What are pharmacologic adjuvants, and which are used in the treatment of chronic pain?
Pharmacologic adjuvants are medications used as analgesics that were originally developed for other indications. These are commonly used in conjunction with analgesics for chronic and refractory pain. Most commonly, antiepileptics, antidepressants, corticosteroids, local anesthetics, and muscle relaxants are used in pain.
Commonly used antiepileptics include gabapentin, pregabalin, and topiramate, as these have been found to be effective analgesics in the management of neuropathic pain. Titration of these medications in the elderly should be slow, as sedation and cognitive impairment are known side effects. Dose adjustment is also required for patients with renal dysfunction.
Antidepressants that are commonly used as analgesics include those in the category of tricyclic antidepressants (TCAs) or serotonin norepinephrine reuptake inhibitors (SNRIs). TCAs include nortriptyline and amitriptyline. In the elderly population, however, caution should be taken, as side effects include cardiac dysrhythmias, cognitive impairment, and anticholinergic effects such as hypotension, urinary retention, and sedation. SNRIs on the other hand, such as duloxetine, are efficacious in neuropathic pain and better tolerated than TCAs.
Local anesthetics are often used in the form of topical patches and are therefore easy to use, and also have a decreased risk of toxicity and drug interactions. Muscle relaxants, in general, have very limited efficacy, if any, as analgesics in chronic pain.