Eyes turning to neuropathic pain market

Neuropathic pain is defined as pain associated with a functional abnormality of the nervous system. Clinical features can include an abnormal, unpleasant sensation (dysesthesia) that frequently has a burning or electrical sensation with occasional brief shooting or stabbing pain. Although the onset of most neuropathic pain is within days after the precipitating injury, there is no absolute temporal relationship to the originating neural trauma. In fact, it can begin weeks, months, or even years later.

Large patient pool

Key sub-types of neuropathic pain include diabetic neuropathic pain (DNP), post-herpetic neuralgia (PHN) and HIV-associated neuropathic pain (HIVNP). DNP offers the larger patient population, although estimates of the actual size of the patient pool vary.

Sometimes it is also difficult to distinguish neuropathic pain from nociceptive pain. Examples of nociceptive pain include postoperative, cancer and arthritis pain. It is important to differentiate nociceptive from neuropathic pain because recommended treatment protocol differs. In general, nociceptive pain responds to opioids and non steroidal anti-inflammatory drugs (NSAIDs), whereas neuropathic pain tends to be partially responsive to opioid therapy and can be alleviated with tricyclic antidepressants (TCAs) and anticonvulsant compounds.

As of June 2005, just five drugs were approved for the treatment of neuropathic pain syndromes in the US: Cymbalta (Eli Lilly), Lidoderm (Endo), Neurontin (Pfizer), Lyrica (Pfizer) and carbamazepine, although a variety of agents are frequently used off-label and an estimate of which is included as the current market size. Despite the presence of these drugs, there is still a large amount of unmet need.

The consensus among physicians is that gabapentin (generic Neurontin) is the gold-standard treatment of neuropathic pain. In a February 2004 study, Datamonitor found that Neurontin is used in over 50% of cases of pharmacologically-treated patients with DNP and PHN in the . However, since this survey was carried out, Neurontin has lost patent protection in the and now a number of generic gabapentin versions are available.

In the , Pfizer's own generic gabapentin had the second highest sales in 2004, closely followed by tablet and capsule versions from Teva and Alpharma, respectively. In the five major EU countries, where Neurontin lost patent protection in 2000, Teva, Hexal and Merckle have strongly performing generic versions of gabapentin. However, in the and the five EU markets, Neurontin still out-performed generic gabapentin, in terms of sales and volume of product in 2004.

The Japanese neuropathic pain market differs significantly from both the EU and US markets: gabapentin and lidocaine patches are not available in , and physicians will often use nerve blocks and vitamin B - often in combination - to control patients' pain. Furthermore, despite a lack of clinical data to warrant their use, physicians in frequently prescribe NSAIDs, such as loxoprofen, for neuropathic pain.

On the flipside, because the Japanese market is significantly different - based on NSAIDs and nerve blockers - to the and , it does present a good opportunity for new treatments in neuropathic pain.

Packed pipeline

At the time of writing, there were at least 97 compounds in development for the treatment of neuropathic pain, making it one of the most active pipelines in the central nervous system area. The rationale for such a big pipeline is simple. The current neuropathic pain market offers a considerable commercial opportunity by combining a large patient potential with a huge need for new therapies. The phase II pipeline is particularly impressive, boasting a whole host of novel compounds under development by specialist companies as well as top tier players.

To succeed in the current market, new products must be at least equivalent in terms of the safety and efficacy to gabapentin, although a product with a proven pain reduction of greater than 50% in a significant majority of patients would be very successful. However, it should be noted that the achievement of such efficacy scores can be as much based on the correct choice of pain scale and trial design as true product efficacy.

Current pipeline products are competing in terms of improved dosing formulations, a key factor in taking market share if the primary efficacy need cannot be met. The mode of drug delivery also has important implications on the ease of drug administration and patient compliance, a key issue in a market where the gold standard has a dosing profile of up to four tablets per day.

The majority of current treatments are orally available, but a single daily treatment with similar efficacy to gabapentin would be very well received in the neuropathic pain market. As many neuropathic pain patients are also being treated for other conditions such as HIV, MS, and diabetes, medication that can be easily taken, for example once-daily oral medication, will improve patient compliance. Drug-drug interactions should also be carefully examined for the same reason.

Related research:

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