By definition, adjuvant analgesics are drugs whose initial use was not
for pain but rather for other conditions. They are a diverse group of
drugs that includes antidepressants, anticonvulsants (antiseizure drugs),
Update on Adjuvant Analgesics (.pdf)
The best studied adjuvant analgesics are the tricyclic antidepressants
(TCAs), such as amitriptyline (Elavil®), and desipramine. There is
overwhelming evidence that this class of drugs can be effective for migraine
headache, tension-type headache, postherpetic neuralgia, painful diabetic
neuropathy, arthritis, low back pain, and other painful conditions. These
drugs have been shown to relieve pain independent of their effects on
depression; that is, patients who are not depressed may experience pain
relief. Once the correct dose is found for the individual patient, favorable
results are usually seen within a week; however, side effects, including
weight gain, dry mouth, blurred vision and constipation, are possible.
There are many newer antidepressants, such as the selective serotonin
reuptake inhibitors (like fluoxetine [Prozac®], paroxetine [Paxil®],
sertraline [Zoloft®]), and others (like venlafaxine [Effexor®]
and nefazadone [Serzone®]. Most of these antidepressant drugs have
not been shown to be effective pain relievers in clinical studies, but
some have, and many pain specialists believe that most, if not all, can
potentially relieve pain. They are usually better tolerated than the TCA's.
Drugs that are primarily used to treat epilepsy (seizures) have been used
to treat nerve pain conditions and migraine headache for several decades.
Many anticonvulsant drugs have been shown in clinical studies to be effective.
The first-line drugs for neuropathic pains are two related anti-seizure
medicines, gabapentin (Neurontin®) and pregabalin (Lyrica®), and a number
of analgesic antidepressants. Gabapentin and pregabalin have been approved
by the U.S. Food and Drug Administration (FDA) for the treatment of specific
neuropathic pains, including painful diabetic neuropathy and shingles.
They are also used for migraine headache and for fibromyalgia. The most
common side effects associated with these drugs are mental clouding and
sleepiness. Other anti-seizure drugs also may be useful as second-line
agents for neuropathic pain. These include carbamazepine [Tegretol®],
phenytoin [Dilantin®], valproate [Depakote®], clonazepam [Klonopin®],
topiramate [Topamax®], and lamotrigine [Lamictal®]. Some of these drugs,
such as valproate and topiramate also are used for headache.
Currently, there are two alpha-2-adrenergic agonists that have some evidence
as pain relievers: tizanidine (Zanaflex®) and clonidine (Catapres®).
There are some studies showing that tizanidine can be effective for tension-type
headache, back pain, neuropathic pain, and myofascial pains. Clonidine
has been used to treat refractory neuropathic pain. Tizanidine tends to
be better tolerated than clonidine and, unlike clonidine, rarely decreases
Mexiletine is a drug that was first approved to treat irregular heart
rhythms. However, several scientific studies have shown this drug to be
effective in chronic nerve pain syndromes. Other oral local anesthetics
are also used. Intravenous infusion of a local anesthetic is a special
technique that may be used by pain specialists.
Corticosteroids can be used as an effective analgesic for treating some
cancer pain syndromes. Also, corticosteroids given as short-term tapers
can be effective in treating migraine headache and complex regional pain
syndrome (reflex sympathetic dystrophy).
Baclofen is on the market as a muscle relaxant and is used to treat nerve
pain syndromes. There is very good evidence that it works in trigeminal
Drugs that block a specific receptor involved in the experience of pain,
the N-methyl-D-aspartate (NMDA) receptor, may also be analgesic in nerve
pain. These include dextromethorphan (the cough suppressant, but at higher
doses than those needed to block cough), ketamine (an anesthetic), and
There are many drugs that are called "muscle relaxants" and
are used to treat minor musculoskeletal pains. These include carisoprodol
(Soma®), cyclobenzaprine (Flexeril®), metaxolone (Skelaxin®),
and others. These drugs do not actually relax skeletal muscle, but they
can relieve pain, and they are commonly used.
Topical drugs are applied directly to the skin, as a patch, gel, or
cream and have their pharmacologic activity directly under the skin
site without any significant amount of drug entering the blood stream.
Thus, true topical drugs should not produce any systemic side effects,
that is, side effects caused by the drug's effects throughout the body.
Currently, only one topical drug has an FDA approved indication for
pain treatment -- a topical lidocaine patch (Lidoderm®) -- for the
treatment of postherpetic neuralgia. This patch can be tried for many
types of nerve pain.
A widely used topical pain reliever is capsaicin, which is available
as an over-the-counter cream. There have been some studies that show
pain relief with capsaicin and others that do not. This drug is being
used to treat nerve pain and arthritis pain.