Drug Interaction Report

Bismuth Subsalicylate and Doxycycline Injection: Interaction Details

A pharmacist-reviewed analysis of the Bismuth Subsalicylate and Doxycycline Injection interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Doxycycline Injection

Acticlate Adoxa Alodox Avidoxy Doryx Doxy Doxy 100® Doxy 200®
+

Bismuth Subsalicylate

Bismarex Bismusal Bismusal® Estomaquil Kaopectate Reformulated Aug 2006 Kaopectate® Peptic Relief® Pepto-bismol
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Aug 8, 2026
Editorial policy · Data sources
LinkedIn
Interaction severity
Moderate
Can be significant — usually manageable with monitoring.
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.

Of 24 documented Bismuth Subsalicylate interactions, 9 are rated moderate — including this one.
Onset
delayed
Evidence
probable
Severity
Moderate

What happens

Reduced doxycycline efficacy

Interaction Deep Dive

Concurrent use of doxycycline and bismuth subsalicylate may reduce efficacy of doxycycline, as absorption of tetracyclines is impaired by bismuth subsalicylate1. The concurrent use of a tetracycline and bismuth subsalicylate may result in a 30% to 50% decrease in the absorption of the tetracycline 23.

Why it happens (mechanism)

Reduced doxycycline absorption

Literature reports

2 reports — tap to read

a) One study evaluated the effect of bismuth subsalicylate on the absorption of doxycycline. Six patients received the following regimens with a two-week washout period separating each course: doxycycline 200 mg with or without bismuth subsalicylate 60 mL; bismuth subsalicylate administered 2 hours before or 2 hours after doxycycline 200 mg; multi-dose regimen of bismuth subsalicylate every 6 hours for 5 doses followed immediately by one dose of doxycycline 200 mg. Bismuth subsalicylate 60 mL significantly reduced peak serum concentrations of doxycycline when administered simultaneously, 2 hours before doxycycline, and with the multi-dose regimen. The bioavailability of doxycycline measured by area under the curve was similarly reduced 37% and 51%, respectively, with the concomitant administration of both preparations and the multi-dose regimen of bismuth subsalicylate 2.

b) The concurrent use of a tetracycline and bismuth subsalicylate may result in a 30% to 50% decrease in the absorption of the tetracycline 23.

Common questions

Can I take Bismuth Subsalicylate and Doxycycline Injection together?

Reduced doxycycline efficacy Always confirm with your pharmacist or prescriber before making any change.

How serious is the Bismuth Subsalicylate and Doxycycline Injection interaction?

It is rated moderate. Can be significant — usually manageable with monitoring.

How quickly could this interaction happen?

The documented onset is "delayed". Effects tend to build up gradually over days to weeks.

How strong is the evidence for this interaction?

The evidence is graded "probable". Good supporting evidence, though not definitively proven.

Questions for your pharmacist

  • Does my dose of Bismuth Subsalicylate or Doxycycline Injection 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)

  1. Product Information: ORACEA(R) oral capsules, doxycycline oral capsules. Galderma Laboratories, L.P. (per DailyMed), Dallas, TX, 2025. DailyMed
  2. Ericsson CD, Feldman S, Pickering LK, et al: Influence of subsalicylate bismuth on absorption of doxycycline. JAMA 1982; 247:2266-2267. DOI
  3. Albert KS, Welch RD, DeSante KA, et al: Decreased tetracycline bioavailability caused by a bismuth subsalicylate antidiarrheal mixture. J Pharm Sci 1979; 68:586-588. PubMed
Was this write-up helpful?
Doxycycline Injection

Keep reading about Doxycycline Injection

All Doxycycline Injection interactions (118) Doxycycline Injection drug information
Also serious with: Acitretin Acenocoumarol Amobarbital Amoxicillin
Bismuth Subsalicylate

Keep reading about Bismuth Subsalicylate

All Bismuth Subsalicylate interactions (24) Bismuth Subsalicylate drug information
Also serious with: Bromfenac Ophthalmic Etodolac Mesalamine Rectal Mesalamine

Check another combination

Our instant two-drug interaction checker is almost here.

Coming soon

The instant two-drug checker is on its way.

In the meantime, browse the directory below to look up any drug and see its documented interactions.

Still have questions about this combination?

Every question gets a real answer from a licensed pharmacist — free, and usually within a day.

Ask the pharmacist
This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.