You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

As spring progresses through to summer pet owners can expect to see an increase in the occurrence of allergies - the main reason for the prescribing of antihistamine drugs.

Histamine is a chemical that is released from immune cells (called mast cells) in the body following contact with a foreign substance that the animal has been in contact with before. Histamine release is a normal process in the body's  immune response and it forms an important part of an inflammatory reaction designed to destroy and remove any foreign material ...such as an infectious agent (eg bacteria) ...that gains access to the body. 

However, when excessive histamine release occurs, as it does during an allergic reaction,  it can be a problem and lead to clinical signs such as asthma (in cats) and skin inflammation with rashes (urticaria),  itching and scratching (cats and dogs). Antihistamine drugs work by blocking the receptors for histamine in the target organs (such as the respiratory tract and skin). Massive histamine release can be very serious and even life-threatening because it causes an anaphylactic reaction - in dogs this results in acute gastrointestinal signs and shock.

Allergies are more common in the summer months because many have seasonal causes - eg pollen allergies, flea allergies, and air pollution in urban areas during hot weather ..but only some of these cases respond well to antihistamines. As a result antihistamines are not used as much in veterinary medicine as they are in human medicine, and other drugs are often preferred because the results are more reliable.

Last updated : September 2013