Methadone with Fosamprenavir Interaction Details
Brand Names Associated with Methadone
- Diskets®
- Dolophine®
- Methadone
- Methadose®
- Methadose® Oral Concentrate
- Westadone®
Brand Names Associated with Fosamprenavir
- Fosamprenavir
- Lexiva®
Medical Content Editor Dr. Brian Staiger, PharmD
Last updated
Jan 02, 2024
Interaction Effect
Decreased methadone plasma levels
Interaction Summary
Fosamprenavir is a prodrug of amprenavir and shares many of the same drug interactions, including a potential interaction with methadone. Methadone plasma concentrations may be decreased when fosamprenavir and methadone are taken together due to induction of CYP3A4-mediated methadone metabolism and/or protein-binding displacement. Based on clinical data though, it appears that the interaction may not be clinically relevant. If fosamprenavir and methadone are coadministered, patients should be monitored for symptoms of opioid withdrawal .
Severity
Moderate
Onset
Delayed
Evidence
Established
How To Manage Interaction
If fosamprenavir and methadone are used concurrently, monitor patients for opiate withdrawal symptoms due the possibility of decreased methadone plasma concentrations.
Mechanism Of Interaction
Induction of CYP3A4-mediated methadone metabolism; protein binding displacement
Literature Reports
A) In a study of 19 patients treated with methadone 70 to 120 mg once daily and fosamprenavir 700 mg/ritonavir 100 mg twice daily for 2 weeks, there were no changes in Cmax, AUC, or Cmin of amprenavir compared with historical controls. While the Cmax, AUC, and Cmin values of the active isomer, R-methadone, decreased by 21% (90% confidence intervals (CI), 30% decrease to 12% decrease), 18% (90% CI, 27% decrease to 8% decrease), and 11% (90% CI, 21% decrease to 1% increase), respectively, the Cmax, AUC, and Cmin of the inactive isomer, S-methadone, decreased by 43% (90% CI, 49% decrease to 37% decrease), 43% (90% CI, 50% decrease to 36% decrease), and 41% (90% CI, 49% decrease to 31% decrease), respectively .
B) In a prospective, open-label, pharmacokinetic study involving 19 opioid-dependent, methadone-maintained healthy subjects, methadone, 44 mg to 100 mg daily, was given for more than 30 days. On study day 1, patients were treated with their usual daily methadone dose. On study days 2 through 11, amprenavir 1200 mg twice daily was given in addition to the usual methadone dose. The Cmax, AUC, and Cmin values of the active metabolite, R-methadone, decreased by 25%, 13%, and 21%, respectively. The Cmax, AUC, and Cmin of the inactive metabolite, S-methadone, decreased 48%, 40%, and 52%, respectively. Compared with the amprenavir levels from a historical control group of 38 healthy men, the methadone plus amprenavir group had decreases of 30%, 27%, and 25% in serum amprenavir AUC, Cmax, and Cmin, respectively. The opioid pharmacodynamics effects did not change significantly. Additionally, there were no signs of opioid withdrawal and methadone dose adjustments were not necessary .
Methadone Overview
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Methadone is used to relieve severe pain in people who are expected to need pain medication around the clock for a long time and who cannot be treated with other medications. It also is used to prevent withdrawal symptoms in patients who were addicted to opiate drugs and are enrolled in treatment programs in order to stop taking or continue not taking the drugs. Methadone is in a class of medications called opiate (narcotic) analgesics. Methadone works to treat pain by changing the way the brain and nervous system respond to pain. It works to treat people who were addicted to opiate drugs by producing similar effects and preventing withdrawal symptoms in people who have stopped using these drugs.
Fosamprenavir Overview
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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:
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.