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Mixing Medications can Spell Trouble for Women
by Sophia Cariati

Women are at an increased risk of adverse drug reactions compared with men in part because they are more likely to use multiple medications and dietary supplements, according to the results of a number of recent studies. Sex-based differences in metabolism, anatomy, and hormone levels also seem to play a role in why women experience more unwanted effects of drugs. 

"Recent findings suggest women are significantly more likely to suffer from adverse drug interactions because of their biology and likelihood of taking more than one medication," said Phyllis Greenberger, MSW, president and CEO of the Society for Women's Health Research. "Women should think twice before combining even commonplace products like ibuprofen, St. John's Wort and oral contraceptives with other drugs."

Adverse drug reactions (ADRs), or any harmful, unintended, or unwanted effect of a medication, are a leading cause of illness and account for an estimated 7,000 deaths annually in the United States. Increasing age, liver problems and kidney disease raise the risk of ADRs. In addition, taking multiple medications puts a patient at greater risk of an ADR. Increasing evidence suggests that female sex is also a strong risk factor for ADRs, partly due to greater simultaneous use of several prescription and over-the-counter drugs by women.

A recent review of 48 studies in the United Kingdom revealed that ADR'S to newly marketed drugs are 60 percent more common in women than in men. This sex difference was observed across all age groups older than 19 years old. Other studies have found less pronounced, yet significantly higher risks of ADRs among women.

Women need not look further than their own medicine cabinet for potentially problematic combinations, warn experts. For instance, oral contraceptives can fail resulting in pregnancy when taken in combination with the antibiotics rifampin, tetracycline or penicillin. Some antacids can inactivate fluoroquinolones, drugs often prescribed for urinary tract infections, allowing infections to progress unchecked. In addition, combining selective serotonin reuptake inhibitors (SSRIs) with other types of antidepressants, pain medications or illegal drugs such as ecstasy and cocaine can have serious consequences.

Dietary supplements, used more often by women than men, can also interact with other drugs to cause serious problems. And because there are no regulatory requirements for testing, doctors and pharmacists know very little about their risks. Despite the paucity of data, numerous combinations of herbs and drugs have emerged as dangerous.

The FDA has specifically warned women taking birth control pills against using St. John's wort as it decreases the effectiveness of oral contraceptives. Combining St. John's wort with antidepressants, some cough syrups, a protease inhibitor used to treat HIV/AIDS, the commonly used chemotherapy drug irinotecan, and the heart medication digoxin can also cause serious adverse events. What's more, a slew of herbs have been shown to interact with heart medications and blood thinners like warfarin.

Other Reasons Women are More Prone
Their greater use of multiple drugs is not the only reason women are at an elevated risk of adverse drug reactions. Research points to a number of other possible mechanisms for this sex-based difference. Variations between men and women in liver and kidney function, which affects drug metabolism, as well as anatomy seem to influence the incidence of adverse drug reactions.

On average, women have a lower body weight, smaller organ size, reduced blood flow and a higher proportion of fat compared with men. Overall differences in hormonal activity between the sexes affect the way drugs are processed, absorbed and cleared by the body as well. Because of these sex-differences, the optimally safe and effective dose of a drug varies between men and women. Research suggests that a significant percentage of adverse drug events among women may be due to unnecessarily high doses of frequently prescribed drugs.

Steering Clear of Drug Interactions
There are a number of ways women can help avoid undesirable effects of medications. Obtaining and reading FDA-approved drug package inserts is a great place to start, according to Larry Sasich, a spokesperson for the Public Citizen Health Research Group in Washington, DC. Sasich recommends women ask their pharmacists for the FDA-approved drug information in place of the computer-generated leaflets that often come stapled to or inside the bag. This FDA-approved information contains a section specifically dedicated to drug interactions. A recent national survey on the unregulated leaflets, however, revealed they were "inconsistent, incomplete and basically useless," according to Sasich. All over-the-counter medications should also contain an FDA-approved insert in the box.

What's more, women should refer to a drug reference book, if possible, according to Maryann Napoli, associate director of the Center for Medical Consumers in New York City. Almost all local libraries have a drug reference book in their collection and there are also some reliable online sources of drug information. Napoli suggests women get in the habit of reading up on every prescription or over-the-counter drug before they start using it.

The Food and Drug Administration suggests women also use the following guidelines to help prevent undesirable side effects and interactions:

  • Tell your doctor about everything you take, including prescription and nonprescription drugs and dietary supplements.
  • Stop taking all herbs at least 2 weeks before surgery as many interfere with anesthesia and affect blood clotting.
  • Drugs may interact with certain foods and beverages, so ask your doctor or pharmacist if there are any dietary modifications you should make.
  • Let your doctor know about any symptoms that may be side effects.
  • Keep track of when you take your medications.

The Society for Women's Health Research is the nation's only not-for-profit organization whose sole mission is to improve the health of women through research. Founded in 1990, the Society brought to national attention the need for the appropriate inclusion of women in major medical research studies and the resulting need for more information about conditions affecting women. The Society advocates increased funding for research on women's health, encourages the study of sex differences that may affect the prevention, diagnosis and treatment of disease, and promotes the inclusion of women in medical research studies. Dr. Donnica Moore has been a member of the Society since 1990 and is a past member of its Board of Directors.

For more information on clinical research, click here.

Created: 8/31/2002  -  Sophia Cariati

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