Estradiol with Fosamprenavir Interaction Details

Brand Names Associated with Estradiol

Brand Names Associated with Fosamprenavir

Medical Content Editor Dr. Brian Staiger, PharmD
Last updated Nov 13, 2023

Interaction Effect

Reduced amprenavir exposure, altered hormonal levels, loss of contraceptive efficacy, and an increased risk of liver enzyme elevations

Interaction Summary

A loss of virologic response and possible resistance to amprenavir may occur when hormonal contraceptives (containing ethinyl estradiol/norethindrone) are used concomitantly. Fosamprenavir is the prodrug of amprenavir. Reduced exposure to amprenavir and altered hormonal levels occurred when combined oral contraceptives (containing ethinyl estradiol/norethindrone) were used concomitantly with amprenavir . Coadministration of ethinyl estradiol/norethindrone and fosamprenavir/ritonavir has resulted in significant decreases in ethinyl estradiol and norethindrone levels  and may also result in hepatic transaminase elevations. Therefore, patients receiving oral contraceptives should be instructed to use alternative methods of non-hormonal contraception .

Severity

Major

Onset

Unspecified

Evidence

Established

How To Manage Interaction

A loss of virologic response and possible resistance to amprenavir may occur when hormonal contraceptives (containing ethinyl estradiol/norethindrone) are used concomitantly. Concomitant administration of amprenavir, the active metabolite of fosamprenavir, and oral contraceptives (containing ethinyl estradiol/norethindrone) has resulted in decreased amprenavir concentrations and altered hormonal levels . Additionally, coadministration of fosamprenavir with ritonavir, and oral contraceptives has resulted in significant decreases in ethinyl estradiol and norethindrone levels  and may result in hepatic transaminase elevations. Alternative methods of non-hormonal contraception are recommended in patients receiving fosamprenavir with or without ritonavir .

Mechanism Of Interaction

Unknown

Literature Reports

A) Concomitant administration of ethinyl estradiol 0.035 mg/norethindrone 0.5 mg once daily for 21 days and fosamprenavir 700 mg/ritonavir 100 mg twice daily for 21 days in 25 patients resulted in decreases (90% confidence interval) of 34% (30% to 37% decrease), 38% (32% to 44% decrease), and 26% (20% to 32% decrease) in norethindrone AUC, Cmax, and Cmin, respectively. The corresponding decreases in ethinyl estradiol were 37% (30% to 42% decrease), 28% (21% to 35% decrease), and minimal or no change, respectively. No change was noted in amprenavir pharmacokinetics .

B) Concomitant administration of ethinyl estradiol 0.035 mg/norethindrone 1 mg for one cycle and amprenavir 1200 mg twice daily for 28 days in 10 patients resulted in a decrease in AUC (90% confidence interval (CI)) by 22% (8% to 35% decrease) and a decrease minimum plasma concentration (Cmin) (90% CI) by 20% (41% decrease to a 8% increase) of amprenavir. No change was noted in the Cmax of amprenavir. No change was noted in the Cmax or AUC of ethinyl estradiol, but the Cmin increased 32% (3% decrease to 79% increase). No change was noted in the Cmax of norethindrone, but the AUC increased 18% (1% to 38% increase) and the Cmin increased 45% (13% to 88% increase) .

Estradiol Overview

• Estrogen is used to treat hot flushes ('hot flashes'; sudden strong feelings of heat and sweating) in women who are experiencing menopause ('change of life', the end of monthly menstrual periods). Some brands of estrogen are also used to treat vaginal dryness, itching, or burning, or to prevent osteoporosis (a condition in which the bones become thin and weak and break easily) in women who are experiencing or have experienced menopause. However, women who need a medication only to treat vaginal dryness or only to prevent osteoporosis should consider a different treatment. Some brands of estrogen are also to relieve symptoms of low estrogen in young women who do not produce enough estrogen naturally. Some brands of estrogen are also used to relieve the symptoms of certain types of breast and prostate (a male reproductive gland) cancer. Estrogen is in a class of medications called hormones. It works by replacing estrogen that is normally produced by the body.

Fosamprenavir Overview

• Fosamprenavir is used along with other medications to treat human immunodeficiency virus (HIV) infection. Fosamprenavir is in a class of medications called protease inhibitors. It works by decreasing the amount of HIV in the blood. Although fosamprenavir does not cure HIV, it may decrease your chance of developing acquired immunodeficiency syndrome (AIDS) and HIV-related illnesses such as serious infections or cancer. Taking these medications along with practicing safer sex and making other life-style changes may decrease the risk of transmitting the HIV virus to other people.

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Definitions

Severity Categories

Contraindicated

These drugs, generally, should not be used together simultaneously due to the high risk of severe adverse effects. Combining these medications can lead to dangerous health outcomes and should be strictly avoided unless otherwise instructed by your provider.

Major

This interaction could result in very serious and potentially life-threatening consequences. If you are taking this drug combination, it is very important to be under close medical supervision to minimize severe side effects and ensure your safety. It may be necessary to change a medication or dosage to prevent harm.

Moderate

This interaction has the potential to worsen your medical condition or alter the effectiveness of your treatment. It's important that you are monitored closely and you potentially may need to make adjustments in your treatment plan or drug dosage to maintain optimal health.

Minor

While this interaction is unlikely to cause significant problems, it could intensify side effects or reduce the effectiveness of one or both medications. Monitoring for changes in symptoms and your condition is recommended, and adjustments may be made if needed to manage any increased or more pronounced side effects.

Onset

Rapid: Onset of drug interaction typically occurs within 24 hours of co-administration.

Delayed: Onset of drug interaction typically occurs more than 24 hours after co-administration.

Evidence

Level of documentation of the interaction.

Established: The interaction is documented and substantiated in peer-reviewed medical literature.

Theoretical: This interaction is not fully supported by current medical evidence or well-documented sources, but it is based on known drug mechanisms, drug effects, and other relevant information.

How To Manage The Interaction

Provides a detailed discussion on how patients and clinicians can approach the identified drug interaction as well as offers guidance on what to expect and strategies to potentially mitigate the effects of the interaction. This may include recommendations on adjusting medication dosages, altering the timing of drug administration, or closely monitoring for specific symptoms.

It's important to note that all medical situations are unique, and management approaches should be tailored to individual circumstances. Patients should always consult their healthcare provider for personalized advice and guidance on managing drug interactions effectively.

Mechanism Of Interaction

The theorized or clinically determined reason (i.e., mechanism) why the drug-drug interaction occurs.

Disclaimer: The information provided on this page is for informational purposes only and should not be considered medical advice. Always consult with a qualified healthcare professional regarding your specific circumstances and medical conditions.

Where Does Our Information Come From?

Information for our drug interactions is compiled from several drug compendia, including:

• Gold Standard Drug Database
• Micromedex
• Lexicomp
• DrugBank

The prescribing information for each drug, as published on DailyMED, is also used. 

Individual drug-drug interaction detail pages contain references specific to that interaction. You can click on the reference number within brackets '[]' to see what reference was utilized.

The information posted is fact-checked by HelloPharmacist clinicians and reviewed quarterly.