Pharmacokinetics of methotrexate and 7-hydroxy-methotrexate after methotrexate infusions

Simultaneous Determination of Urine Methotrexate, 7-Hydroxy Methotrexate, Deoxyaminopteroic Acid, and 7-Hydroxy Deoxyaminopteroic Acid by UHPLC-MS/MS in Patients Receiving High-dose Methotrexate Therapy

Nephrotoxicity, the most important toxicity in high-dose methotrexate (MTX) therapy, is partly caused by the formation of crystal deposits in the kidney due to poor water solubility of MTX and its metabolites 7-hydroxy methotrexate (7-OH MTX), deoxyaminopteroic acid (DAMPA) and 7-hydroxy deoxyaminopteroic acid (7-OH DAMPA). Plasma MTX level-guided urine alkalinization, leucovorin rescue and glucarpidase detoxification are common strategies to overcome MTX-related nephrotoxicity. However, overestimation is a problem for MTX analysis by immunoassays due to the cross-reactivity of MTX metabolites (7-OH MTX and DAMPA). An UHPLC-MS/MS method for the simultaneous determination of MTX, 7-OH MTX, DAMPA and 7-OH DAMPA in human urine was developed, validated and applied in clinical practice. Samples were treated by one-step protein precipitation and analyzed within 3 min. The calibration range was 0.02 to 4 μmol/L for MTX and DAMPA, and 0.1 to 20 μmol/L for 7-OH MTX and 7-OH DAMPA. For all analytes, the intra-day and inter-day bias and imprecision were -8.0 to 7.6 and <9.0%, the internal standard normalized recovery and matrix factor were 92.34 to 109.49 and <20.68%. The plasma MTX and 7-OH MTX levels increased with the urine drug levels, age, serum creatinine and alanine transaminase, but urine could not replace blood for MTX monitoring due to their poor correlation (R², 0.16 to 0.51). Dose-normalized urine and plasma MTX and 7-OH MTX levels were similar between different patient groups (urine pH <7 or ≥7). Due to the large inter-individual variance of the analytes levels in both plasma and urine, these findings should be treated with caution.

High-Dose Methotrexate Treatment in a Breastfeeding Mother with Placenta Accreta: A Case Report

BACKGROUND

Morbidly placenta accreta as a cause of postpartum morbidity is increasing in incidence. One conservative option is use of methotrexate as an adjuvant therapy for the management of placenta accreta. There is concern that use of methotrexate in a lactating mother could potentially expose her neonate to harmful effects of this medication.

CASE REPORT

Here we report a 29-year-old woman subjected to methotrexate treatment for placenta accreta. Her child was delivered at 32 weeks weighing 3 lbs. On postpartum day 5, this patient was diagnosed with placenta accreta and treated with intramuscular methotrexate for 3 consecutive days. She received 92 mg methotrexate intramuscularly daily, and was advised not to breastfeed. She collected milk samples on day 2, the 0 hour before the second dose and at 1, 2, 4, 8, 12, and 24 hours after taking the dose. A high-performance liquid chromatography mass spectrometry method was developed to measure methotrexate and its metabolite 7-hydroxymethotrexate levels in milk samples.

DISCUSSION

Very low levels were found for both methotrexate and 7-hydroxymethotrexate in the milk samples obtained. The results indicate that methotrexate or its metabolite receded to minimum concentration over a period of 24 hours.

CONCLUSION

This case report found the relative infant dose of methotrexate to be 0.11%. Methotrexate does transfer into breast milk, although the levels detected were very low. However, caution should still be used in counseling mothers regarding breastfeeding with this toxic drug.