Simultaneous Quantification of Methotrexate and Its Metabolite 7-Hydroxy-Methotrexate in Human Plasma for Therapeutic Drug Monitoring

Table 4

Stability of MTX and 7-OH-MTX in different conditions (n=5).

Analyte	Nominal concentration; (ng/mL)	three freeze-thaw cycles; (RE/%)	Short-term; (RE/%)	Long-term; (RE/%)	Bench-top (RE/%)
MTX	10	-5.60	-5.99	-2.27	-0.03
	500	4.02	1.56	-7.29	5.10
	5000	4.58	4.99	6.83	8.22
7-OH-MTX	10	-0.91	-5.96	-9.10	7.22
	500	-8.04	-8.66	-12.91	-0.77
	5000	-7.02	-5.80	-5.26	2.41