Serum creatinine methotrexate

Prior to initiating methotrexate therapy, obtain complete blood count, serum creatinine, liver function tests, chest x-ray, and pregnancy test (if female). Monitor blood counts weekly for 1 month, then monthly thereafter. 

Determine serum creatinine and methotrexate levels at least once daily. Continue... 

Determine serum creatinine and methotrexate levels at 24-hour intervals. If the 24-hour serum creatinine has increased 50% over baseline or if the 24 or 48 hour methotrexate level is greater than 5 x 10 M or greater than 9 x lO M, respectively, increase the dose of leucovorin to 100 mg/m IV every 3 hours until the methotrexate level is less than 10 M. 

If serum creatinine increases by 50% in the first 24 hours after methotrexate, increase the dose frequency to every 3 hours untii the methotrexate ievei is iess than 5 mcmoi/L... 

Renal - Methotrexate may cause renal damage that may lead to acute renal failure. Close attention to renal function including adequate hydration, urine alkalinization and measurement of serum methotrexate and creatinine levels are essential for safe administration. 

The picture is not totally clear but it seems possible that the previous use of cisplatin causes kidney damage that may not necessarily be detectable with the usual creatinine clearance tests, llie effect is to cause a marked reduction in the clearance of the methotrexate. The serum methotrexate levels of such patients should be closely monitored so that any delay in its clearance is detected early and folinic acid rescue therapy can be given. This appears to prevent serious toxicity. " ... 

There is also a report that suggests that methotrexate inhibits the renal clearance of cisplatin. The renal clearance of platinum in 4 of 5 patients with non-small-cell lung cancer given cisplatin 50 mg/m and methotrexate 40 mg/m was reduced in the first 6 hours after administration (50% lower in the first 3 hours). Apart from a transient increase in serum urea nitrogen and creatinine in one patient, there was no sign of nephrotoxicity with concurrent use. ... 

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