Ubiquicidin 29-41
A fragment of an antimicrobial peptide that seeks out living bacteria on a scan
Ubiquicidin 29-41 is a 13-amino-acid piece of an antimicrobial protein. It binds bacteria in preference to inflamed tissue, so labelled with technetium-99m it can show on a gamma-camera scan whether a painful joint replacement or a foot ulcer is infected. It has been tested in small hospital studies and is not approved anywhere checked.
Used in human trials: 400 µg peptide labelled with 370–400 MBq, Single injection, Intravenous (Study: first clinical trial, adults) Details ↓
Recommended Dosing
Used in human trials
No manufacturer dose exists for this use: these are amounts given in published trials, not recommendations.
What is it?
Finding infection on a scan is harder than it sounds. Most nuclear medicine tests pick up inflammation, and inflammation follows surgery, fractures, gout and loosened joint replacements whether bacteria are present or not. A tracer that binds the bacteria themselves would avoid that problem, and antimicrobial peptides were an obvious place to look.
Ubiquicidin is an antimicrobial protein, part of the body's innate defences. The synthetic fragment from residues 29 to 41 keeps a strongly positive stretch that binds preferentially to the negatively charged membranes of microbes. A 2002 mouse study reported that the technetium-99m-labelled fragment targets bacterial and fungal infections but not sterile inflammation, and that its uptake depended on its exact sequence: a scrambled version gathered less, and excess unlabelled peptide blocked it.
Animal studies followed in rabbits, rats and mice: infected joint replacements, drug-resistant Staphylococcus aureus endocarditis and thigh infections. Uptake tracked the number of living bacteria rather than the size of the lesion, and it fell when antibiotics worked. It bound Staphylococcus aureus more strongly than Escherichia coli, and a 2019 comparison found that most infection tracers, including this one, bound bacteria poorly in the test tube, so how it accumulates is not fully settled.
The first clinical trial, published in 2005, imaged 18 people with suspected bone, soft-tissue or prosthesis infection and found every infection, with one false positive. The scan was clearest at about 30 minutes and the tracer left mostly through the kidneys. Later studies reported very high accuracy in diabetic-foot osteomyelitis (when read with a bone scan), infected hip and knee replacements, vertebral osteomyelitis and orthopaedic implants, and a fall in uptake when patients responded to antibiotics. A series of 184 patients showed that adding CT to the SPECT images made it much easier to tell bone infection from soft-tissue infection.
Not every result was good. A 2021 prospective multicentre study of infection after spine surgery found the scan either too insensitive or too unspecific, depending on how strictly it was read, while MRI and FDG PET did better. A 2025 case report showed a bone tumour that took up the tracer and nearly passed for infection; reading the time-activity curve, which stayed flat rather than rising, gave it away. Most studies are small, single-centre and unblinded, and a 2026 study of 156 patients proposed a standard target-to-liver threshold of 1.5 to make readings comparable.
UBI 29-41 has no approval from FDA or the EMA, and ClinicalTrials.gov lists no study under its name. Versions joined to metal-binding chelators for gallium-68 or fluorine-18 PET are different molecules and are not covered here. Other antimicrobial peptides, such as LL-37 and pexiganan, have their own pages.
Mechanism of Action
UBI 29-41 is a strongly positive peptide that binds the negatively charged membranes of bacteria; with technetium-99m attached, a gamma camera shows where bacteria are.
Bacterial membranes
Five arginines and a lysine give it a strong positive charge; it binds preferentially to the negatively charged membranes of microbes.
Sequence-specific
In mice a scrambled version gathered less, and excess unlabelled peptide blocked uptake (2002 study).
Counts living bacteria
Uptake fell with effective antibiotics and tracked viable bacteria in animal infections.
Kidney clearance
It leaves the blood within minutes to hours and passes into the urine, so scans are taken 30 to 120 minutes after injection.
Published Research
Studies whose titles name ubiquicidin 29-41 or UBI 29-41 labelled with technetium-99m, read from their PubMed abstracts on October 29, 2026. Gallium-68 and fluorine-18 versions built on chelators are different molecules and are not included.
First clinical trial
Eighteen patients aged 5 to 75 with suspected bone, soft-tissue or prosthesis infection; adults received 400 µg labelled with 370 to 400 MBq. Fourteen scans were positive and four negative; all negatives were confirmed and one positive was false, giving 100% sensitivity and 80% specificity. Target-to-background ratio peaked at 30 minutes. No adverse reactions were seen up to 5 days.
Biokinetics in children
In six children with suspected bone infection, the tracer cleared fast from the blood (mean residence time 0.52 hours), about 85% left in the urine within 24 hours, and positive scans agreed with gallium-67 citrate. The effective dose was 4.34 µSv per MBq; the kidneys received 0.13 mGy per MBq.
Kit labelling in seven patients
A freeze-dried hydrazinonicotinamide and tricine kit gave over 95% labelling purity. Seven patients received 555 to 740 MBq with 40 µg of peptide; five positive and two negative scans were all confirmed, and lesions were visible at 30 minutes.
Mediastinitis after heart surgery
In 13 patients with suspected deep chest-wound infection, visual reading had 83% sensitivity and 71% to 85% specificity across two observers; a count threshold raised specificity to 100% and accuracy to 92%.
Diabetic-foot osteomyelitis
Of 55 diabetic patients with foot ulcers analysed, the scan was positive in all 37 with confirmed bone infection; read alongside a three-phase bone scan it separated bone from soft-tissue infection with 100% sensitivity, specificity and accuracy. Uptake peaked at 30 minutes.
Orthopaedic implants
Nine men with suspected implant infection received 10 MBq/kg (555 to 740 MBq). Five true-positive and four true-negative scans gave 100% on every measure against tissue culture; no adverse reactions were seen.
Loosened hip and knee replacements
In 22 patients awaiting revision surgery, given 370 to 555 MBq from a two-vial kit made in the hospital radiopharmacy, sensitivity was 100% and specificity 85.7%, with images best between 20 and 60 minutes.
Painful knee replacements
In 34 patients, the time-activity curve alone was weak (56% sensitivity), but a target-to-background ratio of 1.83 or more on the 30-minute image separated infected from aseptic loosening with 100% sensitivity and specificity.
Vertebral osteomyelitis
In 27 patients with suspected spinal infection, many after surgery or with implants, the scan had 100% sensitivity and 87.5% specificity, with complete agreement between readers.
Infection after spine surgery, multicentre
In 63 patients at several centres, SPECT/CT with UBI 29-41 gave either 44% sensitivity or 41% specificity depending on the reading criteria, which the authors judged suboptimal; MRI and FDG PET performed better, best of all together.
Adding CT, 184 patients
In musculoskeletal infection, telling bone from soft-tissue infection reached 99.0% sensitivity and 94.5% specificity with SPECT/CT, against 95.0% and 74.3% with planar and SPECT images alone; readers' confidence changed in about half the cases.
A standard threshold, 156 patients
In infected joint replacements, spondylodiscitis, osteomyelitis and fever of unknown origin, a SPECT/CT target-to-liver ratio of 1.5 or more gave specificity above 95% and a negative predictive value of at least 97.8% in every group, making a negative scan a strong rule-out.
Following antibiotic treatment
In 12 patients with orthopaedic infection, uptake fell significantly after 10 to 14 days of antibiotics in those who responded and not in those who did not, while ESR, CRP and the bone scan did not change.
Case: infection after spinal surgery
In a 54-year-old man with suspected infection after spinal instrumentation, SPECT/CT localised the infection and helped avoid a second operation and hardware removal; antibiotics alone worked within two weeks.
Case: a tumour that looked infected
A giant cell tumour of the big toe in a 37-year-old man took up the tracer, but the time-activity curve did not rise over time; surgery confirmed the tumour, showing why curve analysis matters alongside ratios.
Sequence matters, in mice
Direct technetium labelling was fast and clean. The labelled peptide cleared from mouse blood with a half-life of about 16 minutes, mainly through the kidneys, and accumulated in infection more than a scrambled version; excess unlabelled UBI 29-41 blocked its uptake while the scrambled peptide did not.
Staphylococcus against E. coli, in rabbits
In 33 rabbits, a kit-made tracer reached the bladder within an hour; uptake was higher in Staphylococcus aureus thigh infections (ratio 2.2) than in E. coli infections (1.7), and sterile inflammation from turpentine or killed bacteria showed little.
Tracking antibiotic effect in mice
After cloxacillin or erythromycin, uptake at Staphylococcus aureus infection sites fell with the dose and correlated with the number of living bacteria; the tracer bound free and cell-surface bacteria but not bacteria already swallowed by immune cells.
Infected knee replacements in rabbits
In 20 rabbits with knee prostheses, the scan was positive in every infected joint at day 9 and negative in all sterile ones by day 20, when the operated-to-normal knee ratio was 1.75 against 1.13.
MRSA endocarditis in rats
Infected heart-valve growths showed by 15 minutes, sterile ones did not, and uptake correlated with the number of living MRSA (R² = 0.82) rather than the weight of the growth.
Four infection tracers compared, in mice
In mice with infected tissue cages, UBI 29-41 gave a high infected-to-sterile ratio at 24 hours for both E. coli and S. aureus, but like the other tracers it bound bacteria poorly in the test tube, and dead bacteria about as well as live ones.
No genetic damage in cells
In Chinese hamster ovary cells, UBI 29-41 caused no cell death, micronuclei or cell-cycle changes at the concentrations tested, up to 45 ng/mL.
Dosing Data
UBI 29-41 has no approved label. These are amounts given in published human studies, each a single injection of a radioactive tracer before imaging.
Educational information, not medical advice. Each dose above is tagged with its source: an approved label, a published human study, animal data, or amounts reported by users. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose. Full medical disclaimer.
What a Buyer Needs to Know
What is sold, how it is mixed, stored and taken, and what is known about its safety, quality and legal status. Each part names its source. Where we have none, it says unknown.
What is sold
Unknown: we hold no regulator's label that says in what form Ubiquicidin 29-41 is supplied. It is a radioactive drug: the next part says where it is prepared and given.
Mixing a vial: a worked example
Nothing to mix at home, and no syringe units to work out: Ubiquicidin 29-41 is a radioactive drug, prepared and given in nuclear-medicine departments, and its dose is an amount of radioactivity (MBq or GBq), not a weight.
This page's dosing note: “UBI 29-41 is labelled with technetium-99m from a kit in nuclear-medicine departments and dosed by radioactivity.”
Source: this page's own note in Dosing Data below; the amount of each dose row in Dosing Data below.
Storage before and after mixing
Unknown: no label on file says how Ubiquicidin 29-41 is stored. It is a radioactive drug held by the nuclear-medicine department that prepares and gives it (see the part above); the home rules for a mixed vial in the mixing guide do not apply to it.
How it is taken
As it was given in human studies: Intravenous (Single injection; Study: first clinical trial, adults).
Source: Used in human trials: the route and frequency of each row in Dosing Data below.
What to expect, and when
How long it stays in the body: not established by a measurement cited on this entry.
How long the doses were given: Study: first clinical trial, adults: Images from 30 to 240 minutes; Study: freeze-dried kit, 7 patients: Images from 30 to 120 minutes; Study: orthopaedic implants, 9 patients: Images at 30, 60 and 120 minutes.
When effects appear: unknown; no source on this page gives a time to effect for Ubiquicidin 29-41. Results reported in the studies are under Published Research.
Source: Used in human trials, the duration of each row in Dosing Data below.
Side effects, and when to stop or get help
From the Side Effects section: No adverse reactions were seen during imaging or within 5 days in the 2005 trial, the implant study or the joint-replacement study; Radiation exposure: an effective dose of about 4.3 µSv per MBq in children, with the kidneys receiving the most; No cell damage or genetic damage in a cell test at the concentrations tested. Full list and cautions ↓
When to stop or get help: unknown; no label or trial on file sets rules for stopping Ubiquicidin 29-41. Treat a severe or unexpected reaction as a reason to stop and see a doctor.
Source: the Side Effects section below (“From the studies above”).
Interactions
Unknown: a PubMed search for human interaction studies of Ubiquicidin 29-41 (reviewed 2026-10-28) found none. Unknown is not the same as safe to combine.
Every peptide's record, with its source: the interaction matrix.
Checking what you bought
Unknown: no published independent test of Ubiquicidin 29-41 products is in our lab-results database yet, so how products sold under this name measure up is not known.
To read a certificate of analysis, paste it into the COA decoder; it checks the measured mass against Ubiquicidin 29-41's expected mass, 1,693.0 Da, from this entry's molecular data. Trust & Verification explains what independent testing can and cannot show.
Legal status
US: In Clinical Trials (Not approved: Drugs@FDA and the EMA medicines list hold no record (searched October 28 and 29, 2026)). Sport: Prohibited (S0 catch-all).
Country by country ↓ · Regulatory tracker
Source: this entry's approval status and the WADA Prohibited List, as in Legal Status below.
Side Effects & Contraindications
Reported Side Effects
From the studies above.
Contraindications & Cautions
No approved label exists, so there are no official contraindications. Points from the studies above:
Legal Status
UBI 29-41 is investigational in every jurisdiction checked.
Frequently Asked Questions
?What is ubiquicidin 29-41?
A 13-amino-acid fragment, TGRAKRRMQYNRR, of ubiquicidin, an antimicrobial protein of the innate immune system. Labelled with technetium-99m, it is used on scans to look for bacterial infection.
?Why not just use an ordinary bone or white-cell scan?
Many scans also light up healing and sterile inflammation. UBI 29-41 was designed to bind bacteria directly; in rabbits, sterile inflammation from turpentine or killed bacteria took up little of it, and it is made from a kit.
?Is it approved?
No. Drugs@FDA and the EMA hold no record, and no study is registered on ClinicalTrials.gov under its name.
?How accurate is it?
Small studies in bone, diabetic-foot and joint-replacement infection report sensitivities near 100% and specificities of 80% to 100%. A larger multicentre study after spine surgery found it unreliable.
?Can it show whether antibiotics are working?
In 12 patients with orthopaedic infection, uptake fell after 10 to 14 days in those who responded, while blood markers and bone scans did not change.
?Is it an antibiotic?
Not as used here. The amount in a scan is tens to hundreds of micrograms, chosen for imaging. Its parent protein belongs to the body's antimicrobial defences, as LL-37 does.
References
- [other] PubChem CID 16142587, (29-41)-Ubiquicidine: formula C68H121N31O18S, molecular weight 1693.0; its IUPAC name reads Thr-Gly-Arg-Ala-Lys-Arg-Arg-Met-Gln-Tyr-Asn-Arg-Arg. Read October 29, 2026. https://pubchem.ncbi.nlm.nih.gov/compound/16142587
- [clinical-trial] Akhtar MS, et al. "Antimicrobial peptide 99mTc-ubiquicidin 29-41 as human infection-imaging agent: clinical trial." J Nucl Med, 2005;46(4):567-73. PMID: 15809477.
- [pubmed] Meléndez-Alafort L, et al. "Biokinetics of (99m)Tc-UBI 29-41 in humans." Nucl Med Biol, 2004;31(3):373-9. PMID: 15028250.
- [pubmed] Vallejo E, et al. "Clinical utility of 99mTc-labeled ubiquicidin 29-41 antimicrobial peptide for the scintigraphic detection of mediastinitis after cardiac surgery." Arch Med Res, 2008;39(8):768-74. PMID: 18996290.
- [pubmed] Gandomkar M, et al. "Clinical evaluation of antimicrobial peptide [(99m)Tc/Tricine/HYNIC(0)]ubiquicidin 29-41 as a human-specific infection imaging agent." Nucl Med Biol, 2009;36(2):199-205. PMID: 19217532.
- [pubmed] Nazari B, et al. "Role of 99mTc-ubiquicidin 29-41 scintigraphy to monitor antibiotic therapy in patients with orthopedic infection: a preliminary study." Nucl Med Commun, 2011;32(8):745-51. PMID: 21659909.
- [pubmed] Dillmann-Arroyo C, et al. "[Application of the ubiquicidin 29-41 scan in the diagnosis of pyogenic vertebral osteomyelitis]." Acta Ortop Mex, 2011;25(1):27-31. PMID: 21548255.
- [pubmed] Saeed S, et al. "Utility of ⁹⁹mTc-labelled antimicrobial peptide ubiquicidin (29-41) in the diagnosis of diabetic foot infection." Eur J Nucl Med Mol Imaging, 2013;40(5):737-43. PMID: 23361858.
- [pubmed] Beiki D, et al. "(99m)tc-Ubiquicidin [29-41], a Promising Radiopharmaceutical to Differentiate Orthopedic Implant Infections from Sterile Inflammation." Iran J Pharm Res, 2013;12(2):347-53. PMID: 24250609.
- [pubmed] Shinto AS, et al. "Clinical utility of 99mTc-ubiquicidin (29-41) as an adjunct to bone scan in differentiating infected versus noninfected loosening of prosthesis before revision surgery." Nucl Med Commun, 2017;38(4):285-290. PMID: 28244975.
- [pubmed] Sathekge M, et al. "Molecular imaging in musculoskeletal infections with (99m)Tc-UBI 29-41 SPECT/CT." Ann Nucl Med, 2018;32(1):54-59. PMID: 29164482.
- [pubmed] Kiamanesh Z, et al. "Application of 99mTc-UBI 29-41 scintigraphy in knee periprosthetic infection diagnosis." Nuklearmedizin, 2019;58(4):301-308. PMID: 31242515.
- [pubmed] Paez D, et al. "Comparison of MRI, [(18)F]FDG PET/CT, and (99m)Tc-UBI 29-41 scintigraphy for postoperative spondylodiscitis-a prospective multicenter study." Eur J Nucl Med Mol Imaging, 2021;48(6):1864-1875. PMID: 33210240.
- [pubmed] Anzola LK, et al. "Diagnostic Performance of [(99m)Tc]Tc-UBI 29-41 SPECT/CT with a Standardized Semiquantitative Target-to-Liver Ratio Analysis in Four Difficult-to-Diagnose Bacterial Infection Conditions: A Prospective Diagnostic Accuracy Study." J Clin Med, 2026;15(12). PMID: 42355833.
- [pubmed] Flores-Vázquez JG, et al. "Technetium-99m-ubiquicidin 29-41 SPECT-CT to detect postsurgical spinal infection: A case report." Surg Neurol Int, 2024;15:24. PMID: 38344098.
- [pubmed] Ataei Nakhaei S, et al. "99mTc/Tricine/HYNIC ubiquicidin 29-41 uptake in a giant cell tumor of the hallux: insights into the importance of time-activity curve analysis for accurate scan interpretation." Nucl Med Rev Cent East Eur, 2025;28:58-60. PMID: 40926597.
- [pubmed] Welling MM, et al. "Radiochemical and biological characteristics of 99mTc-UBI 29-41 for imaging of bacterial infections." Nucl Med Biol, 2002;29(4):413-22. PMID: 12031876.
- [pubmed] Akhtar MS, et al. "99mTc-labeled antimicrobial peptide ubiquicidin (29-41) accumulates less in Escherichia coli infection than in Staphlococcus aureus infection." J Nucl Med, 2004;45(5):849-56. PMID: 15136636.
- [pubmed] Nibbering PH, et al. "99mTc-Labeled UBI 29-41 peptide for monitoring the efficacy of antibacterial agents in mice infected with Staphylococcus aureus." J Nucl Med, 2004;45(2):321-6. PMID: 14960656.
- [pubmed] Sarda-Mantel L, et al. "Evaluation of 99mTc-UBI 29-41 scintigraphy for specific detection of experimental Staphylococcus aureus prosthetic joint infections." Eur J Nucl Med Mol Imaging, 2007;34(8):1302-9. PMID: 17334764.
- [pubmed] Brouwer CP, et al. "Evaluation of 99mTc-UBI 29-41 scintigraphy for specific detection of experimental multidrug-resistant Staphylococcus aureus bacterial endocarditis." Q J Nucl Med Mol Imaging, 2010;54(4):442-50. PMID: 20823811.
- [pubmed] Auletta S, et al. "Comparison of 99mTc-UBI 29-41, 99mTc-ciprofloxacin, 99mTc-ciprofloxacin dithiocarbamate and 111In-biotin for targeting experimental Staphylococcus aureus and Escherichia coli foreign-body infections: an ex-vivo study." Q J Nucl Med Mol Imaging, 2019;63(1):37-47. PMID: 28849632.
- [pubmed] Ocampo IZ, et al. "In vitro cytotoxic and genotoxic evaluation of peptides used in nuclear medicine (DOTATATE and Ubiquicidin(29-41)) in CHO-K1 cells." Cytotechnology, 2016;68(6):2301-2310. PMID: 27686814.
- [pubmed] Jiang Y, et al. "Current Status of and Perspectives on Radiolabelled Ubiquicidin 29-41 Derivatives for Bacterial Infection Imaging." Mini Rev Med Chem, 2023;23(15):1500-1506. PMID: 36718969.
Sources & Citations
Studies were read from their PubMed abstracts on October 29, 2026. Sequence and formula are from PubChem CID 16142587, whose formula a residue calculation reproduces. Status is from Drugs@FDA, the EMA medicines list and ClinicalTrials.gov. Grey Peptides sells nothing and links to no vendor.
Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Talk to a licensed clinician about your own situation.