What are Adjuvant Analgesics?

Adjuvant analgesics are medications that are used primarily for treating conditions other than pain, but may assist in decreasing patients' perception of pain in certain circumstances. Adjuvant analgesics may be used alone or in combination with an opioid or a non-opioid pain reliever to treat persistent pain conditions, particularly neuropathic pain.

Commonly used adjuvants include tricyclic antidepressants, antiepileptic drugs, and muscle relaxants.

Antidepressants

Analgesic effect of antidepressants occurs at lower doses and more quickly than antidepressant effects. Antidepressants may be considered multipurpose analgesics, appropriate for a trial in any persistent pain condition.

The tricyclic antidepressants (TCAs) have been well studied and are most likely to be effective. TCAs are classified as tertiary amines (amitriptyline, imipramine, doxepin, clomipramine) and secondary amines (nortriptyline, desipramine). The evidence of analgesic efficacy is more extensive for the tertiary amines (particularly amitriptyline), but some persons cannot tolerate their sedating and anticholinergic side effects. The secondary amines are better tolerated than the tertiary amines.

TCAs such as amitriptyline, nortriptyline and desipramine have demonstrated efficacy for migraine, diabetic peripheral neuropathy, post herpetic neuralgia (PHN), arthritis pain and post stroke pain.

Newer antidepressants such as selective serotonin reuptake inhibitors (SSRIs) and selective serotonin and norepinephrine reuptake inhibitors (SNRIs) are less effective at relieving neuropathic pain than the TCAs, but have significantly less side effects. Of the newer antidepressants, the SNRIs appear to be more effective analgesics than the SSRIs. Two SNRIs venlafaxine (Effexor) and duloxetine (Cymbalta) have been shown to be analgesic in several studies. Venlafaxine provides inconsistent effects while duloxetine, the newest of the SNRIs is the first antidepressant to be approved by the US Food and Drug Administration (FDA) for the management of neuropathic pain, specifically pain associated with diabetic neuropathy.

Anticonvulsants (Anti-epileptic drugs)

Anticonvulsants are commonly used in the management of neuropathic pain. They act by suppressing the spontaneous neuronal discharges and neuronal hyperexcitability that occur after nerve injury and may also have a central effect.

Although these medications have been used for decades, their widespread use for pain did not begin until several years after the FDA approval of gabapentin (Neurontin). Gabapentin is currently the most commonly prescribed drug for this indication. It is FDA approved for the treatment of diabetic painful polyneuropathy and postherpetic neuralgia.

Pregabalin, which is a distinct compound but has the same mechanism of action, was recently approved for the same indications. This drug has more stable pharmacokinetics than gabapentin and should be simpler to use. Other antiepileptics, such as phenytoin, carbamazepine, clonazepam and valproic acid, and newer drugs, such as lamotrigine, topiramate, and oxcarbazepine, also are used as analgesics for neuropathic pain.

The most common side effects of the different anticonvulsants are gastric intolerance (nausea and vomiting), sedation, ataxia, dizziness and confusion being.