Continuing Education Activity

Phenazopyridine is a urinary analgesic widely available as both a prescription and over-the-counter medication, yet its appropriate clinical use, safety profile, and limitations remain poorly understood among patients and clinicians alike. This activity examines the pharmacology, approved indications, pharmacokinetics, dosing recommendations, adverse effects, and monitoring considerations associated with phenazopyridine. Particular attention is given to the drug's role as an adjuvant therapy in uncomplicated urinary tract infections, its contraindications in renal and hepatic impairment, and the risks associated with prolonged or inappropriate use. The activity also addresses the importance of patient education regarding the drug's symptomatic, not anti-infective, properties. By completing this activity, clinicians will be better equipped to counsel patients appropriately, recognize serious adverse effects, such as methemoglobinemia and hemolytic anemia, and apply evidence-based guidelines to optimize the safe and effective use of phenazopyridine in clinical practice.

Objectives:

• Identify patients with lower urinary tract infections who could benefit from phenazopyridine as an adjuvant treatment.
• Assess patients for contraindications to phenazopyridine use, including renal insufficiency, hepatic impairment, and glucose-6-phosphate dehydrogenase deficiency.
• Apply current dosing recommendations and treatment duration guidelines to minimize the risk of serious adverse effects associated with phenazopyridine.
• Collaborate with interdisciplinary health care team members, including pharmacists and nursing staff, to promote safe phenazopyridine use, reinforce patient counseling, and optimize treatment outcomes.

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Indications

FDA-Approved Indications

Phenazopyridine, an azo dye, is a urinary analgesic used as an adjuvant medicine in the outpatient setting to treat patients with urinary tract infections (UTIs) and related conditions. This medication is approved by the US Food and Drug Administration (FDA). Phenazopyridine is also used in an outpatient setting to treat patients with dysuria, urgency, and frequency associated with lower UTIs (see Image. Over-the-Counter Phenazopyridine US FDA Labeling).

Owing to its analgesic properties, phenazopyridine can be administered concurrently with antibiotic therapy to relieve patients' pain and enhance their comfort while they await effective treatment of the infection. Phenazopyridine's analgesic properties can reduce the need for other medications and systemic analgesics. In clinical and inpatient settings, phenazopyridine effectively alleviates pain related to trauma, catheter insertions, and surgical procedures. However, the drug's diagnostic applications are confined in scope.

History of Phenazopyridine

Phenazopyridine was initially synthesized in 1914 and later adopted by the US Pharmacopeia in 1928.[1][2] At that time, regulatory mandates did not necessitate preclinical studies to demonstrate the safety and efficacy of medications. Phenazopyridine was commonly prescribed for treating lower UTIs in patients with the mistaken belief that the drug had bactericidal properties. With the advent of antibiotics in the late 1930s, a definitive curative approach for UTIs was introduced, while phenazopyridine persisted as an adjuvant.[1] Over the decades, phenazopyridine has been marketed as a standalone drug or combined with antibiotics or other agents.[3]

Mechanism of Action

Although the mechanism of action of phenazopyridine lacks definitive substantiation, the drug is hypothesized to exert a localized analgesic effect on the urinary tract mucosa.[1][4] Evidence indicates that the drug inhibits nerve fibers in the bladder that respond to mechanical stimuli.[5] The drug also inhibits kinases involved in cell growth, metabolism, and nociception.[6]

Pharmacokinetics

Although the pharmacokinetic characteristics of phenazopyridine are recognized, a comprehensive evaluation of these characteristics is lacking. These characteristics include the following:

Absorption: Following oral administration, the drug is rapidly absorbed in the gastrointestinal tract and reaches peak plasma concentration within 2 to 3 hours.[7][8] Although the exact absorption site of the drug is unknown, evidence suggests that 2 distinct regions are involved.[7] Results from studies investigating the half-life of phenazopyridine have been inconsistent, with 1 study reporting an average half-life of 9.4 hours.[8] The extent of protein binding is also unknown.

Metabolism: Information about the drug's metabolism is derived from animal studies.[9] Aniline and triaminopyridine are the 2 metabolites that could potentially be attributed to hematological and renal adverse effects of the drug, respectively.[10][11] Another metabolite of aniline, N-acetyl-4-aminophenol, is commonly recognized as acetaminophen and paracetamol (see Image. Phenazopyridine Chemical Structure). Nonetheless, this metabolite's clinical relevance is considered negligible (see Image. Phenazopyridine Metabolism).

Elimination: After an oral dose of phenazopyridine, approximately 41% to 65% of the medication is excreted unchanged by the kidneys.[9][10]

Administration

Adult Dosage, Dosage Forms, and Strengths

Typically, phenazopyridine is prescribed at a dosage of 100 to 200 mg 3 times daily for healthy adults. Over-the-counter (OTC) tablets are obtainable in lower strengths, ranging from 50 to 99.5 mg. OTC tablets are frequently taken 2 at a time, 3 times daily, effectively matching the prescription regimen. The OTC formulation is a valuable option for temporary symptom relief while awaiting additional medical attention. To prevent stomach discomfort, phenazopyridine is best taken with or after meals.[12] 

The recommended phenazopyridine treatment duration is 2 days; this short period provides swift relief from discomfort until antibiotics can effectively treat the infection and safeguard the patient from potentially severe adverse effects. Certain clinicians recommend that individuals experiencing uncomplicated UTI symptoms take OTC phenazopyridine alone for 5 days, expecting the infection to resolve spontaneously. However, most patients favor a more assured resolution, and a 5-day therapy duration exceeds current recommendations, a practice not yet substantiated.

The drug is commonly used to enhance comfort among outpatients with uncomplicated UTIs. However, phenazopyridine is not routinely included in treatment protocols for complicated UTIs or inpatient scenarios addressing acute pyelonephritis in patients with risk factors for heightened infection severity. 

Diagnostic use

Results from one study indicate that oral phenazopyridine administration with dextrose instillation can effectively facilitate visualization of ureteral patency during intraoperative cystoscopy.[13] Administering a single 200 mg dose of phenazopyridine the evening before the surgical procedure aids in identifying the urethral orifice.[14] However, phenazopyridine is not a valuable diagnostic tool for detecting incontinence or premature membrane rupture.[14][15]

Cystoscopy use

In a randomized controlled trial, 97 patients undergoing cystoscopy received either 200 mg of phenazopyridine along with lidocaine gel or lidocaine gel alone. The medications were administered in 3 doses, starting with a dose given 20 minutes before the procedure, followed by doses every 8 hours thereafter. Participants who received phenazopyridine and lidocaine gel reported experiencing less discomfort and exhibited lower heart rates than those who received only lidocaine gel. The authors concluded that phenazopyridine reduces the intensity of pain associated with both cystoscopy and the first urination after.[16]

Postoperative use

In results from a randomized controlled study involving 152 women undergoing prolapse surgical procedures, administering a single postoperative dose of phenazopyridine at 200 mg did not demonstrate enhanced postoperative voiding compared to the control group.[17] Findings from a retrospective cohort study of 149 women who underwent retropubic midurethral sling surgery indicate that phenazopyridine improved postoperative voiding.[18]

Radiation-Induced Cystitis Use

Phenazopyridine has been used safely for up to 2 months as a form of supportive care in cases of radiation-induced cystitis.[19]

Specific Patient Populations

Renal impairment: For individuals with mild renal impairment, with a glomerular filtration rate (GFR) greater than 50 mL/min, the recommended dosing frequency is every 8 to 16 hours. Phenazopyridine should not be used in patients with a GFR less than 50 mL/min.[20]

Hepatic impairment: Phenazopyridine is contraindicated in cases of severe hepatitis.

Pregnancy considerations: Phenazopyridine is an FDA pregnancy category B drug known to cross the placenta.[15] Phenazopyridine should be used in pregnancy only if it is indicated. 

Breastfeeding considerations: No specific information is available regarding the drug's use during lactation; however, avoiding its use during breastfeeding is recommended, especially if the infant is younger than 1 month or has known glucose-6-phosphate dehydrogenase (G6PD) deficiency. [21]

Pediatric patients: The recommended dosage for children aged 6 to 12 years is 12 mg/kg/d, divided into 3 equal doses. A specialized pediatric formulation is not commercially available and requires compounding.[22] Although review articles and consensus publications addressing the treatment of pediatric UTIs exist, these resources do not typically reference the use of phenazopyridine.[23][24]

Older patients: Consulting renal dosing guidelines is advised for older adults.

Clinical Studies

Phenazopyridine was marketed before the implementation of regulations that mandated preclinical studies to establish a drug's safety and efficacy. Consequently, comprehensive studies are lacking, and the drug's role in UTI treatment primarily relies on clinical observations. However, a critical analysis of the available studies has been published. Among these studies, one included 118 patients, of which 64% had cystitis or pyelonephritis. All participants received phenazopyridine at 200 mg 3 times daily for 2 weeks, exceeding the recommended duration. The analysis was conducted as an open-label, single-arm study. The authors documented enhanced symptomatic responses, including alleviation of dysuria (95.3%), burning sensation (93.6%), frequency (85.6%), and nocturia (83.7%).[1] Another investigation involved 49 subjects with acute UTIs who received phenazopyridine at a dosage of 200 mg administered 3 times daily. After 24 and 72 hours, patients underwent evaluations for nocturia, burning, and urgency symptoms. Mean symptom scores were reported as slight, with 3 or 4 symptoms after 24 hours and none after 72 hours.[25]

Phenazopyridine was compared to flavoxate, an antispasmodic drug, in a study involving 392 participants displaying UTI symptoms, incontinence, or suprapubic pain. Participants were given either phenazopyridine at 200 mg 3 times daily or flavoxate at 100 mg 4 times daily. The variances in clinical response were not statistically significant. In a separate analysis of men with prostatitis, participants were subjected to a regimen of phenazopyridine at a dosage of 200 mg 3 times daily; only 31% reported satisfactory relief from symptoms.[12] 

Adverse Effects

Phenazopyridine has a favorable safety profile, with infrequent occurrences of severe adverse events. Severe and potentially life-threatening adverse effects are generally confined to instances of overdose, preexisting renal insufficiency, and exceeding the recommended dosing and duration guidelines.[26][27]

The common adverse effects of phenazopyridine include:

• Central nervous system: Headache

• Dermatological: Rash, discoloration, pruritus, and ulceration [28]

• Hypersensitivity: Anaphylactoid-like reaction or hypersensitivity hepatitis

• Gastrointestinal: Nausea, vomiting, and diarrhea

• Hematological: Methemoglobinemia, sulfhemoglobinemia, and hemolytic anemia (may act as a potential hemolytic agent in G6PD deficiency) [29][30][31]

• Renal: Acute interstitial nephritis [32]

• Other effects: Discoloration of body fluids, aseptic meningitis, visual disturbances, renal or hepatic toxicity associated with overdose, jaundice, and renal calculi [4]

The drug is recognized for its potential to induce methemoglobinemia and hemolytic anemia, which are thought to occur via a metabolite, aniline. In cases of hemolytic anemia, a microscopic examination of red blood cells reveals the presence of Heinz bodies and degmacytes (bite cells).[33] Treatment for drug-induced hemolytic anemia involves discontinuing the causative agent and considering corticosteroids.[34]

Interstitial nephritis may manifest following an overdose, and cases have been reported even with therapeutic doses and in individuals with normal renal function.[32] In instances of phenazopyridine-induced nephrotoxicity, the use of roentgenographic contrast media may exacerbate renal damage.[35] Cases of hepatitis appear to be associated with dose-related hypersensitivity.[36][37] Other infrequent adverse effects, such as thrombocytopenia and allergic-like skin reactions, have also been reported.[38][39]

Contraindications

Individuals with known hypersensitivity to phenazopyridine should avoid taking the medication. Furthermore, phenazopyridine is contraindicated in severe renal insufficiency, with a GFR less than 50 mL/min. Patients with severe hepatitis are advised not to take the drug, given these contraindications.

Precautions

Patients with known G6PD deficiency are more susceptible to hemolysis and should avoid receiving phenazopyridine.[29] In addition, the drug should be administered cautiously in cases of impaired hepatic function.

Carcinogenicity

Rats given phenazopyridine developed liver and colorectal tumors, encompassing both malignant and benign growths. However, no established correlation exists between human phenazopyridine use and carcinogenicity.[15th Report on Carcinogens, National Toxicology Program, 2021.Phenazopyridine Hydrochloride]

Interactions

Phenazopyridine has no known drug-drug or drug-food interactions. Due to its dye properties, phenazopyridine is anticipated to interfere with urinalysis tests that rely on color reactions or spectrometry. Theoretically, a heightened risk of methemoglobinemia may occur when phenazopyridine is combined with a local anesthetic such as benzocaine. However, this potential risk lacks confirmation in medical literature, as the drug has been effectively used alongside lidocaine gel.[16]

Table

Which contraindication should be screened for before prescribing phenazopyridine to a patient with dysuria? What is the recommended maximum duration of phenazopyridine therapy when used alongside antibiotics for uncomplicated urinary tract infection symptoms? (more...)

Monitoring

Because phenazopyridine is available as an OTC product, there is the possibility of incorrect drug usage. Effective patient education is of utmost importance while using the medication.[40][41] Clinicians should instruct patients that phenazopyridine is not an antibiotic but provides only symptomatic relief.[42]

Although some uncomplicated lower UTIs might resolve spontaneously and even achieve a bacteriological cure, the overall cure rate remains relatively low. Results from research established that appropriate antibiotic treatment leads to quicker symptom resolution and a higher likelihood of bacteriological cure than a placebo.[43][44] When an antibiotic is prescribed, phenazopyridine can enhance comfort while the antibiotic works to eliminate the causative bacteria. For example, in 2 surveys conducted in Los Angeles County, 71% of OTC phenazopyridine consumers were unaware that a bladder infection or another type of UTI caused their symptoms. Furthermore, 38% reported purchasing the drug as a substitute for medical care.[45][46]

Due to its dye properties, phenazopyridine causes a noticeable change in urine color, turning it reddish-orange (see Image. Urine Colored With Phenazopyridine). Patients should receive counseling about this effect to address concerns proactively; they should be informed that the alteration in urine color results from the drug's color and does not indicate bleeding. Spilled urine can potentially cause staining, particularly on clothing. Extended use beyond appropriate limits may lead to yellowing of the skin and sclerae. The drug is also reported to change the color of tears and ejaculate. Some review articles state that phenazopyridine use may result in contact lens staining; however, which types of lenses (soft, rigid, and so on) are potentially affected are not mentioned, and these statements are not referenced. Patients should also promptly report any urinary tract symptoms that do not improve or that worsen.[22][41]

Toxicity

The occurrence of phenazopyridine-induced methemoglobinemia is rare, with fewer than 50 cases documented since 1951. The National Poison Data System study, conducted in 2020, analyzed data from 2007 to 2017 to identify substances frequently associated with methemoglobinemia. Results from the study indicated that phenazopyridine is linked to a notable number of reported cases of methemoglobinemia.[47] 

Methemoglobinemia can be treated using standard treatments, including methylene blue with ascorbic acid, the preferred antidote. This medication is administered intravenously as a 1% solution at a dose of 1 to 2 mg/kg as required. Methylene blue should not be administered to patients with known or suspected G6PD deficiency or those taking antidepressants, as the drug can elevate the risk of serotonin syndrome.[40][48][49]

In such scenarios, the recommended alternative antidote is intravenous high-dose ascorbic acid. Results from research have elucidated the reasons why phenazopyridine and other drugs, such as dapsone and chloroquine, more commonly induce methemoglobinemia compared to other medications. Oxidative Heinz body hemolytic anemia may also be triggered, and chronic overdose can manifest with bite cells, also known as degmacytes.

In cases of drug overdose, patients can experience renal toxicity, occasional renal failure, and hepatic impairment.[50] Although the mechanism behind renal toxicity remains unclear, a metabolite known as triaminopyridine might damage the distal renal tubules.[11] Life-threatening adverse effects, including hemolytic anemia and renal failure, have been associated with inappropriate OTC phenazopyridine use and intentional drug overdose.[51][52]

Enhancing Healthcare Team Outcomes

Due to its availability as an OTC product, there exists the potential for inappropriate use of phenazopyridine. Therefore, gathering information on both OTC and prescription drugs is imperative when conducting medication reviews.[52] The interdisciplinary health care team should collaborate to deliver comprehensive patient education. Opting for treatment with an appropriate antibiotic leads to significantly faster symptom relief and elimination of the infection. Clinicians may consider prescribing phenazopyridine to alleviate burning, urgency, frequency, and pain associated with lower UTIs, potentially for a brief duration of 2 days until the antibiotic effectively eliminates the causative bacteria. Continued use beyond 2 days could impede the timely diagnosis and initiation of appropriate treatment. Patients must therefore understand that phenazopyridine has no anti-infective properties.

Clinicians should verify the accuracy of the dosage before administering phenazopyridine to patients and counsel them regarding the extended treatment duration, which heightens the risk of severe adverse effects. Patients should also be informed about urine color changes to prevent unnecessary alarms when they notice them. Pharmacists are critical in educating patients that phenazopyridine solely offers symptomatic relief and, therefore, should not serve as a substitute for seeking medical attention. Instead, patients should collaborate with their clinicians, sharing any observations or concerns about their medication regimen. Promoting open communication and fostering collaboration among all interdisciplinary health care team members enhances patient safety and optimizes treatment outcomes when using phenazopyridine.[52]

Review Questions

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Disclosure: John Eastham declares no relevant financial relationships with ineligible companies.

Disclosure: Preeti Patel declares no relevant financial relationships with ineligible companies.