Topical Anesthesia

Overview :

Most drugs in the early 2000s used to cause topical anesthesia have at least some chemical similarity to cocaine, which was recognized as a topical anesthetic in the early 1900s. These drugs work by blocking nerve impulses that carry pain messages to the brain. Commonly used, twenty-first-century drugs include benzocaine, lidocaine, prilocaine, and tetracaine, These drugs come in several application forms, such as cream, jelly, ointment, solution, and spray, are available in varying strengths, and may be used alone or in combinations.

One common use for topical anesthetics is to relieve pain from problems such as sores in the mouth, skin scrapes, and hemorrhoids. A person typically applies a cream or jelly to the affected area. Numbness begins within a few minutes, and the anesthetic effect may last an hour or more. Repeated applications are often necessary.

The other broad category of use for topical anesthetics is to prevent pain from medical examinations or procedures on areas such as the eye, nose, throat, urethra, rectum, or skin. For example, even a single drop of anesthetic may allow examination of a painfully irritated eye or removal of a speck of dirt from the eye surface. Careful inspection of a nostril or insertion of a urinary drainage tube into the urethra may be difficult or impossible without the use of topical anesthetic spray or jelly beforehand.

Many uses of topical anesthetics involve application to the skin. Physicians and patients have long hoped for a way to numb an area of skin without having to use a needle to inject anesthetic. Original topical anesthetics were not effective in this way. A newer drug preparation called eutectic mixture of local anesthetics (EMLA, lidocaine 2.5%, and prilocaine 2.5%) can be used as a cream on intact skin. When applied for about 60 minutes, EMLA numbs the skin and penetrates as far as 5 mm below the surface. EMLA may help patients by decreasing the pain of needle pricks or simple skin procedures, such as repair of small lacerations. The main drawback to EMLA is that it takes so long for the anesthetic effect to begin, thus reducing its usefulness in settings such as the emergency rooms. Other drug combinations such as tetracaine, epinephrine (adrenaline), and cocaine (TAC), or lidocaine, epinephrine, and tetracaine (LET) have their own advantages and disadvantages.

The application of ice to a body area is a primitive method of producing topical anesthesia. Chemicals such as ethyl chloride can be sprayed onto intact skin to produce a momentary freezing and numbing effect.