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The selection of a drug or drugs for PHN is largely a trial-and-error process, which is influenced by the availability of some studies of specific drugs and by the medical assessment of the patient. The most commonly used treatments are as follows:
- Anesthetic skin patches: Some patients with PHN benefit from
using local anesthetics because they reduce the pain messages that
the damaged nerves send to the brain. Topical lidocaine patches were
approved by the United States Food and Drug Administration in 1999
for PHN. The patches are applied to the painful area for at least
12 hours per day. Studies show that a majority of patients treated
with the patch reported moderate or greater pain relief (Kanazi, 2000,
Rowbotham, 1995 and 1996). Topical lidocaine in either gel or patch
form can relieve allodynia in patients with PHN. In another recent
study, the topical lidocaine patch provided significantly more pain
relief for PHN than a placebo patch, did not cause systemic side effects,
and was simple to use (Galer, 1999).
- Topical capsaicin cream: Capsaicin, a chemical found in chili
peppers, is a main ingredient in certain pain relieving creams currently
available for the treatment of a number of pain conditions Regular
and cumulative topical applications of capsaicin cream have been shown
to produce pain relieving effects in some painful medical conditions,
including PHN (Long, 2001). In one double-blind clinical trial, cream
containing 0.075% capsaicin applied three to four times a day greatly
reduced pain (in week 2: 62% for capsaicin cream and 31% for placebo;
in week 4: 77% for capsaicin and 31% for placebo) (Bernstein, 1989).
In another study 0.075% capsaicin reduced pain by 28% at week 2 and
39% at week 6; of 83 patients followed for another 140 days, 86% of
patients reported same or better pain relief with continued use (Watson,
1993).
Several studies have looked at a lower concentration of capsaicin
(0.025%) and found it also to be effective, although two or more weeks
of treatment may be required to get the full benefit of the cream
(Bernstein, 1987). A recent placebo-controlled study reported that
there was an average decrease of approximately 15% of the magnitude
of pain with topical 0.025% capsaicin cream (McCleane, 2000), PHN.
Some people find it difficult to use capsaicin cream because of intense
burning after initial applications. (Kanazi, 2000). However, this
burning may lessen after repeated use of the cream.
- Anticonvulsants: When nerve cells are damaged, they can become
chronically overstimulated and continue to send pain messages to the
brain even when there is no injury present.
Anticonvulsant medications block the sodium channels along nerve membranes
that cause nerve cells to activate, helping to quiet down these overactive
nerves.
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 shingles.
The most common side effects associated with these drugs are mental
clouding and sleepiness.
Numerous scientific studies, case reports and one large multicenter
study have confirmed gabapentin's effectiveness in reducing pain as
well as improving sleep, mood and quality of life. In addition gabapentin
is generally well-tolerated, with a safety profile comparable to antidepressant
treatment. Most frequent adverse effects include sleepiness, dizziness,
unsteadiness, peripheral edema and infection. (Kanazi, 2000) (Rice,
2001) (Nicholson, 2000) (Rowbotham, 1998).
- Antidepressants: Antidepressant drugs are nonspecific analgesics
and the analgesic effects can occur independent of antidepressant
actions (Robertson, 1990). The evidence is best for the so-called
tricyclic antidepressants (Rowbotham, 2001) (Koltzenburg, 2001). Approximately
half of patients with PHN benefit from therapy with a tricyclictricyclic
antidepressant (Watson, 2000), such as amitriptyline (Elavil). In
several small studies, amitriptyline provided significantly better
pain relief than either placebo or other antidepressant medications
(Watson, 1982, 1992) (Max, 1998). Nortriptyline (Aventil, Pamelor)
has also has been found to have a significant analgesic effect and
to have fewer adverse side effects (Kanazi, 2000) (Watson, 1998).
Side effects of tricyclic antidepressants can include dry mouth, constipation,
dizziness, nausea, diarrhea, insomnia, headache, blurred vision and
drowsiness, among others. They should not be used by patients taking
MAOI antidepressants, and should be used cautiously in the elderly,
people with epilepsy, thyroid disease, liver disease, closed-angle
glaucoma, and pregnant or breast-feeding women, among other conditions.
There is also evidence that the newer antidepressants, such as venlafaxine
(Effexor), bupropion (Wellbutrin), and paroxetine (Paxil) have analgesic
properties. The overall effectiveness of these drugs is probably less
than the tricyclic antidepressants, but the likelihood of troubling
side effects is substantially less. Patients who are predisposed to
tricyclic side effects, or who have not been able to tolerate these
drugs, may be good candidates for trials of the newer antidepressants.
- Opioid analgesics: Although opioid drugs are the
most effective analgesics overall, some patients with neuropathic
pain such as PHN do not respond well and many patients, particularly
the elderly, struggle with side effects such as constipation and sleepiness.
Many patients and physicians also fear these drugs because they are
associated with the disease of addiction. Nonetheless, there is good
evidence that PHN can be helped by opioids (Kanazi, 2000, Watson,
1998). The risks, including the risk of addiction are often overstated,
particularly if the decision to try an opioid is made after a careful
assessment that evaluates the severity and impact of the pain, the
risk of side effects, the availability of other approaches, and the
likelihood that the patient will be a responsible drug-taker.
- Corticosteroids: Corticosteroid drugs such as prednisone
and dexamethasone, may help with the pain and duration of shingles.
They do not appear to reduce the likelihood of a patient developing
PHN and are not used to treat the established pain syndrome. There
have been recent positive studies that evaluated the spinal injection
of a steroid for PHN (Kotani, 2000) (Kikuchi, 1999). These studies
are provocative, but the technique has not been widely accepted because
of concern about side effects and toxicity.
- NSAIDS (non-steroidal anti-inflammatory drugs): NSAIDS have
not been shown to be an effective treatment for PHN pain.
- Other Drugs: Many other drugs are used to treat neuropathic
pain and may be tried in cases of PHN. These include the oral local
anesthetics (such as mexiletine), baclofen, and the so-called NMDA
receptor antagonists (such as ketamine, dextromethorphan, amantadine,
and memantine). A large body of experimental evidence in animal models
of neuropathic pain suggests an important role of the activation of
NMDA receptors. Studies using intravenous infusion of the NMDA receptor
antagonist ketamine have shown a reduction in the magnitude of pain
in humans with neuropathic pain, but a high incidence of side effects.
(Eide, 1994) (Leung, 2001). Two small clinical trials tested the use
of dextromethorphan (most commonly used as a cough suppressant medication)
for painful diabetic peripheral neuropathy and PHN (Nelson, 1997).
The results of these studies suggest that dextromethorphan may be
effective for the treatment of painful diabetic peripheral neuropathy
but there was no evidence of efficacy in PHN.
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