Profound Pain Reduction After Induction of Memantine Treatment in Two Patients with Severe Phantom Limb Pain

Abstract

We present the cases of two patients who suffered severe lower extremity injuries and subsequently developed phantom limb pain (PLP) that was refractory to high dose opioids and adjunctive pain medications. Both patients were receiving large doses of oral methadone, IV hydromorphone via a patient-controlled analgesia delivery system, and adjunctive medications including tricyclic antidepressants, nonsteroidal anti-inflammatory medications, and anti-epileptics. Despite these treatments, the patients had severe PLP. Upon induction of the oral N-methyl-D-aspartate receptor antagonist memantine, both patients had a profound reduction in their PLP without any apparent side effects from the medication.

Phantom Limb Pain: Mechanisms and Treatment Approaches

“…Memantine has shown some benefits in some case studies but controlled trials have shown mixed results [63, 64]. A review concluded that memantine may be useful soon after amputation rather than for use in chronic neuropathic pain conditions [65].…”

Role of N-methyl-D-aspartate receptor antagonists in postoperative pain management

“…After termination of brachial plexus block, patients who had received 30 mg of memantine exhibited reduced intensity of phantom limb pain at 4 weeks and 6 months. Two case reports have demonstrated the reduction of phantom limb pain by early administration of 20-30 mg memantine [29]. In opioid-tolerant oncology patients, the intravenous administration of ketamine (5 mg/h) was found to relieve severe pain status and reduced the dose of hydromorphine by 80% [30 ].…”

Prevention of post-mastectomy neuropathic pain with memantine: study protocol for a randomized controlled trial

“…Memantine has shown its efficacy in some studies [15, 36] and presents the advantage of having less adverse effects than ketamine [8–11]. We have shown in a surgical pain model that memantine prevents NP symptoms such as tactile allodynia and mechanical hyperalgesia when administered a few days before surgery [16].…”

“…Another NMDAR antagonist, memantine, prescribed in Alzheimer’s disease to maintain cognitive function, has minimal side-effects at doses within the therapeutic range, probably because of its specific mechanism of action as it is an uncompetitive antagonist with moderate affinity, strong voltage-dependency and rapid unblocking kinetics [9–11]. Concerning NP alleviation, memantine shows controversial results in human studies [6, 12–15]. We recently demonstrated for the first time in an animal surgical NP model, that memantine prevents the development of NP symptoms and the impairment of spatial memory [16].…”