AHFS Class:

• Antipruritics and Local Anesthetics 84:08

Generic Name(s):

• Benzocaine

Benzocaine is a local anesthetic.

Benzocaine is used topically for the temporary relief of pain and itching associated with minor burns, sunburn, minor cuts or scrapes, insect bites, or minor skin irritations. Benzocaine is also used topically for the temporary relief of pain and itching associated with episiotomy, pruritus vulvae, or hemorrhoids and as a male genital desensitizer to aid in slowing the onset of ejaculation.

Benzocaine has been used topically as a water-soluble lubricant for topical anesthesia on urinary catheters, laryngoscopes, proctoscopes, sigmoidoscopes, and vaginal specula. However, methemoglobinemia has been reported when the drug has been applied to mucous membranes.

Benzocaine preparations are applied topically in the form of aerosol sprays, creams, gels, lotions, ointments, and solutions.

For the temporary relief of pain and itching associated with various skin conditions, preparations containing 5-20% benzocaine are usually applied 3 or 4 times daily or as directed by a physician.

For male genital desensitization, a small amount of a preparation containing 3-7.5% benzocaine in a water-soluble base is applied to the head and shaft of the penis before intercourse; after intercourse, patients should wash off any remaining benzocaine to minimize the chance of an allergic reaction occurring.

For topical anesthesia and lubrication during instrumentation, benzocaine is applied to the exterior of the tube or instrument as a 20% water-soluble lubricant prior to use.

When applied topically as recommended, benzocaine is relatively nontoxic; however, sensitization may occur. When used as a male genital desensitizer, benzocaine generally does not adversely affect orgasm in female sexual partners and does not appear to anesthetize the clitoris or vagina. If a rash or irritation develops during use of a benzocaine preparation, the drug should be discontinued and a physician consulted.

Topical benzocaine preparations are for external use only and contact with the eyes should be avoided. Topical benzocaine preparations should not be applied to deep or puncture wounds or to serious burns. Topical benzocaine is not intended for prolonged use. When benzocaine preparations are used for self-medication, the drug should be discontinued and a physician consulted if the condition worsens or symptoms persist for more than 7 days or clear and occur again within a few days, if infection occurs, or if rash or irritation occurs. Benzocaine should not be used in individuals with known hypersensitivity to the drug or other ester-type local anesthetics. When benzocaine is used as a male genital desensitizer, the male should be advised to use the drug with caution if his sexual partner is sensitive to local anesthetics, sunscreens, sulfa drugs, or hair dyes. Topical benzocaine preparations should be used in children younger than 2 years of age only under the direction of a physician.

Serious adverse effects (e.g., seizures, coma, irregular heart beat, respiratory depression) have been reported following topical application of local anesthetics to the skin; these events have occurred following application of extemporaneously prepared topical preparations containing high concentrations of anesthetics for cosmetic procedures and following use for indications approved by the US Food and Drug Administration (FDA).

Life-threatening adverse effects (e.g., irregular heart beat, seizures, breathing difficulties, coma, death) may occur when topical anesthetics are applied to a large area of skin, when the area of application is covered with an occlusive dressing, if a large amount of topical anesthetic is applied, if the anesthetic is applied to irritated or broken skin, or if the skin temperature increases (from exercise or use of a heating pad).101,  102 When applied in such a manner, the amount of anesthetic that is absorbed systemically is unpredictable and the plasma concentrations achieved may be high enough to cause life-threatening adverse effects.101,  102 Use of lidocaine gel has been investigated to reduce discomfort during mammography.101,  103 During the study, the topical anesthetic was spread over a wide area of the chest and covered with an occlusive dressing.101,  103 Whether such use could result in serious reactions has not been determined.101,  103 Patients should speak with their clinician if they are considering using a topical anesthetic before obtaining a mammogram.101

When a topical anesthetic is needed for a procedure, use of an FDA-approved preparation has been recommended. A preparation containing the lowest concentration of anesthetic likely to be effective should be used; a small amount of topical anesthetic should be applied to the affected area for the shortest period necessary for the desired effect. When the topical anesthetic will be applied by the patient, the patient should apply the topical preparation as directed by a clinician, and should not apply the topical preparation to broken or irritated skin.101

Chemistry and Stability

Chemistry

Benzocaine is a local anesthetic of the ester type. Benzocaine occurs as small, white crystals or as a white, crystalline powder, is odorless, and is very slightly soluble in water and freely soluble in alcohol.

Stability

Benzocaine topical creams and ointments should be stored in tight containers and protected from light; prolonged exposure to temperatures greater than 30°C should be avoided. Benzocaine topical aerosols and solutions should be stored at a temperature less than 40°C, preferably between 15-30°C; freezing should be avoided. Because the contents of benzocaine aerosols are under pressure, the aerosol container should not be punctured, used or stored near heat or an open flame, exposed to temperatures greater than 49°C, or placed into a fire or incinerator for disposal.

Additional Information

The American Society of Health-System Pharmacists, Inc. represents that the information provided in the accompanying monograph was formulated with a reasonable standard of care, and in conformity with professional standards in the field. Readers are advised that decisions regarding use of drugs are complex medical decisions requiring the independent, informed decision of an appropriate health care professional, and that the information contained in the monograph is provided for informational purposes only. The manufacturer's labeling should be consulted for more detailed information. The American Society of Health-System Pharmacists, Inc. does not endorse or recommend the use of any drug. The information contained in the monograph is not a substitute for medical care.

Only references cited for selected revisions after 1984 are available electronically.

101. Food and Drug Administration. FDA Public Health Advisory: Potential hazards of skin products containing numbing ingredients for relieving pain from mammography and other medical tests and conditions. 2009 Jan 16. From FDA website. [Web]

102. Food and Drug Administration. Topical Anesthetics. MedWatch alert. Rockville, MD; 2009 Jan 16. From FDA website. [Web]

103. Lambertz CK, Johnson CJ, Montgomery PG et al. Premedication to reduce discomfort during screening mammography. Radiology . 2008; 248:765-72. [PubMed 18647845]