Morphine Sulfate for Chronic Pain Maintains Cognitive Function

SAN DIEGO—The use of morphine sulfate extended-release capsules (Avinza) does not appear to impair cognitive function in patients with chronic, nonmalignant pain. In fact, it may improve pain behavioral scores and lessen pain intensity, leading to better overall cognitive function, according to results of a study presented at the annual meeting of the American Academy of Pain Medicine.

It is well documented that both chronic pain and opioid use can cause cognitive impairment. However, an open-label, single-arm study of 84 patients (mean age, 46 years) indicates that morphine sulfate taken once daily may have fewer effects on cognitive function than other opioids.

An earlier review of 5 controlled studies of the treatment of chronic pain with opioid analgesics found inconsistent results on outcome variables such as disability, emotional distress, quality of life, and psychological impairment (West J Med. 2000; 172:107-115).

This new study looked at the effects of once-daily oral morphine on patients’ performance on neuropsychological tests that assessed cognitive function, while controlling for variables such as pain intensity, pain behaviors, and benzodiazepine use.

More than one third of the patients with chronic nonmalignant pain used benzodiazepines, before enrollment and during the trial, to treat the sequelae of their pain (mainly of the back and spine).

Tests were administered at baseline and after 4 weeks of treatment to assess short-term memory, motor skills, and information processing. There was a negative association between the frequency of behaviors suggestive of pain and digit span test results, as well as between the benzodiazepine dose and digit symbol results.

“When you use a long-acting medication you give patients optimal serum levels over a 24-hour period, so they don’t get undertreated for their pain, but they also don’t get too much medicine, so they don’t get sedation. With this medication you can improve cognitive function,” said investigator Ravi Panjabi, MD, medical director, Ad­vanced Pain Management and Rehab Group, Castro Valley, Calif.

“The study only looked at 4 weeks’ use of the medication, but it is long enough to know if the patient is having cognitive dysfunction or not, because in the first week they would have cognitive dysfunction and might discontinue the drug for that reason,” Dr Panjabi told IMWR.

“This drug is not abused like some of the other drugs on the market. It is safer for primary care physicians to prescribe, because they often don’t have time to monitor for abuse and diversion.”

A total of 30 of the 129 enrolled patients withdrew from the study because of side effects, and 15 were lost to follow-up. The most frequent side effects were constipation, dizziness, fatigue, and itching.