Other Topical Medications at a Glance
- Topical medications not sufficiently covered in other sections of this text comprise:
- Anti-inflammatory agents.
- Antimicrobial and antiparasitic agents.
- Antiperspirants, antipruritics, and astringents.
- Bleaching and keratolytic agents.
- Topical psoriasis and wart therapies.
This chapter reviews topical therapies not covered elsewhere in the text that are used to treat dermatologic diseases. The topic headings are those of the drug designation of the US Pharmacopeia and at times reflect clinical usage rather than specific pharmacologic mechanisms. All topicals when applied to large areas of skin, particularly in the presence of skin disease or to infants and children, have the potential for systemic side effects.
Capsaicin is the molecule that confers the “hotness” to hot peppers of the genus Capsicum, including cayenne, jalapeno, and Tabasco peppers.1 Initial topical application results in itching, pricking, and burning as nociceptor activate. Repeated applications, however, are hypothesized to lead to degeneration of epidermal nerve fibers and nociceptor desensitization, thereby producing hypalgesia.1
Topical capsaicin has been used to treat postherpetic neuralgia, diabetic neuropathy, reflex sympathetic dystrophy, Raynaud phenomenon, nostalgia paresthetica, arthralgias, plantar warts, diabetic neuralgia, and hemodialysis-related pruritus.1 A recent placebo-controlled trial of a high-concentration capsaicin dermal patch showed that the patch significantly reduced postherpetic neuralgia pain with transient application site pain reactions managed effectively with analgesics.2 Other therapies for postherpetic neuralgia should also be considered.3
Numerous topical anesthetics are available.4 Eutectic mixture of local anesthetics (EMLA) cream contains the sodium-channel-blocking amide anesthetics lidocaine 2.5% and prilocaine 2.5%. Application under occlusion to intact skin or genital mucous membranes for at least 1 hour before performance of a painful procedure, including debridement of venous leg ulcers,5 can provide local anesthesia that may persist for up to 2 hours. The cream may cause transient local blanching followed by transient local erythema. Like all products containing lidocaine, it should not be used in patients with hypersensitivity to amide anesthetics. Additionally, the prilocaine component has been linked to cases of methemoglobinemia in patients for whom applications exceeded the recommended dose, application area, or application time.6 Those particularly susceptible to methemoglobinemia include patients who are very young, those with glucose-6-phosphate dehydrogenase deficiency, and those taking oxidizing drugs such as sulfonamides and antimalarials.
Caution regarding dosing should also be used in patients susceptible to systemic effects of lidocaine or prilocaine, including acutely ill, debilitated, and elderly patients. Finally, as EMLA is ototoxic, it should not be used if there is a concern that it could penetrate or migrate beyond the tympanic membrane to the middle ear.
Various topical anesthetic products contain only lidocaine, typically at concentrations of 4% or 5%, which may be applied with or without occlusion. Systemic toxicity from topical lidocaine prepared in a 30% concentration has been reported.7 In 2007, ...