QUESTION: My patient is being treated for trigeminal neuralgia (TN) with 100 mg of carbamazepine (Tegretol) b.i.d. He doesn't have a seizure disorder, so why the anticonvulsant?
ANSWER: Considered an adjuvant analgesic, carbamazepine is the drug of choice for TN, also called tic douloureux. Up to 70% of patients using carbamazepine for TN report pain relief within 48 hours.
Trigeminal neuralgia is a neuropathic pain syndrome that may result from a short circuit of the 5th cranial nerve. According to one theory, a small artery throbbing against the nerve eventually wears off the nerve's insulation, leaving a "bare wire" that's hypersensitive to sensory stimulation.
Something as ordinary as chewing, swallowing, or even feeling a breeze across the face can trigger an attack of pain. Pain may also occur for no apparent reason.
Your patient may describe the pain of TN as excruciating, sudden, sharp, shooting, burning, stabbing, or lancinating. The pain may last several seconds and then recur. It may come and go throughout the day over days or weeks. In some patients, it disappears for months or years, only to recur unexpectedly. These severe, unpredictable pain episodes can evolve into a chronic pain syndrome, resulting in depression and a loss of daily functioning. Even when your patient isn't in pain, fear of the pain returning is never far from his mind.
A sodium channel blocker, carbamazepine inhibits the transmission of excitatory impulses that are perceived as pain. Common adverse reactions are drowsiness, fatigue, dizziness, nystagmus, memory problems, or nausea. To prevent nausea, instruct him to take the medication at mealtime. Adverse reactions may be minimized by increasing the dosage gradually.
Because aplastic anemia and agranulocytosis are potentially serious adverse reactions associated with carbamazepine, obtain a baseline complete blood cell count before starting therapy. Instruct the patient to return for testing after 1 month, 3 months, and every 6 months as directed by his health care provider.
Teach him to report signs and symptoms of infection or bleeding, such as fever, sore throat, rash, mouth ulcers, bruising, and petechial or purpuric hemorrhage. If bone marrow depression is significant, therapy with carbamazepine may be discontinued.
Besides adjuvant medications, opioids and nonopioids may be used to treat neuropathic pain. The use of opioids is controversial, but they may help in some cases. Nonopioid analgesics, such as nonsteroidal anti-- inflammatory drugs and acetaminophen, also may offer pain relief when used in conjunction with other medications.
Copyright Springhouse Corporation Mar 2001
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