Fludeoxyglucose (18F) NUS: Uses, Dosage & Side Effects

What Is Fludeoxyglucose (18F) NUS and What Is It Used For?

Fludeoxyglucose (18F) NUS contains the active substance fludeoxyglucose (18F), which is 2-deoxy-2-[18F]fluoro-D-glucose – a modified sugar molecule in which one hydroxyl group on the glucose molecule has been replaced with the positron-emitting radionuclide fluorine-18. This modification is the key to its diagnostic utility: the molecule is recognized by the body’s glucose transport mechanisms and taken up into cells, but once inside, it cannot be fully metabolized through the normal glycolytic pathway. Instead, it becomes trapped within cells as FDG-6-phosphate, allowing the accumulated radioactivity to be detected externally by a PET scanner.

The fundamental principle behind FDG PET imaging is the Warburg effect – the observation that malignant tumor cells preferentially utilize glucose at a much higher rate than normal cells, even in the presence of adequate oxygen. This phenomenon, first described by Nobel laureate Otto Warburg in the 1920s, forms the biological basis for FDG’s ability to identify cancerous tissue. However, increased glucose metabolism is not exclusive to cancer; it also occurs in activated immune cells, inflammatory tissue, and the normal brain and heart, which explains both the broad clinical utility and the limitations of FDG PET imaging.

After intravenous injection, FDG is rapidly distributed throughout the body via the bloodstream. Cellular uptake occurs through facilitated glucose transporter proteins, primarily GLUT-1 (ubiquitous) and GLUT-3 (predominantly in neural tissue). Once inside the cell, the enzyme hexokinase phosphorylates FDG to FDG-6-phosphate. Unlike glucose-6-phosphate, FDG-6-phosphate is not a suitable substrate for further glycolytic enzymes or for glucose-6-phosphatase (which is present in low concentrations in most tissues other than the liver). This metabolic trapping mechanism results in progressive intracellular accumulation of the radiotracer in proportion to the rate of glucose utilization in each tissue.

The fluorine-18 atom in FDG undergoes positron emission decay with a physical half-life of 109.77 minutes (approximately 110 minutes). Each emitted positron travels a short distance (typically 1–2 mm in tissue) before encountering an electron, resulting in an annihilation event that produces two 511 keV gamma photons traveling in approximately opposite directions. These coincident photons are detected by the ring of detectors surrounding the patient in the PET scanner, and sophisticated mathematical algorithms reconstruct three-dimensional images of radiotracer distribution throughout the body. When combined with computed tomography (CT) in a PET/CT scanner, the metabolic information from PET is precisely co-registered with the anatomical detail from CT, providing clinicians with powerful diagnostic images.

Oncology Applications

FDG PET/CT has become an indispensable tool in modern oncology and is used across virtually all cancer types. Its established clinical roles include initial diagnosis and characterization of suspicious lesions, staging of newly diagnosed cancers to determine disease extent, restaging after treatment to assess response, detection of recurrence during follow-up, and guidance of biopsy site selection. The National Comprehensive Cancer Network (NCCN), the European Society for Medical Oncology (ESMO), and numerous other professional organizations include FDG PET/CT in their clinical practice guidelines for the management of lung cancer, lymphoma, melanoma, colorectal cancer, head and neck cancers, esophageal cancer, breast cancer, and many other malignancies.

The sensitivity and specificity of FDG PET/CT vary by tumor type and clinical scenario. In general, FDG PET/CT is highly sensitive for metabolically active tumors – sensitivity exceeds 90% for most common solid tumors and lymphomas. However, certain tumor types exhibit low FDG avidity due to their biological characteristics: well-differentiated neuroendocrine tumors, mucinous carcinomas, renal cell carcinoma, prostate cancer (especially low-grade), bronchoalveolar carcinoma, and hepatocellular carcinoma may show false-negative results. In these cases, alternative PET tracers (such as gallium-68 DOTATATE for neuroendocrine tumors or PSMA ligands for prostate cancer) may be more appropriate.

Cardiology Applications

In cardiology, FDG PET is used primarily to assess myocardial viability in patients with ischemic cardiomyopathy who are being considered for coronary revascularization. The rationale is that viable but hibernating myocardium (heart muscle that is dysfunctional due to chronic reduced blood flow but still capable of recovery) shifts its metabolic substrate from fatty acids to glucose. By comparing FDG uptake (metabolism) with myocardial perfusion imaging (blood flow), cardiologists can distinguish between viable hibernating myocardium (reduced perfusion with preserved FDG uptake, known as a “mismatch” pattern), scarred non-viable tissue (reduced perfusion and reduced FDG uptake, a “match” pattern), and normal myocardium. Patients with a significant mismatch pattern are most likely to benefit from revascularization procedures such as coronary artery bypass grafting or percutaneous coronary intervention.

Additionally, FDG PET/CT has an emerging role in cardiac imaging for the diagnosis of cardiac sarcoidosis, prosthetic valve endocarditis, and cardiac device infections, where it can detect focal inflammatory activity that may not be visible on conventional imaging modalities.

Neurology Applications

The brain is the organ with the highest glucose consumption in the body, utilizing approximately 20–25% of total body glucose despite representing only about 2% of body weight. FDG PET exploits this high baseline metabolic activity to identify areas of abnormal cerebral metabolism. In epilepsy, FDG PET performed during the interictal (between seizures) period typically shows hypometabolism (reduced FDG uptake) in the epileptogenic zone, helping neurosurgeons to localize seizure foci for potential surgical resection, particularly in patients with medically refractory temporal lobe epilepsy.

In neurodegenerative disease, FDG PET demonstrates characteristic patterns of cerebral hypometabolism that can aid in the differential diagnosis of various forms of dementia. Alzheimer’s disease typically shows bilateral temporoparietal and posterior cingulate hypometabolism; frontotemporal dementia shows frontal and/or anterior temporal lobe predominant hypometabolism; and dementia with Lewy bodies shows occipital cortex involvement in addition to posterior cortical hypometabolism. These distinct metabolic signatures, recognized by the European Association of Nuclear Medicine (EANM) and the Society of Nuclear Medicine and Molecular Imaging (SNMMI), contribute valuable diagnostic information, particularly in cases where clinical presentation is ambiguous.

What Should You Know Before Receiving Fludeoxyglucose (18F) NUS?

Contraindications

There are no absolute contraindications to the administration of Fludeoxyglucose (18F) NUS in situations where the clinical benefit of the diagnostic information clearly outweighs the risks. However, the procedure should not be performed if there is a known hypersensitivity to fludeoxyglucose (18F) or any of the excipients in the formulation, although true allergic reactions to FDG are extremely rare. The only other situation where administration is generally contraindicated is in confirmed pregnancy where the examination is not considered urgently necessary, due to the radiation dose to the fetus.

Blood glucose levels above 11 mmol/L (200 mg/dL) at the time of injection are a relative contraindication for oncological imaging, as hyperglycemia significantly impairs FDG uptake into tumor cells. Elevated blood glucose competes with FDG for glucose transporter binding sites and reduces the contrast between tumor and background tissue, potentially leading to false-negative results. The scan should be rescheduled if blood glucose cannot be adequately controlled.

Warnings and Precautions

Before receiving Fludeoxyglucose (18F) NUS, inform your nuclear medicine team about the following:

• Diabetes mellitus: Patients with diabetes require special preparation to optimize blood glucose levels before the scan. Uncontrolled diabetes can lead to poor image quality and unreliable results. Your nuclear medicine department will provide specific instructions about managing your diabetes medications on the day of the scan. Generally, patients with type 2 diabetes may need to take their oral hypoglycemic medications earlier than usual, and insulin-dependent diabetic patients may need adjusted insulin timing to ensure fasting blood glucose is below 11 mmol/L at the time of injection.
• Renal impairment: Approximately 20% of the injected FDG is excreted through the kidneys. Patients with renal impairment may experience slower clearance of the radiotracer, which can affect image quality and result in a slightly higher radiation dose. Adequate hydration is particularly important in these patients.
• Recent surgery or radiotherapy: Inflammatory changes following surgery, radiotherapy, or other invasive procedures can cause increased FDG uptake that mimics or masks malignant disease. Ideally, FDG PET/CT should be performed at least 4–6 weeks after surgery and 8–12 weeks after the completion of radiotherapy to minimize the risk of false-positive results.
• Active infections or inflammatory conditions: Any active infection, abscess, granulomatous disease (such as sarcoidosis or tuberculosis), or inflammatory condition can cause increased FDG uptake that may be mistaken for malignancy. Inform your doctor about any current infections or inflammatory conditions.
• Recent chemotherapy: FDG PET/CT for treatment response assessment should ideally be performed at least 2 weeks after the last cycle of chemotherapy (and preferably 6 weeks for accurate response assessment) to avoid false-negative results from chemotherapy-induced metabolic stunning of tumor cells.

Pregnancy and Breastfeeding

If you are pregnant, think you may be pregnant, or are planning to become pregnant, inform your nuclear medicine team before the procedure. Any nuclear medicine examination in a pregnant woman involves radiation dose to the fetus. The effective dose to the fetus from a standard FDG PET examination (without CT) is approximately 1–2 mSv, and the additional CT component adds to this exposure. FDG PET/CT should only be performed during pregnancy when the clinical benefit is considered essential and outweighs the potential risk to the fetus – for example, in the staging of a newly diagnosed aggressive cancer where the imaging results will directly influence immediate treatment decisions.

If you are breastfeeding, you should temporarily interrupt breastfeeding and discard the expressed breast milk for at least 12 hours after the injection of FDG (or longer, depending on local regulatory guidelines and the administered activity). This is because small amounts of FDG can be excreted in breast milk, and the radioactivity could expose the infant to unnecessary radiation. During this period, expressed milk should be stored and discarded. Breastfeeding can be safely resumed after the recommended interruption period. You should also avoid close contact with the infant for several hours after the scan, as your body will emit low levels of external radiation during this time.

Children

FDG PET/CT can be performed in children when clinically indicated, but particular attention must be given to minimizing the radiation dose. Pediatric protocols use weight-based activity calculations (typically 3.7 MBq/kg body weight, with a minimum activity of approximately 26 MBq) in accordance with EANM Dosage Card recommendations. The indication for the scan must be carefully justified, as children are more radiosensitive than adults and have a longer expected lifespan during which radiation-induced effects could manifest. Young children may require sedation to remain still during the scan, which requires additional preparation and monitoring.

Driving and Activities After the Scan

There are no restrictions on driving or operating machinery after an FDG PET/CT scan, unless sedation was administered. You can resume normal daily activities immediately after the procedure. However, you should drink plenty of fluids and urinate frequently for several hours after the scan to help clear the radiotracer from your body and minimize radiation dose to the bladder wall. Your nuclear medicine department may recommend limiting prolonged close contact with pregnant women and young children for a period of several hours after the procedure, depending on the administered activity.

How Does Fludeoxyglucose (18F) NUS Interact with Other Drugs?

Unlike conventional pharmaceutical drugs that interact through pharmacokinetic or pharmacodynamic mechanisms at therapeutic doses, fludeoxyglucose (18F) is administered in trace amounts (nanomolar concentrations) that have no pharmacological effect. However, numerous medications and physiological factors can significantly alter the biodistribution of FDG throughout the body, affecting the quality and diagnostic accuracy of PET images. These are more accurately described as “biodistribution interactions” rather than classical drug-drug interactions.

Understanding these interactions is crucial because altered FDG biodistribution can lead to false-positive results (where benign processes are mistaken for disease), false-negative results (where true disease is missed), or poor overall image quality that renders the scan non-diagnostic. The following table summarizes the most clinically significant interactions:

It is essential that you inform your nuclear medicine team about all medications you are currently taking, including over-the-counter drugs, herbal supplements, and any recent changes in your medication regimen. This information allows the interpreting physician to account for potential biodistribution alterations and avoid misinterpretation of the scan results.

In addition to pharmaceutical interactions, several physiological and environmental factors affect FDG biodistribution. Physical exercise within 24 hours before the scan increases skeletal muscle FDG uptake. Cold environmental temperatures during the uptake period can activate brown adipose tissue (brown fat), causing prominent uptake in the neck, supraclavicular regions, and mediastinum that may obscure or mimic pathology. Patients should be kept warm during the uptake period, and some centers administer oral beta-blockers (such as propranolol) or benzodiazepines to suppress brown fat activation in patients undergoing repeated scans.

What Is the Correct Dosage of Fludeoxyglucose (18F) NUS?

Fludeoxyglucose (18F) NUS is always administered by qualified nuclear medicine personnel in an authorized facility. Unlike most medications where a patient self-administers at home, FDG is prepared in specialized radiopharmacy facilities (often using cyclotron-produced fluorine-18) and delivered to the nuclear medicine department for same-day use due to the short half-life of fluorine-18. The radiopharmacist and nuclear medicine physician work together to determine the appropriate activity (measured in megabecquerels, MBq) for each patient.

Adults

The recommended administered activity of FDG for adults varies depending on the clinical indication, the PET scanner technology (older scanners may require higher activities), and institutional protocols. The following table provides the typical dose ranges:

On modern digital PET/CT scanners with silicon photomultiplier (SiPM) detectors and advanced reconstruction algorithms, lower activities (as low as 1.5–2.5 MBq/kg body weight) can produce diagnostic-quality images, reflecting the ongoing trend toward dose reduction in nuclear medicine. Your nuclear medicine department will use the optimal activity for their specific scanner and reconstruction protocols.

Children

Pediatric dosing of FDG follows weight-based activity calculations in accordance with the EANM Dosage Card (updated 2016). The standard recommendation is approximately 3.7 MBq/kg body weight, with a recommended minimum activity of approximately 26 MBq to ensure diagnostic image quality. For example, a 20 kg child would typically receive approximately 74 MBq. Pediatric nuclear medicine specialists may further adjust the activity based on the clinical scenario, the child’s age, and the scanner technology available.

Elderly Patients

No specific dose adjustment is required for elderly patients based solely on age. However, elderly patients may have reduced renal function, which can slightly affect the clearance and radiation dosimetry of FDG. The nuclear medicine physician will consider the patient’s overall clinical condition, including renal function, when determining the administered activity. Adequate hydration is particularly important in elderly patients to promote renal excretion of the radiotracer.

Patient Preparation

Proper patient preparation is essential for obtaining high-quality, diagnostically accurate FDG PET images. The following preparation guidelines apply to most clinical indications:

• Fasting: Fast for at least 4–6 hours before the scheduled injection time. Water (plain, non-flavored, non-sweetened) is permitted and encouraged. All other beverages, food, sweets, chewing gum, and anything that could stimulate insulin release must be avoided.
• Hydration: Drink at least 500 mL of water during the hour before the injection. Adequate hydration improves image quality and reduces radiation dose to the bladder.
• Blood glucose check: Blood glucose will be measured before injection. For oncological indications, FDG should not be administered if blood glucose exceeds 11 mmol/L (200 mg/dL). Some centers use a stricter threshold of 8.3 mmol/L (150 mg/dL).
• Avoid exercise: Avoid any strenuous physical activity for at least 24 hours before the scan to minimize FDG uptake into skeletal muscle.
• Keep warm: Stay warm before and during the uptake period. Cold temperatures activate brown adipose tissue, which can cause confounding FDG uptake. Your nuclear medicine department will provide a warm, quiet room for the uptake period.
• Rest quietly: During the 60-minute uptake period after injection, you should rest quietly in a warm, dimly lit room. Avoid talking (to minimize laryngeal muscle uptake), reading (to minimize eye muscle uptake in brain studies), and any physical activity.

Overdose

Because FDG is administered in trace pharmacological amounts, a pharmacological overdose in the traditional sense is not expected. However, inadvertent administration of an excessive radioactivity (higher than intended activity in MBq) would result in an unnecessarily high radiation dose to the patient. In such cases, the radiation dose to critical organs (particularly the bladder wall) should be minimized by promoting forced diuresis through aggressive hydration and frequent urination. There is no specific antidote for radiation exposure from FDG. The short physical half-life of fluorine-18 (110 minutes) means that the radioactivity will decrease rapidly regardless of intervention.

What Are the Side Effects of Fludeoxyglucose (18F) NUS?

Fludeoxyglucose (18F) NUS has an exceptionally favorable safety profile. Because it is administered in trace pharmacological amounts (nanomolar concentrations), the glucose analogue itself has no pharmacological effect on the body. The administered amount of FDG is approximately one million times less than the amount of glucose normally circulating in the bloodstream. Consequently, pharmacological side effects from the FDG molecule itself are essentially nonexistent.

The primary “side effect” of any nuclear medicine procedure, including FDG PET/CT, is the inevitable exposure to ionizing radiation. The effective radiation dose from a standard FDG PET scan (without CT) is approximately 4–7 mSv for a typical adult dose of 300–400 MBq. The additional CT component adds approximately 5–25 mSv depending on the CT protocol used (low-dose attenuation correction CT vs. diagnostic-quality CT). For context, the average annual background radiation from natural sources is approximately 2.4 mSv (range 1–10 mSv depending on geographic location).

Based on post-marketing pharmacovigilance data and published literature, the following adverse reactions have been reported:

It is important to contextualize the radiation risk associated with FDG PET/CT. Regulatory bodies including the International Commission on Radiological Protection (ICRP) and the IAEA emphasize that the risk associated with diagnostic radiation exposure at the levels used in PET/CT is very small and must be weighed against the substantial clinical benefit of accurate disease diagnosis and treatment planning. For cancer patients, the benefit of precise staging and treatment response assessment almost invariably far exceeds the theoretical long-term risk associated with the radiation dose.

The stochastic (probabilistic) risk of radiation-induced cancer from a single FDG PET/CT scan is estimated at approximately 0.05–0.1% over a lifetime, based on the linear no-threshold (LNT) model. However, this model is conservative and may overestimate risk at low doses. In practice, the diagnostic information provided by FDG PET/CT frequently changes clinical management in ways that significantly improve patient outcomes, and the risk-benefit ratio strongly favors performing the scan when clinically indicated.

Specific organ doses from FDG are highest in the bladder wall (the critical organ, due to urinary excretion of the tracer), followed by the brain and heart (due to high physiological glucose uptake). The effective dose per unit of administered activity is approximately 0.019 mSv/MBq. Adequate hydration and frequent voiding are the most important measures for reducing the radiation dose to the bladder wall. Patients should be encouraged to drink at least 500 mL of water and void at least once during the uptake period and again before the scan begins.

How Should Fludeoxyglucose (18F) NUS Be Stored?

Unlike conventional medications that patients store at home, Fludeoxyglucose (18F) NUS is classified as a radiopharmaceutical and is subject to stringent handling, storage, and disposal regulations governed by national radiation protection authorities. Patients will never need to handle, store, or transport this product. The following information is provided for completeness and to help patients understand the safety measures in place at nuclear medicine facilities.

Key storage and handling requirements include:

• Temperature: Store below 25°C. Do not freeze. Storage at higher temperatures does not affect the radioactive component but may compromise the chemical stability of the formulation.
• Radiation shielding: The product must be stored in appropriate lead-shielded containers (typically lead pots or tungsten vial shields) that reduce external radiation exposure to staff and the environment to acceptable levels as defined by national regulations.
• Shelf-life: Due to the short physical half-life of fluorine-18 (109.77 minutes), the product has a limited shelf-life from the time of manufacture – typically 8 to 12 hours, depending on the initial activity concentration at the time of calibration. The activity decreases by approximately 50% every 110 minutes.
• Labeling: Each vial is labeled with the product name, batch number, calibration date and time, radioactivity at calibration, expiry date and time, and volume. The label also includes the radiation warning trefoil symbol.
• Quality control: Before release for patient administration, each batch undergoes quality control testing for radiochemical purity (typically >95%), radionuclidic purity, chemical purity, pH, sterility, and bacterial endotoxin levels. These tests ensure that the product meets the specifications defined in the European Pharmacopoeia or relevant national pharmacopoeia.
• Disposal: Unused product and all materials that have come into contact with the radiotracer (syringes, needles, swabs, gloves) are treated as radioactive waste. Short-lived radioactive waste (such as fluorine-18 contaminated materials) is typically stored in a designated decay storage area until the radioactivity has decayed to background levels, after which it can be disposed of as conventional waste in accordance with local regulations.

The production of FDG is a complex process that typically involves a medical cyclotron (a particle accelerator that produces fluorine-18 by bombarding oxygen-18 enriched water with protons) and an automated synthesis module that performs the radiochemical synthesis, purification, and formulation of the final injectable product under strict aseptic conditions. The entire process from cyclotron irradiation to finished product typically takes 60–90 minutes. Due to the short half-life, FDG must be produced on the same day it is used, and the logistics of production, quality control, and delivery are tightly coordinated to maximize the available activity at the time of patient injection.

What Does Fludeoxyglucose (18F) NUS Contain?

Fludeoxyglucose (18F) NUS is supplied as a clear, colorless, sterile solution for intravenous injection. Understanding the composition of this product provides context for its pharmaceutical quality and safety.

Active Ingredient

The active substance is fludeoxyglucose (18F), also known chemically as 2-deoxy-2-[18F]fluoro-D-glucose. This is a glucose analogue in which the hydroxyl group at the C-2 position of the glucose molecule has been replaced by the radioactive isotope fluorine-18. The molecule has a molecular weight of approximately 181.15 g/mol (including the fluorine-18 atom). The radioactive concentration varies depending on the time since calibration, with multi-dose vials typically containing between 1 GBq and 90 GBq at the reference time stated on the label.

Inactive Ingredients (Excipients)

Appearance and Pack Sizes

Fludeoxyglucose (18F) NUS is supplied as a clear, colorless solution in glass vials (Type I glass) closed with a rubber septum and sealed with an aluminum crimp. The vials are housed within lead or tungsten shielding containers for radiation protection. The volume per vial varies (typically 1–20 mL) and the total radioactivity ranges from 1 GBq to 90 GBq at the reference date and time. Each vial is intended for multiple patient doses, with individual patient doses withdrawn aseptically by qualified nuclear medicine staff using calibrated dose measurement equipment.

Radionuclide Characteristics

Fluorine-18 is produced in a medical cyclotron by proton irradiation of oxygen-18 enriched water via the 18O(p,n)18F nuclear reaction. Key physical properties include:

• Physical half-life: 109.77 minutes (approximately 110 minutes)
• Decay mode: 96.7% positron emission (β+), 3.3% electron capture
• Maximum positron energy: 0.633 MeV
• Mean positron range in tissue: approximately 0.6 mm (contributing to the high spatial resolution of PET imaging)
• Annihilation photon energy: 511 keV (two photons emitted at approximately 180°)

The short half-life of fluorine-18 is advantageous for patient safety (rapid decay of radioactivity after the scan) while being long enough to allow production, delivery, and clinical use within a practical time frame. After approximately 10 half-lives (roughly 18 hours), the radioactivity has decayed to less than 0.1% of its original value.