Warning about common pain drugs

19 Jan 2016 Warning about common pain drugs

UBC researchers issued a warning this week about the limitations of drugs commonly used to treat chronic pain.

The Therapeutics Initiative’s latest bulletin for British Columbia’s prescribing physicians and pharmacists focuses on four drugs —  gabapentin, pregabalin, duloxetine, venlafaxine — that are popular for treating such conditions as peripheral neuropathy, post-shingles pain, fibromyalgia and chronic back pain.

“Chronic pain is one of the most difficult conditions to treat” said Dr. Tom Perry, a Clinical Assistant Professor in the Department of Anesthesiology, Pharmacology and Therapeutics and Chair of the UBC Therapeutics Initiative Education Working Group. “Patients suffer a lot, but our drug treatments are not very effective. They often cause more harm than good.  Increasing evidence suggests that drugs have relatively little useful role for most patients with chronic pain. We should be much more cautious about prescribing them, and warn patients about their side effects.”

From 2005 through 2014, the number of British Columbians receiving pregabalin increased by 17 fold, compared with a 1.8 fold increase in people receiving gabapentin.  For duloxetine, which was licenced in 2008, there was a 3.6 fold increase through 2014.  Use of venlafaxine, mostly for depression or anxiety, has been stable.

Dr. Aaron Tejani, a Clinical Assistant Professor in the Faculty of Pharmaceutical Sciences and member of the UBC Therapeutics Initiative team, points out that rising prescriptions to treat chronic “neuropathic” pain are driven by doctors’ exaggerated impression of their effectiveness.

“The best available evidence now indicates that as few as one in ten people can expect much pain relief from these drugs” says Dr. Tejani, who specializes in understanding evidence about drugs from randomized clinical trials. “Many people who improve are getting a placebo effect, or would improve in time without any drug treatment.  Others end up sedated, with impaired thinking, balance disturbance, dry mouth, or other side effects that cause more harm than good.”

Combined costs of gabapentin, pregabalin, and duloxetine were over $52 million in British Columbia during 2014, of which PharmaCare paid over $13 million, mostly for gabapentin.  Patients or private insurers paid 97% of the cost of pregabalin and duloxetine dispensed in B.C. in 2014.

The new Therapeutics Letter points out that patients can learn within a few days whether one of these drugs offers a useful benefit, and that high doses are usually no better than lower doses.

Although B.C. PharmaCare does not typically cover the non-benefit drugs pregabalin (Lyrica) or duloxetine (Cymbalta), the costs to individuals or benefit plans can range up to hundreds of dollars per month.

“While government has avoided a lot of pointless costs, individual patients could also save substantially by avoiding these drugs if they are not working well, or using smaller doses,” Dr. Perry says.

Therapeutics Letters, along with the TI’s other work, are funded by the B.C. Ministry of Health through a grant to UBC. The TI provides evidence-based advice about drugs but is not responsible for provincial drug policies.

Read more: Therapeutics Letter 96: Benefits and harms of drugs for “neuropathic’ pain”