TOPICAL ANALGESICS – INTRODUCTION:
Topical pain relievers, or external analgesics, are a group of different medicines that are used “externally,” which means on the skin. Some are intended to relieve minor body aches and pains such as backache, muscle ache, and arthritis.
TOPICAL ANALGESICS – INDICATION:
Tropical NSAIDs are used to relieve minor body aches and pains.
Topical NSAIDs for pain relief remain one of the more controversial subjects in analgesic practice. In some parts of the world their use is regarded as sensible, with adequate evidence for their use. In other parts of the world they are regarded as little more than placebo, with any effect due just to the rubbing. In yet others, their use is almost unknown.
TOPICAL ANALGESICS – INFORMATION:
Capsaicin is available in two formulations, 0.025% (Zacin) and 0.075% (Axsain). It is best used very thinly and four or so times a day: thick application does not work better and sometimes leads to the formation of a dust of the dried cream that can be irritant to the eyes and elsewhere. It is wise to warn the patient to wash the hands carefully after application of the cream particularly before touching the eyes – or going to the toilet.
Topical analgesics for musculoskeletal pain can be used alone or in conjunction with oral analgesics when appropriate and warranted. External analgesic products may contain or more of the following ingredients: methyl salicylate, camphor, menthol, methyl nicotinate, capsicum, and trolamine salicylate.
Topical analgesic products are available in a variety of formulations, including gels, ointments, creams, lotions, and patches in single-entity or combination formulations. Topical heat therapy patches, such as ThermaCare (Wyeth Consumer Healthcare), are also available in various sizes for treating joint and muscle pain and provide 8 to 12 hours of continual, portable heat therapy. Products new to this OTC category include Icy Hot Spray and Icy Hot Powder Gel (sanofi-aventis), Salonpas Pain Relief Patch (Hisamitsu America Inc), and Bengay Pain Relief + Massage (Johnson & Johnson Consumer Companies Inc). OTC topical analgesics are intended to be used for mild-to-moderate pain for no longer than 7 days, unless otherwise directed by a physician. The factors that a pharmacist may consider when recommending a topical analgesic include dosage form, cost, ease of use, and odor of product, as well as the patient’s medical history, including possible allergies.
The first thing needed is a classification of topical analgesics. The problem we face is that of a number of possible definitions for rubefacients and NSAIDs, capsaicin and local anaesthetics. The dimensions are:
- Molecular structure and pharmacology. Some compounds, like salicylates, are related pharmacologically to aspirin and NSAIDs, but in the form that they are often used in topical products (often as amine derivatives) their principal action is to act as skin irritants (called counter irritants in many texts, to ‘counter’ pain). By contrast topical NSAIDs act by penetrating deep into underlying structures to inhibit cyclooxygenase enzymes responsible for development of inflammatory processes.
- Concentration. The concentration of components of topical analgesics varies considerably, and the dose-response relationships are largely unknown. For some agents, like capsaicin, concentration may define prescription or OTC (over-the-counter, no prescription needed) status.
- A number of products contain several agents that may or may not be active in one or other ways.
- Availability with or without prescription.
- Different definitions are used. For instance, PACT (UK prescribing data) combines “rubefacients and other topical anti-rheumatics” and includes topical nonsteroidal drugs, and thus mirrors the definition of the BNF (British National Formulary). The BNF defines the properties of a rubefacient, without defining what a rubefacient actually is, so our definition here is that “rubefacients act by counter-irritation”.
- The Royal Society of Medicine gives a definition thus: “Agents are also called counter-irritant. The name derives from the fact that these agents cause a reddening of the skin by causing the blood vessels of the skin to dilate, which gives a soothing feeling of warmth. The term counter-irritant refers to the idea that irritation of the sensory nerve endings alters or offsets pain in the underlying muscle or joints that are served by the same nerves. See capsaicin; capsicum oleoresin; choline salicylate; ethyl salicylate; glycol salicylate; methyl salicylate; menthol; salicylic acid; turpentine oil.”