| HS Code | 729970 |
| Product Name | L-Lysine-Carboxymethylcysteine Salt |
| Chemical Name | L-Lysine S-(carboxymethyl)-L-cysteine salt |
| Cas Number | 55689-65-1 |
| Molecular Formula | C11H23N3O6S |
| Molecular Weight | 325.38 g/mol |
| Appearance | White or almost white crystalline powder |
| Melting Point | 230°C (decomposes) |
| Solubility | Freely soluble in water; slightly soluble in ethanol; practically insoluble in acetone and chloroform |
| Specific Optical Rotation | [α]20D = -13° to -17° (c = 1, water) |
| Ph | 6.0 to 8.0 (1% aqueous solution) |
| Storage Condition | Store in a cool, dry, well-ventilated area; keep container tightly closed |
| Hygroscopicity | Hygroscopic; protect from moisture |
As an accredited L-Lysine-Carboxymethylcysteine Salt factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Packaged in sealed 25 kg fiber drums with polyethylene liners, labeled for safe handling and secure chemical storage. |
| Container Loading (20′ FCL) | 20′ FCL loading of L-Lysine-Carboxymethylcysteine Salt in sealed drums, palletized and secured for safe, efficient transport. |
| Shipping | Ship L-Lysine-Carboxymethylcysteine Salt in sealed, moisture-proof containers at ambient temperature, away from direct light and heat. Ensure packaging is clearly labeled and complies with all applicable transport regulations. This compound is generally non-hazardous, but avoid dust formation and inhalation during handling. Include SDS with shipment for reference. |
| Storage | Store L-Lysine-Carboxymethylcysteine Salt in a tightly sealed container in a cool, dry, well-ventilated area, protected from light and moisture. Keep away from strong oxidizing agents and incompatible materials. Maintain stable room temperature, avoid excessive heat, and ensure container is labeled. Use appropriate handling and storage practices to preserve stability and purity. |
| Shelf Life | Stable for 2–3 years when stored dry, cool, and away from light; keep container tightly sealed. |
In 316L jacketed mixing vessels fitted with bottom-entry propeller agitators and upper counter-rotating scraped-surface agitators, the adult aqueous syrup line is prepared as a 9.0% w/v solution of L-lysine-carboxymethylcysteine salt monohydrate, equivalent to 90 mg/mL in the final packaged liquid. The manufacturing sequence charges purified water at 25 ± 5 °C, disperses 30.0% w/v liquid sorbitol 70% non-crystallisable under low shear, then hydrates 0.25% w/v hydroxyethylcellulose until the solution is free of fisheyes. The active salt is charged only after batch temperature falls below 30 °C; addition under nitrogen blanketing at 0.02–0.05 bar overpressure keeps dissolved oxygen below 1.0 mg/L, limiting oxidative degradation of the thioether group. Sodium benzoate 0.10% w/v and potassium sorbate 0.10% w/v form the preservative system, with pH adjusted using 1 M citric acid or sodium hydroxide to 6.0–6.5 so that benzoate remains within its effective dissociation window. The bulk solution is recirculated through a 20 µm polypropylene cartridge before transfer to a nitrogen-purged filling line. Terminal product types are 200 mL Type III amber soda-lime-silica glass bottles with tamper-evident HDPE closures and graduated polypropylene dosing cups of 5 mL or 15 mL. Compliance is maintained under Ph. Eur. 5.1.4 for microbiological quality of non-sterile oral preparations, Ph. Eur. 2.6.12/2.6.13 for total aerobic microbial count and specified micro-organisms, Ph. Eur. 2.9.5 for uniformity of mass in delivered doses, and ICH Q3D for elemental impurity control.
A single-dose granule formulation loads 2.7 g L-lysine-carboxymethylcysteine salt monohydrate per sachet at a final fill weight of 4.0 g ±5%, giving an active loading of 67.5% w/w in each 4.0 g dose. Top-spray fluidised-bed granulation on a Glatt GPCG 60 or equivalent uses a 1.2 mm two-fluid nozzle, inlet air temperature 55–65 °C, product temperature 28–32 °C, and atomising air pressure 0.13–0.16 MPa; exhaust humidity is maintained between 9–12 g/kg dry air. The dry mix comprises mannitol Pearlitol 160 C and pregelatinised maize starch; a binder solution of povidone K30 5.0% w/w in purified water is sprayed at 120–180 g/min until granules reach a target moisture endpoint of 1.5–2.5% by halogen moisture analyser at 105 °C. Milling through a 1.25 mm conical screen precedes external addition of 0.5% w/w colloidal silicon dioxide and flavour; the final blend is filled into PET/aluminium/PE 12/9/60 µm triple-laminated sachets on a vertical form-fill-seal line with sealing-jaw temperature 140–160 °C. Terminal product type is a single-dose granule for oral solution. Compliance references include Ph. Eur. 2.9.40 for uniformity of dosage units, Ph. Eur. 2.9.5 for single-dose mass of granules, Ph. Eur. 2.2.32 for loss on drying, and Ph. Eur. 5.1.4 for microbial limits. The operational boundary is narrow: if product temperature exceeds 35 °C, the salt forms amorphous bridges in the spray zone, causing bag-filter blinding, agglomerates larger than 1.6 mm, and fill-weight drift above 4.2 g; residual moisture below 1.5% produces electrostatic fines that reduce blend uniformity during auger filling.
Because the 5 mL dosing syringe imposes a viscosity ceiling of 45 mPa·s at 20 °C, the paediatric sugar-free solution line is structured differently from the adult syrup line. The formulation delivers 450 mg L-lysine-carboxymethylcysteine salt monohydrate in each 5 mL dose, equivalent to 90 mg/mL, but replaces sorbitol and sucrose with 20.0% w/v xylitol and 5.0% w/v maltitol to reduce fermentable carbohydrate load and minimise dental caries risk in long-term paediatric administration. Sodium citrate 10 mM buffers the solution at pH 6.0–6.5; sodium benzoate 0.08% w/v and potassium sorbate 0.08% w/v are used because the lower concentration reduces the risk of benzoate-associated tolerance issues in children while maintaining preservative efficacy within the same pH window. The solution is prepared in a 500 L closed stainless-steel vessel, nitrogen-sparged to dissolved oxygen below 0.8 mg/L, and passed through a 10 µm polyethersulfone filter before filling under low-speed peristaltic transfer at 20–40 L/h to avoid foaming. Terminal product types are 60 mL amber PET bottles with child-resistant closures conforming to EN ISO 8317 and a graduated 5 mL oral syringe. Preservative efficacy is evaluated according to Ph. Eur. 5.1.3, microbial quality under Ph. Eur. 5.1.4, and delivered-dose uniformity according to Ph. Eur. 2.9.5. The critical control point for this line is that temperatures above 35 °C during filling accelerate oxidative discoloration of the solution, and the filled bottles must be stored below 25 °C in light-protected cartons to maintain colour and assay.
For 10 mL blow-fill-seal unit-dose cups, the fill solution is prepared at 9.0% w/v, delivering 900 mg L-lysine-carboxymethylcysteine salt monohydrate per 10 mL cup, and is passed through a 0.22 µm inline membrane filter before entering the BFS filling circuit. The BFS machine operates with extrusion temperatures of 180–210 °C for low-density polyethylene, fill weight controlled at 10.0 g ±0.2 g, and positive-pressure fill rooms with ISO 14644-1 Class 8 background and Class 5 critical zone. The polymer contact layer is a pharmaceutical-grade low-density polyethylene with compliance under FDA 21 CFR 177.1520, USP <660> for plastics, and USP <1207> for package integrity; extractables and leachables are assessed under USP <1663> and USP <1664>. Closure integrity is verified by methylene blue dye penetration and vacuum decay at -30 kPa for 30 s. Terminal product type is the 10 mL oral solution unit-dose cup, intended for direct oral administration to adults with swallowing difficulty. The filled cups are subsequently packed in aluminium overpouches with a moisture barrier of ≤0.1 g/m²/day at 38 °C/90% RH, because LDPE alone permits oxygen ingress that would accelerate oxidation of the thioether function. Microbiological limits follow Ph. Eur. 5.1.4, delivered-dose uniformity follows Ph. Eur. 2.9.5, and degradation products are monitored by HPLC according to Ph. Eur. 2.2.29.
Once filled into 150 mL moisture-barrier PET bottles with desiccant-lined HDPE closures, the alcohol-free dry syrup powder contains 9.0 g L-lysine-carboxymethylcysteine salt monohydrate per bottle, reconstituted with 95 mL purified water to produce 100 mL at 90 mg/mL. The powder is built in a 1000 L double-cone blender at 10 rpm for 20 min, blending the active with mannitol, maltodextrin, sodium citrate buffer, sucralose, and 0.5% w/w colloidal silicon dioxide; the final blend is filled by auger filler under relative humidity below 30%. Terminal product type is a powder for oral solution in a 150 mL bottle, reconstituted at the point of dispensing in tropical pharmacies without refrigeration. The dry state is controlled by Karl Fischer titration under Ph. Eur. 2.5.32 with a moisture limit of 1.0%; after reconstitution, pH is 6.0–6.5, and the solution is labelled for disposal after 14 days at 25 °C. Microbiological quality follows Ph. Eur. 5.1.4, and the mass uniformity of the powder for multi-dose bottle presentation is checked according to Ph. Eur. 2.9.5. The reconstitution constraint is that water temperature must remain below 30 °C; use of warm water above 40 °C increases dissolution time beyond 5 min and accelerates degradation of the active substance. Bottles must be kept tightly closed and inside silica-gel desiccant containers during storage at 25 °C, relative humidity ≤60%, to prevent caking and loss of free-flowing powder properties.
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L-Lysine-Carboxymethylcysteine Salt is a stoichiometric addition salt formed from S-carboxymethyl-L-cysteine and L-lysine. The anhydrous 1:1 salt is described by the molecular formula C11H23N3O6S and a relative molecular mass of 325.38 g/mol. The compound is prepared by neutralising S-carboxymethyl-L-cysteine with L-lysine in purified water, followed by controlled crystallisation, spray drying, or freeze drying. The resulting material is typically a white to off-white crystalline or amorphous powder, depending on the isolation route. The L-lysine counterion confers markedly higher aqueous dissolution than the free acid, while retaining the mucoregulatory activity associated with the S-carboxymethyl-L-cysteine moiety. The product is not a physical mixture of the two amino acid components; infrared absorption spectroscopy shows the carboxylate shift from the free acid, and differential scanning calorimetry generally reveals a single thermal transition rather than separate melting endotherms.
Model differentiation for this substance is manufacturer-specific rather than compendial. No harmonised monograph in Ph.Eur. or USP-NF is specific to the lysine salt, so supplier codes are used to distinguish crystalline API-grade material from spray-dried direct-compression grade or freeze-dried analytical reference material. A technical data sheet should be requested for particle-size distribution, bulk density, residual moisture, residual solvent profile, and packaging configuration. The model designation alone does not indicate compliance with a defined release specification; the batch certificate of analysis remains the operative document.
The release specification for L-Lysine-Carboxymethylcysteine Salt is built around identity, assay, optical purity, water content, related substances, residual solvents, elemental impurities, particle size, and microbial quality. Salt stoichiometry is controlled indirectly because the material may dissociate during reversed-phase HPLC. Assay of S-carboxymethyl-L-cysteine after acid dissociation by high-performance liquid chromatography according to Ph.Eur. 2.2.29 is combined with a separate L-lysine determination by amino acid analysis or pre-column derivatisation. A deviation from the 1:1 molar ratio alters the aqueous pH and dissolution behaviour; therefore the assay is not limited to the carbocisteine component alone. Hydration state varies with the isolation route. Spray-dried material may be obtained as an anhydrous or low-hydrate form with equilibrium moisture dependent on ambient humidity. Loss on drying by USP <731> is therefore interpreted against the supplier’s package desiccant and exposure history rather than as a single universal limit.
Identity testing is performed by infrared absorption spectrophotometry per Ph.Eur. 2.2.24. Specific optical rotation per Ph.Eur. 2.2.7 is included to detect racemisation of the L-lysine or S-carboxymethyl-L-cysteine chiral centres during processing. Residual solvent analysis follows ICH Q3C; ethanol, isopropyl alcohol, or acetone may be detected when crystallisation from aqueous-organic solvent mixtures is used. Elemental impurity testing follows ICH Q3D, with particular attention to stainless-steel contact metals such as chromium, nickel, and iron if the process stream is not passivated. Particle-size distribution is measured by laser diffraction according to ISO 13320. Powder flow and fineness may be evaluated with USP <1174> and USP <811>. Because no harmonised monograph fixes the acceptance criteria, the specification must be linked to the intended dosage form and processing route.
| Parameter | Method | Purpose |
|---|---|---|
| Identification | Ph.Eur. 2.2.24 infrared absorption spectrophotometry | Confirm carboxylate and amine salt structure |
| Assay of S-carboxymethyl-L-cysteine | Ph.Eur. 2.2.29 HPLC after acid dissociation | Quantify anion stoichiometry |
| Assay of L-lysine | Amino acid analysis or derivatisation | Quantify cation stoichiometry |
| Specific optical rotation | Ph.Eur. 2.2.7 | Detect amino acid racemisation |
| Loss on drying | USP <731> | Control hydrate and residual moisture |
| Residual solvents | ICH Q3C headspace GC | Control ethanol, isopropyl alcohol, acetone |
| Elemental impurities | ICH Q3D ICP-MS | Control processing metal residues |
| Particle size distribution | ISO 13320 laser diffraction | Match dissolution and segregation behaviour |
The stability-indicating method should separate S-carboxymethyl-L-cysteine sulfoxide and the free acid from the intact salt. Because the lysine cation can mask the anion retention under reversed-phase conditions, an ion-pairing reagent or an acid-dissociation step is often required. Method validation follows ICH Q2(R1) for specificity, linearity, accuracy, repeatability, intermediate precision, and range. Detection limits for related substances depend on detector type and sample matrix; published data for this specific configuration is limited, so each production site must establish its own reporting threshold.
In oral liquid preparations, the salt is selected where neutral or only weakly acidic pH is required and where rapid dissolution is needed for dosing accuracy. A stock solution in purified water may be prepared for paediatric or geriatric administration; the pH of such a solution is a function of residual free L-lysine, carbon dioxide uptake, and batch stoichiometry. The free acid S-carboxymethyl-L-cysteine is only sparingly soluble in water and normally requires salt formation or an alkaline buffer for complete dissolution. The lysine salt therefore simplifies the preparation of sugar-free syrups and sachets. The mucoregulatory action is associated with the S-carboxymethyl-L-cysteine component, which normalises the pathological sialomucin-to-fucomucin ratio in bronchial secretions and reduces mucus viscoelasticity. The lysine salt does not introduce a free thiol group, because the sulphur atom is present as a thioether. As a result, the volatile sulphur odour characteristic of free-thiol agents such as N-acetyl-L-cysteine is absent, and aqueous solutions do not require the same level of antioxidant stabilisation.
In oral solid dosage forms, the primary amine groups of L-lysine introduce compatibility constraints not present with the free acid. Reducing sugars such as lactose and glucose can participate in Maillard-type reactions under elevated moisture and temperature. Accelerated compatibility studies at 40 °C/75% RH according to ICH Q1A(R2) are used to detect discoloration and related substance formation. Isomalt or mannitol may be considered as alternative crystalline diluents, but each formula must be verified because mannitol can reduce tablet hardness under low moisture. Sodium starch glycolate is generally preferred over crospovidone as a disintegrant when wet granulation is used, because the primary amine may interact with polyvinylpyrrolidone under moist conditions. Dry granulation by roller compaction is an alternative when moisture-sensitive excipients are present; compaction pressure must be controlled to avoid sticking at the rolls.
A critical process risk is disproportionation during wet granulation. The 1:1 salt can revert to free S-carboxymethyl-L-cysteine and L-lysine under localised acidic conditions. This risk is highest when the granulating fluid contains citric acid, ascorbic acid, or another acidic binder component. In situ Raman spectroscopy may be used to monitor the carboxylate band during granulation; a shift back toward the free-acid carbonyl stretch indicates disproportionation. The granulating fluid should therefore be purified water or a mildly alkaline binder solution, with pH measured before spraying. If a pH modifier is required, sodium bicarbonate or trisodium citrate may be evaluated, but the amount must be optimised to avoid excessive sodium load and pH-mediated degradation of the active.
Dissolution testing of oral solid dosage forms containing the salt is often performed in water, pH 1.2 hydrochloric acid, pH 4.5 acetate buffer, and pH 6.8 phosphate buffer as a multi-point profile. The salt dissolves rapidly in water, but the free acid may precipitate in the gastric pH range if the medium is poorly buffered. This precipitation depends on the pKa values of the carboxylate groups and the ionic strength of the medium. Formulators may add a weak acid buffer or apply an enteric coating if acid precipitation is observed during in vitro testing. Published data for this specific configuration is limited, so dissolution method development should include a pH-profile evaluation before final specification setting.
The principal difference between L-Lysine-Carboxymethylcysteine Salt and other mucoactive agents is mechanistic. N-Acetyl-L-cysteine is a free-thiol compound that directly reduces disulfide bonds within mucus glycoproteins, producing rapid mucolysis. S-Carboxymethyl-L-cysteine and its lysine salt are mucoregulators; they shift the relative biosynthesis of sialomucins and fucomucins rather than depolymerising existing mucus gels. Erdosteine is a thiol-containing prodrug requiring metabolic activation to active thiol metabolites. Ambroxol hydrochloride is a secretolytic agent associated with stimulation of surfactant production and mucociliary clearance. These differences influence both therapeutic onset and formulation stability. A direct disulfide-cleaving agent such as N-acetyl-L-cysteine can oxidise in aqueous solution and may require metal chelation and inert-gas blanketing. The carbocysteine lysine salt is stable to atmospheric oxygen but hygroscopic and requires desiccant-protected packaging.
| Substance | Active chemical group | Mechanism | Aqueous solubility | Compendial status | Principal incompatibility |
|---|---|---|---|---|---|
| L-Lysine-Carboxymethylcysteine Salt | Thioether carboxylate and lysine ammonium | Mucoregulator; modifies mucin glycoprotein composition | High, conferred by salt counterion | No specific monograph; free acid used as analytical reference | Reducing sugars; strong oxidising agents |
| S-Carboxymethyl-L-cysteine free acid | Thioether carboxylic acid | Mucoregulator | Low; pH-dependent | Regional monographs available | Alkaline pH above precipitation threshold |
| N-Acetyl-L-cysteine | Free thiol | Direct disulfide cleavage | High | USP, Ph.Eur. | Oxidation by atmospheric oxygen and metal ions |
| Erdosteine | Thiol-containing prodrug | Active thiol metabolites | Low | Not harmonised in all regions | Alkaline hydrolysis |
| Ambroxol hydrochloride | Hydrochloride salt of an amine | Secretolytic and surfactant modulator | High | USP, Ph.Eur. | Strong alkalis |
In dissolution testing, the intrinsic dissolution rate of the L-lysine salt in water is higher than that of the free acid, but the exact ratio depends on particle size and solid-state form. For a formulation change from free acid to lysine salt, the dissolution medium may be simplified from an alkaline or surfactant-containing buffer to purified water, provided sink conditions are maintained. When compared with N-acetyl-L-cysteine, the absence of a free thiol group eliminates the need for sodium edetate as a metal-ion chelator for colour stability. However, the primary amine groups of L-lysine can react with aldehyde-containing flavour components, so flavour selection should include a Schiff-base compatibility evaluation. The salt also has a higher acid-buffering capacity than free carbocisteine, which can alter the microenvironmental pH in a tablet matrix and affect pH-sensitive release modifiers.
Batch release should include a chromatographic purity test capable of detecting oxidative sulfoxide and reduced dicarboxymethyl analogues. Preparative HPLC conditions may require an ion-pairing reagent because the lysine cation can alter anion retention. Alternatively, the salt may be dissociated with dilute acid and the free S-carboxymethyl-L-cysteine determined by a validated compendial method. Residual solvent analysis by headspace gas chromatography per ICH Q3C is needed when isopropanol is used as a crystallisation solvent, because the amino acid salt can retain solvent within the crystal lattice. The product should not be exposed to prolonged drying above 60 °C; discoloration may occur even without a reducing sugar, although the degradation pathway is not described in the public literature for this exact salt and published data for this specific configuration is limited.
Packaging specifications are based on moisture protection rather than oxygen protection. Aluminium-aluminium blister packs with silica gel desiccant are suitable for high-humidity regions. High-density polyethylene containers with induction-sealed closures may be used for bulk packaging if the closure liner is polyolefin-based and the desiccant mass is matched to the fill volume. Cotton or rayon coil is not recommended, because the fibres can retain moisture and create a local high-humidity environment. For shipment, the product should be stored below 25 °C and protected from direct light. Refrigerated storage is not normally required, but freeze-thaw cycles should be avoided because condensation can cause powder caking and recrystallisation.
