Ouch! Topical pain relievers come in many forms

OTCs Today

Mary Warner

Topical analgesics are often used to relieve pain associated with aches and pains in muscles and joints, such as backaches, arthritis, strains, bruises, and sprains. Several types are available, including those with local analgesic, anesthetic, antipruritic, and/or counterirritant effects, and in various forms, such as creams, gels, sprays, and patches. Because the ingredients are absorbed through the skin, most topical pain medications are best used on joints that are close to the skin’s surface, such as those in your hands and knees. Primary ingredients include salicylates, capsaicin, menthol, camphor, and anesthetics.

How do they work?

All topical pain relievers depend on absorption through the skin, but they relieve pain in different ways. Salicylate creams such as Aspercreme and Bengay relieve pain in the same way as oral aspirin products, though potentially faster due to direct absorption.

Meanwhile, capsaicin products such as Capzasin and Zostrix elicit a feeling of warmth, and sometimes burning pain, through stimulation of the TRPV1 receptor and also deplete the levels of substance P from sensory neurons, resulting in pain relief. Capsaicin is most effective if used several times a day because its duration of action is only 4–6 hours and may take up to two weeks to work.

Counterirritant products containing menthol or camphor produce a sensation of hot or cold, which may temporarily mask pain by producing a less severe pain to counter a more intense one. Topical anesthetics such as lidocaine produce a local numbing sensation to reduce pain; examples include Salonpas and Lidocare.

In February 2020, FDA approved the OTC use of topical diclofenac sodium 1% (Voltaren) for the temporary relief of arthritis pain in the hand, wrist, elbow, foot, ankle, or knee in adults. Like oral NSAIDs, topical diclofenac decreases the production of prostaglandins to reduce pain and inflammation but is applied locally to the targeted joint. Topical diclofenac comes as a 1% gel to apply on up to two joint areas 4 times daily. When applied according to the prescription package insert recommendations (e.g., 4 g applied 4 times per day to one knee), the amount of medication absorbed systemically is 17 times lower than the systemic exposure from oral diclofenac. Unlike other topical pain relievers that mask pain, diclofenac treats the pain. It also results in less stomach irritation than oral NSAIDs commonly used for treating osteoarthritis.

Do they work? And are they safe?

Opinions differ on the effectiveness of OTC topical pain medications. While many say these products help relieve their arthritis pain, research reveals only modest benefits. A 2017 Cochrane Database of Systematic Reviews study by Derry and colleagues concluded that topical diclofenac is effective in reducing pain for osteoarthritis, but that no evidence supports its use in other chronic pain conditions.  The authors also concluded that high-concentration topical capsaicin may be of limited use in people with postherpetic neuralgia, and that the efficacy of topical salicylates, low‐concentration capsaicin, and lidocaine is not well-supported by evidence, though there may be beneficial effects for some patients.

The ingredients in topical pain relievers are safe, although these products should not be used on broken or irritated skin or with a heating pad or bandage. All topical analgesics should be kept away from the eyes, nose, and mouth. Patients with sensitivity to salicylates or those taking blood thinners should use salicylate products or diclofenac with caution.

What to tell your patients

Ensure that patients understand that use of topical pain relievers, especially diclofenac and capsaicin, may take up to 7 days to provide relief, and that once topical capsaicin has begun to relieve pain, it must be used continuously 3 or 4 times per day. Patients should wear gloves when applying capsaicin products or use a roll-on applicator or patch. If pain is not relieved using an OTC topical pain reliever, patients should be advised to consult their pharmacist or physician for an alternative means of relief, including prescription forms of topical NSAIDs or lidocaine.

For further information, please see Chapter 7 in APhA’s Handbook of Nonprescription Drugs, available in print via the bookstore on pharmacist.com or online through Pharmacy Library. ■