Phenazopyridine hydrochloride

What it is

Phenazopyridine is a red-to-violet azo dye taken as a tablet. It is not an antibiotic and does not treat infection. Two-thirds of a swallowed dose leaves the body unchanged in the urine, and it is in the urine that it acts, numbing the lining of the lower urinary tract. It is sold on prescription at 100 mg and 200 mg in the United States and also over the counter in lower strengths.

What the research says

The trial evidence behind it is thin. The only placebo-controlled randomised trial we could reach enrolled 60 women with acute cystitis and gave a single 200 mg dose; symptom scores six hours later were better than placebo. A second multicentre randomised trial of 152 women compared it plus fosfomycin against drotaverine plus fosfomycin and found faster pain relief. Three randomised trials of off-label uses, for catheter discomfort after gynaecological surgery, for voiding problems after a midurethral sling, and for seeing ureteric urine during cystoscopy, all missed their primary endpoints. Against that sits a body of case reports of methaemoglobinaemia, oxidative haemolysis, acute interstitial nephritis and liver injury, and a National Toxicology Program listing as reasonably anticipated to be a human carcinogen on animal evidence.

Evidence grade: Limited evidence.

How it works

Drug class: Azo dye used as a urinary tract analgesic (local anaesthetic-like action on bladder and urethral mucosa); not an antibacterial

It is excreted into the urine and acts there on the surface of the bladder and urethral lining, dulling pain, burning, urgency and frequency. The label states outright that the precise mechanism is not known and that the drug's pharmacokinetic properties have not been determined. It is this urinary excretion that also turns urine bright reddish-orange. (Source 1)

What it is used for

• One small double-blind placebo-controlled trial in 60 women with acute cystitis, published as a Russian-language article, found better symptom scores six hours after a single 200 mg dose. An open-label randomised trial of 152 women, also Russian-language, found faster pain relief when it was added to fosfomycin. Both are small, both are single-country studies, and the label itself says there is no evidence of added benefit beyond 2 days when it is combined with an antibacterial. Evidence: limited. (Source 2)
• A trial that randomised 240 women found no difference from placebo in postoperative pain scores or in how much pain medicine people used. Evidence: not-supported. (Source 3)
• A randomised trial of 88 analysable patients found no reduction in failed voiding trials, 27% with the drug against 21% without. Evidence: not-supported. (Source 4)
• A randomised trial of 104 women found no difference in the primary endpoint, time to see urine coming from the ureter, but surgeons reported less frustration and fewer failed void trials, and the authors concluded it was useful. Evidence: disputed. (Source 5)
• A four-arm randomised trial of 120 patients found less frequency, urgency and dysuria than placebo, though celecoxib performed better overall. A network meta-analysis of six studies and 556 participants found phenazopyridine best for pelvic pain. Evidence: limited. (Source 6)
• A retrospective matched cohort of 90 patients given more than a 14-day supply found no excess of adverse drug reactions compared with matched comparators, but measured safety only, not benefit, and the authors note the lack of evidence for extended use. Evidence: unknown. (Source 7)

Interactions

• Ascorbic acid (vitamin C) (case reports): High-dose ascorbic acid is used as a treatment for phenazopyridine-induced methaemoglobinaemia when methylene blue cannot be given, and the label lists oral ascorbic acid as an option alongside methylene blue. This is an interaction in the therapeutic direction rather than a hazard; the evidence is case reports and the label, not trials. Limit: The quoted sentence carries an error that is in the published source: the abstract writes "glucose-6-phosphatase deficiency" where the condition it means is glucose-6-phosphate dehydrogenase (G6PD) deficiency. We have kept the quotation as the journal printed it. The contraindication that matters is G6PD deficiency, and glucose-6-phosphatase deficiency is a different, unrelated disorder. (Source 8)
• Methylene blue (case reports): Methylene blue is the first-line antidote for the methaemoglobinaemia phenazopyridine can cause, but it is itself contraindicated in G6PD deficiency and in people on serotonergic drugs, which is exactly the group most at risk of phenazopyridine haemolysis. Limit: The quoted sentence carries an error that is in the published source: the abstract writes "glucose-6-phosphatase deficiency" where the condition it means is glucose-6-phosphate dehydrogenase (G6PD) deficiency. We have kept the quotation as the journal printed it. The contraindication that matters is G6PD deficiency, and glucose-6-phosphatase deficiency is a different, unrelated disorder. (Source 8)
• Food (meals) (label): The label's dosing instruction is to take it after meals. We found no pharmacokinetic study of the food effect, and the label states outright that phenazopyridine's pharmacokinetic properties have not been determined, so the instruction rests on tolerability rather than on measured absorption. (Source 1)
• Alcohol (label): We found no trial, pharmacokinetic study or case series describing an interaction between alcohol and phenazopyridine. Nothing can be said either way, and the drug's basic pharmacokinetics have never been characterised, which is the reason. (Source 1)
• Other oxidant drugs, such as trimethoprim-sulfamethoxazole, dapsone and local anaesthetics (case reports): Phenazopyridine is one of several drugs that oxidise haemoglobin. The published cases of methaemoglobinaemia include patients taking more than one oxidant agent, and G6PD deficiency compounds the risk. The evidence is case reports and the label's overdose section, not controlled study. (Source 9)

Stopping it

• There is no withdrawal syndrome and no taper. The label's instruction is the opposite: stop as soon as the symptoms are controlled, because the drug only masks them. (Source 10)
• When it is used alongside an antibacterial for a urinary tract infection, the label caps the course at 2 days. (Source 11)
• A yellow tinge to the skin or the white of the eye means the drug is building up because the kidneys are not clearing it, and is an explicit signal to stop rather than continue. (Source 12)
• Where harm has occurred, stopping the drug is the first step. The authors of the single case report go on to say, in their discussion of earlier literature, that recent studies indicate early steroids improve renal recovery - that is their summary of other, unnamed papers, not a result of their own case, and the abstract cites no study for it. (Source 13)

What goes wrong

The National Toxicology Program lists phenazopyridine hydrochloride as reasonably anticipated to be a human carcinogen, on animal evidence; the human data are inadequate. (Source 14)

• Official position, Certainty not rated.
• Size: not applicable; based on rodent bioassays reported by the National Cancer Institute in 1978.
• Who: rats and mice fed phenazopyridine hydrochloride in the diet.
• How long: long-term dietary exposure.
• Result: benign and malignant liver tumours in female mice; benign or malignant colorectal tumours in rats of both sexes; epidemiological data in humans judged inadequate.
• Funding: US federal programme, Report on Carcinogens, Fifteenth Edition.

Phenazopyridine hydrochloride is reasonably anticipated to be a human carcinogen based on sufficient evidence of carcinogenicity from studies in experimental animals.

The animal tumours were at two sites in two species: liver in female mice and colorectum in rats of both sexes. (Source 14)

• Animal study, Certainty not rated.
• Size: not stated in the profile.
• Who: rats and mice.
• How long: long-term dietary exposure.
• Result: hepatocellular adenoma and carcinoma in female mice; colorectal adenoma, adenocarcinoma or sarcoma in rats of both sexes.
• Funding: US National Cancer Institute bioassay, 1978, as summarised by the National Toxicology Program.

Dietary exposure to phenazopyridine hydrochloride caused tumors in two rodent species and at two different tissue sites. In female mice, it caused benign and malignant liver tumors (hepatocellular adenoma and carcinoma).

The product label itself records that long-term administration caused tumours in rats and mice, and that no human epidemiology has been done. (Source 15)

• Official position, Certainty not rated.
• Size: not applicable.
• Who: rats and mice given long-term administration.
• How long: long-term.
• Result: neoplasia in rats (large intestine) and mice (liver); no association with human neoplasia reported, but adequate epidemiological studies have not been conducted.
• Funding: FDA-approved labelling, effective 14 July 2026.

Long-term administration of Phenazopyridine HCl has induced neoplasia in rats (large intestine) and mice (liver). Although no association between Phenazopyridine HCl and human neoplasia has been reported, adequate epidemiological studies along these lines have not been conducted.

The label records methaemoglobinaemia, haemolytic anaemia, and kidney and liver toxicity as reported adverse reactions, usually at overdose levels. (Source 16)

• Official position, Certainty not rated.
• Size: not applicable.
• Who: people taking phenazopyridine, particularly at excessive doses or with impaired kidney function.
• How long: not stated.
• Result: no rates are given; headache, rash, pruritus and occasional gastrointestinal disturbance are listed, plus an anaphylactoid-like reaction.
• Funding: FDA-approved labelling, effective 14 July 2026.

Methemoglobinemia, hemolytic anemia, renal and hepatic toxicity have been reported, usually at overdosage levels

Methaemoglobinaemia has occurred at ordinary over-the-counter doses, not only in overdose: an 89-year-old woman taking 200 mg three times daily for two weeks reached a methaemoglobin level of 21.5% and needed methylene blue. (Source 17)

• Case report, Very low certainty.
• Size: a single reported case.
• Who: an 89-year-old woman with chronic dysuria using over-the-counter phenazopyridine.
• How long: 200 mg three times daily for two weeks.
• Result: methaemoglobin level 21.5%, severe hypoxia, shortness of breath, headache, nausea and dizziness; rapid improvement after methylene blue.
• Funding: not stated.

She was found to have a methemoglobin level of 21.5% and was treated with methylene blue, leading to a rapid improvement of her symptoms. She was taking one over-the-counter phenazopyridine 200 mg tablet three times daily for two weeks for her chronic dysuria.

In people with G6PD deficiency, phenazopyridine can trigger haemolysis as well as methaemoglobinaemia, though published cases are rare. (Source 18)

• Case report, Very low certainty.
• Size: a single reported case.
• Who: an 80-year-old man treated with phenazopyridine for a urinary tract infection two weeks earlier.
• How long: two weeks after treatment.
• Result: syncope and jaundice, with G6PD deficiency and methaemoglobinaemia found on investigation; the authors note only a few cases in 60 years.
• Funding: not stated.

Historically, phenazopyridine has been associated with causing methemoglobinemia and triggering hemolysis in G6PD deficient individuals. However, only a few cases have been reported in the last 60 years, making it a very rare occurrence.

Acute interstitial nephritis has been reported at therapeutic doses, without methaemoglobinaemia or any other explanation for the kidney injury. (Source 13)

• Case report, Very low certainty.
• Size: a single biopsy-proven case, with a narrative review of previously published cases.
• Who: a patient taking therapeutic doses of phenazopyridine.
• How long: not stated.
• Result: biopsy-proven acute interstitial nephritis; the review also notes previously reported acute renal failure from acute tubular necrosis and pigment nephropathy following haemolysis.
• Funding: not stated.

Limit of this finding: This is one case report with a narrative review of earlier cases attached. A single case can show that something has happened at ordinary doses; it cannot show how often it happens.

We report a case of biopsy proven acute interstitial nephritis, associated with therapeutic doses of phenazopyridine without any evidence of methemoglobinemia or other mechanism of renal injury.

Over-the-counter availability leads to substantial misuse: in a survey of purchasers, fifty-one percent used it inappropriately and 38% used it instead of seeing a clinician. (Source 19)

• Survey study, Low certainty.
• Size: 434 purchasers surveyed in 31 Los Angeles retail pharmacies, 58% response rate.
• Who: adults aged 18 and over buying an over-the-counter phenazopyridine product.
• How long: survey conducted over 5 months.
• Result: Fifty-one percent of the respondents used OTC phenazopyridine inappropriately; 38% substituted it for medical care; incorrect knowledge of its mode of action carried 1.9 times greater odds of inappropriate use and 2.2 times greater odds of substitution.
• Funding: not stated in the abstract.

Fifty-one percent of the respondents used OTC phenazopyridine inappropriately, and 38% substituted it for medical care.

Most buyers did not understand what the drug does: in a survey of purchasers, only 42% correctly characterised what was likely behind their symptoms and only 57% correctly characterised the action of the drug. (Source 20)

• Survey study, Low certainty.
• Size: 434 purchasers, 58% response rate.
• Who: purchasers of over-the-counter phenazopyridine in 31 Los Angeles pharmacies.
• How long: cross-sectional survey.
• Result: 42% correctly characterised what was likely behind their symptoms; 57% correctly characterised the action of the drug; worse knowledge was associated with non-white race, first-time use and less contact with health providers.
• Funding: not stated in the abstract.

Limit of this finding: The survey measured what purchasers understood, not whether the drug harmed them. The source itself prints "the likely cause of their symptoms"; that is the survey's own wording about what buyers were asked to identify, and it is not a causal finding about the drug.

Only 42% correctly characterized the likely cause of their symptoms, and only 57% correctly characterized the action of the drug.

Because it is an azo dye, phenazopyridine can corrupt urine tests that depend on colour or spectrometry, which can mask or mimic the very infection it is being taken for. (Source 21)

• Official position, Certainty not rated.
• Size: not applicable.
• Who: anyone having a urinalysis while taking it.
• How long: while the drug is in the urine.
• Result: no rate given; interference with urinalysis based on spectrometry or colour reactions.
• Funding: FDA-approved labelling, effective 14 July 2026.

Due to its properties as an azo dye, Phenazopyridine HCl may interfere with urinalysis based on spectrometry or color reactions.

A yellow tinge to the skin or the white of the eye is a sign that the drug is accumulating because the kidneys are not clearing it, and is a reason to stop. (Source 12)

• Official position, Certainty not rated.
• Size: not applicable.
• Who: people with impaired renal excretion, including older people whose kidney function has declined.
• How long: not stated.
• Result: no rate given; yellowish tinge of skin or sclera signals accumulation; urine turns reddish-orange and may stain fabric; staining of contact lenses has been reported.
• Funding: FDA-approved labelling, effective 14 July 2026.

A yellowish tinge of the skin or sclera may indicate accumulation due to impaired renal excretion and the need to discontinue therapy.

What the evidence supports

In the only placebo-controlled randomised trial we could reach - 60 women, one 200 mg dose, symptoms scored six hours later - cystitis symptom scores improved more than on placebo. (Source 22)

• Randomized trial, Low certainty.
• Size: 60 women in two groups of 30.
• Who: women with acute uncomplicated cystitis accompanied by pain, mean age 32.6 years in the drug group and 35.53 years in the placebo group.
• How long: single dose, assessed at 6 hours, with follow-up for three days.
• Result: general discomfort fell by 53.4% versus 28.8% on placebo; pain on urination 57.4 versus 35.9%; urination frequency 39.6 versus 27.6%; adverse event rates comparable between groups.
• Funding: not stated in the abstract; published in a Russian national urology journal.

Limit of this finding: The limits of this trial matter as much as its result. It is the English abstract of a Russian-language article in Urologiia; it randomised 60 women, 30 per group; each woman received one 200 mg dose; and the outcome was read six hours later, before antibiotics were started. It shows a single dose can take the edge off symptoms for a few hours. It says nothing about a course of the drug, about men, or about any outcome beyond six hours.

The average assessment of general discomfort in the main group decreased by 53.4% in comparison with 28.8% in the control group, while the severity of pain during urination and urination frequency decreased by 57.4 vs. 35.9% and 39.6 vs. 27.6%, respectively.

That placebo-controlled trial was small, single-dose and short, and published as a Russian-language article: 60 women, one 200 mg dose, outcomes read at six hours before antibiotics were started. (Source 2)

• Randomized trial, Low certainty.
• Size: 60 women.
• Who: women with acute uncomplicated cystitis.
• How long: single 200 mg dose; symptoms scored 6 hours later.
• Result: 2 tablets of 100 mg orally, total dose 200 mg, once, against matching placebo.
• Funding: not stated in the abstract.

Limit of this finding: The limits of this trial matter as much as its result. It is the English abstract of a Russian-language article in Urologiia; it randomised 60 women, 30 per group; each woman received one 200 mg dose; and the outcome was read six hours later, before antibiotics were started. It shows a single dose can take the edge off symptoms for a few hours. It says nothing about a course of the drug, about men, or about any outcome beyond six hours.

A total of 60 women were divided into two groups of 30 patients. In the main group (average age 32.6+/-7.4 years) phenazopyridine was prescribed (2 tablets of 100 mg p.o., with a total dose of 200 mg, once).

Added to fosfomycin in acute cystitis, phenazopyridine gave faster pain relief than drotaverine plus fosfomycin in an open-label randomised trial. (Source 23)

• Randomized trial, Low certainty.
• Size: 152 women in two groups of 76.
• Who: working-age women with acute uncomplicated cystitis at 5 polyclinics in the Perm Territory.
• How long: phenazopyridine 200 mg three times daily for 2 days; outcomes read at 6, 12, 24 and 48 hours and days 3 and 6.
• Result: visual analogue pain score fell from 7.2+/-0.5 to 1.6+/-0.2 at 12 hours and 0.4 +/- 0.05 at 24 hours, with pain gone in all patients by 48 hours; the control group was significantly less improved at every time point (p<0.001)
• Funding: not stated in the abstract; open-label design, no placebo.

In the main group, the severity of pain according to the VAS decreased from the initial 7.2+/-0.5 points to 1.6+/-0.2 points after 12 hours, to 0.4 +/- 0.05 points after 24 hours. Pain syndrome completely disappeared in all patients after 48 hours.

In a four-arm placebo-controlled trial of urinary symptoms after intravesical BCG, phenazopyridine reduced frequency, urgency and dysuria compared with placebo. (Source 6)

• Randomized trial, Low certainty.
• Size: 120 patients (10 female, 110 male) across four arms.
• Who: patients with bladder tumours receiving intravesical BCG, mean age 59.65 years.
• How long: weekly assessment during BCG therapy.
• Result: urinary frequency OR 0.17 (95% CI 0.09, 0.31, P <.001) versus placebo; urgency OR 0.16 (95% CI 0.07, 0.37, P <.001); dysuria also significantly reduced.
• Funding: not stated in the abstract.

The results of multivariate analysis show that there is a significant decrease in urinary frequency for patients who received phenazopyridine (95% CI: 0.09, 0.31, OR = 0.17, P <.001) and also celecoxib group (95% CI: 0.10, 0.43, OR = 0.21, P <.001) compared to those in placebo group.

A retrospective matched cohort of long-term users for radiation cystitis found no excess of adverse drug reactions over matched comparators. (Source 7)

• Cohort study, Very low certainty.
• Size: 90 exposed patients matched to 90 comparators, drawn from 272 who received more than a 14-day supply.
• Who: cancer patients, largely men with prostate cancer, who received radiation and at least one chronic medication between 1 July 2008 and 30 June 2017.
• How long: most received between a 30- and 60-day supply.
• Result: 13 adverse drug reactions in the phenazopyridine group versus 18 in the comparator group (p = 0.32); no difference in emergency department visits, hospitalisations, or new hepatocellular or colorectal cancer diagnoses.
• Funding: not stated in the abstract; retrospective single-system chart review.

There were a total of 13 adverse drug reactions in the phenazopyridine group and 18 in the comparator group (p = 0.32). No differences were identified between the phenazopyridine and comparator groups for the incidence of individual adverse drug reactions, emergency department visits, hospitalizations, or new diagnoses of hepatocellular or colorectal cancer.

What the evidence does not support

For catheter discomfort after gynaecological surgery, phenazopyridine was no better than placebo. (Source 24)

• Randomized trial, Moderate certainty.
• Size: 240 women randomised, 219 received study medication (112 drug, 107 placebo)
• Who: adult women having gynaecological surgery and needing an indwelling Foley catheter.
• How long: postoperative period.
• Result: no significant difference in bladder visual analogue score, overall visual analogue score or pain medication use; blinding was adequate, with only 25 of the 45 participants who guessed getting it right.
• Funding: not stated in the abstract.

In all, 219 patients received study medications (112 phenazopyridine and 107 placebo). There was no significant difference in demographics, procedure type, bladder VAS, overall VAS, and pain medication use.

That null trial used orange dye in the catheter bag of both groups so that patients could not tell which arm they were in. (Source 3)

• Randomized trial, Moderate certainty.
• Size: 240 adult women randomised.
• Who: women having gynaecological surgery with an indwelling Foley catheter.
• How long: postoperative, primary outcome mean postoperative visual analogue score.
• Result: placebo-controlled with dye masking; primary outcome was the mean postoperative visual analogue score.
• Funding: not stated in the abstract.

This trial randomized 240 adult women, who were undergoing gynecologic surgery and requiring an indwelling Foley catheter, to placebo or phenazopyridine hydrochloride. Group assignment was masked by instillation of orange dye in the Foley bag of both groups.

Given before a midurethral sling, phenazopyridine did not reduce failed voiding trials after surgery. (Source 4)

• Randomized trial, Low certainty.
• Size: 88 patients in the final analysis, 44 per arm, of ninety-two enrolled.
• Who: women having a retropubic midurethral sling under general anaesthesia with no concomitant procedures.
• How long: a single preoperative oral dose of 200 mg, with a standardised voiding trial before discharge.
• Result: failed voiding trial 27% with phenazopyridine versus 21% without (P = 0.453); the postoperative pain difference (1.76 versus 1.21, P = 0.046) disappeared after adjustment (P = 0.087)
• Funding: not stated in the abstract; single-institution trial.

Phenazopyridine did not reduce the proportion of patients who failed the voiding trial (27%) compared with subjects who did not receive the medication (21%) (P = 0.453).

When used to help see ureteric urine during cystoscopy, phenazopyridine did not shorten the time to visualise urine efflux. (Source 5)

• Randomized trial, Low certainty.
• Size: 104 women randomised.
• Who: women having pelvic surgery with intraoperative cystoscopy, April to December 2015.
• How long: single preoperative dose; intraoperative measurement.
• Result: mean time to visualise ureteric urine efflux 2 minutes 40 seconds in controls versus 2 minutes 53 seconds in the treated group (P=.77); surgeon-reported frustration was lower in the treated group (1.5 versus 2.0, P=.007)
• Funding: not stated in the abstract; registered as NCT02424149.

Time to visualize ureteral urine efflux did not differ between study groups with a mean time of 2 minutes 40 seconds (±2 minutes 38 seconds) in the control group and 2 minutes 53 seconds (±4 minutes 35 seconds) in the treatment group (P=.77).

The label itself states there is no evidence that adding phenazopyridine to an antibacterial helps beyond 2 days. (Source 10)

• Official position, Certainty not rated.
• Size: not applicable.
• Who: people being treated for a urinary tract infection with an antibacterial.
• How long: beyond 2 days of combined treatment.
• Result: no benefit demonstrated for combined administration beyond 2 days.
• Funding: FDA-approved labelling, effective 14 July 2026.

Treatment of a urinary tract infection with Phenazopyridine HCl should not exceed 2 days because there is a lack of evidence that the combined administration of Phenazopyridine HCl and an antibacterial provides greater benefit than administration of the antibacterial alone after 2 days

Where the evidence is mixed

The fosfomycin comparison was open-label, with no placebo and no masking of patients or assessors. (Source 25)

• Randomized trial, Low certainty.
• Size: 152 women.
• Who: women with acute uncomplicated cystitis.
• How long: 2 days of phenazopyridine 200 mg three times daily, total 1200 mg.
• Result: multicentre, randomised, open-label; comparator was fosfomycin 3 g once plus drotaverine 80 mg three times daily for 2 days.
• Funding: not stated in the abstract.

A total of 152 women with acute uncomplicated cystitis were included in multicenter, randomized, open-label study which were carried out in 5 polyclinics of the Perm Territory.

A network meta-analysis of six studies ranked phenazopyridine best for pelvic pain after BCG but ranked celecoxib and prulifloxacin ahead of it for the urinary symptoms themselves. (Source 26)

• Meta-analysis, Low certainty.
• Size: 6 studies with 556 participants.
• Who: patients receiving BCG immunotherapy for bladder tumours.
• How long: not stated in the abstract.
• Result: celecoxib and prulifloxacin reduced the incidence of frequency, urgency and dysuria; phenazopyridine performed best for pelvic pain.
• Funding: not stated in the abstract.

The analysis included 6 studies with 556 participants. The results of the NMA revealed that celecoxib and prulifloxacin effectivelty reduce the incidence of LUTS including frequency, urgency and dysuria. Phenazopyridine showed the best performance in improving pelvic pain.

Where the research disagrees

Whether preoperative phenazopyridine is worth giving to help confirm ureteric patency at cystoscopy

• The randomised trial's primary endpoint, randomised controlled trial of 104 women, powered to detect a 3-minute difference: Time to visualize ureteral urine efflux did not differ between study groups with a mean time of 2 minutes 40 seconds (±2 minutes 38 seconds) in the control group and 2 minutes 53 seconds (±4 minutes 35 seconds) in the treatment group (P=.77). (Source 5)
• The same trial's authors, in their conclusion, same trial, relying on secondary surgeon-reported outcomes and void-trial results: Preoperative phenazopyridine is a useful and cost-saving medication for use in planned cystoscopy for evaluation of ureteral patency. (Source 27)

Whether phenazopyridine's rare but serious blood and kidney harms are confined to overdose

• The FDA-approved label, regulatory position, label effective 14 July 2026: Methemoglobinemia, hemolytic anemia, renal and hepatic toxicity have been reported, usually at overdosage levels (Source 16)
• Published case reports, single case report; the interstitial nephritis case likewise occurred at therapeutic doses: She was found to have a methemoglobin level of 21.5% and was treated with methylene blue, leading to a rapid improvement of her symptoms. She was taking one over-the-counter phenazopyridine 200 mg tablet three times daily for two weeks for her chronic dysuria. (Source 17)

How much

• Reference intake: Dosing is set by the prescriber. As a position, the current FDA-approved label gives an average adult dosage of two 100 mg tablets three times a day after meals, or one 200 mg tablet three times a day after meals, and says that when it is used alongside an antibacterial for a urinary tract infection it should not be given for more than 2 days. (Source 11)
• Upper limit: No formal upper limit is set. The label's limit is one of duration rather than dose: not more than 2 days alongside an antibacterial. It also warns that exceeding the recommended dose, or giving a usual dose to someone with impaired kidney function, can raise serum levels into the toxic range, and the drug is contraindicated outright in renal insufficiency. (Source 9)
• Studied: A single oral 200 mg dose (two 100 mg tablets) against matching placebo in 60 women with acute cystitis. (Source 2)
• Studied: 200 mg three times a day for 2 days, a total of 1200 mg, alongside a single 3 g dose of fosfomycin trometamol, in 152 women. (Source 25)
• Studied: A retrospective cohort of long-term use defined as more than a 14-day supply, with most patients receiving between a 30- and 60-day supply. (Source 7)

A common belief, and what the research shows

The belief: Phenazopyridine treats a urinary tract infection.

What the research shows: It does not touch the infection. The label states that "Because it provides only symptomatic relief, prompt appropriate treatment of the cause of pain must be instituted and Phenazopyridine HCl should be discontinued when symptoms are controlled." It also records that "there is a lack of evidence that the combined administration of Phenazopyridine HCl and an antibacterial provides greater benefit than administration of the antibacterial alone after 2 days". This misunderstanding has measurable consequences: in a survey of over-the-counter purchasers, "Fifty-one percent of the respondents used OTC phenazopyridine inappropriately, and 38% substituted it for medical care."

Questions and answers

What is it?

Phenazopyridine is an azo dye, a red-to-violet crystalline powder pressed into tablets. It is not an antibiotic. Its only job is to numb the lining of the lower urinary tract so that burning and pain are less noticeable while something else, usually an antibiotic, deals with the cause. (Source 28)

What does it do in the body?

Swallowed, it passes through the body largely unchanged: as much as 66% of a dose comes out in the urine still intact. It is in the urine that it works, acting on the bladder and urethral lining to dull pain, burning, urgency and frequency. The label is candid that nobody knows exactly how it does this and that its pharmacokinetics have never been worked out. (Source 1)

Is it good or bad for you?

It is a short-term comfort measure with thin evidence and real risks. One small placebo-controlled trial found symptom scores improved more than placebo six hours after a single dose. Three randomised trials of off-label uses found nothing. The harms, methaemoglobinaemia, oxidative haemolysis, interstitial nephritis and liver injury, are mostly case reports but some occurred on ordinary over-the-counter doses, and the National Toxicology Program lists it as reasonably anticipated to be a human carcinogen on rodent evidence. It is contraindicated in renal insufficiency. (Source 14)

How do you get more of it?

It is not a nutrient and there is no reason to want more of it. In the United States it is sold as 100 mg and 200 mg prescription tablets and also as lower-strength over-the-counter products. The label's stated adult dosage is two 100 mg tablets or one 200 mg tablet three times a day after meals, and no more than 2 days alongside an antibacterial. (Source 11)

If it is harmful, what reduces it?

Stopping the tablets is the first step; there is no taper. If methaemoglobinaemia has developed, the label describes methylene blue 1 to 2 mg/kg intravenously or ascorbic acid 100 to 200 mg orally as reducing it. Ascorbic acid at high dose has been used in case reports where methylene blue was contraindicated, such as G6PD deficiency. (Source 9)

Why might someone be low in it or missing it?

The question does not apply directly: phenazopyridine is a manufactured dye, not something the body makes. The people who should not have it at all are those with renal insufficiency, where it is contraindicated, and those who have reacted to it before. Declining kidney function with age is the reason older people accumulate it. (Source 29)

Which whole foods contain it or feed it?

No whole food contains phenazopyridine and no food feeds it. The only dietary instruction in the label is to take the tablets after meals. There is no pharmacokinetic study of a food effect, because, as the label states, the drug's pharmacokinetic properties have never been determined. (Source 1)

What happens if you do not have it?

Nothing happens to the body if you never take it, because it treats a symptom rather than a deficiency. Going without it when an infection is present is not dangerous provided the infection itself is treated: the label states there is no evidence it adds anything to an antibacterial beyond two days. The real danger runs the other way, with 38% of over-the-counter purchasers in one survey using it instead of seeing a clinician. (Source 19)

How can you test for it?

There is no routine blood test for the drug itself. What gets measured is its harm: a methaemoglobin concentration on an arterial blood gas confirms methaemoglobinaemia, which is suspected when low oxygen saturation does not improve with oxygen. A full blood count and film can show Heinz bodies and bite cells in oxidative haemolysis, and creatinine and liver enzymes catch the kidney and liver effects. Note that the drug's own colour can corrupt colour-based and spectrometric urine tests. (Source 8)

References

1. DailyMed, U.S. National Library of Medicine (Genus Lifesciences Inc.). PHENAZOPYRIDINE HYDROCHLORIDE tablet - FDA prescribing information (section: CLINICAL PHARMACOLOGY). 2026. Read the source
2. Urologiia. [Efficiency and safety of phenazopyridine for treatment of uncomplicated urinary tract infection: results of multi-center, randomized, placebo-controlled, clinical study] — abstract, Materials and methods. 2020. PMID 32597580, DOI 10.18565/urology.2020.3.15-21. Read the source
3. American Journal of Obstetrics and Gynecology. Phenazopyridine does not improve catheter discomfort following gynecologic surgery (Study design). 2011. PMID 21376167, DOI 10.1016/j.ajog.2010.12.045. Read the source
4. Female Pelvic Medicine & Reconstructive Surgery. The Effect of Oral Phenazopyridine on Perioperative Voiding After Midurethral Slings (EPIPhANy Study) — abstract, Results. 2018. PMID 29474280, DOI 10.1097/spv.0000000000000497. Read the source
5. Obstetrics and Gynecology. Phenazopyridine for Evaluation of Ureteral Patency: A Randomized Controlled Trial — abstract, Results. 2016. PMID 27399998, DOI 10.1097/aog.0000000000001472. Read the source
6. Urology Journal. Comparison of the Efficacy of Oxybutynin, Phenazopyridine, Celecoxib, and Placebo in the Treatment of Urinary Tract Symptoms after BCG Therapy in Patients with Bladder Tumors (Results). 2020. PMID 32981029, DOI 10.22037/uj.v16i7.5947. Read the source
7. Journal of Oncology Pharmacy Practice. Safety analysis of long-term phenazopyridine use for radiation cystitis (Results). 2020. PMID 31006341, DOI 10.1177/1078155219842646. Read the source
8. Hematology Reports. Phenazopyridine-Induced Methemoglobinemia in a Jehovah's Witness Treated with High-Dose Ascorbic Acid Due to Methylene Blue Contradictions: A Case Report and Review of the Literature. 2023. PMID 37367083, DOI 10.3390/hematolrep15020034. Read the source
9. DailyMed, U.S. National Library of Medicine (Genus Lifesciences Inc.). PHENAZOPYRIDINE HYDROCHLORIDE tablet - FDA prescribing information (section: OVERDOSAGE). 2026. Read the source
10. DailyMed, U.S. National Library of Medicine (Genus Lifesciences Inc.). PHENAZOPYRIDINE HYDROCHLORIDE tablet - FDA prescribing information (section: INDICATIONS AND USAGE). 2026. Read the source
11. DailyMed, U.S. National Library of Medicine (Genus Lifesciences Inc.). PHENAZOPYRIDINE HYDROCHLORIDE tablet - FDA prescribing information (section: DOSAGE AND ADMINISTRATION). 2026. Read the source
12. DailyMed, U.S. National Library of Medicine (Genus Lifesciences Inc.). PHENAZOPYRIDINE HYDROCHLORIDE tablet - FDA prescribing information (section: General). 2026. Read the source
13. Renal Failure. Phenazopyridine associated acute interstitial nephritis and review of literature. 2014. PMID 24575779, DOI 10.3109/0886022x.2014.890054. Read the source
14. National Toxicology Program, U.S. Department of Health and Human Services. Report on Carcinogens, Fifteenth Edition: Phenazopyridine Hydrochloride. 2021. Read the source
15. DailyMed, U.S. National Library of Medicine (Genus Lifesciences Inc.). PHENAZOPYRIDINE HYDROCHLORIDE tablet - FDA prescribing information (section: Carcinogenicity, Mutagenicity, Impairment of Fertility). 2026. Read the source
16. DailyMed, U.S. National Library of Medicine (Genus Lifesciences Inc.). PHENAZOPYRIDINE HYDROCHLORIDE tablet - FDA prescribing information (section: ADVERSE REACTIONS). 2026. Read the source
17. Clinics and Practice. A Case of Severe Hypoxia Caused by Phenazopyridine-Induced Methemoglobinemia: A near Fatal Event from Over-the-Counter Medication Use. 2022. PMID 36412668, DOI 10.3390/clinpract12060089. Read the source
18. Journal of Community Hospital Internal Medicine Perspectives. Syncope Following Treatment of UTI: A Case of Acute Hemolytic Anemia, Methemoglobinemia and Acute Renal Dysfunction Following Phenazopyridine Use in a Patient With G6PD Deficiency. 2023. PMID 36817304, DOI 10.55729/2000-9666.1144. Read the source
19. Journal of General Internal Medicine. Usage patterns of over-the-counter phenazopyridine (pyridium) — abstract, Results. 2003. PMID 12709095, DOI 10.1046/j.1525-1497.2003.20709.x. Read the source
20. Annals of Family Medicine. Consumer knowledge of over-the-counter phenazopyridine — abstract, Results. 2004. PMID 15209201, DOI 10.1370/afm.61. Read the source
21. DailyMed, U.S. National Library of Medicine (Genus Lifesciences Inc.). PHENAZOPYRIDINE HYDROCHLORIDE tablet - FDA prescribing information (section: Laboratory Test Interaction). 2026. Read the source
22. Urologiia. [Efficiency and safety of phenazopyridine for treatment of uncomplicated urinary tract infection: results of multi-center, randomized, placebo-controlled, clinical study] — abstract, Results. 2020. PMID 32597580, DOI 10.18565/urology.2020.3.15-21. Read the source
23. Urologiia. [Phenazopyridine and fosfomycin for the acute cystitis treatment: results of multicenter randomized study] — abstract, Results. 2021. PMID 34251097, DOI 10.18565/urology.2021.3.20-27. Read the source
24. American Journal of Obstetrics and Gynecology. Phenazopyridine does not improve catheter discomfort following gynecologic surgery — abstract, Results. 2011. PMID 21376167, DOI 10.1016/j.ajog.2010.12.045. Read the source
25. Urologiia. [Phenazopyridine and fosfomycin for the acute cystitis treatment: results of multicenter randomized study] — abstract, Material and methods. 2021. PMID 34251097, DOI 10.18565/urology.2021.3.20-27. Read the source
26. BMC Urology. Comparison of treatments for preventing lower urinary tract symptoms after BCG immunotherapy of bladder tumors: a systematic review and network meta-analysis (Result). 2025. PMID 39875945, DOI 10.1186/s12894-024-01675-6. Read the source
27. Obstetrics and Gynecology. Phenazopyridine for Evaluation of Ureteral Patency: A Randomized Controlled Trial — abstract, Conclusion. 2016. PMID 27399998, DOI 10.1097/aog.0000000000001472. Read the source
28. DailyMed, U.S. National Library of Medicine (Genus Lifesciences Inc.). PHENAZOPYRIDINE HYDROCHLORIDE tablet - FDA prescribing information (section: DESCRIPTION). 2026. Read the source
29. DailyMed, U.S. National Library of Medicine (Genus Lifesciences Inc.). PHENAZOPYRIDINE HYDROCHLORIDE tablet - FDA prescribing information (section: CONTRAINDICATIONS). 2026. Read the source