Topical preparations for pain relief: efficacy and patient adherence

Abstract

There has been an increasing focus on development of new routes of drug administration to provide tailored treatments for patients, without decreasing efficacy of analgesia, in proportion to the progression of the knowledge of pain mechanisms. While acute pain acts as an alarm, chronic pain is a syndrome requiring meticulous selection of analgesic drugs of high bioavailability for long-term use. Such criteria are challenges that topical medications aim to overcome, allowing progressive delivery of active component, maintaining stable plasma levels, with a good safety profile. This review presents recent findings regarding topical formulations of the most widely used drugs for pain treatment, such as nonsteroidal anti-inflammatory agents, anesthetics, and capsaicin, and the role of physical agents as delivery enhancers (phonophoresis and iontophoresis). Although the number of topical agents is limited for use in peripheral conditions, increasing evidence supports the efficacy of these preparations in blocking nociceptive and neuropathic pain. Patient adherence to medical treatment is also a challenge, especially in chronic painful conditions. It is known that reduction of treatment complexity and pill burden are good strategies to increase patient compliance, as discussed here. However, the role of topical presentations, when compared to traditional routes, has not yet been fully explored and thus remains unclear.

A phase III randomized, placebo-controlled study of topical amitriptyline and ketamine for chemotherapy-induced peripheral neuropathy (CIPN): a University of Rochester CCOP study of 462 cancer survivors

“…A topical treatment option would be beneficial for patients who do not tolerate systemic treatments well. Further, local, topical administration of effective agents would reduce systemic adsorption and side effects while maximizing local dosage and treatment effects[5], allowing for the safe combination of multiple drugs that could not be given in combination systemically.…”

Does the Use of Nitroglycerin Patch Improve Local Anaesthetic Effects in Bier’s Block? A Double-Blind Placebo Controlled Study

“…The mechanism of action of nitroglycerin seems to be augmented by the direct potent vasodilatory effect that allows distribution of lidocaine to nerves that is mainly dose-dependent [9]. Several studies explained the pain-relieving mechanism of nitroglycerin [10, 11].…”

The Effectiveness and Safety of Topical Capsaicin in Postherpetic Neuralgia: A Systematic Review and Meta-analysis

“…Patients need to continuously reapply capsaicin cream throughout the day due to the low concentration of the active ingredient (0.025–0.075%) (Das et al, 2013). The four-times-daily application may threaten medication compliance (Jorge et al, 2011). …”

“…This could be accounted for by the down-regulation of TRPV-1 receptors (Jorge et al, 2011). The use of a capsaicin patch allows the medication regimen to be simplified and hence improves medicine adherence.…”