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Pharmacy shelves are full of medications that can be prescribed to men or women. But most people are not aware that all drugs do not work the same for men as they do for women. Some medications need to be prescribed in different doses for different sexes, and some medications that work well for one sex may not work at all for the other.
Pharmacokinetics is the study of how drugs travel into, through, and out of the body. Pharmacodynamics considers what the drug does to the body while it is there. This combination of factors determines how much of a drug is available to the body, how well it will get to the desired location in the body, how effectively it will work, and how long the effects will last. For example, a drug that is injected directly into a blood vessel will become effective in the body much faster than a drug that is swallowed as a pill and must first be digested before it can work.
One of the considerations in both pharmacokinetics and pharmacodynamics is the sex of the patient receiving the drug. For many years, drug testing was conducted only on men. Researchers reasoned that women should not have the risk of drug testing during their childbearing years since men and women are basically the same. Doctors were taught that the only adjustment needed for women vs. men in prescribing drugs was to account for the differences in weight. New research has revealed that men and women can react very differently to medications, beyond the differences caused by body size.
Most medications, whether over-the-counter (OTC) or prescription, are taken by mouth. This means the medication must first be digested by the stomach or intestines before it can enter the blood stream. For example, some drugs including certain antibiotics need stomach acid in order to reach the state where the body can make use of them.
Researchers now know that men tend to have steady levels of stomach acid while acid levels in women are lower much of the month except in the middle of the menstrual cycle. This can affect how well a woman’s stomach can absorb certain medications. Women’s stomachs also tend to empty slower than men’s stomachs, which can cause differences between the sexes in how medications are absorbed.
Another factor in determining drug doses is how long the drug will remain active in the body. Many medications are removed from the blood by the kidneys. The general rule is the kidneys of a person with higher body weight filter faster than those of someone with a lower body weight. So medications generally remain active in a young woman’s bloodstream longer than in a man’s. Pregnancy causes a woman’s kidneys to filter faster, as does age. So a doctor prescribing medication for a woman needs to take all of these factors into consideration to determine the appropriate dose.
The basic lesson doctors are learning is that the sex of the patient is an important consideration when prescribing medications. In some cases, women may need a higher dose of medication than men or women may need different doses depending on the time of month or stage of life.
If you have an unusual reaction to a medication, consider talking to your doctor about how the drug was tested and whether there are differences in reactions for the medication based on the sex of the patient.
Sources:
Legato, Marianne J., M.D. Eve’s Rib New York: Harmony Books, 2002. Print.
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