Adjuvant analgesics are drugs that are used primarily for treating
conditions other than pain, but may be analgesic or assist in
decreasing patients' perception of pain in certain circumstances.
Adjuvant analgesics may be used alone or in combination with an opioid
or a nonopioid pain reliever to treat persistent pain conditions,
particularly neuropathic pain. Effective adjuvants typically include
tricyclic antidepressants, antiepileptic drugs, 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 patients cannot tolerate their sedating and anticholinergic
effects. The secondary amines are better tolerated than the tertiary
amines, and adverse effects are less associated with these drugs.
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 adverse effects. Of the newer
antidepressants, the SNRIs appear to be more effective analgesics than
the SSRIs. Paroxetine (Paxil) is the only SSRI that has some evidence
for efficacy in treating chronic pain. 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 FDA for the treatment 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 drugs have been used for decades, their widespread use
for pain did not begin until several years after the FDA approval of
gabapentin (Neurontin). Gabapentin (Neurontin) 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, tiagabine, and oxcarbazepine, also are used as
analgesics for neuropathic pain.
The most common adverse effects of the different anticonvulsants are
gastric intolerance (nausea and vomiting), sedation, ataxia, dizziness
and confusion being.
More information on
analgesic
medications is available on author's website -
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