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May 2012

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Do Men and Women Process Drugs Differently?

There are some PK differences in men and women. At the same doses, some women have higher levels of certain drugs in their bloodstreams and experience more side effects than men. Despite the differences, women seem to benefit as much from HIV therapy as men.

These PK sex differences (male vs. female) may be related to hormone changes that occur when women get their periods. PK differences also may be linked to basic biology and physiology of cells (there are differences in the cells of men and women). They may also be linked to weight differences or differences in body composition (amount of fat vs. lean muscle).

Standard doses of drugs are usually based upon research done predominantly in men. This means a woman, who generally weighs less than a man, may get a higher amount of the drug in her body than is needed to be effective. Although differences between men and women have been seen in studies, no changes to dosing have been recommended for women. However, a few HIV drugs are given at lower doses if your weight is below a certain cut-off (e.g., Sustiva).

If you are experiencing side effects, ask your health care provider for help. Do not change your dose or stop your drugs without speaking to your provider.

Other factors can also affect PK, including:

  • Genetic differences in drug processing
  • Food
  • Tobacco and alcohol use
  • Medication interactions
  • Race/ethnicity
  • Hepatitis or other liver problems

Pharmacokinetic Testing


Because of PK differences, new tests are being developed to help figure out if patients are receiving the right amount of drug.

Therapeutic Drug Monitoring (TDM): TDM is designed to measure your drug levels specifically. Basically it measures minimum concentration (Cmin) by drawing blood before morning meds. This can help your health care provider decide if the dose of your HIV drugs should be changed. TDM is expensive and is most often used in research studies. It may or may not be available in your health care provider's office.

Inhibitory Quotient (IQ): The IQ of a drug shows how much drug is necessary to control the virus effectively. The IQ is different for each drug. This concept is still being proven.

How to Make PK Work for You

The timing of medication doses has been carefully calculated to keep the drug in your bloodstream at levels that will control HIV. When you do not take a dose on time, the blood level of the drug will fall too low to be effective.

When this happens, HIV has a chance to make more copies of itself, which causes your viral load to go up. Having too little of an HIV drug in your blood also makes it easier for HIV to become resistant to the drug you are taking, causing it to stop working. Consequently, your viral load could go up, your CD4 cells could go down, and you might need to change drug treatments. The best way to avoid this is to take your HIV drugs the way they are prescribed. This maintains the blood level of the drugs necessary to fight the virus effectively.

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This article was provided by The Well Project. Visit The Well Project's Web site to learn more about their resources and initiatives for women living with HIV. The Well Project shares its content with to ensure all people have access to the highest quality treatment information available. The Well Project receives no advertising revenue from or the advertisers on this site. No advertiser on this site has any editorial input into The Well Project's content.
See Also
More on HIV Drug-Drug Interactions

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