Question Regarding Doxycycline - Magnesium Interaction
In our latest question and answer, the pharmacist discusses the interaction between magnesium and doxycycline.
Why not use magnesium with doxycycline treatment for bacterial infections?
May 31, 2024- Magnesium can bind to doxycycline in your stomach and prevent it from being absorbed into your bloodstream, which may reduce how well the antibiotic works.
- To avoid this interaction, take doxycycline at least one hour before or two hours after taking magnesium supplements.
Answer
Thanks for your question!
I assume you are referring to our herbal-drug interaction checker when you ask why no interaction is showing between magnesium and doxycycline. I double-checked, and our checker does show an interaction. It states:
Magnesium decreases the absorption of tetracyclines. Magnesium can form insoluble complexes with tetracyclines in the gut and decrease their absorption and antibacterial activity. Advise patients to take these drugs 1 hour before or 2 hours after magnesium supplements.
If you are seeing conflicting information anywhere, please let us know so we can look into it.
More Discussion on Interaction
Although studies vary on just how much magnesium can affect tetracycline absorption (doxycycline is considered a tetracycline), it is well known that it can have an impact. The mechanism behind this is that tetracycline drugs bind to magnesium ions in the gastrointestinal tract, forming a complex that cannot be absorbed into your system.
Again, the results of studies vary, but one study showed that when tetracycline (250 mg) was taken together with 30 mL of aluminum-magnesium hydroxide gel, its oral bioavailability (rate and extent of absorption) dropped by 90%. This decrease in bioavailability could significantly affect how effective the antibiotic is in treating an infection.
To avoid this interaction, be sure to separate the administration of magnesium-containing products with tetracycline drugs by at least a few hours.
Final Words
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References & sources
- Effect of cimetidine and antacids on gastrointestinal absorption of tetracycline — PubMed
Glossary — Terms in This Answer
- Tetracyclines
- A class of antibiotic drugs that includes doxycycline, used to treat bacterial infections.
- Absorption
- The process by which a drug passes from the digestive system into the bloodstream.
- Insoluble complexes
- Chemical combinations that cannot dissolve and be absorbed by the body.
- Gastrointestinal tract
- The digestive system, including the stomach and intestines where drugs are processed.
- Bioavailability
- The amount and rate at which a drug enters the bloodstream and becomes available to affect the body.
- Antibacterial activity
- The ability of a drug to kill or stop the growth of bacteria.
- Aluminum-magnesium hydroxide gel
- An antacid medication that contains both aluminum and magnesium compounds used to treat heartburn.
Dr. Brian Staiger, PharmD
Doctor of Pharmacy, board certified clinical pharmacist (BCPS), American Herbalist Guild, Medication Therapy Management certified
Brian Staiger, PharmD, BCPS, is a licensed pharmacist with more than 13 years of experience across retail pharmacy, clinical pharmacy, medication safety, pharmacy program development, and healthcare administration. He is the founder of HelloPharmacist.com, where he helps patients...
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