Epilepsy Drugs versus HIV Meds - a Neuropathy Problem?

One of the standard treatments for HIV-related neuropathy pain, is the taking of anti-seizure or epilepsy drugs (Gabapentin, Carbamazepin amongst others). However, by definition, everybody is also taking HIV medications. Today's article from medpagetoday.com (see link below) looks at a study which suggests possible clashes between the two types of drug - something HIV-patients really don't want to hear! The problem is that most drug-interaction sites don't show any counter-indications for the two types of drug at the moment. If you are in this situation and are at all concerned, it's probably wise to bring it to the attention of your HIV-specialist.
That said, the authors of the article itself point out the following:
'A new guideline from the American Academy of Neurology and the International League Against Epilepsy suggests careful dosing of antiepileptic drugs in HIV-infected patients since drug interactions might decrease efficacy of antiretrovirals in some cases.
Note that the evidence base for the guidelines was judged to be weak.'

Guideline Urges Care in Mixing HIV, Seizure Drugs
By Michael Smith, North American Correspondent, MedPage Today Published: January 04, 2012

Although the evidence is weak, doctors should be aware that combining anti-HIV and anti-epileptic medications may lead to drug-on-drug interactions, according to a new guideline.

The issue is growing in importance as more and more people -- especially in the developing world -- are living with HIV as a chronic disease, according to Gretchen Birbeck, MD, of Michigan State University in East Lansing, Mich. and colleagues.

And up to 55% of people taking antiretroviral medications may need epilepsy control drugs at some point, although not for seizures in every case, Birbeck and colleagues reported online and in the Jan. 10 issue of Neurology.

But, the authors noted, there are no formal guidelines to assist physicians in making drug choices. To help fill the gap, the American Academy of Neurology and the International League Against Epilepsy convened an international panel to sift through evidence and come up with guidelines.

The bad news, the panel found, was that the data are limited; only 42 articles yielded data, most of them reporting on Class II and Class III studies. As a result, the panel's recommendations are all level C -- any effect is only "possibly" valid.

Birbeck and colleagues noted that indications for anti-epileptic drugs have expanded beyond seizures to include such conditions as peripheral neuropathy and some psychiatric disorders.

But up to 11% of HIV patients may have seizure disorders and many more will suffer some form of peripheral neuropathy, leading to "substantial" concurrent use of anti-HIV and anti-epileptic medications worldwide, they argued.

The data analysis found that some combinations may need dose adjustments:
Patients receiving phenytoin (Dilantin) may need about a 50% increase in the dosage of lopinavir/ritonavir (Kaletra) to maintain serum concentrations at the right level
Patients taking valproic acid may need a lower dose of zidovudine (AZT) to keep serum concentrations unchanged
Patients receiving atazanavir/ritonavir (Reyataz/Norvir) may require about a 50% increase in the dose of lamotrigine (Lamictal) to keep serum concentrations unchanged

On the other hand, the limited evidence suggests that:
Using atazanavir or raltegravir (Isentress) with lamotrigine may not require lamotrigine dosage adjustment
Giving raltegravir and midazolam together may not require adjusting the midazolam dosage
Using valproic acid and efavirenz (Sustiva) may not require efavirenz dosage adjustment

It also may be important to avoid enzyme-inducing anti-epileptics for people whose HIV regimens include protease inhibitors or non-nucleoside reverse transcriptase inhibitors, the panel found.

While the evidence is still weak, the panel argued, those drug classes both use the cytochrome P450 system, and pharmacokinetic interactions might lead to virologic failure, with implications for disease progression and development of resistance.

"It is important that patients know exactly which drugs they are taking and provide that information to all prescribing health care providers caring for them," Birbeck said in a statement. "Doctors may need to watch and adjust drug doses in people with HIV/AIDS who take seizure drugs."

Source reference:
Birbeck GL, et al "Evidence-based guideline: antiepileptic drug selection for people with HIV/AIDS" Neurology 2012; 78: 139–145.

http://www.medpagetoday.com/Neurology/Seizures/30489