OTC Transdermal Analgesic Patches in Pain Management

Donna M. Lisi, PharmD, BCPS, BCPP, BCGP, BCACP

Disclosures

US Pharmacist. 2019;44(3):15-21. 

In This Article

Abstract and Introduction

Abstract

OTC topical analgesic patches offer both convenience and consistent drug administration. Among the active ingredients available in these products are lidocaine, capsaicin, methyl salicylate, and menthol. There is a paucity of studies about the efficacy and safety of these medications. Studies that are available are often of poor quality. While generally considered safe when used according to product labeling, these medications can also be associated with adverse effects. Pharmacists need to be familiar with the available evidence regarding the use of these products in order to help patients safely self-medicate.

Introduction

According to the latest report from the CDC, 20.4% of adults in the United States experience chronic pain.[1] Among the therapeutic options for the management of pain are OTC or nonprescription topical analgesic patches.

In the February 1983 Federal Register, the FDA published (48 FR 5852), the tentative final monograph on OTC external analgesic drug products, which included patch, plaster, and poultice dosage forms. In July 2003, the FDA reopened the administrative record for the rulemaking for OTC external analgesic to include more recent data on these medications.[2]

Patches offer advantages over oral analgesic medications (Table 1).[3–6] However, drawbacks to the use of topical analgesics exist, including local irritation or skin sensitization; interindividual variability of skin properties that can affect absorption (e.g., adult vs. pediatric patients); limited availability of medications that can be delivered via this route of administration; inappropriateness of the topical route of administration for patients with decreased peripheral blood flow (e.g., shock); and cost.[3,6]

Another caveat is that some transdermal products contain metallic backings, which can lead to excessive burns and local tissue damage if the patch is not removed prior to undergoing an MRI scan.[4] Similarly, reports of severe burns have occurred when these products are used in conjunction with a heat source such as a heating pad or sauna or when the patch has been positioned over an implantable cardioverter defibrillator.[7,8] In 2012, the FDA issued a drug-safety communication stating that rare cases of serious burns (including second- and third-degree burns) have occurred with the use of OTC topical muscle and joint pain relievers. This problem was seen particularly with the use of products containing menthol as the single active ingredient or products containing both menthol and methyl salicylate (MS), in concentrations greater than 3% menthol and 10% MS (see Table 2).[9] Few cases were described involving the use of capsaicin-containing products. Healthcare professionals should counsel patients about how to use these products appropriately, including discussing the risk of serious burns.[9]

These medications can also cause acute toxicity in children even when ingested in small amounts.[10] The barrier function of the skin is incomplete in premature infants, putting them at increased risk from dermal exposure.[11] Medicated patches may retain up to 95% of the initial total amount of drug, even after the duration of use has passed, which can pose a risk to curious, unattended children.[11]

A search of the National Institute of Health's website, Daily Med, revealed the following active ingredients in topical OTC analgesic patches: lidocaine (up to 4%), capsaicin or capsicum (0.002%-3.75%), MS (0.04%-20%), menthol (0.2%-16%), camphor (0.13%-11%), wintergreen oil (0.5%), eucalyptus oil, l-menthol (1.25%-3%), peppermint (0.3%-1.95%), glycol salicylate (4.66%), nonivamide (0.01%), allantoin (2%), zinc oxide (18.77%), sulfur, petrolatum (30%), and tocopherol acetate (Table 2).[12] Among these agents, menthol, MS, wintergreen oil, camphor, and capsaicin are topical counterirritants. Counterirritants are medications that cause irritation and reddening of the skin that distract from more deepseated pain.[13,14]

Topical counterirritants are classified into four groups based on their properties: (1) rubefacients or those drugs that increase blood flow, such as MS; (2) those that produce a cooling sensation, such as camphor and menthol; (3) those that cause vasodilation, such as histamine dihydrochloride; and (4) those that incite irritation without an increase in blood flow, e.g., capsaicin.14 Trials involving rubefacients/counterirritants are fraught with difficulties, such as the inability to completely mask the drugs' effects due to their irritant properties. Most trials involve few numbers of patients, are of short duration (i.e., longest trial 28 days; most were 14 days), and have questionable quality and validity.[15]

This article will focus on the OTC active ingredients that are commonly found in topical analgesic patches. Despite their prevalent use, there is a lack of clinical evidence supporting the efficacy of these topical nonprescription analgesic products.

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