Antihistamines

Antihistamines are useful in the management of some cases of atopy (atopic dermatitis). They are rarely of much benefit if used alone, but may be useful when combined with other treatments. They may improve the response to corticosteroids and/or reduce the amount that has to be given. They vary greatly in their efficacy, dosage, side effects and cost.

Antihistamines are very safe, and the older (first-generation) ones generally work better than the newer, more expensive ones. They sometimes cause temporary sedation, but this will usually resolve after a few days (If sedation lasts for more than a few days, the dose can be reduced).

The response to antihistamines is very individual and it is usually necessary to try at least 3 or 4 different ones to find what works best in your pet. Give each antihistamine alone for a 10-14 day trial, moving on to the next one if there is no response. If there is a partial response, it is still worth trying others, as another antihistamine may work even better. In this case, wait 3 days for the effects of the first one to subside, before trying the next one.

The following table lists the dose rates of some of the available antihistamines. It is a guide only and is intended only for the use of patients of this hospital that have been diagnosed with atopy. We will calculate the dose rate for your pet, and take no responsibility for misuse of the information provided in this table. We can provide you with Iramine® and the rest should be available from your local pharmacy. The order that you try them is not strictly important, though we suggest you start with Iramine®. If the brand names listed are not available, generic substitution should be OK if necessary. But don't use human cold and flu preparations that have other ingredients in them too - ask your pharmacist for advice.

Patient's Name: ____________________ Bodyweight: ________ kg

Drug Name Tablet
Size
Dogs (Dose Calculation) Cats Frequency Notes
Dose Rate x BW (kg)
=dose (mg)
/size=
No. of tabs
Chlorpheniramine
(Iramine®)
4mg tablet 0.4 mg/kg 2-8 mg/dog  Half Twice daily First choice for cats
Promethazine (Phenergan®) 10mg tablet 1 mg/kg     Half Twice daily Can't halve
Dexchlorpheniramine (Polaramine®) 2mg tablet 0.4 mg/kg 2-6 mg/dog   One Twice daily  
Cyproheptadine (Periactin ®) 4mg tablet 0.1-0.2 mg/kg 2-12 mg/dog   Half Every 8-12 hours Thirst may increase
Diphenhydramine (Benadryl®)   2-4 mg/kg     ? Twice daily  
Terfenidine (Teldane®) 60mg tablet 2-4 mg/kg       Twice daily Non-sedating
Diphenylpyraline (Histalert®) 2.5mg tablet 0.1-0.2 mg/kg       Every 8 hours  
Azatadine
(Zadine®)
1mg tablet - 0.5-1 mg/dog   Half Twice daily  
Loratadine (Claratyne®) 10mg tablet 0.5 mg/kg 5-10 mg/dog   Half Once daily  
Cetirizine
(Zyrtec®)
10mg tablet - 0.25-1 mg/dog   ? Once daily  
Hydroxyzine (Atarax®) 25mg capsule 2-4 mg/kg     0.2-0.4 Every 8 hours Prescription required

Please do not hesitate to call if you have any doubts about the correct dose, or any further questions.