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Pirifur (Phenazopiridine, Nalidixic Acid)

Active Ingredient: Nalidixic Acid, Phenazopyridine
Dosage: 500 mg/50 mg
Route of Administration: Oral
Dosage Form: Tablets
Quantity per package: 24
Availability: Out of stock

Why Pirifur Is Not Used in the USA

Pirifur is not used in the USA primarily due to concerns over the resistance development associated with the use of older antibiotics like Nalidixic Acid. The U.S. FDA also has stringent regulations regarding the approval of drugs, especially those that contain ingredients with potential side effects and interactions, such as Nalidixic Acid. Moreover, newer and more effective treatments are available that reduce the reliance on older antibiotics.

Equivalent Drugs Sold in the USA

For similar symptoms of urinary discomfort and infections, here are some antibiotics used in the United States:

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These medications provide similar therapeutic benefits for treating symptoms related to urinary tract conditions, adhering to the regulatory standards and pharmaceutical advancements observed in the United States.

What Is Pirifur?

Pirifur is a combination drug prescribed in pain relief in urological diseases’ symptoms. It is used as emergency assistance. It is prescribed to treat urinary tract infections. The drug guarantees fast relief.

Nalidixic Acid is an antibacterial agent primarily used to treat urinary tract infections by inhibiting the replication of bacterial DNA. Phenazopyridine is a urinary tract analgesic that relieves pain, burning, irritation, and discomfort caused by urinary tract infections or diagnostic procedures. This dual-action makes Pirifur particularly effective for managing symptoms associated with urological conditions.


Pirifur is indicated for the treatment of urinary infections and concomitant symptoms, produced by gram-negative microorganisms sensitive to nalidixic acid including E. coli, Enterobacter sp, Klebsiella sp and most Proteus sp.

Countries in Which Pirifur Is Popular

Pirifur is particularly popular in countries where there is a high prevalence of urinary tract infections and where healthcare systems allow for the availability of such combination medications. These include:

  • Latin America: Countries like Mexico and Brazil, where broader-spectrum antibiotics and symptomatic treatments are commonly used and accessible.
  • Some Asian Countries: Regions with higher instances of urological issues and less strict regulations on antibiotic usage also see significant use of Pirifur.

Why It Is Used There: In these regions, Pirifur is favored for its effectiveness in quickly alleviating the discomfort and pain associated with urinary tract infections. The availability of over-the-counter options like Pirifur helps provide immediate relief for symptoms while also addressing the underlying bacterial infection.

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Dosage and Administration

Initial therapy (acute conditions, 7 to 14 days): 2 tablets every 6 hours. Maintenance therapy (chronic conditions, more than 14 days): 2 tablets every 8 hours in symptomatic patients or 2 tablets every 12 hours in asymptomatic patients. Take 2 tablets at once. It is recommended to administer this drug on an empty stomach, preferably one hour before meals.


Pirifur should not be administered to patients with known hypersensitivity to nalidixic acid or related compounds, with a history of seizures or porphyria, or to children under 1 year of age. Because of its phenazopyridine content, its use is contraindicated in liver and kidney failure.

Side Effects

The reactions reported after administration of Pirifur tablets included drowsiness, weakness, headache, paraesthesia and vertigo. Rarely, patients complained of subjective and reversible visual disturbances. These reactions included photosensitivity, change in color perception, difficulty focusing, decreased visual acuity and diplopia. These alterations disappeared when the treatment was suspended. In rare cases, patients experienced toxic psychosis or mild seizures (mainly in geriatric patients who have received an overdose or who are predisposed to these effects). Neonatal and pediatric patients receiving therapeutic doses of nalidixic acid had an occasional elevation of intracranial pressure with bulging of the anterior fontanel, papilledema and headache. A few patients had sixth cranial nerve paralysis. Even if the mechanisms of these reactions are unknown, the signs and symptoms usually disappear quickly after discontinuation of treatment. Other side effects: cholestasis, metabolic acidosis, thrombocytopenia, leukopenia or hemolytic anemia that may be associated with a difference in the activity of glucose-6-phosphate dehydrogenase.


Methemoglobinemia may occur in patients with associated susceptibility. Hemolytic anemia and liver and / or renal toxicity can also be observed. Treatment: these reactions are usually short-lived, due to the rapid excretion of the medication. If overdose is detected, it is recommended to perform gastric lavage. If absorption has already occurred, it is recommended to administer abundant fluids and establish supportive measures such as oxygen or artificial respiration. Although there is no data on the use of anticonvulsant therapy, it can be indicated in severe cases.

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Cross-resistance has been observed between Pirifur and other quinolones (such as oxolinic acid) but this has not been observed with other antibiotics. Nalidixic acid can increase the effects of oral anticoagulants such as warfarin to bishydroxycoumarin, through a considerable displacement of plasma albumin binding sites.