“A study investigated the efficacy of a new contraceptive patch. The patch has a surface area of 20 cm². It delivers 150 μg/dose of norelgestromin and 20 μg/dose of ethinyl estradiol. Norelgestromin is a form of progestin, a synthetic molecule with effects similar to progesterone. Physician’s recommend that one patch be applied weekly for three weeks, followed by one patch-free week.

One thing that differentiates a patch from oral contraceptives is the patient’s ability to administer the patch via different locations. To examine this, researchers had randomly assigned participants to wear the patch for one week in one of four locations (abdomen, arm, buttock and torso. Blood samples were used to measure the concentrations of norelgestromin and ethinyl estradiol. The data for ethinyl estradiol is displayed below. The dotted lines represent the reference range. It is based on oral contraceptives.

Figure 1. Mean contraception concentrations in various body locations over time.

In the review of the patch’s efficacy, it was tested for drug interactions. Specifically, researchers were concerned that tetracycline might prove to reduce the effectiveness of the patch. Researchers performed an experiment to analyze the patch’s ability to pass on norelgestromin and ethinyl estradiol in the presence of tetracycline. A patch-only condition was used as a control. The results for norelgestromin are shown below.

Figure 2. Mean norelgestronin concentration in patch vs. patch + tetracycline over time.

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