Cholestyramine and Fluvastatin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Cholestyramine
Fluvastatin
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
Decreased fluvastatin effectiveness
Interaction Deep Dive
Cholestyramine has been shown to significantly reduce the bioavailability of fluvastatin when given as combination therapy1. When fluvastatin was given two hours after the cholestyramine, the AUC decreased by 89%; when given four hours apart, the AUC decreased by 51%. Although combination therapy appears to substantially enhance efficacy when given four hours apart (31% reduction in LDL cholesterol versus 19% with either agent alone), it is not known if this enhanced efficacy is maintained when doses are separated by a shorter time interval.
Why it happens (mechanism)
Binding of fluvastatin to the cholestyramine resin
Literature reports
4 reports — tap to read
a) A group of three studies was conducted to evaluate the effect of cholestyramine on fluvastatin bioavailability and the efficacy of combined therapy 1.
b) In the first study, nineteen healthy men were administered fluvastatin 20 mg in solution either two hours after or concurrently with cholestyramine 8 g after an overnight fast. Comparing concurrent administration with fluvastatin given alone, the AUC and Cmax decreased by 89% and 96%, respectively. Tmax increased by about 65%. Comparison of fluvastatin administration two hours after cholestyramine with fluvastatin given alone showed a decrease of just over 50% in both AUC and Cmax, with Tmax again increasing by about 65% 1.
c) In a second study, after an eight hour fast and four hours after taking cholestyramine 8 g with an evening meal, 20 healthy men were given fluvastatin 20 mg in capsule form. The combined effects of the meal and cholestyramine resulted in decreased fluvastatin AUC (by 51%) and Cmax (by 82%) and a 2.8-fold increase in Tmax 1.
d) In the third study, a placebo-controlled, randomized study was conducted in 224 hypercholesterolemic patients who were randomized to receive either placebo or fluvastatin 20 mg in addition to randomized open-label cholestyramine 8 g twice daily to half the study population. Cholestyramine was given with the morning and evening meals and fluvastatin or placebo were given four hours after the evening meal. Reductions in LDL-C from baseline of 19.4% and 19.2% were seen with fluvastatin alone and cholestyramine alone, respectively. The combination of the two drugs resulted in a 31.4% LDL-C reduction, indicating an additive therapeutic effect that is more relevant clinically than the pharmacokinetic interaction with this dosing schedule 1.
Common questions
Can I take Cholestyramine and Fluvastatin together?
Decreased fluvastatin effectiveness Always confirm with your pharmacist or prescriber before making any change.
How serious is the Cholestyramine and Fluvastatin interaction?
It is rated minor. Usually limited clinical impact.
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 Cholestyramine or Fluvastatin 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 (1)
- Smith HT, Jokubaitis LA, Troendle AJ, et al: Pharmacokinetics of fluvastatin and specific drug interactions. Am J Hypertens 1993; 6:375S-382S. PubMed
Keep reading about Cholestyramine
Keep reading about Fluvastatin
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