Doxycycline Injection and Methotrexate: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Doxycycline Injection
Methotrexate
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
Increased methotrexate exposure, an increased risk of methotrexate toxicity, reduced active metabolite formation, possibly reduced methotrexate efficacy and an increased risk of hepatotoxicity
Interaction Deep Dive
Coadministration of methotrexate with a highly protein bound drug like doxycycline may increase methotrexate exposure, which may increase the risk of methotrexate severe adverse reactions. In some cases, the coadministration of methotrexate with doxycycline may also subsequently reduce active metabolite formation, which may reduce the clinical effectiveness of methotrexate. If coadministration cannot be avoided, monitor closely for methotrexate adverse reactions1. A patient with malignant osteogenic sarcoma developed methotrexate-induced gastrointestinal and hematologic toxicities following a course of therapy with high-dose methotrexate and doxycycline, which was being administered for an eye infection. Previous cycles of methotrexate, which did not include doxycycline, had not resulted in toxicities. Possible mechanisms for this interaction include the displacement of methotrexate from its binding to plasma proteins, inhibition of methotrexate metabolism, competition for renal tubular secretion, or the inhibition of renal synthesis of prostaglandins 2.
Why it happens (mechanism)
Reduced methotrexate absorption; displacement of methotrexate from its binding to plasma proteins; decreased enterohepatic recycling; suppression of bacterial metabolism; additive hepatotoxicity
Literature reports
1 report — tap to read
a) A 17-year-old female with osteosarcoma of the left femur had received ten cycles of high-dose methotrexate (12 g/m2). She developed a palpebral abscess in her left eye which was treated with topical tobramycin, chloramphenicol, and hydrocortisone ointment. System therapy with doxycycline 100 mg twice daily was also prescribed. Her eleventh cycle of methotrexate was administered while therapy for her eye abscess continued. Within the first 24 hours following chemotherapy, she developed facial erythema, malaise, and vomiting. None of these problems had occurred during the first ten cycles of methotrexate. Doxycycline therapy was discontinued, but methotrexate hematologic toxicity grade 3 (hemoglobin 7.7 g/dL, white blood cell count 2.7 x 10(3)/mm3, platelets 137 x 10(3)/mm3) was apparent on day 6 following chemotherapy. Pharmacokinetic data revealed that the plasma concentration of methotrexate from 10 minutes to 168 hours following infusion was higher during the eleventh cycle as compared to the first ten cycles. Similarly, the half-life of methotrexate was 2.27 hours and 2.46 hours at 12 hours and 24 hours, respectively, for the first ten cycles, and was 4.67 hours and 5.43 hours, respectively, during the eleventh cycle. The patient's hospital stay was prolonged by eleven days because of the methotrexate toxicity, and 48 hours after discharge she was readmitted for an additional 12 days, which had obvious repercussions on quality of life and associated costs 2.
Common questions
Can I take Doxycycline Injection and Methotrexate together?
Increased methotrexate exposure, an increased risk of methotrexate toxicity, reduced active metabolite formation, possibly reduced methotrexate efficacy and an increased risk of hepatotoxicity Always confirm with your pharmacist or prescriber before making any change.
How serious is the Doxycycline Injection and Methotrexate interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "rapid". Effects can appear quickly, often within about 24 hours of combining the drugs.
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 Doxycycline Injection or Methotrexate 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 a safer alternative to one of these medications for me?
References (2)
Keep reading about Doxycycline Injection
Keep reading about Methotrexate
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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