title: [Topical ambroxol for the treatment of neuropathic pain: A first clinical observation. German version].
abstract: BACKGROUND
  Neuropathic pain is difficult to treat and available options are frequently not sufficient. The expectorant ambroxol also works as a strong local anesthetic and blocks sodium channels about 40 times more potently than lidocaine. Ambroxol preferentially inhibits the channel subtype Nav 1.8, which is expressed particularly in nociceptive C fibers. Due to the low toxicity, topical ambroxol seemed to represent a reasonable therapeutic attempt for treatment of neuropathic pain resistant to other standard options.
  
  
  METHODS
  Medical records of 7 patients with severe neuropathic pain, in whom many attempts at treatment with approved substances were not sufficient or possible, are reported retrospectively. Patients were then treated with topical ambroxol 20% cream applied in the area of neuropathic pain.
  
  
  RESULTS
  Causes of neuropathic pain were postherpetic neuralgia (2-×), mononeuropathy multiplex, phantom pain, deafferentation pain, postoperative neuralgia and an unclear allodynia of the foot. Mean pain intensity was reported as 4-6/10 on a numeric rating scale (NRS) and maximum pain intensity as 6-10/10. Pain reduction following ambroxol cream was 2-8 points (NRS) within 15-30 min and lasted 3-8 h. Pain attacks were reduced in all 5 patients presenting this problem. Topical ambroxol achieved pain reduction in 4 patients with no improvement after lidocaine 5% and 1 patient with no response to capsaicin 8%. No adverse events or skin changes have been observed, and the longest treatment duration is currently 4 years.
  
  
  CONCLUSIONS
  Ambroxol acts as a strong local anesthetic and preferentially inhibits the nociceptive-relevant sodium channel subtype Nav 1.8. For the first time, we report relevant pain reduction following topical Ambroxol 20% cream in patients with neuropathic pain. Regarding the advantageous profile with rare side effects, the clinical benefit for pain patients should be further investigated.
authors.affiliation: Institut für Schmerzmedizin / Schmerzpraxis Wiesbaden, Wiesbaden, Deutschland. dr.kern@schmerzpraxis-wiesbaden.de.|Boehringer Ingelheim Pharma GmbH & Co. KG, Ingelheim am Rhein, Deutschland. dr.kern@schmerzpraxis-wiesbaden.de.
authors.forename: K-U
authors.initials: KU
authors.lastname: Kern
authors.affiliation: Boehringer Ingelheim Pharma GmbH & Co. KG, Ingelheim am Rhein, Deutschland.
authors.forename: T
authors.initials: T
authors.lastname: Weiser
mesh_terms: D000287:Administration, Topical; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000551:Ambroxol / Q000008:administration & dosage* / Q000009:adverse effects; D002211:Capsaicin / Q000008:administration & dosage; D005260:Female; D006801:Humans; D008012:Lidocaine / Q000008:administration & dosage; D008134:Long-Term Care; D008297:Male; D008875:Middle Aged; D009437:Neuralgia / Q000188:drug therapy* / Q000209:etiology; D010147:Pain Measurement / Q000187:drug effects; D010149:Postoperative Pain / Q000188:drug therapy / Q000209:etiology; D012189:Retrospective Studies
chemical_list: D000551:Ambroxol; D008012:Lidocaine; D002211:Capsaicin
keywords: Administration, topical; Anesthetics, local; C fibers; Nav 1.8 voltage-gated sodium channel; Pain management