Gabapentin has been shown to be superior to pregabalin in the management of patients with chronic sciatica in an Australian trial.
A double-blind crossover trial of 20 patients attending a Queensland neurosurgery clinic found both drugs were efficacious but leg pain was significantly reduced with gabapentin.
Patients received eight weeks of treatment with either gabapentin three times a day titrated from 400 to 800 mg or pregabalin twice a day titrated from 150 to 300 mg and crossing over to the alternate treatment after a one-week washout period.
Patients receiving gabapentin reported a mean reduction in pain of 1.72 on a 0-10 visual analog scale for pain intensity compared to 0.94 with pregabalin (p=0.035).
The study found gabapentin had superior efficacy irrespective of whether it was used before or after pregabalin.
Both drugs also led to a significant reduction in pain-associated disability using the Oswestry Disability Index from baseline to eight weeks. However there was no significant difference between treatment groups when compared head to head (p=0.63).
There were significantly more adverse events with pregabalin (81%) than gabapentin (19%) and particularly when pregabalin was prescribed first.
“Specifically, pregabalin adverse events were doubled when pregabalin was prescribed first,” the study authors wrote in JAMA Neurology.
“This suggests that gabapentin may in some way sensitize tissues such that, despite subsequent washout, tolerance to pregabalin adverse events was significantly enhanced.”
“Given these findings, this study suggests that gabapentin should be commenced before pregabalin to permit optimal crossover wherever pregabalin may ultimately be warranted.”
Researcher Kelvin Robertson, an advanced pharmacist specialising in clinical trials at the Townsville Hospital, told the limbic the study was the first to compare the drugs head to head.
“In Australia they are considered equivalent and our study is the first step to prove that there is a difference between the two medicines.”
The fact pregabalin is on the PBS for neuropathic pain and gabapentin is not makes it difficult for prescribers and patients in terms of continuation of care when they leave hospital.
“So if you want to get gabapentin, you would have to get it from the hospital. You couldn’t get it on the PBS yet. We will definitely be passing on our results to the PBS because obviously there is a difference and at least the PBS should make both drugs available for neuropathic pain in the community.”
Mr Robertson said the study was stopped early because of the results including the high rate of side effects with pregabalin.
“Anything that effects cognition is a bit of a worry. Any CNS side effects are probably alarming because they will affect these people the most. These people are in pain already; we don’t want to be messing with any of their cognitions as well.”
He added that patients were often on one of the two drugs for long periods as the penultimate step while they were waiting for surgery or because they were not fit for surgery.
Meanwhile, the UK government has decided to reclassify gabapentin and pregabalin as controlled drugs because of ongoing misuse.
The restrictions, which take effect from April 2019, follow a significant rise in deaths linked to the drugs, with 111 deaths related to pregabalin in 2016 and 59 related to gabapentin, compared with four and eight respectively in 2012, according to Pulse.
The British Medical Association welcomed the move, saying there was evidence that the drugs were being misused recreationally.