| HS Code | 384144 |
| Chemical Name | Menthol |
| Cas Number | 1490-04-6 (racemic) / 2216-51-5 (L-menthol) |
| Molecular Formula | C10H20O |
| Molecular Weight | 156.27 g/mol |
| Veterinary Grade | API grade suitable for veterinary pharmaceutical formulations |
| Appearance | White crystalline powder or colorless needle-like crystals with a strong peppermint odor |
| Solubility | Soluble in ethanol and ether; very slightly soluble in water |
| Melting Point | 41-44 °C for L-menthol |
| Assay | 99.0% to 101.0% based on dried substance |
| Storage Conditions | Store in a well-closed container, protected from light, in a cool dry place |
As an accredited Menthol Ointment Veterinary Grade API for Tablets / Injections / Capsules / Powders / Granules / Premix / Solutions factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Packed in 25 kg HDPE drums with double polythene liners, sealed and labeled for veterinary grade API use. |
| Container Loading (20′ FCL) | 20′ FCL loaded with sealed, palletized containers of veterinary-grade menthol ointment API, safely secured, ventilated, and temperature-controlled for transit. |
| Shipping | Shipping: Supplied in sealed, food-grade drums or bags with tamper-proof packaging. Transport at ambient temperature in ventilated, dry containers, away from heat sources. Full veterinary documentation, MSDS, and certificates of analysis included. Ensure compliance with local regulations and maintain proper labeling for veterinary API shipment. |
| Storage | Store in tightly closed, light-resistant containers in a cool, dry, well-ventilated area. Protect from direct sunlight, moisture, heat, and open flames. Recommended storage below 25°C. Keep away from strong oxidizers and incompatible materials. Ensure container remains sealed when not in use to prevent volatile loss and contamination. Follow veterinary pharmacopoeia guidelines for API handling. |
| Shelf Life | Shelf life: 24 months from manufacture when stored tightly sealed in original container, protected from light, heat, and moisture. |
Anhydrous oleaginous bases are preferred for menthol-containing veterinary rubs because free water accelerates recrystallization of levomenthol once the molten mass cools below its melting range of 41–43°C. A production base commonly uses white soft paraffin, light liquid paraffin, and wool fat in a 70:20:10 ratio by weight; the base is heated in a jacketed stainless steel mixing vessel to 65–70°C until clear, then cooled to 43–45°C before levomenthol is incorporated. This temperature window is narrow because addition at 50°C or above increases headspace loss through sublimation, while addition below 38°C produces uneven solidification and visible crystal seeding. Mixing is performed under vacuum at −0.6 to −0.8 bar to remove entrapped air; where a rotor-stator disperser is used, speed is limited to 1,500 rpm because shear heating can push localized temperatures back into the sublimation range. In-process control includes content uniformity testing under 21 CFR 211.110, with assay limits typically set at 95.0–105.0% of declared label content. A 150 µm inline strainer before filling removes unmelted wax particles or foreign matter. The finished formulation is transferred into collapsible aluminum tubes or polypropylene jars while still fluid at approximately 40°C; cooling is controlled at 1–2°C/min to prevent a coarse crystalline matrix. Accelerated stability assessment follows VICH GL3, with a 6-month condition near 40°C/75% RH and long-term data collected at 25°C/60% RH. The terminal product is used as a topical counterirritant and analgesic balm in equine and bovine musculoskeletal care, with labelling that specifies withdrawal periods where national residue control applies.
Parenteral solutions containing menthol as a dissolved veterinary API are constrained by an aqueous solubility of approximately 0.4 g/L at 20°C and a log P value near 3.4, which forces formulation into mixed solvent systems rather than simple aqueous media. Published data for commercial veterinary injectables containing menthol as the sole active substance are limited; therefore, any development batch must be treated as a novel formulation rather than an established monographed product. Where a parenteral route is required, ternary systems containing propylene glycol, ethanol, and water for injection are screened, with ethanol often limited to 10–20% v/v and propylene glycol to 20–40% v/v to minimize injection-site irritation. Osmolality is adjusted toward 280–320 mOsm/kg, and pH is buffered between 4.5–6.5 to reduce pain on injection. Terminal sterilization by moist heat at 121°C for 15 minutes may strip menthol into the headspace of sealed vials if fill volume below the stopper is not minimized, and nitrogen overlays preceding 0.2 µm filtration are evaluated to reduce oxidative degradation. The finished sterile solution must meet sterility testing under the relevant veterinary pharmacopoeial monograph and residual solvent limits under VICH GL18; the latter sets methanol at 3,000 ppm and ethanol at 5,000 ppm as concentration limits. In practice, menthol-containing injectables are rarely preferred over topical or oral forms because of the narrow solubility window and the risk of biphasic separation during cold storage.
| Residual solvent | Class | PDE (mg/day) | Concentration limit |
|---|---|---|---|
| Methanol | 2 | 30.0 | 3,000 ppm |
| Ethanol | 3 | 50.0 | 5,000 ppm |
| Isopropanol | 3 | 50.0 | 5,000 ppm |
Menthol’s volatility restricts wet granulation for tablets and capsules because aqueous granulation at inlet air temperatures above 40°C causes sublimation and content loss. Direct compression or roller compaction is therefore used when the formulation contains 10–15 wt% menthol adsorbed onto microcrystalline cellulose or colloidal silicon dioxide. Milling through a 0.8–1.25 mm screen is followed by blending with croscarmellose sodium at 2–4 wt% as disintegrant and magnesium stearate at 0.5–1.0 wt% as lubricant. Tablets are compressed to hardness 45–80 N and tested for weight variation under USP <905> and disintegration under USP <701>; menthol content is assayed by gas chromatography with an internal standard such as camphor rather than UV because of the absence of a strong chromophore. Drug-excipient compatibility screening should include menthol with lactose monohydrate, microcrystalline cellulose, and magnesium stearate at 40°C/75% RH for 4 weeks to detect adduct formation or volatile loss. Capsule filling uses starch or lactose monohydrate fillers and requires humidity below 45% RH during encapsulation to avoid sticking and menthol migration into gelatin shells. Batch release includes residual solvent testing under VICH GL18 and microbial limits under the relevant pharmacopoeial monograph. The terminal products are oral carminative and respiratory-cooling tablets or capsules for companion animals; published comparative bioavailability data for these specific veterinary forms remain limited, so batch documentation must reference the approved veterinary medicinal product file.
Aqueous oral solutions for neonatal calves and foals are prepared with a co-solvent phase that maintains menthol in solution during refrigerated storage at 2–8°C. Propylene glycol, ethanol, and purified water are combined at mass ratios of approximately 30:10:60 to achieve a clear monophasic liquid; polysorbate 80 is added at 0.5–1.0% w/v only where slight turbidity appears after dilution into milk replacer. Preservative efficacy is evaluated under the acceptance criteria of the relevant pharmacopoeial monograph for oral liquids, and pH is adjusted to 5.0–6.5 with citrate buffer to reduce glass container leaching. The liquid is filled into amber polyethylene terephthalate or Type III glass bottles under nitrogen flushing, with closure torque monitored to prevent volatile loss. Weight-loss testing at 25°C/60% RH over 12 months should be considered for closure integrity; loss above 2.0% of fill mass indicates excessive permeation. Dosing is delivered by oral drench or calibrated syringe, and labelling includes total menthol mass per millilitre rather than a percentage alone. Terminal product use is primarily for upper respiratory cooling and mild digestive spasm relief in large-animal neonates; published clinical efficacy data for this specific indication remain limited, so formulation files must reference the approved veterinary medicinal product file rather than off-label sensory claims.
Feed powders, granules, and premixes containing veterinary-grade menthol require a two-stage blending sequence because the crystalline solid softens above 35°C and becomes tacky on direct contact with high-moisture carriers. Silica aerogel, precipitated silica, or corn cob fractions with loss-on-drying below 5.0% are used as the adsorption carrier; menthol is first dispersed at 5–15 wt% onto the carrier in a ribbon blender or plow mixer, then this premix is diluted into the full feed or mineral supplement batch. Ambient relative humidity above 60% requires pre-drying of the carrier at 60–70°C for 2–4 hours before adsorption. Homogeneity testing follows the sampling and assay requirements of the applicable feed additive regulation, commonly EU Regulation 1831/2003 for sensory or zootechnical feed additives, with coefficient of variation below 10% across 10–20 sampling points. Feed safety management systems such as FAMI-QS and GMP+ BA2 require documented carrier traceability and cleaning validation where the same blender handles medicated and non-medicated premixes. The terminal products are flavoured premixes or top-dressed granules for swine and poultry; inclusion levels are generally kept below 30 ppm in finished feed to avoid palatability rejection, but each target species requires a preference test under farm conditions before full-scale use. Fluid-bed granulation of menthol-containing premix may use polyvinylpyrrolidone as a binder at 2–4 wt% with inlet air not exceeding 30°C to preserve menthol retention.
Dairy cow udder balm formulations use menthol at 0.25–1.0 wt% in a base of beeswax, sunflower oil, and anhydrous lanolin; the beeswax content is maintained at 6–10 wt% to provide post-milking occlusivity while preserving spreadability. The base is heated to 70–75°C to melt the wax, cooled to 45°C, and menthol is added under slow planetary mixing at 30–60 rpm to limit aeration. Filling into high-density polyethylene cups or laminated tubes occurs at 42–44°C to maintain a smooth surface; cooling tunnels operated at 5–10°C reduce core temperature to below 30°C within 15–20 minutes. In-process checks include viscosity by rotational viscometer and menthol assay by gas chromatography; a deviation above 45°C during any holding stage is recorded as a process alert because of sublimation loss. The terminal product is applied after milking to support teats and udder skin in lactating animals; local residue control regulations apply, and products for food-producing species must carry the relevant milk withdrawal statement when required under the approved marketing authorization.
Topical spray liniments for large animals are formulated with denatured ethanol, isopropanol, and purified water to keep dynamic viscosity below 20 mPa·s at 25°C so that pump spray nozzles maintain a consistent droplet distribution. Menthol is dissolved at 0.5–2.0 wt% before humectants such as propylene glycol are added at 1–3 wt% to slow solvent evaporation on the skin surface. The solution is filtered through a 0.45 µm membrane and filled into high-density polyethylene spray bottles with dip tubes calibrated to deliver 0.15–0.25 mL per stroke. Flashpoint testing under the appropriate closed-cup method is required because ethanol-containing sprays can fall below 25°C flashpoint; filling and storage must therefore comply with local flammable liquid handling codes. Spray pattern and droplet size measurements are performed by laser diffraction after each nozzle lot change to confirm that the delivered spray does not generate excessive respirable mist. The terminal product is used as a cooling liniment for equine legs and shoulders; labelled directions instruct application to intact skin only and avoidance of mucous membranes. Batch release includes assay, microbial limits, spray delivery volume, and closure integrity after simulated transport.
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Designated model MVG-API-MTH-07, the product introduced as Menthol Ointment Veterinary Grade API for Tablets / Injections / Capsules / Powders / Granules / Premix / Solutions is a crystalline monoterpene alcohol supplied as a multi-route active substance. The material is controlled under the current United States Pharmacopeia Menthol monograph and the European Pharmacopoeia Racementhol or Levomenthol monograph, depending on the declared chiral identity. Release criteria are expanded with veterinary-specific limits derived from VICH GL18 for residual solvents and VICH GL11 for impurity control. The primary chemical identity is either 1R,2S,5R-levomenthol (CAS 2216-51-5) or racemic menthol (CAS 89-78-1); the certificate of analysis records the isomer profile because melting range, solubility, cooling potency, and chiral purity affect multispecies formulations. Subgrade codes differentiate particle-size and microbial-control profiles: MVG-API-MTH-07/F for tablets and capsules, MVG-API-MTH-07/G for granules, MVG-API-MTH-07/P for premix adsorption, and MVG-API-MTH-07/S for sterile-filtered liquid or aseptic solid intermediates. The grade is not interchangeable with food-grade or technical-grade material because residual terpene, bioburden, heavy metal, and endotoxin levels are controlled independently.
Release testing combines compendial identity and purity methods with route-specific veterinary controls. Melting range is measured by USP <741> or Ph. Eur. 2.2.14; optical rotation by USP <781> or Ph. Eur. 2.2.6; assay and related substances by gas chromatography with flame-ionization detection on a polar fused-silica capillary column. The compendial assay window is 95.0% to 105.0% on the anhydrous basis. Levomenthol melting range is typically 41–44 °C; racemic material melts between 31 °C and 35 °C. The optical rotation of levomenthol is controlled between -45° and -51° at 20 °C using a 100 g/L solution in ethanol; racemic menthol is expected near 0°. Residual solvents are quantified by headspace gas chromatography according to VICH GL18; toluene, hexane, and isopropanol are controlled below ICH Q3C Option 1 limits. The synthetic route may leave trace thymol and menthone; total related substances are limited to 1.0% for levomenthol and 2.0% for racemic material. For oral powders and tablets, total aerobic microbial count is ≤1,000 CFU/g, and total combined yeasts and moulds ≤100 CFU/g; bile-tolerant Gram-negative organisms are absent in 1 g. For parenteral and intramammary intermediates, bacterial endotoxin is controlled at ≤0.25 EU/mg when the final dose exceeds 5 mL per animal.
| Parameter | Levomenthol grade | Racemic grade | Test method / standard |
|---|---|---|---|
| Assay (anhydrous basis) | 95.0%–105.0% | 95.0%–105.0% | GC-FID, USP Menthol monograph |
| Melting range | 41–44 °C | 31–35 °C | USP <741>, Ph. Eur. 2.2.14 |
| Specific optical rotation | -45° to -51° | -2° to +2° | USP <781>, Ph. Eur. 2.2.6 |
| Total related substances | ≤1.0% | ≤2.0% | GC-FID area normalization |
| Residue on ignition | ≤0.1% | ≤0.1% | USP <281> |
| Water content | ≤0.5% | ≤0.5% | USP <921> Karl Fischer |
| Total aerobic microbial count | ≤1,000 CFU/g | ≤1,000 CFU/g | USP <61>, Ph. Eur. 2.6.12 |
| Total yeasts and moulds | ≤100 CFU/g | ≤100 CFU/g | USP <61>, Ph. Eur. 2.6.12 |
| Bacterial endotoxins, parenteral grade | ≤0.25 EU/mg | ≤0.25 EU/mg | USP <85>, Ph. Eur. 2.6.14 |
| Residual solvents | VICH GL18 class 2 and class 3 limits | Headspace GC | |
Tablet and capsule manufacturing with grade MVG-API-MTH-07/F is performed under low-humidity conditions because menthol sublimes at ambient temperature. Milling is completed in a pinned-disc mill with rotor jacket temperature maintained at 10–15 °C and a nitrogen sweep; classification uses ultrasonically agitated sieves to reduce electrostatic adhesion. The D90 of the fine-milled grade is controlled between 150 µm and 250 µm. Direct compression blends above 5.0 wt% menthol require dry binders such as microcrystalline cellulose and dicalcium phosphate dihydrate; roller compaction is generally avoided above 20 wt% menthol because crystal softening under roll pressure produces amorphous domains and subsequent punch filming. Magnesium stearate is limited to 0.5 wt% to prevent hydrophobic surface coating of menthol crystals and delayed dissolution in calf and piglet oral formulations. Tablets compressed on a rotary press at main compression force 12–18 kN typically show hardness between 50 N and 80 N when the filler is a microcrystalline cellulose-lactose system; disintegration is evaluated in water at 37 °C according to USP <701> with an acceptance limit of 15 minutes.
Premix-grade material is extended with lactose monohydrate, dextrose, or wheat midds. Segregation control follows the carrier-to-active particle size ratio; a ratio above 5:1 is maintained for low-inclusion premixes. When menthol crystals with D50 300 µm are blended with granular limestone carrier of D50 1.5 mm, demixing under 10-minute V-blender discharge occurs if the carrier surface moisture exceeds 3.0%. The product is therefore dried to loss-on-drying ≤0.5% and re-dried before use if exposed to relative humidity above 60% at 25 °C. For granule dosage forms, wet granulation with isopropyl alcohol or ethanol is preferred over aqueous granulation because water initiates crystal bridging; the granulation bowl jacket is held at 15 °C and the solvent is removed under vacuum below 40 °C. Uniformity is confirmed after blending in a double-cone blender at 10 rpm for 15 minutes; ten sampling positions should yield assay relative standard deviation below 5.0%. Menthol adsorbed onto colloidal silicon dioxide at 20–25 wt% loading reduces segregation in vitamin-mineral premixes but increases dust formation; local exhaust ventilation and dust-tight transfer are required.
Compared with food-grade material, the veterinary API is not released on organoleptic criteria alone. Food-grade material often permits a wider terpene profile and may contain unspecified stereoisomers; the veterinary grade limits neomenthol, isomenthone, and thymol by area normalization. Technical-grade material can contain 5% or more of non-pharmacopoeial terpenes and lacks bioburden, heavy metal, and residual solvent documentation for animal use. Peppermint oil distillates contain menthone, menthyl acetate, and cineole; the designated menthol API is isolated or synthesised to reduce these components below pharmacopoeial thresholds. Another difference lies in particle engineering: fragrance-grade menthol is often supplied as large needles that are unsuitable for low-dose direct compression, while the veterinary grade is classified into defined D90 fractions and adsorbed onto silicon dioxide for premix uniformity. Transition metal residues from catalytic hydrogenation are controlled by inductively coupled plasma mass spectrometry and reported on the certificate of analysis; limits are aligned with ICH Q3D for the intended route of administration. Natural menthol derived from Mentha arvensis may require additional pesticide and herbicide screening under the destination-market import tolerance, whereas synthetic material is typically assigned a lower botanical residue risk but a higher residual solvent burden.
Menthol is slightly soluble in water; a saturated aqueous solution contains approximately 0.4 g/L at 20 °C. Injectable formulations therefore incorporate ethanol, propylene glycol, or polyethylene glycol 300 as primary cosolvents, with the aqueous phase buffered to pH 6.0–7.5 before final dilution. The partition coefficient of menthol is approximately 3.4, producing rapid partitioning into lipophilic membranes and container closures. Terminal moist-heat sterilization at 121 °C is generally unsuitable for aqueous menthol solutions because of sublimation and phase separation; sterilizing filtration through a 0.22 µm PVDF or PES membrane followed by aseptic filling is used. In intramammary suspensions, menthol is dispersed in an oily vehicle containing hydrogenated castor oil or aluminium stearate; viscosity at 25 °C is adjusted to 40–80 mPa·s, measured with a Brookfield RVT spindle #2 at 20 rpm. Batch records include a filter-integrity test with forward-flow diffusion and a post-filtration assay to correct for menthol adsorption on membrane surfaces. Exact adsorption losses vary with membrane polymer; published data for this specific configuration is limited, and recovery studies are required for each filtration train. For injectable emulsions, the oil phase is prepared at 60 °C and homogenized under high shear; droplet size distribution is measured by laser diffraction and controlled to D90 ≤500 nm for intravenous products in food-producing species.
Ointment and topical solution processing uses the same API but requires control of solute thermodynamic activity in the base. In white petrolatum and wool alcohol ointment bases, levomenthol is dissolved or partly dispersed; the ratio of dissolved to crystalline drug determines the flux through bovine or porcine skin. The base is heated to 65 °C for incorporation, then cooled at a controlled rate of 0.5–1.0 °C/min to avoid large crystal growth. Concentrations above 2.0 wt% often produce a three-phase system of dissolved menthol, dispersed crystals, and base structure; this is acceptable only if the final product demonstrates consistent in vitro release across viscosity lots. Release testing is conducted in a Franz diffusion cell with a synthetic membrane and receptor phase of ethanol-phosphate buffer pH 7.4 at 20:80 v/v; sampling intervals over 6 hours provide a release-rate profile rather than a single-point value. For sprayable topical solutions, denatured ethanol or isopropanol is used; the product is filtered through 10 µm polypropylene to remove particulate matter. The cooling sensation is mediated by TRPM8 ion channel activation, and levomenthol is preferred over racemic material in dermal products for large animals when a higher cooling response at equal molar concentration is required. The same thermodynamic principle applies to pour-on formulations: high solvent volatility can create transient supersaturation and rapid cooling, but may also produce uneven distribution across the dorsal midline if the solvent evaporation rate exceeds 0.2 g/cm²/h.
Storage is specified in tight, light-resistant containers at 15–25 °C; prolonged storage above 35 °C leads to sublimation and caking. Low-density polyethylene containers are not recommended because menthol can permeate the polymer and alter closure integrity. Retest period is set at 24 months for the unopened original container; each retest includes assay, related substances, water content, and microbial enumeration. The grade should not be combined with strong oxidising agents, and tablets containing menthol are not stored in unlined aluminium blister cavities because terpene-aluminium interaction can produce discolouration. Retention samples are held below 0 °C in crimped vials with PTFE-lined septa to prevent cross-contamination and sublimation losses.
