title: Topical ambroxol for the treatment of neuropathic pain. An initial clinical observation.
abstract: BACKGROUND
  Neuropathic pain is difficult to treat, and the available options are often inadequate. The expectorant ambroxol also acts as a strong local anaesthetic and blocks sodium channels about 40 times more potently than lidocaine. It preferentially inhibits the channel subtype Nav 1.8, which is expressed especially in nociceptive C-fibres. In view of the low toxicity of ambroxol, it seemed reasonable to try using it for the treatment of neuropathic pain that failed to respond to other standard options.
  
  
  METHODS
  The medical records of seven patients with severe neuropathic pain and pain reduction following topical ambroxol treatment are reported retrospectively. As standard therapies had not proved sufficient, a topical ambroxol 20% cream was repeatedly applied by the patients in the area of neuropathic pain.
  
  
  RESULTS
  The reasons for neuropathic pain were postherpetic neuralgia (2 ×), mononeuropathy multiplex, phantom pain, deafferentation pain, postoperative neuralgia and foot neuropathy of unknown origin. The individual mean pain intensity reported was between 4 and 6/10 (NRS), maximum pain at 6-10/10 (NRS). The pain reduction achieved individually following ambroxol cream was 2-8 points (NRS) within 5-30 min and lasted for 3-8 h. Pain attacks were reduced in all five patients presenting with this problem. Four patients with no improvement after lidocaine 5% and one patient with no response to capsaicin 8% nevertheless experienced a pain reduction with topical ambroxol. No patient reported any side effects or skin changes during a treatment that has since been continued for up to 4 years.
  
  
  CONCLUSIONS
  Ambroxol acts as a strong local anaesthetic and preferentially inhibits the nociceptively relevant sodium channel subtype Nav 1.8. For the first time, we report below on a relevant pain relief following topical ambroxol 20% cream in patients with neuropathic pain. In view of the positive side effect profile, the clinical benefit in patients with pain should be investigated further.
authors.affiliation: Institut für Schmerzmedizin/Schmerzpraxis Wiesbaden, Sonnenberger Str. 68, 65193, Wiesbaden, Germany. dr.kern@schmerzpraxis-wiesbaden.de.
authors.forename: K-U
authors.initials: KU
authors.lastname: Kern
authors.affiliation: Boehringer Ingelheim Pharma GmbH & Co. KG, Ingelheim, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Weiser
mesh_terms: D000287:Administration, Topical; D000328:Adult; D000368:Aged; D000551:Ambroxol / Q000008:administration & dosage*; D000588:Amines / Q000008:administration & dosage; D000779:Anesthetics, Local; D003509:Cyclohexanecarboxylic Acids / Q000008:administration & dosage; D004334:Drug Administration Schedule; D004359:Drug Therapy, Combination; D005260:Female; D000077206:Gabapentin; D006801:Humans; D008297:Male; D008875:Middle Aged; D009437:Neuralgia / Q000175:diagnosis / Q000188:drug therapy*; D010147:Pain Measurement / Q000187:drug effects; D010149:Postoperative Pain / Q000188:drug therapy; D017060:Patient Satisfaction; D012189:Retrospective Studies; D005680:gamma-Aminobutyric Acid / Q000008:administration & dosage
chemical_list: D000588:Amines; D000779:Anesthetics, Local; D003509:Cyclohexanecarboxylic Acids; D000551:Ambroxol; D005680:gamma-Aminobutyric Acid; D000077206:Gabapentin
keywords: Ambroxol; Local anaesthetic; Nav 1.8; Neuropathic pain; Topical therapy