Drug Interactions Can Worsen CMT Article

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Drug Interactions Can Worsen Peripheral Nerve Disorder

Jane Salodof MacNeil, Medical Writer

Introduction

http://www.cbshealthwatch.com/cx/viewarticle/233687

There's a hidden dilemma dogging an estimated 200,000 Americans who have an

inherited nerve disease called Charcot-Marie-Tooth (CMT) disorder. CMT can be so

mild that people don't notice any symptoms or deformities and doctors don't spot

a disorder. Some relatives mistake the odd-shaped feet or hands that are

characteristic of CMT for a harmless family trait.

Some relatives mistake the odd-shaped feet or hands that are characteristic of

CMT for a harmless family trait.

About two dozen drugs have the potential to turn mild CMT into a crippling

condition, however. The most dangerous is vincristine--a chemotherapy drug that

has caused at least one death. Dr. D. Bird, a professor of neurology and

medical genetics at the University of Washington in Seattle, reported on

vincristine after he saw severe reactions in three CMT patients who were treated

for cancer.

" What's clear is, if you have an underlying neuropathy, or nerve disease, you

shouldn't be getting vincristine, because it's just too dangerous, " he says.

" The key thing is that people in the cancer field recognize that. "

Other risky drugs are widely prescribed remedies for common disorders: for

example, metronidazole (sold as Flagyl, Protostat, and under other brand names)

lithium, and gold. Nitrous oxide, a popular anesthetic in dentists' offices, may

cause or aggravate peripheral nerve conditions such as CMT. So might megadoses

of vitamin B6.

Uncommon but Not Rare

Yet, except for vincristine, the hazards are not well documented. Although three

doctors--named, respectively, Charcot, Marie, and Tooth--each identified CMT in

1886, little research was done until recently because it was considered rare.

Today, experts dispute that label, calling CMT " uncommon " and suggesting that

too many cases are undiagnosed for it to be possible to pinpoint how many may be

affected. Dr. Fischbeck, chief of the neurogenetics branch at the

National Institute of Neurological Disorders and Stroke, says, " I see it in

people walking down the street. I see it in colleagues. Once you know what to

look for, you see it all the time. People go about their lives with it. "

Feet with high arches and hammertoes that make walking, running, and balance

more difficult are a telltale sign. So are hands that stay contracted, impeding

activities such as writing. These deformities occur because CMT causes the

peripheral nerves--the nerves in the body's extremities--to deteriorate. As a

result, muscles weaken from lack of stimulation.

In severe cases, patients are confined to wheelchairs. More often, CMT

disability can be overcome with leg braces, custom-made shoes, adaptive devices,

and, occasionally, foot or hand surgery. But first CMT has to be diagnosed.

Even though progressive CMT is obvious to neurologists, other doctors often are

not familiar with the disorder, according to Ann Lee Beyer, executive director

of the Charcot-Marie-Tooth Association in Upland, Pennsylvania. One of its

goals, she says, is to educate more doctors about " a disease no one knows

anything about or even heard of. "

Drug Advisory: Circumstantial Evidence

Another is to alert doctors and patients to possible drug reactions.

Eline, 42, of ville, New Jersey, was a computer programmer in 1990

when a gynecologist prescribed Flagyl for what appeared to be a yeast infection.

Eline says she told the doctor that she had mild CMT, but the doctor did not

foresee a problem. Several days later, Eline felt some numbness and tingling in

her hands. Soon she had difficulty typing. Muscle weakness followed, and Eline

was hospitalized.

" The change was so fast and dramatic, which you don't ordinarily get with CMT, "

she says. Although her condition slowly improved, she has not gone back to work.

The CMT Association looked at the experiences of Eline and patients like her to

compile a list of potentially toxic drugs. It also included drugs associated

with damage to peripheral nerves. Dr. Linton C. Hopkins, chief of the

neuromuscular group at Emory University School of Medicine, chairs an

association subcommittee responsible for the medical alert list.

" If there seems to be evidence that a drug itself could cause neuropathy, we

think patients with other neuropathies would be more vulnerable, " he says.

Hopkins explains that he started compiling the first list " after a patient with

CMT was given nitrofurantoin [Furadantin and other brand names] for a minor

urinary condition and became much more severe. "

Do You Have CMT?

Even if you show no sign of CMT, experts say your doctor should ask whether

anyone in your family has or might have the condition. If yes, they want you to

be tested before taking any drugs that might affect the nervous system.

Bird says genetic testing will identify about half of CMT cases. If your test

comes out negative, he recommends that you have a nerve conduction study called

an electromyogram (EMG) to be sure you don't have any nerve damage.

A positive finding does not mean you can't take any drugs on the warning list.

That will depend on the alternatives and your other medical needs.

" Some are more likely to cause nerve damage than others, " says Dr. E.

Shy, director of the CMT Clinic at Wayne State University. " A patient needs to

discuss this list with the physician because sometimes they have to make a value

judgment. "

Shy is compiling a database of CMT patients and families for future research

into CMT. For information about participating, call genetic counselor

Krajewski at 313-577-8317.

For information about CMT, call the CMT Association at 1-800-606-CMTA.

Drugs That May Aggravate CMT

Here are some common conditions and some drugs used to treat them that may

aggravate Charcot-Marie-Tooth disorder. If you have CMT--or anyone in your

family does--discuss possible toxic side effects with your doctor.

Alcohol abuse: disulfiram (Antabuse)

Anesthetic: nitrous oxide (chronic repeated inhalation)

Antibiotic: chloramphenicol (sold under many brand names)

Cancer drugs: doxorubicin hydrochloride (Adriamycin), cisplatin (Platinol),

misonidazole, suramin (many brand names), taxol (Paclitaxel),

vincristine--potentially lethal (Oncovin, Vincasar)

Heart disease: amiodarone (Cordarone and Pacerone for irregular heartbeat),

perhexiline (Pexid for angina).

High blood pressure: hydralazine (Apresoline)

Manic-depressive illness and headaches: lithium

Rheumatoid arthritis: gold, penicillamine--sometimes misprinted as penicillin,

which is a different drug (Cuprimine and Depen)

Skin disease: dapsone

Seizures and pain: diphenylhydantoin (Dilantin)

Sleeping pill: glutethimide (Doriden)

Trichomonas infection: metronidazole (Flagyl)

Tuberculosis: ethionamide, isoniazid (also called INH)

Urinary tract infection: nitrofurantoin (Furadantin, Macrodantin)

Vitamin: Megadoses of vitamin B6 (pyridoxine) and normal doses of less than 100

mg a day are not a problem.

* From the Charcot-Marie-Tooth Association.

Jane Salodof MacNeil is a veteran freelancer who often writes about health and

medicine.

Reviewer: Beth Israel Deaconess Medical Center. Reviewed for medical accuracy by

physicians at Be