Alfentanil and Bicalutamide: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Jul 11, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Alfentanil
No brand names on recordBicalutamide
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 ALfentanil exposure and an increased risk of respiratory depression
Interaction Deep Dive
Concomitant use of ALfentanil with CYP3A4 inhibitors may increase ALfentanil exposure resulting in increased or prolonged opioid effects. These effects could be more pronounced with concomitant use of ALfentanil and CYP3A4 inhibitors, particularly when an inhibitor is added after a stable dose of ALfentanil is achieved. After stopping a CYP3A4 inhibitor, as the effects of the inhibitor decline, the ALfentanil exposure will reduce, resulting in reduced opioid efficacy or a withdrawal syndrome in patients who had developed physical dependence to ALfentanil. If concomitant use is necessary, consider dosage reduction of ALfentanil until stable drug effects are achieved. If a CYP3A4 inhibitor is discontinued, it may result in lower than expected ALfentanil exposure, reduced efficacy, or, possibly, lead to a withdrawal syndrome in a patient who had developed physical dependence to ALfentanil. When discontinuing CYP3A4 inhibitors, monitor patients closely at frequent intervals and consider increasing ALfentanil1. During another study, dilTIAZem was shown to increase the half-life of ALfentanil by 50%. ALfentanil is metabolized by cytochrome P450 3A enzymes, which are inhibited by dilTIAZem 4.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated metabolism of ALfentanil
Literature reports
3 reports — tap to read
a) A study observed a reduction in clearance and distribution volume as well as prolongation of half-life of ALfentanil following concomitant treatment with fluconazole 2.
b) The effects of IV and oral fluconazole on the pharmacokinetics of ALfentanil were studied in 9 healthy volunteers using a randomized, double-blind, placebo-controlled, cross-over study design. Three phases, at 4-week intervals, were studied and consisted of either oral fluconazole 400 mg and IV saline, oral placebo and IV fluconazole 400 mg, or oral placebo and IV saline. Sixty minutes after the oral administration of fluconazole or placebo, IV ALfentanil 20 mcg/kg was infused over 2 minutes. Intravenous fluconazole decreased the clearance of ALfentanil by approximately 60% (3.1 mL/min/kg vs. 1.3 mL/min/kg) while oral fluconazole decreased the clearance by 55% (3.1 mL/min/kg vs. 1.4 mL/min/kg). The half-life of ALfentanil was prolonged by the presence of IV and oral fluconazole (1.5 hours vs 2.7 hours and 2.5 hours, respectively). Fluconazole also increased ALfentanil-induced subjective effects and respiratory depression. Overall, the route of fluconazole administration had no significant effect on the magnitude of the interaction with ALfentanil. Because ALfentanil is intravenously administered, it bypasses the presystemic metabolism in the intestinal wall and liver so its pharmacokinetics are not dependent on the fluconazole route of administration 3.
c) A double-blind, randomized, placebo-controlled study of 30 patients undergoing coronary artery bypass surgery was conducted to determine the effects of dilTIAZem on midazolam and ALfentanil pharmacokinetics. Two hours prior to surgery, patients received dilTIAZem 60 mg orally or placebo. DilTIAZem (0.1 mg/kg/hr) or placebo (saline) infusions were initiated prior to anesthesia and continued until the next morning. Anesthesia was induced with midazolam 0.1 mg/kg, ALfentanil 50 mcg/kg, and propofol. Continuous infusions of midazolam 1 mcg/kg/min and ALfentanil 1 mcg/kg/min were started at the beginning of induction and were maintained until skin closure. From the induction time to 23 hours post-operatively, dilTIAZem increased the area under the concentration-time curve (AUC) of midazolam by 15% and ALfentanil by 24%. When evaluating the data from the end of surgery to 23 hours post-op, the AUCs of midazolam and ALfentanil were increased by 24% and 40%, respectively. The mean half-life of midazolam and ALfentanil was increased by 43% and 50%, respectively, when compared to the placebo group. In patients receiving dilTIAZem, extubation was 2.5 hours later on average than the placebo controls. These results indicate that dilTIAZem inhibits the cytochrome P450 3A enzymes which are responsible for midazolam and ALfentanil metabolism 4.
Common questions
Can I take Alfentanil and Bicalutamide together?
Increased ALfentanil exposure and an increased risk of respiratory depression Always confirm with your pharmacist or prescriber before making any change.
How serious is the Alfentanil and Bicalutamide 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 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 Alfentanil or Bicalutamide 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 (4)
- Product Information: Alfentanil HCl intravenous injection, alfentanil HCl intravenous injection. Rising Pharma Holdings, Inc (per FDA), East Brunswick, NJ, 2025.
- Product Information: DIFLUCAN(R) oral tablets, suspension, fluconazole oral tablets, suspension. Roerig (per FDA), New York, NY, 2023. DailyMed
- Palkama VJ, Isohanni MH, Neuvonen PJ, et al: The effect of intravenous and oral fluconazole on the pharmacokinetics and pharmacodynamics of intravenous alfentanil. Anesth Analg 1998; 87:190-194. DOI
- Ahonen J, Olkkola KT, Salmenpera M, et al: Effect of diltiazem on midazolam and alfentanil disposition in patients undergoing coronary artery bypass grafting. Anesthesiology 1996; 85:1246-1252. PubMed
Keep reading about Alfentanil
Keep reading about Bicalutamide
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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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