Despite approval disappointments over in the EU, UK firm GW Pharmaceuticals and partner Bayer have had good news this week, with Canadian authorities approving their cannabis-derived drug Sativex for cancer pain.

This is the second Canadian endorsement of the drug, having been approved for the treatment of neuropathic pain in patients with multiple sclerosis (MS) back in 2005. Canada is currently the only country in which the drug has been approved in any indication, though it is available on a named-patient basis in some European countries in the MS indication.

In this latest positive opinion from the Canadian authorities, Sativex has been approved as an adjunctive analgesic treatment in adult patients with advanced cancer who experience moderate to severe pain during the highest tolerated dose of strong opioid therapy for persistent background pain.

Sativex is delivered orally via a spray, and is currently the only cannabis-derived pharmaceutical product available.

Studies were conducted in patients with advanced cancer who were experiencing pain that proved impossible to treat with traditional strong opioid medication such as morphine. All patients remained on their original medication during the trial, but those who were also treated with Sativex experienced a statistically significant reduction in pain relief compared to those on placebo.

In patients with advanced cancer who were already taking the strongest possible pain medication, Sativex was still able to achieve a reduction in pain in just under 50 per cent of subjects.

Opioid cancer pain medications, such as the mainstay drug morphine, are often associated with unpleasant side effects, but Sativex side effects are limited to mild or moderate cases of nausea, fatigue, dizziness and application site reactions.

"Satviex has a much more benign side effect profile than some of the opioid treatments," GW managing director Justin Gover told US-PharmaTechnologist.com.

"There is no risk of respiratory depression, there have been no recorded deaths, and there isn't the addiction risk that's associated with some treatments such as morphine."

Sativex is GW Pharmaceuticals first product, and is based on a combination of two well-characterised cannabinoids (chemical compounds found only in the cannabis plant), delta-9 tetrahydrocannabinol (THC) and cannabidiol (CBD).

THC has been shown to have analgesic, anti-spasmodic, anti-tremor, anti-inflammatory, appetite stimulant and anti-emetic properties, while CBD has shown anti-inflammatory, anti-convulsant, anti-psychotic, anti-oxidant, neuroprotective and immunomodulatory effects.

The drug is currently being developed for approval in four target indications: MS spasticity, MS neuropathic pain, cancer pain and peripheral neuropathic pain.

This latest Canadian approval comes with conditions, approved under Health Canada's Notice of Compliance with Conditions (NOC/c) policy. This policy allows approval of a product to treat a serious medical condition following the successful completion of only one Phase III trial, with the condition that additional research is carried out and second Phase III study results are submitted within five years.

The previous neuropathic pain approval for MS patients was also under the NOC/c policy.

Following the company's withdrawal of its EU application last month after UK regulators demanded additional clinical data on the drug, this Canadian approval completes the current round of applications GW has filed for the drug.

However, the company sees this latest approval as a good sign for the drug's prospects in the US, where cancer pain represents the lead target indication. Patients are due to be enrolled in late stage trials of the drug in the US in the next few months.

Japanese partner Otsuka will be funding these US trials, with Bayer responsible for the Canadian and UK markets.