A multi-day intravenous infusion of the local anesthetic lidocaine appears to offer some pain relief to patients battling otherwise untreatable daily migraines.

That's the takeaway from a new study that examined the effectiveness of lidocaine infusion treatment — a much debated therapy that requires a hospital stay — as a means to address "refractory chronic migraines" (rCM).

A diagnosis of rCM means patients have suffered at least eight migraines a month for a minimum of six months without responding to standard treatment and prevention strategies.

Those first-line treatments include standard pain killers and beta blockers; corticosteroids; antidepressants; anti-convulsants; calcium blockers; Botox injections, and/or noninvasive electrical stimulation.

"Lidocaine is a local anesthetic — a numbing medicine — but also reduces inflammation in studies," said study author Dr. Eric Schwenk, director of orthopedic anesthesia at the Sidney Kimmel Medical College at Thomas Jefferson University in Philadelphia.

The findings suggest that chronic migraine patients experienced pain relief for about a month after hospital treatment with IV medications including lidocaine, he said.

Between 1% and 2% of the population get the chronic migraine headaches.

The researchers looked at hospital records for just over 600 patients, most of them women (average age: 46).

All had been admitted to a Philadelphia hospital between 2017 and 2020 for lidocaine infusion treatment, typically for five to seven days.

Prior to treatment, patients had experienced moderate to severe headaches for about 27 out of every 30 days. Each migraine attack was at least four hours long.

Upon admission, lidocaine infusions were initially started at 1 mg per minute, then increased up to 4 mg per minute. (Other IV medications were administered at the same time, including ketorolac — a nonsteroidal anti-inflammatory drug -- and the corticosteroid methylprednisolone.)

At a follow-up appointment 25 to 65 days later, patients reported that on average, they had headaches on 23 of the last 30 days — four fewer than before treatment.

While the benefit may seem small, Schwenk said it still represented improvement for these patients who typically experience headache pain almost constantly.

"For them, lidocaine may help break the cycle of continuous pain," he said.

Researchers also noted that about 88% of patients reported some degree of pain relief, with pain intensity plummeting from a self-reported score level of 7 at intake, down to 1 at discharge, out of 10.

As for side effects, Schwenk said that the most common issue was nausea and vomiting, which affected nearly 17% of patients.

"But lidocaine was well tolerated overall," he noted. "No serious adverse events occurred."

On the downside, however, an average hospital stay of more than five days may not be feasible for many patients, Schwenk noted.

It also remains unclear just how lidocaine works to alleviate rCM. "Its mechanism of action in migraine is unknown," he said.

Schwenk and his colleagues also noted that because of the nature of their look-back analysis, the study could not definitively prove that lidocaine was the direct cause of a reduction in rCM frequency. A similar study earlier this year also evaluated the infusion therapy.

Dr. Teshamae Monteith, a fellow with the American Academy of Neurology, and chief of the headache division at the University of Miami's Miller School of Medicine, reviewed the new findings.

She said she was "not surprised by the benefits of lidocaine," having used the treatment often for patients with these hard-to-treat headache disorders.

Monteith noted that the infusion therapy is already in use in many headache centers and is "generally considered safe with side effects that are transient."

As to the source of the benefit, she said the therapy likely works by interrupting a major pain-signaling connection to the brain, a neural route known as the trigeminovascular pathway.

Nevertheless, Monteith emphasized the need for further study "to determine which patients are best candidates for intravenous lidocaine [and] long-term follow-up studies post-discharge."

The findings were published May 23 in the journal Regional Anesthesia & Pain Medicine.