“Neuropathic pain can be treated with capsaicin, tricyclic antidepressants, anticonvulsants, and local anesthetics.”
Topical amitriptyline 2 to 4% with ketamine 1 to 2% have been compared to placebo.
Researchers noted that the higher dose significantly lowered pain intensity, with more subjects attaining 30% reduction in pain and recommended the use of higher doses of amitriptyline coupled with ketamine for longer periods for dull, chronic pain. “In clinical practice, we always recommend starting with the lower dose and slowly titrating upward if needed.” Practitioners should exercise caution regarding potential cardiac adverse effects of ketamine and amitriptyline such as QT prolongation, and consider if the patient is concurrently taking other QT-prolonging medications.
A retrospective study of 51 patients using 2%, 4%, or 6% gabapentin in Lipoderm® cream base 3 times daily for 8 weeks demonstrated a 4 to 5 point reduction in pain scores on a 10-point pain scale. No systemic side effects were reported.
Topical application of 5% lidocaine gel (without occlusion) relieves post-herpetic neuralgia by a direct drug action on painful skin. In a study of 39 patients, no systemic adverse effects were reported and blood levels measured less than 6 μg/ml. However, extreme caution should be exercised when using topical anesthetics because concentration of each agent and amount applied is critical. If topical anesthetics are over- prescribed and over-applied, patients are prone to serious cardiac side effects, such as deadly arrhythmias.
Ketamine 5% gel applied 2 to 3 times a day provided pain relief in 16 of 23 patients with post-herpetic neuralgia. Additionally, Gammaitoni et al. demonstrated the efficacy of topical ketamine in managing mixed neuropathic pain 15 minutes after its administration, with no systemic side effects reported.
The quotes and recommendations represent a synopsis of a comprehensive CME article “Use of Topical Pain Medications in the Treatment of Various Pain Syndromes” written by Sahar Z. Swidan, PharmD (Adjunct Clinical Associate Professor of Pharmacy, University of Michigan College of Pharmacy, and Chief Executive Officer of Pharmacy Solutions) and Hagar A. Mohamed, MS (Pharmacist and Researcher, Ann Arbor, Michigan) and published in Topics in Pain Management, February, 2016. 31(7): 1-10.