Ketoconazole Topical and Praziquantel: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Ketoconazole Topical
Praziquantel
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 praziquantel exposure
Interaction Deep Dive
Concomitant administration of praziquantel with drugs that decrease the activity of drug metabolizing liver enzymes (CYP450 inhibitors) such as ketoconazole may increase praziquantel exposure2. Caution is advised if ketoconazole (CYP3A4 inhibitor) and praziquantel (CYP3A4 substrate) are coadministered. Upon coadministration, closely monitor patients for signs or symptoms of increased or prolonged effects or side effects of praziquantel, and reduce praziquantel dosage as deemed necessary 1. Increased exposure and reduced total clearance of praziquantel were reported with concomitant administration of ketoconazole in 10 healthy volunteers 3.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated metabolism of praziquantel
Literature reports
1 report — tap to read
a) In an open-label, randomized, two-phase crossover study (2- week washout) conducted in 10 healthy male volunteers, the concurrent administration of ketoconazole and praziquantel increased the mean AUC and Cmax, and decreased total clearance of praziquantel. Study subjects were given a single dose of 20 mg/kg praziquantel alone, or following 400 mg ketoconazole orally daily for 5 days. Venous blood samples were collected at predetermined times over 24 hours. For praziquantel, the mean +/- standard error (SE) AUC was significantly increased by 93% (955.94 +/- 307.74 vs 1843.1 +/- 446.39 ng x hr/mL; p less than 0.01) and the mean +/- SE Cmax increased by 102% (183.38 +/- 43.9 vs 371.31 +/- 44.63 ng/mL; p less than 0.01). The mean total clearance of praziquantel was significantly decreased by 58% (2.65 +/- 0.64 vs 1.11 +/- 0.35 mL/hr/kg; p less than 0.01). Although no adverse effects occurred during treatment with praziquantel alone, 7 subjects reported mild adverse events, including gastrointestinal discomfort and headache, while receiving praziquantel and ketoconazole concurrently. The proposed mechanism of this drug interaction is the inhibition of CYP3A metabolism and P-glycoprotein transport of praziquantel by ketoconazole 3.
Common questions
Can I take Ketoconazole Topical and Praziquantel together?
Increased praziquantel exposure Always confirm with your pharmacist or prescriber before making any change.
How serious is the Ketoconazole Topical and Praziquantel 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.
Questions for your pharmacist
- Does my dose of Ketoconazole Topical or Praziquantel 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 (3)
- Product Information: Ketoconazole oral tablet, ketoconazole oral tablet. Taro Pharmaceuticals U.S.A. Inc. (per DailyMed), Hawthorne, NY, 2024. DailyMed
- Product Information: BILTRICIDE oral tablets, praziquantel oral tablets. Bayer HealthCare Pharmaceuticals Inc (per FDA), Whippany, NJ, 2023. DailyMed
- Ridtitid W, Ratsamemonthon K, Mahatthanatrakul W, et al: Pharmacokinetic interaction between ketoconazole and praziquantel in healthy volunteers. J Clin Pharm Ther 2007; 32(6):585-593. PubMed
Keep reading about Ketoconazole Topical
Keep reading about Praziquantel
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