Cannabis-inspired: The clear gel, ZYN002, is a synthetic form of a compound in the plant
A gel made from a substance based on the cannabis plant could be an unlikely new treatment for sore knees.
The clear, odourless gel, named ZYN002, is a synthetic form of a compound in the plant.
It is rubbed on the front and back of the knee twice a day. The drug is thought to work by blocking receptors involved in transmitting pain signals to the brain.
It is currently undergoing trials on 450 patients in the U.S., and initial tests suggest it can soothe the agony of osteoarthritis of the knee.
An estimated nine million people in Britain have some degree of osteoarthritis. As the body ages, the joints suffer wear and tear. Other risk factors include being overweight, a family history of the condition and sports injuries.
As the cushioning cartilage in the joints breaks down, the bones come into contact with each other, causing inflammation and pain. Patients often rely on anti-inflammatory painkillers to ease their symptoms. While these help, they can damage the stomach if used for long periods.
Steroid injections can dampen down inflammation but these sometimes worsen the condition by causing cortisone flare — where the injected steroid (cortisone) crystallises inside the joint and triggers more inflammation.
Around 100,000 people a year in the UK have a knee replacement due to badly eroded joints.
The new gel, developed by U.S. company Zynerba Pharmaceuticals, could provide pain relief without the side-effects seen with the current treatments.
For years there have been anecdotal reports that compounds in cannabis can relieve chronic pain. It is illegal to use or sell the cannabis plant. However, researchers and manufacturers are now developing synthetic forms of compounds found in the plant. The pain-relieving element of cannabis is a chemical called cannabidiol.
Getting it safely into the body to target areas affected by pain is a key focus. A tablet would be an option but cannabidiol gets broken down by enzymes in the liver, which would reduce the amount in the bloodstream — and its effectiveness as a painkiller.
Game-changer? The new gel, developed by U.S. company Zynerba Pharmaceuticals, could provide pain relief without the side-effects seen with the current treatments
The gel may be more effective as it bypasses the liver and directly targets the painful joint itself. However, cannabidiol molecules, even synthetic ones like those in the gel, are relatively large and do not penetrate the skin easily.
The new gel therefore contains a chemical called a permeation enhancer, which makes skin more permeable by enlarging pores.
Once the cannabidiol molecules are inside the knee joint, they lock on to receptors involved in transmitting pain signals to the brain. Recent results from tests by the manufacturers on 320 people with knee osteoarthritis showed the gel led to a reduction in pain severity of more than 30 per cent within the first eight weeks, compared to patients using a placebo gel.
Larger studies are planned for next year. If these prove successful, the knee gel could be available in the UK in two to three years.
Dr Natalie Carter from Arthritis Research UK said research suggests cannabidiol could ease osteoarthritis pain for some, but added: ‘More research is needed to clearly demonstrate benefits of cannabis-based treatment’.
Meanwhile, bisphosphonates — drugs used to treat the bone-thinning illness osteoporosis — could also prevent osteoarthritis, according to a report in Annals of the Rheumatic Diseases.
Scientists at Boston University in the U.S. compared 2,006 patients on the medication with the same number not on them and found the drugs reduced the risk of needing knee replacement surgery due to arthritis by 26 per cent.
Bone in joints affected by osteoarthritis often wears down faster due to inflammation, causing pain. The researchers believe bisphosphonates slow that process.