Tektrotyd (HYNIC-[Tyr3]-Octreotide)
A technetium-99m radiopharmaceutical kit for SPECT imaging of neuroendocrine tumors
Quick Facts About Tektrotyd
Key Takeaways About Tektrotyd
- Diagnostic, not therapeutic: Tektrotyd is used exclusively to produce images of tumors — it is not a treatment for cancer
- Receptor-specific imaging: It binds to somatostatin receptors (mainly SSTR2) that are overexpressed on neuroendocrine and some other tumor cells
- Labeled with technetium-99m: The peptide is combined with 99mTc in the hospital radiopharmacy; the short 6-hour physical half-life keeps radiation exposure low
- One-time injection: A single intravenous injection is given, followed by SPECT or SPECT/CT imaging 2 to 4 hours later (sometimes also at 24 hours)
- Excellent safety profile: Because only microgram quantities of peptide are injected, pharmacologic side effects are very rare and typically mild
What Is Tektrotyd and What Is It Used For?
Tektrotyd is a technetium-99m radiopharmaceutical imaging agent used in nuclear medicine to detect, stage and follow neuroendocrine tumors and other somatostatin receptor (SSTR) positive lesions. Doctors use the scan to find primary tumors, locate metastases and help choose between surgery, medical therapy and peptide receptor radionuclide therapy.
Tektrotyd is a diagnostic kit manufactured by the National Centre for Nuclear Research Radioisotope Centre POLATOM in Poland. It contains a lyophilized (freeze-dried) peptide called HYNIC-[D-Phe1,Tyr3]-octreotide, commonly abbreviated as HYNIC-TOC. Before it can be used in a patient, the peptide must be reconstituted in the radiopharmacy and labeled with freshly eluted sodium pertechnetate (99mTc) solution from a technetium generator. The finished product — 99mTc-HYNIC-TOC — is what is actually injected into the patient.
The injected molecule behaves like a small, synthetic version of the body's natural hormone somatostatin. It circulates briefly in the blood, then binds to somatostatin receptors on cell surfaces. These receptors are present on many healthy tissues but are massively overexpressed on the surface of most well-differentiated neuroendocrine tumors. When an SSTR-positive tumor takes up the radiotracer, the decay of 99mTc emits low-energy gamma photons (140 keV) that are detected by a gamma camera, producing detailed tomographic images of the tumor burden throughout the body.
Tektrotyd is most often used to investigate or follow patients with known or suspected neuroendocrine tumors (NETs), including gastroenteropancreatic (GEP) NETs such as carcinoid tumors of the small bowel, pancreatic NETs (insulinoma, gastrinoma, VIPoma, glucagonoma and non-functioning NETs), as well as pheochromocytomas, paragangliomas, medullary thyroid carcinoma, small cell lung cancer, Merkel cell carcinoma and some cases of meningioma, medulloblastoma and neuroblastoma. In addition, clinicians may use it to select patients for peptide receptor radionuclide therapy (PRRT), which uses similar somatostatin analogues labeled with therapeutic beta-emitting isotopes such as 177Lu or 90Y.
How Tektrotyd Works
Somatostatin is a regulatory hormone produced throughout the body that inhibits the secretion of many other hormones. It acts through a family of five closely related receptors labeled SSTR1 through SSTR5. The peptide in Tektrotyd is a long-acting analogue of somatostatin that binds primarily to SSTR2 and, with lower affinity, to SSTR3 and SSTR5. Because well-differentiated neuroendocrine tumors express SSTR2 densely on their surface, they act as natural “targets” for this tracer.
In the radiopharmacy, the peptide is conjugated to HYNIC (6-hydrazinonicotinic acid), a chelating group that forms a stable complex with technetium-99m in the presence of tricine and EDDA coligands supplied in the kit. After intravenous injection, the labeled peptide rapidly leaves the bloodstream, distributes to SSTR-rich tissues (spleen, liver, pituitary, thyroid, adrenals, kidneys), and is cleared predominantly through the kidneys into the urine. Unbound tracer is excreted, while receptor-bound tracer is internalized by tumor cells and remains detectable on scans performed 2 to 4 hours — and sometimes 24 hours — after injection.
Compared with older agents such as 111In-pentetreotide (OctreoScan), 99mTc-HYNIC-TOC offers higher count rates, better image quality, a lower radiation dose to the patient, a shorter overall examination time and the ability to perform SPECT and SPECT/CT acquisitions without the long delays required by indium-111. These advantages have made Tektrotyd a widely used option in European centers that do not have routine access to 68Ga-DOTATATE or 68Ga-DOTATOC positron emission tomography (PET/CT).
Tektrotyd is a diagnostic tool, not a therapy. A scan with 99mTc-HYNIC-TOC does not treat the tumor — it simply shows where somatostatin receptor-positive cells are located. The information gained is then used by your multidisciplinary team to plan surgery, medical therapy, radionuclide therapy or further investigations.
Clinical Indications
International nuclear medicine societies (EANM and SNMMI) and oncology guidelines (ENETS, NCCN, ESMO) recognize the following clinical uses for somatostatin receptor scintigraphy with 99mTc-HYNIC-TOC:
- Detection and localization of primary neuroendocrine tumors and their metastases
- Staging and re-staging of known NETs, including after surgery or medical therapy
- Identification of unknown primary tumors in patients with biopsy-proven NET metastases
- Evaluation of somatostatin receptor expression to select candidates for peptide receptor radionuclide therapy
- Monitoring of treatment response and surveillance for recurrence
- Characterization of indeterminate lesions seen on other imaging modalities
What Should You Know Before Taking Tektrotyd?
Before a Tektrotyd scan, your nuclear medicine team will confirm that the benefit of the information outweighs the small radiation exposure involved. Pregnancy must be excluded; breastfeeding is temporarily interrupted; long-acting somatostatin analogues are usually paused; adequate hydration is recommended; and patients with insulinoma or severe renal impairment are monitored with extra care.
Tektrotyd is a well-tolerated tracer, but — like all radiopharmaceuticals — it must only be used when the diagnostic benefit justifies the radiation dose. Your referring physician and nuclear medicine specialist will review your medical history, current medications, and recent imaging to make sure the examination is appropriate for you. The preparation and handling of the radiopharmaceutical are strictly regulated, and the product is only administered in licensed nuclear medicine departments by trained personnel.
Contraindications
Tektrotyd must not be administered to patients with:
- Known hypersensitivity to HYNIC-[Tyr3]-octreotide, to any of the excipients in the kit (tricine, EDDA, mannitol, stannous chloride), or to sodium pertechnetate (99mTc)
- Pregnancy — unless, in exceptional circumstances, the expected diagnostic benefit clearly outweighs the risk of fetal radiation exposure
Absolute contraindications are few because the mass of peptide injected is very small (typically <20 µg per study). However, every radiopharmaceutical administration requires a careful individual risk-benefit assessment, especially in children, pregnant or breastfeeding women, and patients with severe comorbidities.
Warnings and Precautions
Talk to your doctor and nuclear medicine team before your scan if any of the following apply to you:
- Diabetes mellitus or insulinoma: Although the dose of peptide is very small, somatostatin analogues can suppress insulin and glucagon release, potentially causing hypoglycemia in patients with insulinoma. Blood glucose is monitored during and after injection; a source of glucose must be available
- Renal impairment: Because the tracer is cleared predominantly via the kidneys, severe renal failure prolongs retention and can alter image interpretation. Hydration is particularly important in these patients
- Hepatic impairment: Severe liver disease may alter tracer biodistribution and radiation dosimetry
- Current or recent somatostatin analogue therapy: Long-acting agents (octreotide LAR, lanreotide) can saturate somatostatin receptors and reduce tumor uptake. Imaging timing should be coordinated with your oncologist
- High-dose corticosteroid therapy: May down-regulate SSTR expression — relevant for image interpretation
- Allergic predisposition: Patients with a history of allergic reactions to other peptide drugs or radiopharmaceuticals should be observed closely during and after injection
- Cardiovascular instability: Rare transient effects on heart rate and blood pressure may occur; patients with unstable cardiac status should be monitored
Tektrotyd contains a radioactive substance. It must only be received, stored, prepared, administered and disposed of in a designated nuclear medicine facility under the supervision of authorized medical personnel, in accordance with local radiation protection regulations. Patients, their families and attending staff should follow the radiation safety instructions given by the nuclear medicine department, particularly regarding close contact with pregnant women and small children immediately after the scan.
Pregnancy and Breastfeeding
Before a Tektrotyd scan is scheduled for a woman of child-bearing potential, pregnancy must be considered and, where appropriate, ruled out with a pregnancy test or a clear menstrual history. If a patient is pregnant or may be pregnant, alternative non-radiation imaging (such as magnetic resonance imaging or ultrasound) is preferred whenever clinically feasible. Tektrotyd should only be used during pregnancy if the expected diagnostic benefit for the mother is judged to clearly outweigh the risk to the fetus.
For breastfeeding women, nursing should be interrupted for at least 12 hours after administration. Milk expressed during this interval should be discarded. In some situations, longer interruption or temporary replacement with formula may be advised. Your nuclear medicine team will provide specific instructions tailored to your study activity and individual situation.
Use in Children and Adolescents
Somatostatin receptor scintigraphy can be performed in children when clinically indicated, for example in the evaluation of pediatric neuroendocrine tumors, neuroblastoma, paraganglioma or medullary thyroid carcinoma. The administered activity is calculated from the child's body weight according to the EANM Pediatric Dosage Card, which minimizes radiation exposure while preserving image quality. Children should be examined only in centers with pediatric nuclear medicine expertise.
Driving and Operating Machinery
Tektrotyd has no known direct effect on the ability to drive or operate machinery. However, the diagnostic process itself (fasting, waiting, injection, anxiety) may cause fatigue, and some patients feel dizzy or lightheaded. You may wish to arrange for someone to accompany you home, particularly if you feel unwell after the study or if you have an underlying condition that could be affected by the examination.
Preparation Before the Scan
Your nuclear medicine department will give you detailed written and verbal instructions. Typical preparation includes:
- Drinking plenty of fluids on the day of the scan (unless contraindicated) to support tracer clearance
- Temporary discontinuation of short-acting octreotide (usually for at least 24 hours) if you take it
- Scheduling the scan toward the end of the dosing interval of long-acting somatostatin analogues (typically 4 to 6 weeks after the last injection)
- A light meal before the injection (fasting is generally not required)
- Bringing previous imaging studies and a current medication list
- Removing metallic items before imaging
How Does Tektrotyd Interact with Other Drugs?
The most important interactions involve other somatostatin analogues (octreotide, lanreotide, pasireotide), which compete for the same receptors and can reduce tumor uptake of Tektrotyd. High-dose corticosteroids, recent radiotherapy, and other radiopharmaceuticals may also affect image interpretation. Always give your nuclear medicine team a complete list of your current medications.
Because 99mTc-HYNIC-TOC is a receptor-specific tracer, any drug that influences somatostatin receptor expression, occupancy or internalization has the potential to alter scan results. The amount of peptide injected is too small to produce meaningful pharmacodynamic interactions, but receptor blockade by therapeutic somatostatin analogues is clinically relevant and routinely managed before imaging.
Major Interactions
| Interacting Drug / Class | Effect on Tektrotyd Scan | Recommendation |
|---|---|---|
| Long-acting octreotide (LAR) and lanreotide | Receptor blockade reduces tumor uptake and can cause false-negative findings | Perform imaging toward the end of the dosing interval, typically 4–6 weeks after the last injection |
| Short-acting octreotide (subcutaneous) | Temporary receptor occupancy | Withhold for at least 24 hours before Tektrotyd administration, if clinically acceptable |
| Pasireotide | Binds broadly to SSTR1, 2, 3 and 5 and may reduce tracer uptake | Coordinate timing with the prescribing endocrinologist / oncologist |
| High-dose systemic corticosteroids | Can down-regulate SSTR expression on tumor cells | Document dose and duration; interpret images in context |
| Recent external-beam radiotherapy | May transiently alter receptor expression and cause reactive uptake | Ideally wait at least 6–8 weeks after radiotherapy; note on request form |
| Other 99mTc tracers (same day) | Residual activity produces overlapping signal and interpretation errors | Do not administer on the same day; allow several half-lives between scans |
| Peptide receptor radionuclide therapy (177Lu-DOTATATE) | Residual activity and receptor saturation can interfere with diagnostic images | Plan diagnostic imaging before therapy cycles or well after completion, per local protocol |
Minor and Theoretical Interactions
The following interactions are generally considered minor but should still be disclosed to the nuclear medicine team:
- Diuretics: Alter urinary tracer clearance and pelvic activity
- Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs): May alter renal handling and influence apparent renal uptake
- Beta-blockers and calcium channel blockers: No specific receptor interaction, but useful to know for interpretation of cardiovascular side effects
- Recent iodinated contrast media: Do not directly interfere with 99mTc-HYNIC-TOC but may alter SPECT/CT image fusion quality
- Dopamine agonists: Can affect tumor hormone secretion and secondary imaging features in some pituitary tumors
Always provide a complete, up-to-date list of prescription drugs, over-the-counter medications, herbal products and supplements. Seemingly “minor” medications can sometimes change the pattern of tracer uptake, and the nuclear medicine team will use this information to correctly interpret your images.
What Is the Correct Dosage of Tektrotyd?
Tektrotyd is given as a single intravenous injection containing 370–740 MBq (10–20 mCi) of 99mTc-HYNIC-TOC. The peptide mass per study is typically 10–20 micrograms. The activity is adjusted for body weight in children and for clinical context in adults. Imaging begins 2 to 4 hours after injection; optional late images are acquired at 24 hours.
Unlike conventional drugs, a radiopharmaceutical dose is described in units of radioactivity (megabecquerels, MBq, or millicuries, mCi) rather than milligrams. The amount of peptide actually injected is tiny — well below any pharmacologic threshold — which is why 99mTc-HYNIC-TOC does not behave as a “treatment” dose of octreotide. The entire treatment protocol is designed around the ALARA principle: As Low As Reasonably Achievable radiation exposure consistent with good image quality.
Kit Preparation
Radiopharmacy Labeling
The Tektrotyd kit is supplied as three vials of lyophilized powder. In the radiopharmacy, the peptide vial (containing 20 µg HYNIC-TOC) is reconstituted with freshly eluted sodium pertechnetate (99mTc) and the coligand solutions (tricine, EDDA). The mixture is heated for a defined time and cooled to room temperature, then quality control is performed (radiochemical purity >90%). The labeled product must be used within 6 hours of preparation.
Adults
Recommended Activity: 370–740 MBq (10–20 mCi)
For adults with normal body habitus, the typical injected activity is 500 to 740 MBq per study, administered as a slow intravenous injection over 15–30 seconds, followed by a saline flush. The activity may be adjusted upward for larger patients and downward for smaller patients. The mass dose of peptide is usually 10–20 µg.
Children
Pediatric Dose (EANM Dosage Card)
In children, the administered activity is calculated from body weight using the EANM Pediatric Dosage Card. A typical recommendation is approximately 5.6 MBq/kg, with a minimum activity of 20–40 MBq to ensure diagnostic image quality. Pediatric studies should only be performed in centers experienced in pediatric nuclear medicine.
Elderly and Special Populations
Dose Adjustment
No specific dose adjustment is required on the basis of age alone. However, the examination should take comorbidities into account. In severe renal impairment, extra attention is given to hydration and delayed imaging may be required. In severely obese patients, some centers increase the activity modestly or add SPECT/CT to improve sensitivity.
Administration
Injection and Monitoring
A peripheral intravenous cannula is placed. After flushing with saline, the 99mTc-HYNIC-TOC solution is injected slowly over 15–30 seconds. The cannula is then flushed with at least 10 mL of saline to ensure full delivery of the dose. Vital signs (blood pressure, heart rate) are checked before and after injection. Extravasation must be avoided because it can delay clearance and produce focal activity that mimics disease on later images.
Imaging Protocol
Typical Imaging Times
Whole-body planar scintigraphy is usually acquired at 2 and 4 hours after injection. Single-photon emission computed tomography (SPECT or SPECT/CT) over regions of interest — abdomen, thorax, head and neck or the entire body — is acquired at 2–4 hours. Optional late imaging at 24 hours improves target-to-background contrast when the primary tumor or metastases are in the abdomen, where bowel activity can obscure lesions.
Radiation Dosimetry
| Target Organ | Approximate Absorbed Dose (mGy/MBq) | Clinical Relevance |
|---|---|---|
| Kidneys | 0.025–0.045 | Primary route of elimination — hydration is important |
| Urinary bladder wall | 0.020–0.050 | Reduced by frequent voiding |
| Spleen | 0.025–0.040 | High physiologic SSTR expression |
| Liver | 0.012–0.018 | Site of hepatic metastases |
| Thyroid | 0.005–0.010 | Physiologic SSTR expression |
| Whole body (effective dose) | ~0.005–0.008 mSv/MBq | ~3.7–5.9 mSv for a 740 MBq study (comparable to standard nuclear medicine scans) |
Missed or Repeated Studies
If a scheduled Tektrotyd scan is missed, the radiopharmaceutical cannot be stored indefinitely because of 99mTc's short half-life. Reappointment will require new reconstitution of the kit on the day of the new scan. Repeat scans are possible when clinically indicated but are carefully spaced out to minimize cumulative radiation exposure; diagnostic nuclear medicine scans are not routinely repeated within short intervals unless the question being asked is truly different.
Overdose
Because the peptide dose is extremely small, pharmacological overdose in the conventional sense does not occur. In the very rare event that excessive radioactivity is administered accidentally, the radiation dose to the patient can be reduced by frequent diuresis and hydration, and by encouraging frequent bowel movements (since a fraction of the tracer is excreted through the intestines). Patients are monitored clinically, and radiation protection staff assist with ongoing risk assessment.
What Are the Side Effects of Tektrotyd?
Tektrotyd has an excellent safety profile because only microgram amounts of peptide are injected. Side effects are uncommon and usually mild and transient — flushing, nausea, dizziness, mild blood pressure changes, or minor injection-site reactions. Serious events, including hypersensitivity reactions and hypoglycemia in patients with insulinoma, are rare. Long-term radiation-related risks exist but are very small at standard diagnostic activities.
The clinical safety of 99mTc-HYNIC-TOC has been evaluated in both registration trials and post-marketing experience across Europe and Asia. Across published studies, the overall incidence of any acute adverse event after administration is typically well under 1%, and serious adverse events are very rare. Because the tracer behaves pharmacologically similarly to a micro-dose of octreotide, the theoretical side-effect profile mirrors that of somatostatin analogues — but at far lower intensity and duration.
Tell the nuclear medicine team right away if you experience: sudden skin rash or hives, swelling of the lips or face, wheezing or difficulty breathing, severe chest pain, a rapid drop in blood pressure, severe dizziness, unusual shaking, or symptoms of hypoglycemia (sweating, trembling, confusion, rapid heart rate). Although rare, these may indicate a hypersensitivity reaction, cardiovascular event, or hypoglycemia in patients with insulinoma.
Side Effects by Frequency
The frequencies below are based on published clinical studies of 99mTc-HYNIC-TOC and on the known safety profile of related somatostatin analogues. All reported events have been mild to moderate in the large majority of cases.
Very Common (affects more than 1 in 10 patients)
- No very common pharmacologic side effects are expected from the small peptide dose used in Tektrotyd.
- Radiation exposure itself is an unavoidable feature of any nuclear medicine procedure but, at the activities used, does not cause clinically detectable acute effects.
Common (affects up to 1 in 10 patients)
- Transient warmth or flushing during or shortly after injection
- Mild nausea in the first minutes after administration
- Headache or a brief sensation of lightheadedness
- Minor injection-site reactions: small bruise, transient pain, or warmth at the cannulation site
- Tiredness during the imaging session, often related to prolonged immobility
Uncommon (affects up to 1 in 100 patients)
- Short-lived changes in blood pressure (mild increase or decrease)
- Mild increase or decrease in heart rate
- Mild abdominal discomfort or a brief sensation of bowel cramping
- Transient change in blood glucose — relevant in patients with insulinoma or on insulin therapy
- Short-lived itching or skin warmth without rash
Rare (affects up to 1 in 1,000 patients)
- Hypersensitivity or allergic-type reactions: skin rash, hives, angioedema or rarely anaphylactoid reactions
- Symptomatic hypoglycemia in patients with untreated insulinoma due to residual somatostatin-like activity
- Vasovagal reactions: pallor, sweating and fainting at the time of injection
- Extravasation of the radiopharmaceutical with local pain and a hot focus on subsequent images
- Transient mild elevations of liver enzymes reported in isolated cases
- Long-term stochastic risk from the radiation dose (very small increase in lifetime cancer risk, typical of standard nuclear medicine procedures)
Radiation-Related Considerations
Every radiopharmaceutical administration carries a small theoretical radiation risk. For an adult who receives 740 MBq of 99mTc-HYNIC-TOC, the effective dose is approximately 3.7 to 5.9 millisieverts. This is comparable to many other routine nuclear medicine studies and is considered acceptable when weighed against the clinical value of identifying treatable tumors. If a SPECT/CT is combined with the scintigraphy, an additional contribution from the CT component (usually 2–8 mSv) must be considered. Children and young adults are more radiosensitive, which is why pediatric protocols use weight-based dose reduction.
What to Do If You Feel Unwell
If you feel unwell during your injection or imaging session, alert the nuclear medicine staff immediately. They are specifically trained to recognize and manage the rare acute reactions associated with radiopharmaceuticals. If symptoms develop after you leave the department — particularly swelling, breathing difficulty or significant hypoglycemia — contact your doctor or your local emergency services without delay and mention that you recently received a radiopharmaceutical. Most mild symptoms resolve within a few hours without any specific treatment.
Reporting Suspected Side Effects
Any suspected adverse reaction should be reported to your nuclear medicine team and, where applicable, to your national pharmacovigilance authority (e.g., EMA EudraVigilance, MHRA Yellow Card Scheme, FDA MedWatch). Reporting helps strengthen the safety database for this and other radiopharmaceuticals and benefits future patients.
How Should You Store Tektrotyd?
Tektrotyd is stored exclusively by the hospital pharmacy and nuclear medicine department. The unlabeled kit is kept refrigerated at 2–8°C in its original packaging. After labeling with technetium-99m, the product must be kept below 25°C and used within 6 hours. All handling follows national and European regulations for radioactive medicinal products.
As a patient, you will not handle, transport or store Tektrotyd at any stage. The product is received, stored, prepared and administered in specialized hospital environments that comply with good manufacturing practice (GMP) requirements and national radiation protection laws. Nevertheless, understanding the handling requirements illustrates why the logistics of nuclear medicine are so precise.
Storage of the Unlabeled Kit
The freeze-dried Tektrotyd kit is supplied in three sealed vials packed together. It must be stored:
- In a refrigerator at 2–8°C
- In the original carton to protect from light
- Out of reach of unauthorized personnel, in a locked pharmacy or hot lab area
- Until the expiry date printed on the outer carton and individual vial labels
The unlabeled kit itself is not radioactive; radiation-safety handling only becomes necessary once 99mTc is added during labeling.
Storage of the Labeled Product
After reconstitution with sodium pertechnetate (99mTc), the labeled 99mTc-HYNIC-TOC solution must be:
- Kept at a temperature below 25°C, shielded with appropriate lead containers
- Stored in the “hot lab” area of the nuclear medicine department under supervision of an authorized radiopharmacist
- Used within 6 hours of preparation (the radiochemical stability window)
- Discarded, if not used, as radioactive waste according to local and national regulations
Handling and Disposal
All preparation and handling must be performed by authorized personnel wearing appropriate protective equipment, behind adequate lead shielding, using aseptic technique. Radioactive waste (empty vials, syringes, swabs, gloves and residual product) is collected, labeled and stored in shielded containers until it has decayed sufficiently to be disposed of as non-radioactive waste, as prescribed by national regulations.
Technetium-99m has a physical half-life of approximately 6.0 hours. After this time, the radioactivity remaining is already reduced by half, and image quality suffers. Radiochemical impurities also increase slowly after labeling. The 6-hour shelf life guarantees both adequate activity and diagnostic-grade purity at the moment of patient administration.
What Does Tektrotyd Contain?
Tektrotyd consists of three vials containing the peptide HYNIC-[Tyr3]-octreotide together with tricine, EDDA, mannitol, stannous chloride and buffering agents. These are lyophilized and sterile. The radioactive component (99mTc) is added in the hospital radiopharmacy from a separate sodium pertechnetate (99mTc) solution supplied by a generator.
The active ingredient is HYNIC-[D-Phe1,Tyr3]-octreotide trifluoroacetate, a synthetic cyclic octapeptide analogous to somatostatin, covalently conjugated to the HYNIC chelator group. Each vial contains approximately 20 micrograms of HYNIC-TOC. The kit is designed to be labeled with sodium pertechnetate (99mTc) in an appropriate radioactivity (typically 400–1,100 MBq added in the radiopharmacy to produce a patient dose of 370–740 MBq after volume adjustment).
Excipients (Inactive Ingredients)
The Tektrotyd kit contains the following excipients distributed across the three vials:
- Tricine (N-[tris(hydroxymethyl)methyl]glycine) — coligand required for stable 99mTc chelation
- EDDA (ethylenediamine-N,N′-diacetic acid) — second coligand for optimal labeling yield
- Mannitol — bulking agent stabilizing the lyophilized formulation
- Stannous chloride dihydrate (SnCl2·2H2O) — reducing agent that converts Tc(VII) to lower, reactive oxidation states capable of binding HYNIC
- Sodium hydroxide / hydrochloric acid — pH adjustment
- Nitrogen — used to flush vials and prevent oxidation
The sodium pertechnetate (99mTc) solution added at the time of labeling is a separate medicinal product, typically eluted from a molybdenum-99 / technetium-99m (99Mo/99mTc) generator. Its quality — chemical purity, radiochemical purity and sterility — is strictly controlled by the radiopharmacy.
Appearance
Before labeling, the content of each Tektrotyd vial is a white to off-white lyophilized powder or cake. After reconstitution and labeling, the final product is a clear, colorless to slightly yellow solution, free of visible particles. If discoloration, cloudiness or particulate matter is observed, the preparation must not be administered and should be discarded as radioactive waste.
Packaging
The commercial kit is supplied in an outer carton containing three glass vials sealed with rubber stoppers and aluminum crimp caps, together with a prescribing information leaflet for healthcare professionals. Storage conditions, expiry date, batch number and manufacturer details are printed on both the outer carton and the individual vials.
Frequently Asked Questions About Tektrotyd
Tektrotyd is a diagnostic radiopharmaceutical kit containing HYNIC-[Tyr3]-octreotide (HYNIC-TOC), which is labeled with technetium-99m in the hospital radiopharmacy. The resulting 99mTc-HYNIC-TOC is injected into a vein and used to produce images of tumors that overexpress somatostatin receptors — most commonly neuroendocrine tumors such as carcinoid, pancreatic NETs, pheochromocytoma, paraganglioma, medullary thyroid carcinoma, small cell lung cancer and others. The images help doctors find primary tumors, stage disease, plan treatment and select patients for peptide receptor radionuclide therapy.
Tektrotyd is administered as a single intravenous injection of 99mTc-HYNIC-TOC. A peripheral cannula is placed, the labeled solution is injected slowly, and the line is flushed with saline. No premedication is routinely required. Whole-body and SPECT/CT imaging is performed 2 to 4 hours after injection; optional additional images can be acquired at 24 hours to improve abdominal contrast. The entire appointment usually lasts several hours, although most of that time is spent waiting between the injection and the scan itself.
Generally, yes. Long-acting somatostatin analogues such as octreotide LAR or lanreotide can occupy the same receptors that Tektrotyd binds to and may reduce the sensitivity of the scan. Imaging is usually scheduled toward the end of the dosing interval, approximately 4 to 6 weeks after the last long-acting injection, so receptor occupancy is lower. Short-acting subcutaneous octreotide is typically withheld for at least 24 hours before the scan, when clinically acceptable. Always follow the specific instructions of your nuclear medicine physician and oncologist — continuity of treatment for aggressive hormonal syndromes sometimes takes priority over a perfect scan.
For a typical adult activity of 740 MBq of 99mTc-HYNIC-TOC, the effective dose is approximately 3.7 to 5.9 millisieverts, depending on patient size and biodistribution. This is comparable to a bone scan or a perfusion myocardial scintigraphy. When SPECT/CT is performed, an additional low-dose CT contribution (typically 2 to 8 mSv) should be considered. The nuclear medicine team always applies the ALARA principle to keep your radiation exposure as low as reasonably achievable while still obtaining diagnostic-quality images.
Tektrotyd is generally very well tolerated because only microgram amounts of peptide are injected. Side effects are uncommon and almost always mild and transient, such as brief flushing, nausea, a sensation of warmth at the injection site, dizziness, or a slight change in blood pressure. Allergic or hypersensitivity reactions are rare. Because the peptide has weak somatostatin-like activity, patients with insulinoma may occasionally experience hypoglycemia and should be monitored. Serious adverse events are uncommon and most patients report no symptoms at all.
Yes, in most situations ordinary contact with family and coworkers is safe within a few hours of the scan. Technetium-99m has a short physical half-life of approximately 6 hours, and most of the activity is excreted in the urine within the first 24 hours. Your nuclear medicine team will ask you to drink plenty of fluids, urinate frequently, and may recommend limiting close, prolonged contact with pregnant women and young children for roughly 12 to 24 hours. Specific advice depends on your administered activity and the local radiation-protection protocol, so always follow the written instructions you receive from the department.
68Ga-DOTATATE (or 68Ga-DOTATOC) PET/CT uses a positron emitter and generally offers higher spatial resolution and higher sensitivity for small lesions than 99mTc-HYNIC-TOC SPECT/CT. However, 68Ga tracers require a 68Ge/68Ga generator or cyclotron access and are not universally available. Tektrotyd SPECT/CT provides excellent diagnostic performance for larger lesions and well-differentiated NETs, is widely available in Europe and Asia, and has a very favorable cost profile. The choice between the two techniques depends on local availability, lesion size, clinical question and the recommendation of your multidisciplinary team.
References
- European Medicines Agency (EMA). Somatostatin receptor imaging with technetium-99m labeled peptides — Summary of product characteristics and European public assessment reports. Available at: ema.europa.eu. Accessed January 2026.
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