As the pain message is processed, there is a release of endogenous opiates, enkephalin and dynorphin, serotonin, and norepinephrine. It is at this level that tricyclic antidepressants work by preventing the reuptake of serotonin and norepinephrine. While their exact mechanism is unknown, antidepressants also improve sleep, mood, and anxiety in addition to pain. Anticonvulsants or membrane stabilizers (e.g., carbamazepine, gabapentin) work at the peripheral nerve membrane, preventing the transmission of pain. Complaints of continuous burning may best respond to antidepressants, whereas lancinating complaints may best respond to anticonvulsants. The anticonvulsant gabapentin, however, has been used in the treatment of burning and episodic neuropathic pain.
Acute pain: There are many medications at our disposal for the management of pain in the emergency department. Physicians are frequently concerned about thepotential for addiction when prescribing opiates; however, there have been studies suggesting that addiction rarely evolves in the setting of painful conditions. 75 76
Tables 9 and 10 , provide an overview of analgesics and dosing regimens. The route of administration of medication should be selected based on the severity of pain. In a patient with mild to moderate pain, offering an oral dose of the planned discharge analgesic early in the patient's visit in the ED not only addresses their pain, but offers the opportunity to see how effective the medication will be. In patients with moderate to severe pain, an IV catheter should be placed so that IV opioids can be given and titrated to an appropriate level of pain relief. 28 There is a limited role of the IM route in acute pain management. Often, health care providers use the IM route with the thought that IM dosing provides a more rapid onset of action and has greater analgesic properties than oral dosing. However, the onset of action of IM and oral medications can be similar as seen with toradol. 77 IM dosing is problematic as it exhibits variable absorption, is painful, is not easy to titrate and has the potential for hematoma formation. Additionally, it is more expensive than oral medication to administer and poses a needlestick risk to the care provider. 78
Chronic pain: Chronic pain warrants special mentioning. As previously discussed, there are 4 types of chronic pain. Using the type of pain to guide therapy is prudent. See Table 11 outlining therapeutic options . Many patients with chronic pain have a primary care physician or a pain specialist involved in their care. Often these patients may have a "contract" with these physicians for the amount of narcotics that they use. It is reasonable to consult with that physician prior to prescribing narcotics if feasible.
Five percent lidocaine patches for post-herpetic neuralgia have been described in multiple articles. The patches have provided significant relief to patients without any more side effects than placebo.79
Lidocaine patches have been studied for neuropathic pain of other etiologies as well. In one study, patients with a variety of pathologies including diabetic polyneuropathy, post-surgical pain, and radiculopathy were treated with topical lidocaine patches after failing anti-depressant, anti-convulsant, antiarrhythmic and opioid medications. Most patients had a reduction in their pain without significant side effects. 80 Open-label studies also provide initial evidence that lidocaine patches may be beneficial in the management of myofascial pain and osteoarthritis, even when used as monotherapy.81-83 Using lidocaine patches has not been shown to cause significant systemic absorption, serum lidocaine levels remained well below those that cause anti-arrhythmic effects. There was no report of local loss of sensation. 84 Additionally, no toxicities were noted in either healthy volunteers, patients with post-herpetic neuralgia or in patients with acute herpes zoster. 85