(Reuters Health) - Compounded pain creams are no better for chronic pain than topical treatments that contain no medicine at all, a U.S. study suggests.

Compounded medicines are custom-blended by pharmacists to give patients a different dose or formulation than they can get with mass-produced prescription drugs. The current study focused on pain creams made from medicines that are often prescribed for pain in pill form such as muscle relaxants, anticonvulsants and non-steroidal anti-inflammatory (NSAID) drugs.

Researchers randomly assigned 399 patients with different types of chronic pain to receive either a compounded cream containing an analgesic or a placebo cream without any medicine.

After one month, 36 percent of patients who used pain creams and 28 percent who got placebo creams reported less pain than they had at the start, a difference that was too small to rule out the possibility that it was due to chance.

“We know from other studies that some of the agents (lidocaine, non-steroidal anti-inflammatory drugs) may be effective for certain types of acute and chronic pain, so it is surprising that the difference here did not reach statistical significance in any of the pain types,” said senior study author Dr. Steven Cohen, a pain researcher at Walter Reed National Military Medical Center in Bethesda, Maryland, and Johns Hopkins Medicine in Baltimore.

“This matters because compounded pain creams are much more expensive than prescribed (lidocaine, diclofenac) or over-the-counter (capsaicin) pain creams, but they didn’t provide meaningful benefit compared to placebo cream,” Cohen said by email.

All of the patients in the current study were treated at pain clinics at Walter Reed and had one of three types of pain syndromes. Within these three groups, patients were randomly chosen to receive either a compounded cream or a placebo cream.

One third of the patients had neuropathic pain, which happens due to nerve damage and includes phantom limb pain experienced by amputees. Patients in this group who got compounded creams received anticonvulsants.

Another third had so-called nociceptive pain, the most common kind that is often due to an injury or infection, not nerve damage. Patients in this group who got compounded creams received muscle relaxants and NSAIDs.

And one third had “mixed” pain caused by a variety of things; many of the compounded creams were similar to drugs provided for nerve damage or nociceptive pain.

None of the patients reported serious side effects from their assigned treatment, but more of them experienced skin irritation, rashes and redness with compounded pain creams than with placebo creams: 7 percent compared with 2 percent.

When patients rated their pain levels on a 10-point scale, with 10 being the most painful, the average pain reductions reported by both compounded-cream users and the placebo group after a month were nearly identical. The difference between groups was 0.1 points for neuropathic pain and 0.3 points for both nociceptive and mixed pain.

One limitation of the study is that many participants had already tried conventional pain relievers without success, increasing the likelihood that compounded pain creams would be ineffective too, the researchers note in the Annals of Internal Medicine.

The study may also have had too few patients to detect subtle but clinically meaningful differences between compounded and placebo pain creams, the authors point out.

Still, the study tested the most frequently used combinations of medicines in compounded pain creams and found them lacking in three different types of pain, said Dr. Nebojsa Nick Knezevic, a pain researcher at Advocate Illinois Masonic Medical Center in Chicago who wasn’t involved in the study.

“This does not mean that we should abandon the use of topical analgesics for different types of localized pain, because it is safer and easier to use than systemic drugs, especially in elderly patients with other (complex chronic medical problems),” Knezevic said by email.

“However, more randomized placebo-controlled trials are needed with a different combination of medications prior to their use in everyday practice,” Knezevic added.

SOURCE: bit.ly/2G8fNud Annals of Internal Medicine, online February 4, 2019.