Why it’s important to understand that prescription drugs aren’t one-size-fits-all

April 28, 2015 in Personalized Healthcare  •  By Miles Varn

A man and a woman each visit their doctor and leave with a prescription for the tricyclic antidepressant Elavil. The prescriptions are for the same dosage of the drug, but what many people don’t know is that the drug may not work as well for the female patient as the male. This is one of many drugs that affect men and women differently, and sometimes those differences can have serious health effects.

One of the better known cases of this gender difference in how drugs work centers on the sleeping pill Ambien. Two years ago, the FDA lowered the dosage of Ambien for women by half because during the process of evaluating a new shorter-acting sleep aid with the same active ingredient, zolpidem, they discovered that men metabolized the drug much faster. Ten to 15 percent of the women studied had a level of the drug that could impair their ability to drive still in their bloodstream after eight hours. Only three percent of the men studied had a blood level that could impair them behind the wheel.

How does gender affect drug metabolism?

While the difference between the physical size and weight of average men and women has some effect on how certain medications are metabolized, researchers have found that there are other important factors at play. Women have a higher percentage of body fat than men. Many drugs are attracted to fat cells and remain in those cells and active in the body for longer periods than water-based drugs that are metabolized in the bloodstream.

Other biological differences that affect drug metabolism in women include:

  • the slower movement of women’s gastrointestinal tracts and slower filtration by the kidneys, which means drugs clear the body more slowly than in men
  • low estrogen levels that occur during the menstrual cycle, while using oral contraceptives or hormone replacement therapy, and menopause, which have been linked by some studies to a need for higher doses of angiotensin receptor blockers used to lower blood pressure
  • less activity by enzymes in the intestines, which means drugs are dissolved and excreted more slowly

What the drug gender gap means for you

For years, women were not permitted to participate in drug trials and the number of female trial participants is still lower than male for many drugs. That means that much of the data collected on these medications is based on observations of how they work in men only. As researchers begin to include more women in drug trials, they continue to find more medications that affect women differently than men. Some of these effects can be serious, for example, women who take digoxin for treatment of heart failure have an increased risk of mortality and require a lower dosage.

Other medications that act differently in men and women include:

  • beta blockers, which have an enhanced effect on lowering blood pressure and heart rate in women when exercising
  • anti-anxiety medications, which dissolve more slowly because women’s stomachs are less acidic can cause the drug’s effects to be felt more quickly and powerfully
  • anti-convulsants, which are metabolized faster due to higher levels of certain liver enzymes in young women and may be less effective for these patients
  • opioid pain killers, which are more effective in women and some studies have found that if women become addicted, they are more likely to relapse, especially during periods of hormonal fluctuation
  • aspirin for heart attack prevention, which has been found not to be effective for prevention of a second heart attack in women at the dosage that’s effective for men
  • the blood thinner warfarin, which studies have shown that women need 2.5 to 4.5 mg less a week than men to achieve the same effect

A personalized approach to healthcare is one important way that you can protect yourself against medication errors and adverse effects and ensure that you receive the most appropriate care tailored to your individual needs. You should also keep the lines of communication open with your doctor. Ask about potential side effects and interactions of prescribed medications and share any adverse reactions you’ve had to medications in the past.