Topical ambroxol for the treatment of neuropathic pain. An initial clinical observation

K-U Kern, T Weiser, K-U Kern, T Weiser

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.

Material and 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.

Conclusion: 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.

Keywords: Ambroxol; Local anaesthetic; Nav 1.8; Neuropathic pain; Topical therapy.

Conflict of interest statement

In the past 3 years Dr. K.-U. Kern has worked as a consultant and/or expert for the following companies: Astellas, Berlin Chemie, Boehringer Ingelheim, betapharm, Grünenthal, Hexal, Lilly, MSD, Mundipharma and Reckitt Benckiser. Dr. T. Weiser is an employee of Boehringer Ingelheim.

Figures

Fig. 1
Fig. 1
Pain reduction following topical ambroxol 20 % in neuropathic forefoot pain (Exemplary documentation of patient 1, NRS numerical rating scale)
Fig. 2
Fig. 2
Early pain reduction, 30 min after topical ambroxol 20 % (exemplary documentation of some patients, NRS numerical rating scale)
Fig. 3
Fig. 3
Pain reduction following topical ambroxol 20 % in postherpetic neuralgia (exemplary documentation of patient 5, NRS numerical rating scale)
Fig. 4
Fig. 4
Pain reduction following topical ambroxol 20 % in mononeuropathia multiplex, (exemplary documentation of patient 6, NRS numerical rating scale)

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