By the Peptide Insider Research Desk · 17 October 2026 · 10 min read
Laboratory procurement logs for research-grade amino acid derivatives frequently contain queries such as "buy injectable l carnitine," "injectable l carnitine for sale," "l-carnitine peptide injection," "l carnitine vial," "l carnitine 5000 mg" and "l-carnitine injection buy." These search strings reflect growing investigator interest in parenteral L-carnitine formulations that bypass the saturable intestinal OCTN2 transporter and the gut-microbiome-mediated trimethylamine N-oxide (TMAO) pathway. This review maps each catalogue query to its pharmacological referent, traces the carnitine palmitoyltransferase (CPT) shuttle mechanism through verified peer-reviewed literature, and provides a crosswalk table classifying each string by RUO scope status. All information is presented strictly for research reference; not for human or veterinary use.
Systematic name: (3R)-3-hydroxy-4-(trimethylazaniumyl)butanoate
CAS: 541-15-1
Molecular formula: C7H15NO3 · MW 161.20 g/mol
Endogenous biosynthesis: Liver, kidney and brain from lysine and methionine precursors [1]
Primary transporter: OCTN2 (SLC22A5)
Structural class: Quaternary ammonium betaine — not a peptide (no peptide bond)
Is L-Carnitine a Peptide?
The query "l-carnitine peptide injection" conflates two distinct molecular classes. L-Carnitine (MW 161.20) is a quaternary ammonium compound biosynthesised from lysine and methionine; it contains no amide (peptide) bond and is therefore not a peptide by IUPAC definition [1]. Its appearance in peptide-supplier catalogues alongside compounds such as BPC-157 (MW 1 419) and TB-500 (MW 4 963) is a consequence of shared parenteral formulation requirements — lyophilised vials, bacteriostatic water reconstitution, cold-chain storage — rather than structural homology. Investigators encountering "l carnitine vial" or "l carnitine 5000 mg" listings should note this distinction when designing comparative assays.
Carnitine Palmitoyltransferase (CPT) Shuttle Mechanism
The inner mitochondrial membrane is impermeable to long-chain fatty acyl-CoA esters (C14-C20). L-Carnitine serves as the obligate acyl-group carrier within the three-enzyme CPT shuttle [2,3]:
- CPT-I (outer mitochondrial membrane) — catalyses the transfer of the acyl group from coenzyme A to the hydroxyl group of L-carnitine, yielding acylcarnitine and free CoA [3].
- CACT (carnitine-acylcarnitine translocase, inner membrane) — exchanges acylcarnitine inward for free carnitine outward across the inner membrane [2].
- CPT-II (matrix-facing inner membrane) — reconverts acylcarnitine to acyl-CoA and free L-carnitine; the acyl-CoA then enters the beta-oxidation spiral [3].
CPT-I exerts approximately 80% of the flux control over hepatic beta-oxidation under physiological conditions [4]. Its activity is allosterically inhibited by malonyl-CoA, the committed intermediate of de novo fatty acid synthesis, creating a reciprocal gate: when anabolic lipogenesis is active the catabolic beta-oxidation arm is suppressed [4,5]. Bremer's 1983 landmark review established the bioenergetic framework for this shuttle and remains the standard reference for carnitine metabolism [2].
Preclinical and Clinical Evidence Table
| Research Model | Signal Vector | Key Finding | Citation |
|---|---|---|---|
| Healthy human volunteers (IV) | Carnitine homeostasis, fuel metabolism | IV L-carnitine achieved near-100% bioavailability; did not significantly alter respiratory exchange ratio during moderate exercise | Brass 1994 [6] |
| Healthy volunteers (IV acetyl-L-carnitine) | Pharmacokinetics, disposition | IV administration produced rapid plasma peak; renal clearance dominated elimination; t1/2 approximately 4.2 h | Marzo 1989 [7] |
| Hemodialysis patients (IV vs. oral switch) | Lipid metabolism | Switching from oral to IV L-carnitine significantly decreased serum triglycerides and increased free carnitine; TMAO pathway bypassed | Fukami 2014 [8] |
| Maintenance hemodialysis (multicenter RCT) | Clinical biochemistry, erythropoiesis | IV L-carnitine improved pre-dialysis free carnitine and acyl/free ratio; modest effect on haematocrit | Ahmad 1990 [9] |
| ESKD hemodialysis (systematic review, 49 RCTs) | Erythropoietin dose, lipids, CRP | L-carnitine supplementation significantly decreased LDL and CRP; no significant haemoglobin benefit | Chen 2014 [10] |
| Hemodialysis patients (IV series) | Beta-cell response, insulin sensitivity | Consecutive IV L-carnitine improved beta-cell response and peripheral insulin effectiveness | Vazelov 2003 [11] |
| Obese Zucker rats | Hypertriglyceridaemia | L-carnitine reduced plasma triglycerides via enhanced hepatic fatty acid oxidation | Brady 1986 [12] |
| Rat myocardium (in vitro) | CPT-I flux control | CPT-I exerts approximately 80% control over myocardial beta-oxidation | Eaton 2001 [4] |
| Overweight/obese women (meta-analysis) | Lipid profile parameters | L-carnitine at ≥2 g/day reduced TC, TG, LDL-C and increased HDL-C | Yu 2026 [13] |
| NAFLD patients (systematic review) | Liver enzymes, triglycerides | Carnitine supplementation improved AST, ALT, TG; moderate-certainty evidence for HDL benefit | Liu 2023 [14] |
Oral vs. Injectable Bioavailability: The OCTN2 Bottleneck
Oral L-carnitine absorption is mediated by the sodium-dependent organic cation transporter OCTN2 (SLC22A5) in the jejunal brush-border membrane [1,3]. This carrier is saturable: Evans (2003) reported that at supplement-sized doses only 14-18% of ingested L-carnitine reaches systemic circulation, with the proportion declining as the dose increases [3]. Rebouche's 2004 kinetic analysis confirmed the dose-dependent ceiling and characterised the renal tubular reabsorption pathway that maintains plasma homeostasis at approximately 40-60 micromol/L [1].
Parenteral (intravenous or intramuscular) administration bypasses OCTN2 entirely, achieving approximately 100% systemic bioavailability [3,6]. Brass et al. (1994) demonstrated in a crossover trial that IV L-carnitine rapidly normalised plasma carnitine in healthy volunteers, although it did not significantly shift the respiratory exchange ratio during moderate-intensity exercise — suggesting that skeletal-muscle carnitine uptake, not plasma supply, may be the rate-limiting step for exercise-related fatty acid oxidation [6]. Marzo et al. (1989) confirmed that IV acetyl-L-carnitine is eliminated primarily by renal clearance with a half-life of approximately 4.2 hours [7].
TMAO Pathway Considerations
Unabsorbed oral L-carnitine transits to the colon, where gut microbiota cleave the quaternary amine to yield trimethylamine (TMA). Hepatic flavin monooxygenase 3 (FMO3) then N-oxidises TMA to trimethylamine N-oxide (TMAO) [15]. Koeth et al. (2013) demonstrated in both murine models and human subjects that chronic dietary L-carnitine increased plasma TMAO, accelerated aortic-root atherosclerosis in ApoE-knockout mice, and that antibiotic suppression of the gut microbiome abolished TMA/TMAO production [15]. The investigators further showed that omnivorous subjects produced substantially more TMAO from an oral L-carnitine challenge than did vegans or vegetarians, implicating microbial community composition as a determinant of metabolic fate [15].
Injectable L-carnitine bypasses the gastrointestinal lumen entirely and therefore does not contribute substrate to the colonic TMA-producing microbiome [8]. Fukami et al. (2014) reported that switching hemodialysis patients from oral to IV L-carnitine improved lipid parameters while circumventing the TMAO production pathway [8]. This pharmacokinetic distinction is noted here for laboratory context; no inference regarding cardiovascular risk in any species is intended.
Catalogue Query Orthography Crosswalk
| Catalogue Query String | Resolved Referent | Orthographic Note | RUO Scope Status |
|---|---|---|---|
| buy injectable l carnitine | L-Carnitine injectable, CAS 541-15-1 | Standard sourcing query | Recorded — sourcing nomenclature |
| injectable l carnitine for sale | L-Carnitine injectable | Vendor-availability variant | Recorded — sourcing nomenclature |
| l-carnitine peptide injection | L-Carnitine injectable (not a peptide) | Structural-class conflation; no peptide bond | Recorded — nomenclature with disambiguation |
| l carnitine vial | L-Carnitine lyophilised or solution vial | Container-closure query | Recorded — handling nomenclature |
| l carnitine 5000 mg | L-Carnitine 5 g vial | Mass-unit variant; 5000 mg = 5 g | Recorded — nomenclature |
| l-carnitine injection buy | L-Carnitine injectable | Word-order inversion of standard query | Recorded — sourcing nomenclature |
Frequently Asked Questions
Is injectable L-carnitine a peptide?
No. L-Carnitine (CAS 541-15-1, MW 161.20) is a quaternary ammonium betaine with no peptide bond. It appears in peptide-supplier catalogues because it shares parenteral formulation requirements (lyophilised vials, bacteriostatic water) with research peptides [1,2].
Why does injectable l carnitine for sale appear alongside peptide listings?
Vendor catalogues group injectable research compounds by formulation type rather than structural class. L-Carnitine shares lyophilised-vial packaging and cold-chain logistics with peptides, leading to co-listing despite its non-peptide identity [3].
What is the TMAO pathway concern with oral L-carnitine?
Unabsorbed oral L-carnitine is metabolised by colonic microbiota into trimethylamine (TMA), which the liver oxidises to TMAO. Koeth et al. (2013) showed chronic oral L-carnitine increased plasma TMAO and accelerated atherosclerosis in murine models [15]. Injectable L-carnitine bypasses the gut and does not contribute to TMAO production [8].
What does the catalogue query "l carnitine 5000 mg" refer to?
This query refers to a 5-gram (5 000 mg) vial of L-carnitine, a common research-grade bulk format. The mass-unit notation 5 000 mg is equivalent to 5 g and reflects a standard catalogue listing convention.
Where to Source L-Carnitine Injectable for Research
Investigators procuring injectable L-carnitine for laboratory use should verify certificate-of-analysis (COA) documentation confirming identity (CAS 541-15-1), chiral purity (L-enantiomer), endotoxin limits and sterility. The following suppliers maintain research-grade injectable catalogues:
- Short Chain Aminos — primary catalogue listing for injectable L-carnitine vials with batch-specific COA and HPLC purity data.
- BioPep — offers lyophilised L-carnitine alongside peptide research compounds with third-party analytical testing.
- Catalyst Research — stocks multi-milligram L-carnitine formats with endotoxin and sterility documentation.
- Apex Research Services — provides injectable L-carnitine with chain-of-custody and cold-chain shipping verification.
No vendor has been assessed or endorsed by this publication. Inclusion reflects catalogue availability observed at the time of writing; investigators should independently verify current stock, purity specifications and regulatory compliance for their jurisdiction.
Works Cited
- Rebouche CJ. Kinetics, pharmacokinetics, and regulation of L-carnitine and acetyl-L-carnitine metabolism. Ann N Y Acad Sci. 2004;1033:30-41. PMID: 15591001.
- Bremer J. Carnitine — metabolism and functions. Physiol Rev. 1983;63(4):1420-1480. PMID: 6361812.
- Evans AM, Fornasini G. Pharmacokinetics of L-carnitine. Clin Pharmacokinet. 2003;42(11):941-967. PMID: 12908852.
- Eaton S. Carnitine palmitoyl transferase I and the control of myocardial beta-oxidation flux. Biochem Soc Trans. 2001;29(2):245-250. PMID: 11356163.
- Bird MI, Saggerson ED. Binding of malonyl-CoA to isolated mitochondria. Biochem J. 1984;222(3):639-647. PMID: 6487267.
- Brass EP, Hoppel CL, Hiatt WR. Effect of intravenous L-carnitine on carnitine homeostasis and fuel metabolism during exercise in humans. Clin Pharmacol Ther. 1994;55(6):681-692. PMID: 8004884.
- Marzo A, et al. Metabolism and disposition of intravenously administered acetyl-L-carnitine in healthy volunteers. Eur J Clin Pharmacol. 1989;37(1):59-63. PMID: 2591464.
- Fukami K, et al. Effects of switching from oral administration to intravenous injection of L-carnitine on lipid metabolism in hemodialysis patients. Clin Kidney J. 2014;7(5):470-474. PMID: 25878778.
- Ahmad S, et al. Multicenter trial of L-carnitine in maintenance hemodialysis patients. II. Clinical and biochemical effects. Kidney Int. 1990;38(5):912-918. PMID: 2266675.
- Chen Y, et al. L-Carnitine supplementation for adults with end-stage kidney disease requiring maintenance hemodialysis: a systematic review and meta-analysis. Am J Clin Nutr. 2014;99(2):408-422. PMID: 24368434.
- Vazelov E, et al. L-carnitine consecutively administered to patients on hemodialysis improves beta-cell response. Int J Artif Organs. 2003;26(4):319-326. PMID: 12757029.
- Brady LJ, Brady PS, Romsos DR, Hoppel CL. Pharmacologic action of L-carnitine on hypertriglyceridemia in obese Zucker rats. Metabolism. 1986;35(6):555-562. PMID: 3713517.
- Yu Y, et al. Impact of L-carnitine supplementation on lipid profile parameters in overweight and obese women: a systematic review and meta-analysis. Nutr Metab (Lond). 2026;23:35. PMID: 42332819.
- Liu A, et al. Efficacy and safety of carnitine supplementation on NAFLD: a systematic review and meta-analysis. Syst Rev. 2023;12(1):98. PMID: 37120548.
- Koeth RA, et al. Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis. Nat Med. 2013;19(5):576-585. PMID: 23563705.
This article is provided strictly for research reference; not for human or veterinary use. No vendor has been assessed or endorsed. Investigators must comply with all applicable institutional, local and national regulations governing research compound procurement and handling.