"Once you silence that NMDA receptor you might get prolonged effects. This is really wonderful for our palliative care/hospice population because it means they get one less medication while it adds to their comfort. You can’t get better than that: a medicine that you can stop and still get some mileage out of it," he continued.
In the Australian multicenter VCOG PM 1-00 study, the burst ketamine protocol used in palliative care patients with refractory cancer pain began with a continuous subcutaneous infusion of 100 mg/24 hours. If that proved ineffective after 24 hours, the dose was increased to 300 mg/24 hours. And if patients didn’t have good analgesia after 24 hours on ketamine at 300 mg/24 hours, the dose was bumped to 500 mg/24 hours. When the effective or maximum tolerated dose was reached, it was continued for 3 days and then stopped. Thus, patients ceased taking ketamine after a maximum of 5 days whether it was effective or not.
Half of patients were rated as responders using strict criteria and 9% became pain free. Moreover, 50% of responders experienced pain relief lasting 2 weeks or longer while off ketamine. The toxicities were mainly neurologic and occurred at 300 or 500 mg/24 hours dosing (J. Palliat. Care 2010;26:176-83).
"It was very interesting: There really weren’t a lot of cardiovascular adverse effects in this study," Dr. Prommer commented.
A variant of the burst technique proved effective in patients with complex regional pain syndrome type 1 in a Dutch placebo-controlled study. The 60 participants had a median 7.4-year disease duration. Investigators utilized a 4.2-day intravenous infusion of low-dose ketamine with individualized stepwise tailoring of dosage based upon pain relief and side effects. The final dose was 22.2 mg/hour/70 kg. Pain relief in the ketamine group lasted for nearly 12 weeks after the drug was stopped (Pain 2009;145:304-11).
Other randomized studies show efficacy for ketamine in patients with post-herpetic neuralgia or ischemic pain. But Dr. Prommer stressed that while it’s clear ketamine provides relief in patients with chronic noncancer pain, he believes the drug’s long-term use should be restricted to the clinical trial setting.
"There are just no good long-term safety data for 6-8 months of therapy," he emphasized.
Dr. Prommer said a single dose of ketamine is helpful for painful dressing changes when adequate analgesia can’t be gained with opioids alone. Case reports attest to the usefulness of ketamine as an oral rinse in patients with mucositis; however, Dr. Prommer has tried it and found it didn’t work.
He reported having no financial conflicts.