Metronidazole with Phenobarbital Interaction Details
Brand Names Associated with Metronidazole
- Flagyl®
- Flagyl® 375
- Flagyl® ER
- Metronidazole
Brand Names Associated with Phenobarbital
- Phenobarbital
Medical Content Editor Dr. Brian Staiger, PharmD
Last updated
Jan 04, 2024
Interaction Effect
An increased risk of QT interval prolongation, reduced metroNIDAZOLE exposure and reduced metroNIDAZOLE efficacy
Interaction Summary
Concomitant PHENobarbital and metroNIDAZOLE therapy may result in enhanced metroNIDAZOLE hydroxylation and metabolism producing a shorter metroNIDAZOLE half-life resulting in reduced metroNIDAZOLE plasma levels . Also, avoid the concomitant use of PHENobarbital with other products with a known potential to prolong the QTc interval or products that may increase concentrations of PHENobarbital. PHENobarbital causes QTc interval prolongation. Concomitant use of PHENobarbital with other products that prolong the QTc interval like metroNIDAZOLE may result in a greater increase in the QTc interval and adverse reactions associated with QTc interval prolongation. If concomitant use of metroNIDAZOLE and PHENobarbital is unavoidable, monitor patients for increased risk of QTc interval prolongation .
Severity
Major
Onset
Delayed
Evidence
Probable
How To Manage Interaction
Concomitant PHENobarbital and metroNIDAZOLE therapy may result in enhanced metroNIDAZOLE hydroxylation and metabolism producing a shorter metroNIDAZOLE half-life, resulting in reduced metroNIDAZOLE plasma levels . Also, avoid the concomitant use of PHENobarbital with other products with a known potential to prolong the QTc interval or products that may increase concentrations of PHENobarbital. PHENobarbital causes QTc interval prolongation. Concomitant use of PHENobarbital with other products that prolong the QTc interval like metroNIDAZOLE may result in a greater increase in the QTc interval and adverse reactions associated with QTc interval prolongation. If concomitant use of metroNIDAZOLE and PHENobarbital is unavoidable, monitor patients for increased risk of QTc interval prolongation .
Mechanism Of Interaction
Additive QT interval prolongation; increased hepatic metabolism
Literature Reports
A) In a case study with six Crohn's disease patients, the concurrent use of metroNIDAZOLE and PHENobarbital resulted in decreased half-life (9.7 hr vs 7.5 hr) and AUC (79 vs 56 mg/L/hr) .
B) This is also demonstrated in a young female with recurrent episodes of vaginal trichomoniasis. Although the patient responded to metroNIDAZOLE therapy, symptomatic and microbiologic relapses occurred almost immediately following therapy withdrawal. The patient was also taking PHENobarbital (100 mg daily), a known stimulator of microsomal enzymes. The pharmacokinetics of metroNIDAZOLE were studied in this patient. The half-life (3.5 hours) was significantly reduced from normal (8 to 9 hours), and the hydroxy metabolite was present in higher than normal amounts. It was therefore concluded that PHENobarbital was inducing metroNIDAZOLE hydroxylation and the patient required twice the standard oral dose of metroNIDAZOLE (500 mg three times daily for seven days) to eradicate the organism .
C) A study provides further evidence that PHENobarbital can significantly increase the metabolism of metroNIDAZOLE, thus reducing the drug's half-life. It is reported that complete cure in children with epilepsy treated with PHENobarbital and giardiasis occurred only when three times the recommended dosage of metroNIDAZOLE was administered. Upward dosage adjustments are indicated in children receiving PHENobarbital who are treated with metroNIDAZOLE for giardiasis .
Metronidazole Overview
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Metronidazole capsules and tablets are used to treat infections of the reproductive system, gastrointestinal (GI) tract, skin, heart, bone, joint, lung, blood, nervous system, and other areas of the body. Metronidazole capsules and tablets are also used to treat sexually transmitted diseases (STDs). Metronidazole extended-release (long-acting) tablets are used to treat bacterial vaginosis (an infection caused by too much of certain types of harmful bacteria in the vagina) in women. Metronidazole is in a class of medications called nitroimidazole antimicrobials. It works by stopping the growth of bacteria.
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Antibiotics will not work for colds, flu, or other viral infections. Using antibiotics when they are not needed increases your risk of getting an infection later that resists antibiotic treatment.
Phenobarbital Overview
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Phenobarbital is used to control seizures. Phenobarbital is also used to relieve anxiety. It is also used to prevent withdrawal symptoms in people who are dependent ('addicted'; feel a need to continue taking the medication) on another barbiturate medication and are going to stop taking the medication. Phenobarbital is in a class of medications called barbiturates. It works by slowing activity in the brain.
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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.