Obesity and preoperative analgesic use were the strongest predictors of the ongoing use of analgesics 1 year after joint replacement surgery, according to Finnish researchers, in Arthritis Research & Therapy.

Among patients whose body mass index (BMI) was above 35, the adjusted risk ratio for use of any analgesic medication a year after the procedure was 1.4 (95% CI 1.3-1.6). In addition, the adjusted risk ratio for postoperative analgesic use was 2.6 (95% CI 2.5-2.8) among those who reported preoperative use of these medications, the researchers note, in a media release from MedPage Today.

Recent attention has focused primarily on the excessive use of opioids in the general population, but little is known about the patient characteristics and risk factors associated with high postoperative use of analgesics, including not only opioids but also acetaminophen and NSAIDs.

To investigate this, Tuomas Jaakko Rajamäki, MD, of Tampere University, and colleagues reviewed the data from 13,739 joint replacements (6,238 hips and 7,501 knees) for osteoarthritis in one orthopedic hospital in Finland from 2002 to 2013. Information on medications was obtained from a national drug prescription register.

Patients’ mean age was 68.7 years, 61.1% were women, and mean BMI was 29.1. Mean Charlson Comorbidity Index was 1 in approximately 20% of the patients and above 2 in 7%.

At 1 year post-surgery, 26.1% of patients had filled one or more analgesic prescriptions, including NSAIDs (15.5%), acetaminophen (10.1%), and opioids (6.7%).

Age was a clear predictor of analgesic use, reported by 29% of those older than 75, 26.2% of those 65 to 75, and 23.7% of those younger than 65 (P<0.001). In an adjusted model, those older than 75 had a risk ratio of 1.2 (95% CI 1.1-1.3) for the use of any analgesic compared with those younger than 65. The risk ratio among the oldest patients was also higher for acetaminophen, at 2.2 (95% CI 1.9-2.5), but was lower for NSAIDs, at 0.77 (95% CI 0.68-0.86).

Women more often filled prescriptions for analgesics then men (28.8% vs 22%, P<0.001), and had a higher risk ratio for any analgesic use, at 1.2 (95% CI 1.1-1.3), and for acetaminophen, at 1.4 (95% CI 1.2-1.6), and NSAIDs, at 1.2 (95% CI 1.1-1.3).

When the researchers considered the specific joint replaced, they found that more patients having knee rather than hip surgery used any analgesics postoperatively (28.8% vs 23%, P<0.001), the release continues.

Severe obesity (BMI above 35) was associated with not only any postoperative analgesic use, but also with all types of analgesics:

  • Acetaminophen, RR 1.6 (95% CI 1.4-2)
  • NSAIDs, RR 1.5 (95% CI 1.3-1.7)
  • Opioids, RR 1.4 (95% CI 1.1-1.8)

Furthermore, those with the highest BMIs also had greater preoperative analgesic use (RR 1.3, 95% CI 1.2-1.4). In addition, risk ratios for preoperative and postoperative use were elevated for those whose BMIs were in the lower range of obesity, at 30-35 (RR 1.1, 95% CI 1.05-1.2 and RR 1.1, 95% CI 1.04-1.2).

“Our main finding is that obesity was associated with a higher risk ratio for the consumption of all the studied analgesic drugs both pre- and postoperatively,” the researchers noted.

The presence of comorbidities also increased patients’ risk of analgesic use. For those whose Charlson Comorbidity Index score was zero, 24.1% had prescriptions for any analgesic, compared with 30.7% of those with a score of 1 and 33.1% of those with a score of 2 or higher.

In an adjusted model, a score of 2 or higher was associated with any analgesic use (RR 1.2, 95% CI 1.1-1.4) and also for the use of acetaminophen (RR 1.4, 95% CI 1.2-1.6) and opioids (RR 1.8, 95% CI 1.5-2.2).

“It is remarkable that older age and higher number of comorbidities predicted analgesic use despite these patients also being the most vulnerable to adverse drug events,” Rajamäki and co-authors write. “Clinicians should therefore inform patients with obesity (especially BMI > 35 kg/m2) about the elevated risk for prolonged use of analgesics (including opioids) after surgery.”

A limitation of the study, the team said, was the lack of information about over-the-counter drug use.

[Source: MedPage Today]