Maintenance of high urinary pH is important during methotrexate treatment because:
Methotrexate is a weak acid and is reabsorbed in acidic urinary pH. Higher plasma concentration may result in toxicity. Therefore, to decrease the reabsorption through renal tubules, high urinary pH must be maintained.
Bladder irritation is reduced
It decreases renal tubular secretion of methotrexate
Leucovorin toxicity is increased in a dehydrated patient
Methotrexate is a weak acid