A wafer that slowly releases a painkiller as it dissolves inside the body could aid recovery after knee replacement surgery.
The implant, about the size of a 20p coin, is sewn into the new joint during the operation, which is carried out on around 100,000 NHS patients a year.
Inside each wafer, made from the same material as the absorbable stitches, is 500 mg of bupivacaine, a local anesthetic widely used in dental procedures and childbirth.
As the wafer slowly degrades over three to four weeks, bupivacaine leaks into the surrounding nerve endings in the knee, blocking pain signals.
The delivered dose is highest in the first few weeks after surgery, when pain is usually worst.
A wafer that slowly releases the drug could help relieve pain after knee replacement surgery (file photo)
Allay Therapeutics, the US company that developed the wafer, is also planning trials in patients needing other joint replacements and abdominal surgery.
British doctors testing the wafer, called ATX101, are hopeful that it will eventually enable thousands of NHS patients to reduce their consumption of opioid drugs, such as morphine, which are routinely used to control pain after joint replacement operations.
Although effective at controlling pain, morphine and other opioids wear off within 24 hours and can cause side effects ranging from nausea to breathing problems and dependence, even after a few days of use.
“A small but significant proportion of patients may become addicted to opioids,” says Professor Hemant Pandit, an expert in hip and knee surgery at the University of Leeds and Leeds Teaching Hospitals NHS Trust, who is leading the UK arm of an international trial involving the pain-relieving wafer.
‘The goal is to reduce or even eliminate the need for knee replacement patients to take opioids.’
In the UK, around nine million people suffer from osteoarthritis, a condition where the protective cartilage in a joint breaks down and bones rub against each other, causing pain and problems moving the joint. It usually develops through wear and tear, although other risk factors include being overweight and sports injuries.
While anti-inflammatory painkillers and steroid injections can help, many will end up needing a knee replacement, and opioid medications such as morphine, oxycodone and tramadol are the mainstay for addressing pain after surgery.
But in addition to serious side effects, the drugs often need to be taken several times a day for them to be effective.
The tablet, however, is designed to provide around-the-clock relief for up to a month. It is designed to dissolve in such a way that it releases half of the medication’s contents in the first few days and then smaller amounts as the pain subsides.
File photo of a surgical team operating on a patient. The new wafer is expected to provide around-the-clock relief for up to a month after the procedure.
A recent trial involving 112 patients from the United Kingdom, Canada and Australia (not yet published in a medical journal) showed that 22 percent of those who received the wafer did not need opioids during their recovery from knee surgery, compared with just 2 percent of those who did not.
In addition, after the operation they were able to stand up more quickly, climb stairs more quickly and sleep better than those who depended on strong painkillers.
A larger trial involving about 200 patients is now being planned.
Dr Wendy Holden, consultant rheumatologist and medical adviser to the charity Arthritis Action, said the wafer “appears to be much more effective at reducing pain and is great news for patients. We hope it will soon be available on the NHS.”
