Urea C-13

Urea C-13 Overview

Urea C-13 (13C-Urea) is a synthetic, non-radioactive, stable isotope-labeled organic compound. Chemically, it belongs to the ureas class within the organic carbonic acids and derivatives superclass, consisting of a carbonyl functional group bonded to two amino groups, where the central carbon atom is enriched with the stable isotope carbon-13 (13C).

In clinical gastroenterology and diagnostic nuclear medicine/spectrophotometry, Urea C-13 is classified as an in vivo diagnostic agent for Helicobacter pylori (H. pylori) identification (ATC code V04CX05). It is the gold-standard substrate for the 13C-Urea Breath Test (UBT), indicated for the qualitative detection of gastric urease activity. It is used for the non-invasive initial diagnosis of H. pylori infection in adult and pediatric patients, as well as for post-treatment monitoring to confirm bacterial eradication. Marketed under brand names such as Pranactin-Citric, Pylobactell, and Helicobacter Test INFAI, 13C-Urea is preferred over radioactive 14C-Urea because carbon-13 is a naturally occurring, stable, non-radioactive isotope, making it completely safe for children, pregnant women, and repeated monitoring.

What Is Urea C-13 and How Does It Work?

Urea C-13 acts as a target enzymatic substrate for bacterial urease, an enzyme produced in abundance by Helicobacter pylori.

Its primary physiological, enzymatic, and diagnostic mechanisms include:

• Absence of Endogenous Human Urease: Human mammalian cells do not synthesize or express urease. Therefore, any rapid hydrolysis of ingested urea within the gastric lumen indicates the presence of urease-producing micro-organisms, specifically H. pylori.
• Enzymatic Cleavage by H. pylori Urease: Upon ingestion of 13C-Urea, gastric H. pylori urease rapidly catalyzes the cleavage of labeled urea into carbon dioxide (13CO2​) and ammonia (NH3​) at the interface of the gastric mucosal epithelium:
  13C-Urea+H2​OUrease​13CO2​+2NH3​
• Systemic Absorption & Exhalation: The generated 13CO2​ dissolves into gastric mucosa, enters systemic venous circulation, travels to the lungs, and is exhaled in the patient’s breath.
• Spectrophotometric Ratio Measurement: Breath samples collected before (baseline) and 15 to 30 minutes after swallowing 13C-Urea are analyzed using an Infrared Spectrophotometer or Isotope Ratio Mass Spectrometer (IRMS). A significant increase in the ratio of exhaled 13CO2​ to naturally occurring 12CO2​ above a established threshold confirms active H. pylori infection.
• Role of Co-administered Citric Acid: UBT kits (such as Pranactin-Citric) include citric acid to lower gastric pH. Acidification delays gastric emptying, ensuring prolonged contact between 13C-Urea and gastric mucosa, while simultaneously enhancing bacterial urease activity.

Is Urea C-13 FDA Approved?

Yes, Urea C-13 is approved by the US FDA. It received its official New Drug Application approval on September 17, 1997 under the trade name Pranactin-Citric (manufactured by Otsuka America Pharmaceutical) as an active in vivo diagnostic agent for the detection of gastric Helicobacter pylori urease activity. It is widely utilized across clinical laboratories and endoscopy centers in the United States for both initial diagnosis and verification of bacterial eradication following antibacterial therapy.

What Is Urea C-13 Used For?

• Qualitative non-invasive detection of gastric urease associated with Helicobacter pylori infection in patients presenting with dyspepsia or suspected peptic ulcer disease.
• Post-treatment monitoring to confirm H. pylori eradication (performed at least 4 weeks following completion of antimicrobial/antisecretory therapy).

Before Taking Urea C-13: Contraindications & Precautions

Do not use if you have a documented severe hypersensitivity to Urea C-13, citric acid, or product excipients. Urea C-13 (Pranactin-Citric) is an FDA-approved in vivo diagnostic agent indicated for the non-invasive qualitative detection of active gastric Helicobacter pylori infection in adult and pediatric patients.

Who Should Not Take Urea C-13?

• Patients with a documented hypersensitivity to Urea C-13, citric acid, or formulation excipients.
• Individuals unable to follow breath-sampling protocols or swallow oral test solutions.

Urea C-13, Pregnancy & Fertility

Unlike 14C-Urea (which emits low-dose ionizing beta radiation), 13C-Urea utilizes a naturally occurring, non-radioactive stable carbon isotope. Systemic exposure to single diagnostic doses produces no radiation risks, embryotoxicity, or teratogenicity. Urea C-13 is considered completely safe for use during pregnancy and lactation.

Tell Your Doctor Before Taking Urea C-13

Inform your gastroenterologist if you have recently taken antibiotics, proton pump inhibitors (PPIs), or bismuth compounds, as these medications cause false-negative test results.

Urea C-13 Dosage & Administration

Formulated as a powder for oral solution or soluble tablets. Standard adult diagnostic protocols (e.g., Pranactin-Citric) utilize 75 mg of Urea reconstituted in an aqueous citric acid solution (or a 100 mg soluble tablet).

Standard Urea C-13 Dosing

• Adult Diagnostic Protocol (Pranactin-Citric / Pylobactell): Standard single adult diagnostic dose consists of 75 mg 13C-Urea reconstituted in an aqueous citric acid solution (or 100 mg soluble tablet).
• Pediatric Diagnostic Protocol (3 to 11 Years): Reduced dosage kits containing 45 mg 13C-Urea are formulated specifically for young children.

How Urea C-13 Is Administered

• Administered strictly via the oral route following a mandatory fasting period (typically at least 4 hours).
• Test Procedure Steps:

1. Collect a baseline breath sample into a dedicated collection bag or tube.
2. Drink the freshly reconstituted 13C-Urea test solution completely within 2 minutes.
3. Sit quietly for 15 to 30 minutes (depending on kit instructions).
4. Collect the post-dose breath sample into a second collection container for spectrographic analysis.

Urea C-13 Clinical Efficacy & Research

Clinical trials demonstrate that the 13C-Urea Breath Test achieves diagnostic sensitivity and specificity exceeding 95% to 98% for detecting active H. pylori infection, outperforming serological antibody testing (which cannot distinguish between past and active infection). Comparative trials confirm that co-administration with citric acid maximizes diagnostic accuracy by eliminating false-negative results caused by rapid gastric emptying.

Urea C-13 Side Effects & Safety Profile

Adverse reactions are rare and mild. Common side effects secondary to citric acid ingestion include transient nausea, a sour taste, epigastric discomfort, eructation (burping), and mild lightheadedness. Serious adverse events such as systemic anaphylaxis occur in fewer than 1 in 100,000 administrations. Holds no FDA Black Box Warning.

Common Urea C-13 Side Effects

• Transient gastrointestinal effects: Mild nausea, sour taste, epigastric discomfort, or eructation (burping) secondary to citric acid ingestion.
• Mild transient dizziness or warmth.

Serious Urea C-13 Adverse Events

• Severe adverse events are extremely rare. Anaphylaxis or systemic hypersensitivity reactions to test components occur in fewer than 1 in 100,000 cases.

Managing Urea C-13 Side Effects

Mild gastric upset resolves spontaneously within minutes following completion of the breath test. Drinking a small amount of plain water after test completion alleviates residual sour taste.

Urea C-13 Drug Interactions & What to Avoid

Co-administration with medications that suppress H. pylori density or urease activity leads to false-negative diagnostic results.

Medications Causing False-Negative Results

• Antibiotics (e.g., Amoxicillin, Clarithromycin, Metronidazole): Suppress bacterial counts, leading to false-negative UBT results. Discontinue antibiotics for at least 4 weeks prior to testing.
• Proton Pump Inhibitors (PPIs – e.g., Omeprazole, Esomeprazole): Directly suppress H. pylori urease activity and gastric acid. Discontinue PPIs for at least 2 weeks prior to testing.
• Bismuth Preparations (e.g., Pepto-Bismol, Pylera): Exhibit direct anti-bacterial activity against H. pylori. Discontinue bismuth for at least 2 to 4 weeks prior to testing.
• H2-Receptor Antagonists (e.g., Famotidine): May weakly reduce test sensitivity; holding H2-blockers for 24 to 48 hours prior to testing is recommended in some clinical protocols.

Urea C-13, Food & Alcohol

Fast completely from food and liquids for at least 4 hours prior to taking the test. Eating before the test delays gastric mixing and can compromise diagnostic precision.

Urea C-13: Missed Dose, Overdose & Storage

Because Urea C-13 is administered as a single, one-time diagnostic reagent in a clinical facility, missed-dose protocols do not apply. Single diagnostic doses (75 mg to 100 mg) are minimal relative to endogenous human urea pools; overdose does not cause systemic toxicity, though excess citric acid may trigger transient stomach upset or diarrhea. Store un-reconstituted powders and tablets at controlled room temperature (15°C–30°C) protected from moisture; administer reconstituted solutions immediately.

Missed Dose of Urea C-13

Because Urea C-13 is administered as a single, one-time diagnostic reagent in a healthcare setting, missed dose protocols do not apply.

Urea C-13 Overdose & Emergency

Single-dose diagnostic quantities (75 mg to 100 mg) are minimal relative to endogenous human urea production. Overdose does not cause systemic toxicity, though excess citric acid may cause transient stomach upset or diarrhea.

How to Store Urea C-13

Store un-reconstituted diagnostic kit powders and tablets at controlled room temperature between 15°C and 30°C (59°F to 86°F). Reconstituted oral solutions must be administered immediately. Keep strictly out of reach of children.

Urea C-13 Patient Management & Monitoring

Verify that all antibiotics and bismuth preparations have been held for at least 4 weeks, PPIs held for at least 2 weeks, and that the patient has fasted for a minimum of 4 hours before testing. No continuous hemodynamic or laboratory monitoring is required during the 30-minute diagnostic protocol. Ensure both baseline and post-ingestion breath samples are collected properly in designated containers for isotope ratio mass spectrometry or infrared spectrophotometry analysis.

Preparation Checklist Before the Test

• Verify that all antibiotics and bismuth drugs have been stopped for at least 4 weeks.
• Verify that all proton pump inhibitors (PPIs) have been stopped for at least 2 weeks.
• Fast from food and drink for at least 4 hours prior to test arrival.

Monitoring During Urea C-13 Testing

No hemodynamic or laboratory monitoring is required during testing.

Urea C-13 Do’s and Don’ts

• Do inform your doctor about all recent heartburn or antibiotic medications.
• Do fast for at least 4 hours before the test.
• Do drink the entire diagnostic solution within 2 minutes.
• Do not take the test while actively taking PPIs or antibiotics.

Frequently Asked Questions

References

• DrugBank Database – Urea C-13 Clinical Profile (DB09510)
• Official FDA Prescribing Information – Pranactin-Citric (Urea C-13 Diagnostic Kit)

Legal Disclaimer

The detailed medical and chemical information provided on this specific web page is intended strictly for educational and informational purposes regarding complex pharmacological mechanisms. It absolutely does not constitute professional medical advice, medical diagnosis, or specific treatment recommendations. Always consult a licensed healthcare provider before making any personal decisions regarding complex medical conditions, medication adjustments, or dietary changes.