OAKLAND, CALIF. — Two anticonvulsants are competing in popularity for treating peripheral neuropathy in patients with HIV infection: gabapentin and lamotrigine, said Lisa Capaldini, M.D., at a conference sponsored by the American Foundation for AIDS Research.
Lamotrigine is winning the popularity contest because it appears to be especially effective, said Dr. Capaldini, who practices internal medicine in San Francisco.
She said she has no relationships with the companies that make anticonvulsants.
Older anticonvulsants that are used to treat neuropathic pain in HIV-negative patients can interfere with the metabolism of anti-HIV medications.
But gabapentin does not interact with antiretrovirals and is now a generic drug—both attributes that make it appealing for patients with HIV and neuropathy, she said at the meeting, cosponsored by the Pacific AIDS Education and Training Center.
Gabapentin dosing in these patients starts at 300 mg t.i.d. and often must be titrated up as high as 1,200 mg t.i.d. to be effective. These dosages can cause significant sedation, and the thrice-daily regimen can be challenging for patients who already take multiple HIV medications.
For lamotrigine to be effective in treating HIV-related neuropathy, dosing usually needs to reach at least 200 mg b.i.d., but it's essential to start with a very small dose, Dr. Capaldini cautioned. The drug can cause a life-threatening hypersensitivity reaction in some patients.
She tells patients starting on lamotrigine to break a 25-mg pill in half and take half a pill per day for 3 days before moving up to a b.i.d. regimen and higher doses.
Physicians should warn patients about hypersensitivity symptoms. “I tell them that if they get a rash and don't know what it is, to call me,” she said. Usually the rash will appear around 6 weeks after starting low-dose therapy.
Older anticonvulsants such as carbamazepine, divalproex sodium, or phenytoin remain options for treating neuropathy in patients with HIV, but are more complicated to use because they interact with HIV medications. Their serum levels can be measured, but it can be hard to gauge their effects on HIV therapy, particularly with phenytoin.
“We find Dilantin [phenytoin] very hard to use with HIV medications because it has such unpredictable effects on other drugs metabolized in the liver,” Dr. Capaldini said, adding, “That doesn't mean you shouldn't use it” if needed.
Tricyclic depressants and analgesics also can be used to treat neuropathic pain in patients with or without HIV.