Azithromycin and Aluminum Phosphate: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Jul 11, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Azithromycin
Aluminum Phosphate
No brand names on record
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Reduced azithromycin exposure
Interaction Deep Dive
In a study of 10 healthy males, concomitant use of azithromycin regular-release capsules and an oral antacid suspension containing aluminum hydroxide and magnesium hydroxide resulted in the azithromycin Cmax being reduced by 24% compared with azithromycin alone; however, azithromycin AUC and Tmax were not affected3. Therefore, the manufacturer recommends that regular-release azithromycin and products that contain aluminum or magnesium not be coadministered 2. When azithromycin extended-release oral suspension was coadministered with aluminum- and magnesium-containing antacid, there were no changes in azithromycin Cmax or AUC. Therefore, extended-release azithromycin and aluminum- and magnesium-containing antacids may be used concomitantly 1.
Why it happens (mechanism)
Reduced azithromycin absorption due to chelation
Literature reports
2 reports — tap to read
a) Concomitant use of antacids and azithromycin regular-release capsules resulted in decreased azithromycin Cmax values compared with those seen with azithromycin alone in an open, randomized, crossover trial of 10 healthy males; however, azithromycin AUC and Tmax were unaffected. Five participants were randomized to receive azithromycin 500 mg (two 250-mg capsules) alone on day 1 and to receive azithromycin at the same dose plus a 30-mL dose of antacid (Maalox(R), aluminum hydroxide 225 mg/magnesium hydroxide 200 mg per 5 mL) on day 8. The other 5 participants received the same regimen, but in the reverse order. The mean azithromycin Cmax decreased by approximately 24% from 0.34 mcg/mL (0.45 mcmol/L) with azithromycin monotherapy to 0.26 mcg/mL (0.35 mcmol/L) when azithromycin was coadministered with the antacid. There was no effect on azithromycin AUC or Tmax 3.
b) In a study (n=39), coadministration of a single 2 g dose azithromycin extended-release oral suspension with a single 20 mL dose of an aluminum- and magnesium hydroxide-containing antacid did not affect azithromycin mean Cmax (ratio (with/without coadministered drug), 0.99; 90% confidence interval (CI), 0.93 to 1.06) and mean AUC (ratio, 0.99; 90% CI, 0.92 to 1.08) 1.
Common questions
Can I take Azithromycin and Aluminum Phosphate together?
Reduced azithromycin exposure Always confirm with your pharmacist or prescriber before making any change.
How serious is the Azithromycin and Aluminum Phosphate interaction?
It is rated minor. Usually limited clinical impact.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Azithromycin or Aluminum Phosphate need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there anything you'd monitor while I'm on both?
References (3)
- Product Information: ZMAX(R) oral extended-release suspension, azithromycin oral extended-release suspension. Pfizer Inc (per FDA), New York, NY, 2021. DailyMed
- Product Information: ZITHROMAX(R) oral tablets, oral suspension, azithromycin oral tablets, oral suspension. Pfizer Labs (per FDA), New York, NY, 2017. DailyMed
- Foulds G, Hilligoss DM, Henry EB, et al: The effects of an antacid or cimetidine on the serum concentrations of azithromycin. J Clin Pharmacol 1991; 31:164-7. PubMed
Keep reading about Azithromycin
Keep reading about Aluminum Phosphate
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