Estrogen dosing with oral contraceptives can be a challenging issue that may feel overwhelming to many clinicians. The most common synthetic estrogen analog is ethinyl estradiol. In this article, I’ll discuss the reasons why we might select one dose of estrogen over another.
Ethinyl estradiol dosing in oral contraceptives can vary significantly. The usual dose range is between 10 mcg per day up to 50 mcg per day. 10 mcg is classified as the lowest dose of estrogen while 50 mcg and above is noted as a high dose. In practice, it is most common to see dosages of ethinyl estradiol somewhere in the 20-35 mcg per day range.
Our friends at Pyrls.com have put together a really nice list of all the oral contraceptive products and list their estrogen components. Simply creating a free account will get you access to this resource at no cost to you! Please take advantage of this free resource!
Why Use A Different Dose of Estrogen?
Naturally, one might question why would we use a different dose of estrogen? Wouldn’t a clinician want to use the minimum effective dose? Do we use a higher dose for improved efficacy at preventing pregnancy?
Interestingly, efficacy rates in preventing pregnancy are very similar between ultra-low dosages and high doses of ethinyl estradiol in combined oral contraceptives. Keep in mind that the progesterone component can vary in each commercially made product and obviously plays a role in preventing ovulation and pregnancy.
If efficacy rates are comparable between lower and higher dosage combinations, why wouldn’t we always use very low dosages? Breakthrough bleeding is one of the most troublesome and common issues as we drop the dose of estrogen while keeping the progesterone dosing consistent. In addition to the frustration of breakthrough bleeding, excessive bleeding during menses can ultimately increase the risk for anemia.
On the flip side, as we increase the dose of ethinyl estradiol, we can increase the risk of GI upset and cause symptoms of nausea and vomiting. These issues of breakthrough bleeding and GI adverse effects are the two most common reasons why we might alter the dose of estrogen.
Other Estrogen Adverse Effects To Consider
The risk for DVT/PE and clot formation also has to be considered when using oral contraceptives containing estrogen. The risk for complicating certain cancers also exists with estrogen. Recall that patients with certain risk factors should generally avoid the use of combined oral contraceptives (NOTE: FREQUENT BOARD EXAM QUESTION!). Some of those risk factors include:
- Smokers 35 years of age and over
- Blood clot risk factors
- Breast Cancer
- Liver disease
- Uncontrolled hypertension
- Certain cardiovascular conditions
- Migraine with aura
For a complete list of medical issues that should be considered with the use of oral contraceptives, the CDC has a chart available on this topic which you can find here.
Estrogen dosing with oral contraceptives is not an exact science and will vary from patient to patient. Understanding the risks of higher dosages versus lower dosages will help you better find the ideal dose of estrogen for your patient. If you are looking for more on oral contraceptives, be sure to check out this post on drug interactions!
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