cardiac arrhythmias. They are safe and often well-tolerated by dogs at a dose of 1 g fish oil per 4-5 kg bodyweight.

Bad Stuff: Although they are useful, omega 3 fatty acids do not exert a strong effect in most dogs. Dont give up too soon though; they can take 3 weeks to show an effect. They should be avoided in dogs prone to pancreatitis.

Pain Relief for Dogs

So what can you give a dog for pain? The best of a bad lot is paracetamol, sold as Panadol, Calpol or Tylenol (called acetaminophen in the US). It is sometimes used by vets at a dose of 10 mg/kg twice daily.

Bad Stuff:My strong advice is to avoid paracetamol unless its impossible to get to a vet. Paracetamol is nowhere near as safe or effective as pain meds made for dogs. It is extremely toxic to cats.

Skin Creams

Hydrocortisone 0.5% cream (e.g. Dermaid) is available without prescription. It can be used for areas of minor irritation or allergy.

Many antifungals (e.g. Canesten) can be used in pets.

Bad Stuff: Do not use creams on broken skin, and always be aware of how much is being swallowed by pets. You could easily reach a toxic dose by reapplying creams that are licked off. Its best to fit an elizabethan collar if using and see your vet if there isnt rapid improvement. Prolonged use can cause skin damage.

Fungal infections in dogs are very unlikely. If it looks like ringworm, its usually bacterial. The best thing for this is our magic pink chlorhexidine disinfectant scrub (available OTC).

Vomiting Suppression in Dogs

Bad Stuff: Antiemetics & antacids should never be used in dogs without veterinary advice. If your dog is vomiting, there is usually a good reason, and suppressing the vomiting is probably not the best answer. Antacids are used commonly in people but have almost no place in canine medicine.

Disclaimer

None of these drugs has been properly tested for safety in animals so pet owners need to accept that there may be unknown and possibly serious adverse effects. Always check first with your vet if these medications are suitable for your dog and be very careful if your pet has any other health problem or is on other drugs. Doses in mg/kg are estimates only; a 20kg dog X 2 mg/kg diphenhydramine would receive 40mg.

*Why Are Vet Drugs Different?

There are four reasons why most animal drugs dont get used in people and vice versa.

1. Different diseases: many of the common problems of dogs or cats are rare in humans
2. Different drugs: even when the disease is the same, another medicine may work better in animals
3. Different metabolism: many drugs successfully used in people have a ridiculously impractical half-life or dose, or actually are toxic
4. Different legislation: for reasons lost to me, but possibly related to points 1, 2 & 3, companies often release separate drugs onto the veterinary market than the human one

Have something to add? Comments (if open) will appear within 24 hours.By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. Meet his team here.