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Letter to the editor

Editor, – We write to take issue with the article 'Gabapentin documents raise concerns about off-label promotion and prescribing' (Aust Prescr 2003;26:18-9) and the associated editorial comment. Statements in the article are unfounded and are not relevant to the promotion of gabapentin by Pfizer in Australia, which has always been in accordance with the terms of its registration and the Medicines Australia Code of Conduct.

The use of gabapentin for the treatment of neuropathic pain was approved by the Therapeutic Goods Administration (TGA) in 2000. It is therefore not surprising, as the author notes, that there is an 'increasing use' of this drug for this purpose. Use of a simple comparison of sales trends for gabapentin, lamotrigine and vigabatrin to argue that gabapentin is being promoted in appropriately is misleading. Lamotrigine is subject to a boxed safety warning, and concerns about well-documented adverse effects on visual fields may have directed prescribers away from vigabatrin.

The Cochrane Collaboration1 may have found 'surprisingly few trials' supporting anticonvulsant use in the treatment of chronic pain. However, the two studies involving gabapentin2,3were pivotal in nature and provided the basis for the TGA's approval after evaluation. Three subsequent randomised controlled studies4,5,6-the last an independent study not sponsored by the manufacturer - have confirmed the effectiveness of gabapentin in the treatment of neuropathic pain in a wide range of diseases. In light of this, it would be more accurate to say that there is scant evidence of anticonvulsants, other than gabapentin (i.e. conventional anticonvulsants), being effective in chronic pain.

In summary, gabapentin has now been shown in five well-designed and published studies of 1095 patients to be effective and acceptably safe for the treatment of neuropathic pain.

While not promoting the use of gabapentin in unapproved indications, Pfizer maintains the right to respond in a professional and balanced manner to doctors' questions about unregistered uses of gabapentin or any other product, allowing doctors to observe the 'extra imperative to carefully weigh the potential benefits and harms involved, and to ensure these are openly canvassed, where possible and appropriate, with patients and their families'.7 It is then the doctor's prerogative to decide whether gabapentin should be used in such conditions.

William Lam
Medical Director, Neurosciences
Medical Department
Pfizer Australia
West Ryde, NSW

References

  1. Wiffen P, Collins S, McQuay H, Carroll D, Jadad A, Moore A. Anticonvulsant drugs for acute and chronic pain. In: The Cochrane Library, 4, 2002. Oxford: Update Software.
  2. Backonja M, Beydoun A, Edwards KR, Schwartz SL, Fonseca V, Hes M, et al.Gabapentin for the symptomatic treatment of painful neuropathy in patients with diabetes mellitus: a randomized controlled trial. JAMA 1998;280:1831-6.
  3. Rowbotham M, Harden N, Stacey B, Bernstein P, Magnus-Miller L. Gabapentin for the treatment of postherpetic neuralgia: a randomized controlled trial. JAMA 1998;280:1837-42.
  4. Rice AS, Maton S. Postherpetic Neuralgia Study Group. Gabapentin in postherpetic neuralgia: a randomised, double blind, placebo controlled study. Pain 2001;94:215-24.
  5. Serpell MG. Neuropathic Pain Study Group. Gabapentin in neuropathic pain syndromes: a randomised, double-blind, placebo-controlled trial. Pain 2002;99:557-66.
  6. Simpson DA. Gabapentin and venlafaxine for the treatment of painful diabetic neuropathy. J Clin Neuromusc Dis 2001;3:53-62.
  7. Sweet M. Gabapentin documents raise concerns about off-label promotion and prescribing. Aust Prescr 2003;26:18-9.