High-dose methotrexate (HD-MTX) requires urine alkalinization to pH ≥ 7 for adequate excretion to prevent toxicity. Due to shortages of IV sodium bicarbonate (IV-NaHCO3), few reports have demonstrated utility of oral bicarbonate (PO-NaHCO3); however, the addition of acetazolamide (Acet) has not been well described. Our study compares outcomes between alkalinization methods of IV-NaHCO3 monotherapy versus IV-NaHCO2 + Acet and PO-NaHCO3 + Acet.
A single-center, IRB exempt, retrospective review was conducted from Jan 2016 to Sept 2019 of adults receiving HD-MTX ≥ 500 mg/m2. The primary outcome was time from start of alkalinization to pH ≥ 7. Secondary outcomes included time from start of alkalinization to initiation of HD-MTX, time to MTX clearance, length of stay (LOS), percentage of urine pH assessments < 7, and incidence of MTX toxicity. Statistical analysis was performed using SAS9.4 with alpha 0.05.
Overall demographics (n = 196 HD-MTX cycles for 55 patients) include a mean age 55 years, HD-MTX dose ~ 5400 mg/m2, and 69% with a diagnosis of lymphoma. Adjusting for baseline demographic differences among groups, median time from first dose alkalinization to pH ≥ 7 and to start of HD-MTX was longer for those receiving IV-NaHCO3 (n = 41) vs either IV-NaHCO3 + Acet (n = 70) or PO-NaHCO3 + Acet (n = 76) (p = 0.0001). HD-MTX clearance to a level < 0.1 μmol/L was not improved with the addition of Acet. No difference existed among groups for pH results < 7, LOS, or incidence of MTX toxicity (p > 0.05).
Addition of Acet to NaHCO3 reduces time to pH ≥ 7 and initiation of HD-MTX but does not appear to improve LOS, MTX toxicities, or time to MTX clearance.
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Clemmons, A.B., Chase, A., Duong, P. et al. Assessing the impact of adding acetazolamide to oral or intravenous sodium bicarbonate as compared with intravenous bicarbonate monotherapy as urinary alkalinization in adults receiving high-dose methotrexate. Support Care Cancer 29, 1527–1534 (2021). https://doi.org/10.1007/s00520-020-05646-z