What Matters

Duloxetine for knee osteoarthritis


In primary care, the sun never sets on a day in which we are not managing a rheumatologic or orthopedic issue. Obesity seems to be making knee pain an epidemic, and most patients seem to complain about knee pain at some point or another.

Knee osteoarthritis (OA) is one of the most common complaints we see. In addition to knee pain, the clinical diagnosis of knee OA can be secured with at least three of the following six clinical characteristics: age greater than 50 years; morning stiffness for less than 30 minutes; crepitus on active knee motion; bony tenderness; bony enlargement; and lack of palpable warmth.

These criteria result in a sensitivity and specificity for OA of 95% and 69%, respectively.

Once the diagnosis has been made, the easy part is over. Many of us may suggest stretching exercises from the patient information racks. And we may recommend steroid injections, physical therapy, or weight loss. Unfortunately, many patients instead may "settle on" long-term narcotics to manage knee OA pain.

But clinicians are nothing if not creative and enterprising. So what else can we try?

Investigators from Egypt evaluated the efficacy of duloxetine for pain and function management in older adults with knee OA. Duloxetine is a serotonin and norepinephrine reuptake inhibitor that has a proposed centrally acting analgesic effect.

In this study, 288 patients aged at least 65 years were randomized to 60 mg/day of duloxetine or placebo for 16 weeks (Age Ageing 2012;41:646-52). To enroll, patients had to have clinical and radiologic criteria of primary knee OA. The researchers excluded patients with a body mass index greater than 32 kg/m2 or inflammatory arthritides. Patients could continue on their usual NSAIDs but could not increase the dose. Primary outcome measures included pain reduction and improved physical function.

Of 411 screened patients, 288 patients were randomized. Mean patient age was 68.5 years; 84% were female. Mean BMI was 26.5. NSAIDs were used by 89% of subjects.

At 16 weeks, 48% of subjects in the duloxetine group had a 20% reduction in pain or physical function, compared with 9% in the placebo group (P less than .05). After 16 weeks, duloxetine was associated with a significant reduction in pain, improvement in physical function, decreased depression, and reduced NSAID use. Side effects included constipation, nausea, hyperhidrosis, cough, myalgia, arthralgia, and palpitations.

Thus, duloxetine may be an appropriate step in selected older patients with knee OA before considering more aggressive and risky medications such as narcotic analgesics.

This column, What Matters, appears regularly in Internal Medicine News. Dr. Ebbert is professor of medicine and a primary care clinician at the Mayo Clinic in Rochester, Minn. He reports having no conflicts of interest. The opinions expressed are those of the author. Reply via e-mail at imnews@frontlinemedcom.com.

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