Background and importance To alert clinicians to the potential problems of combining docetaxel (and taxanes in general) with fluvoxamine.

Aim and objectives To report a live conditioning interaction between docetaxel and fluvoxamine in a breast cancer patient.

Material and methods A 60-year-old woman (60 kg,164 cm) was diagnosed with triple negative right breast ductal carcinoma (TNM stage T1N0M0). The treatment plan consisted of four cycles of neoadjuvant chemotherapy with cyclophosphamide 600 mg/m² and epirubicin 95 mg/m² (EC) biweekly, four cycles of carboplatin AUC5 and docetaxel 75 mg/m² followed by pegfilgrastrim 6 mg on day +2 and surgical intervention. After completion of the EC scheme, the patient showed haematological tolerance and clinical improvement. The patient completed the first dose of the carboplatin–docetaxel regimen with proper tolerance. However, before the second cycle, the patient experienced syncope, asthenia and hyporexia. A complete blood count (CBC) was performed at the second consult, showing that the patient was in range to receive chemotherapy. However, due to the syncopal episode and suspicion of neutropenia on that day, the oncologist decided to decrease the dose of docetaxel to 70 mg/m². On day +9, the patient presented to the emergency room with a recurring syncopal episode and neutropenia, and was admitted with septic shock. Blood cultures were obtained and were positive for Pseudomonas aeruginosa. Meropenem was started. Furthermore, it was discovered that the patient had started taking fluvoxamine as an antidepressant the same day she started the first cycle of docetaxel–carboplatin. The interaction between docetaxel and fluvoxamine was assimilated, and fluvoxamine was discontinued and exchanged for mirtazapine.

Results Fluvoxamine is an inhibitor of the CYP3A4 isoenzyme. Docetaxel is metabolised through CYP3A4, and the concomitant use may increase concentrations, leading to toxicity. Although the score was 4 (possible) for the drug interaction probability scale, if pharmacokinetic analysis had been performed, we could have proven that the AUC of docetaxel had reached toxic levels.

Conclusion and relevance Although SSRIs are often prescribed to combat depression, in breast cancer patients they can also be used to control hot flushes. It is mandatory to avoid using SSRIs that are metabolised through CYP3A4, such as fluvoxamine, fluoxetine, paroxetine, sertraline and venlafaxine in the setting of docetaxel. Therefore, it would be best to recommend SSRIs such as mirtazapine, citalopram and escitalopram.

Conflict of interest No conflict of interest