Trospium / Xanomeline and Meperidine: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 2, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Meperidine
Trospium / Xanomeline
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.
Here's the concern: Meperidine (Demerol) is an opioid pain medicine, and Cobenfy contains trospium, which has anticholinergic effects. Both of these can slow down your gut and make it harder to empty your bladder. When you take them together, those effects can add up.
That means you could have more constipation or trouble urinating than with either drug alone. In rare cases, very slow gut movement can become a serious blockage. The good news is this is a theoretical risk, and your care team can keep an eye on things. Just let your pharmacist or doctor know you take both, and speak up if you notice constipation or difficulty peeing.
Interaction: Additive antimotility/antimuscarinic effects. Meperidine (opioid) plus trospium (a muscarinic antagonist within Cobenfy) can compound reduced GI motility and detrusor relaxation.
- Direction/effect: Increased risk of urinary retention and/or severe constipation, potentially progressing to paralytic ileus.
- Mechanism: Pharmacodynamic additive reduction in gastric/GI motility (not a metabolic prodrug interaction).
- Evidence: Theoretical; severity major; onset unspecified.
- Management: Monitor for signs of urinary retention and reduced gastric motility (abdominal distension, absent bowel sounds, decreased stool output). Individualize therapy and consider prophylactic bowel regimen where appropriate.
What happens
Increased risk of urinary retention and/or severe constipation leading to paralytic ileus
Interaction Deep Dive
Taking meperidine together with anticholinergics can heighten the likelihood of urinary retention and/or severe constipation, potentially progressing to paralytic ileus. When these agents are administered alongside meperidine, patients should be watched for indications of urinary retention or diminished gastric motility1.
Why it happens (mechanism)
Reduced gastric motility
How to manage this interaction
If both medicines are prescribed, keep taking them as directed unless your prescriber tells you otherwise. Your care team can manage this by watching you more closely.
- Watch for constipation, belly bloating or cramping, and any trouble passing urine.
- Tell your care team right away about severe or worsening constipation, no bowel movements, or an inability to urinate.
- Your team may suggest steps to keep your bowels moving and may adjust your treatment, individualized to you, if problems appear.
Bring up any concerns with your pharmacist or doctor so they can tailor monitoring to your situation.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Trospium / Xanomeline and Meperidine together?
Taking meperidine (Demerol) with Cobenfy (trospium) can add up to more constipation and trouble urinating, so watch for those symptoms and report them to your care team. This is a theoretical but potentially serious risk that your team can monitor and manage. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Trospium / Xanomeline and Meperidine interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Trospium / Xanomeline and Meperidine interaction managed?
If both medicines are prescribed, keep taking them as directed unless your prescriber tells you otherwise. Your care team can manage this by watching you more closely. Watch for constipation, belly bloating or cramping, and any trouble passing urine. Tell your care team right away about severe or worsening constipation, no bowel movements, or an inability to urinate. Your team may suggest steps to… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
Questions for your pharmacist
- Does my dose of Trospium / Xanomeline or Meperidine 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 (1)
- Product Information: MEPERGAN intramuscular, intravenous injection, meperidine HCl, promethazine HCl intramuscular, intravenous injection. West-Ward Pharmaceuticals Corp (per FDA), Eatontown, NJ, 2023.
Keep reading about Meperidine
Keep reading about Trospium / Xanomeline
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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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