Neuropathic pain is pain arising as a direct consequence of a lesion or disease affecting the somatosensory system, or put more simply, pain due to injury to sensory nerves. Neuropathic pain can be broadly divided into peripheral neuropathic pain and central neuropathic pain. Until relatively recently, a limited number of older tricyclic antidepressants and anti-epileptics had demonstrated efficacy in peripheral neuropathic pain but none were approved by the FDA for this purpose. Presently, clinicians treat neuropathic pain using one of many different classes of drugs, including opioid analgesics. Dr. Najib Babul, an esteemed pharmaceutical expert with more than 20 years of experience bringing new drugs to the market, discusses the benefits and limitations of prescribing opioids for neuropathic pain.
Dr Babul notes that examples of peripheral neuropathic pain include painful diabetic neuropathy, painful HIV-associated neuropathy, postherpetic neuralgia, post-amputation pain and post-traumatic neuropathic pain. Examples of central neuropathic pain include post-stroke pain, spinal cord injury pain and multiple sclerosis-associated pain. Neuropathic pain can be ongoing or steady pain superimposed by brief or shooting pain and allodynia (pain upon light non-painful touch). Painful diabetic neuropathy and painful HIV-associated neuropathy are characterized by burning sensations in the soles of the feet, as well as paresthesia (“pins and needles”) of the dorsum and soles of the feet. Postherpetic neuralgia on the other hand is due to nerve damage caused by the varicella zoster (chicken pox) virus after a herpes zoster (shingles) infection. Postherpetic neuralgia involves the skin over the thoracic, trigeminal and cervical spinal nerves.
Although opioid analgesics have been used to treat neuropathic pain for many decades, their use was restricted to severe pain that was unresponsive to other drugs. There was considerable skepticism about the efficacy of opioids for neuropathic pain, explains Dr. Babul. Neuropathic pain was thus widely viewed as “opioid resistant” and when effective, it was thought to require much higher doses of opioids. That changed after publication of Dr. Babul’s randomized placebo controlled clinical trial of OxyContin® (Watson & Babul, Neurology 1998;50:1837-41) which demonstrated for the first time that OxyContin provided significant reductions in ongoing pain, shooting pain and allodynia in patients with postherpetic neuralgia. The magnitude of pain relief observed with OxyContin was at least comparable if not superior to that demonstrated with other drugs. Since then, OxyContin has also demonstrated efficacy in painful diabetic neuropathy. It is thought that the results with OxyContin are likely applicable to other strong opioids. In the published studies of OxyContin, side effects were generally consistent with its pharmacology, namely nausea, vomiting, drowsiness, fatigue, dry mouth and constipation. However, patient selection in clinical trials is carefully controlled and does not always reflect eventual post-marketing use, where clinicians have continued reticence to prescribing opioids Chief among the concerns are the risk of iatrogenic addiction and diversion into illicit distribution channels for eventual non-medical use.
Accomplished drug developer, inventor, and biotech entrepreneur, Dr. Najib Babul, PharmD, MBA is an expert in clinical pharmacology, dosage form design, and clinical drug development. His clients rely on his deep knowledge of pharmaceutical licensing, orphan drug applications, scientific and FDA and EMA meetings, pediatric studies and pediatric exclusivity, and attaining FDA fast track and breakthrough therapy designation. His expertise also extends to dosage form design, drug development planning, clinical trial design, contract research organization (CRO) selection and management, protocol development and data analysis.
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