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Histamine is produced by the body during an allergic reaction, an antihistamine counteracts this.

Try different antihistamines to see which works best for you. There are older ones that may cause drowsiness and newer ones that don’t. The older ones are very effective, particularly if you have difficulty sleeping in hay fever season. However, don’t drive or operate machinery if affected by drowsiness.

You don’t develop a tolerance to antihistamines. But some antihistamines may work better for you than others. If one antihistamine is not working for you, speak with your pharmacist and try alternatives.

Many of the same antihistamine medication is marketed by different drug companies, look carefully at the generic name of the medication and you may find it is possible to buy the identical medication much cheaper as a generic brand. Ask your pharmacist to help and advise.

Take your medication consistently and start it early, well before the start of the pollen season.

Do not stop taking them; take your medication consistently throughout the season.

Food and other drinks do not affect most antihistamines, but check the leaflet that comes with your medicine to make sure.

Pregnancy

Hay fever is harder to manage in pregnancy, discuss with your doctor or pharmacist. Most antihistamine medications are not recommended in pregnancy.

Grapefruit

Grapefruit can work both ways. Sometimes it blocks the metabolism and allows too much of the drug to enter the bloodstream. Sometimes it has the opposite effect and with some medication it reduces the amount of drug in the blood stream.

For example, with Fexofenadine (commonly taken for allergies); grapefruit juice can cause less fexofenadine to enter the blood, decreasing the potency of the medication and how well it works.

Fexofenadine is also affected by orange or apple juice, so the drug label states “do not take with fruit juices.”

This opposite effect is caused by grapefruit juice affecting specific proteins in the body known as drug transporters. These proteins help move drugs into our cells for absorption. If the drug transporters are affected by the fruit juice, then less of the drug will enter the blood and the drug is not likely to be as effective.

Alcohol

Alcohol contains histamine; which is also released as part of the body’s reaction to allergies – it is therefore strongly suggested that alcohol can increase the sensitivity of the body to pollen and other allergens. It is also sedative, therefore it should not be combined with antihistamines. Alcohol is also likely to make your symptoms worse .

Interaction with other medications

Speak to a pharmacist or GP before taking antihistamines if you’re already taking other medicines.

There may be a risk the medicines don’t mix, which could increase the risk of side effects or stop either from working properly.

Medicines that could cause problems if taken with antihistamines include:

• antidepressants
• stomach ulcer or indigestion medicines
• cough and cold remedies that also contain an antihistamine

Antihistamines should not be given as first line treatment for Anaphylaxis

This medication does not treat the life-threatening features of anaphylaxis.

However, Antihistamines may help with:
• Itching
• Rash
• Hives.

But do not treat:
• Airway swelling
• Shock
• Breathing difficulty
• Circulatory collapse.

Giving other medications in the treatment of anaphylaxis delays the administration of adrenaline, which is the current best available first-line therapy for anaphylaxis.

Anti-histamines are H1 receptor antagonists and are a generally helpful treatment for urticaria and itch caused by the release of histamine from mast cells. They do not prevent progression to, or treat, airway obstruction, hypotension or shock.

Antihistamines should not be used as first-line treatment for anaphylaxis because they delay the administration of adrenaline but can be useful additional therapy once adrenaline has been administered. There is no evidence that prophylaxis with oral antihistamines decreases the risk of severe allergic reactions on subsequent exposure to food allergens

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Author: Emma Hammett