Allergy to benzocaine

What is benzocaine and where is it found?

Benzocaine is a widely used local and topical anaesthetic. It is used in pharmaceutical preparations and rarely cosmetics. Doctors and dentists use benzocaine preparations, especially on mucosal surfaces such as the mouth, to prepare or 'numb' a site for injection.

Preparations containing benzocaine

Wound and burn preparations Sunburn remedies Haemorrhoidal preparations Oral and gingival products Sore throat sprays/lozenges Callous and wart remedies Creams for treatment of poison ivy Toothache and denture irritation products

Benzocaine is a para-aminobenzoic acid (PABA) derivative and cross-reacts with other benzoic acid derived local anaesthetics (both topical and injectable forms). It also has the potential to cross-react with paraphenylenediamine found in permanent hair dyes, sulfonamides, sulfonylureas, PABA-based suncreens, and thiazide-related diuretics.

What are the reactions to benzocaine allergy?

Benzocaine sensitivity produces classic allergic contact dermatitis reactions. Sometimes it may be seen as a flare or spread of an existing treated rash. Occasionally injection of PABA-derived local anaesthetics to benzocaine-allergic individuals may cause swelling of the oral mucosa at the site of the injection. Rarely, more severe reactions such as generalised urticaria or anaphylaxis may result.

Dermatitis due to benzocaine

Am I allergic to benzocaine?

Benzocaine allergy is diagnosed by performing special allergy tests, i.e. patch tests with 5% benzocaine in petrolatum.

Allergy to benzocaine may also mean you are allergic to other local anaesthetic agents.

Cross-reacting local anaesthetics
Para-aminobenzoic acid based	Meta-aminobenzoic acid based	Benzoic acid based
Procaine Butethamine Tetracaine (amethocaine) Propoxycaine	Metabutethamine	Meprylcaine Isobucaine

Treatment of benzocaine allergy

If you are diagnosed with benzocaine allergy then avoid exposure to benzocaine containing products. Once the dermatitis appears on the skin, treatment is as for any acute dermatitis/eczema, i.e. topical corticosteroids, emollients, treatment of any secondary bacterial infection (Staphylococcus aureus), etc.

What should I do to avoid benzocaine allergy?

Read product labels and avoid products that contain benzocaine or any of its alternative names. Avoid related substances that you may also be allergic to. This includes PABA, meta-aminobenzoic acid or benzoic acid local anaesthetics (both topical and injectable forms), paraphenylenediamine found in permanent hair dyes, sulfonamides, sulfonylureas, PABA-based suncreens, and thiazide-related diuretics.

Any products that are labelled 'anaesthetic' or 'caine' should be suspected of containing benzocaine or a related compound. These should be avoided. Ask your pharmacist for advice and a suitable alternative.

Alert your doctor and dentist to the fact that you have an allergy to benzocaine. Your dermatologist may have further specific advice, particularly if you are highly sensitive.

Alternative names for benzocaine

Benzocaine is also known by several other names. These include:

• Ethyl aminobenzoate
• Ethyl 4-aminobenzoate
• 4-aminobenzoic acid ethyl ester
• p-aminobenzoic acid ethyl ester

The chemical formula of benzocaine is C₉H₁₁NO₂.

Reference

Book: Fisher's Contact Dermatitis. Ed Rietschel RL, Fowler JF. Lippincott Williams & Wilkins 2001