The popular anti-wrinkle jab, Botox, is unlikely to offer much benefit in its most recently licensed use – as a treatment for chronic migraine – says the new look Drug and Therapeutics Bulletin (DTB).

Botulinum toxin is a neurotoxin derived from the bacterium Clostridium botulinum. It is used as a treatment for various conditions involving muscle spasm and is available in several formulations.

These include Botox (a form of botulinum toxin A), which is widely used, though not actually licensed, for the smoothing out of facial wrinkles.

Botox has now been licensed for use to relieve the symptoms of chronic migraine as a series of regular injections into up to 39 sites in the head and neck muscles. How it is supposed to work in chronic migraine has not been clearly established, but this action appears distinct from Botox’s well known paralysing effect on muscles.

Each treatment with Botox for chronic migraine costs around £276 and the injections have to be given every 12 weeks.

Each year, around 3% of migraineurs who have episodic headaches (a few times a month) develop chronic migraine (headaches on most days), frequently accompanied by reduced ability to function and impaired quality of life.

DTB considers the published evidence on Botox’s effectiveness as a treatment for chronic migraine is limited and unconvincing.

And, crucially, Botox leads to worsening of headache symptoms in around one in 10 people, with a similar proportion developing itching, rash, pain, stiffness and muscles spasms, it says.

Rarely, Botox can prompt anaphylactic shock. And despite screening and control procedures, the possibility of transmitting an infection with Botox cannot be ruled out entirely, because the drug contains human serum albumin.

The UK’s drugs regulator, the Medicines and Healthcare products Regulatory Agency (MHRA), which green-lighted the move, said that Botox offered a “unique approach” to the treatment of chronic migraine.

Botox avoided the systemic side effects of tablets and had a better safety profile, the agency said, adding that its efficacy was likely to improve over time with repeated treatment sessions.

But DTB points out that some headache specialists have criticised the evidence on which the MHRA reached its conclusions.

They say that the diagnosis of chronic migraine used in the trials was incorrect as almost two thirds of trial participants overused headache treatments. This is important, because medication overuse headache – in which headache treatments end up causing rather than relieving headache – rules out the diagnosis of chronic migraine, according to international definitions.

“These discrepancies and the limited evidence of benefit make it difficult for us to see a place for botulinum toxin A as treatment for chronic migraine,” concludes DTB.

The review of Botox is part of a redesigned DTB, which from the February issue has increased pagination and additional content. Included for the first time is educational material comprising multiple choice questions based on DTB reviews, designed specially for continuing medical education/continual professional development (CME/CPD).

A new section – DTB Select – includes succinct summaries of, and DTB’s view on, key healthcare developments, such as new guidelines, evidence and safety warnings.

Drug and Therapeutics Bulletin (BMJ)