Epilepsy drugs for Neuropathy and HIV medications - a dangerous mix?

Today's post from medpagetoday.com (see link below) could be more than a little worrying for many HIV patients who take anti-convulsants (seizure/epilepsy drugs) to help controle their neuropathy symptoms. It has to be said that the authors admit that the evidence is not very strong but say also that this may be due to the lack of evidence based studies.
Basically, the article warns about possible clashes between certain epilepsy drugs and HIV medications. The end result being a reduction in the strength of the HIV drug, with all the potential ensuing complications. It goes without saying that if you're concerned, you should bring this to the attention of either your neurologist or your HIV specialist. They may be unaware of any problem but will be able to advise you whether you need to alter your medication.

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

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.

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."

The guideline was developed with financial support from the American Academy of Neurology and the International League Against Epilepsy. The authors were not compensated for their work.

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