From the FDA Drug Label
Laboratory Test Interaction Due to its properties as an azo dye, Phenazopyridine HCl may interfere with urinalysis based on spectrometry or color reactions. NOTE : Patients should be informed that Phenazopyridine HCl produces a reddish-orange discoloration of the urine Phenazopyridine affects urinalysis results by:
- Producing a reddish-orange discoloration of the urine
- Possibly interfering with urinalysis based on spectrometry or color reactions due to its properties as an azo dye 1
From the Research
Effects of Phenazopyridine on Urinalysis Results
- Phenazopyridine can cause orange discoloration of urine 2
- The drug has been associated with acute renal failure, which can lead to changes in urinalysis results, such as the presence of casts, proteinuria, and hematuria 3, 2, 4
- Phenazopyridine-induced methemoglobinemia can also affect urinalysis results, as it can cause a false positive test for hematuria 2
- Acute interstitial nephritis, a rare side effect of phenazopyridine, can also alter urinalysis results, including the presence of leukocyturia and hematuria 2
Mechanism of Action
- Phenazopyridine acts as a local analgesic on the bladder mucosa, which can help reduce pain and discomfort during urination 5
- The drug can also cause changes in urine color and composition, which can affect urinalysis results 2
Clinical Studies
- A study published in 2020 found that phenazopyridine reduced pain intensity during and after cystoscopy, and alleviated pain during first urination 5
- Another study published in 2021 found that the combination of phenazopyridine and fosfomycin was effective in treating acute uncomplicated cystitis, with a significant reduction in pain and symptoms 6
- However, phenazopyridine has also been associated with adverse effects, such as nausea, and can cause changes in urinalysis results, which should be considered when interpreting test results 3, 2, 4, 6