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Life’s needs push chemistry forward, and Polyoxyethylene 35 Castor Oil, often called EL35, tells a story that spans continents and decades. Scientists in the early 20th century hunted for safe, effective ways to dissolve drugs that do not mix easily with water. Regular castor oil, pressed from the beans of the Ricinus communis plant, had long been around for medicinal use. But the issue always came down to solubility and stability. The game changed once researchers found they could attach many ethylene oxide units to castor oil’s molecules — making the product far more dispersible in water. Over time, as pharmaceutical science boomed, EL35 appeared in the European Pharmacopoeia (EP), British Pharmacopoeia (BP), and United States Pharmacopeia (USP). Its use in massive, once ground-breaking injectable medicines underscores how urgently industry needed a robust, trusted nonionic surfactant.
At its core, EL35 brings together the fatty backbone of castor oil and the hydrophilic punch of about 35 ethylene oxide units per triglyceride. The industry sometimes calls this product by several names—Cremophor EL, Kolliphor EL, PEG 35 Castor Oil. These synonyms have cropped up over the years, especially across different pharmacopoeias and supplier catalogs. Pharmaceutical manufacturers reach for EL35 to help solubilize otherwise stubborn, lipophilic drug molecules—turning difficult formulations into injectable, oral, and topical medicines.
EL35 has a pale yellow color, a characteristic mild odor, and a sticky, viscous texture that many chemists know by feel. It dissolves in water at a wide range of ratios, producing clear or slightly hazy mixtures depending on concentration. The product carries a specific gravity between 1.06 and 1.09 at room temperature, and it avoids freezing until the temperature plummets below -10°C. The high degree of ethoxylation means EL35 blends hydrophilic and lipophilic tendencies. Its HLB value (hydrophile-lipophile balance) sits between 12 and 14 — putting it in the sweet spot for solubilizing and emulsifying.
Any serious EL35 supplier aims for tight specifications, because pharmaceutical standards don’t allow much leeway: Acid value stays below 2, saponification value falls between 50 and 60, hydroxyl number lands near 65 to 80. Water content remains below 2%. Heavy metal residues rarely get above 10 ppm. GMP-certified packaging always includes full batch traceability, date of manufacture, and detailed safety/handling labels, so any slip-up or recall can be traced in hours, not days.
Manufacturers synthesize EL35 by reacting pure castor oil with ethylene oxide, under pressure, at controlled temperatures. Catalysts facilitate the chemical bonding of dozens of ethylene oxide molecules onto each triglyceride unit, but strict regulation of reaction time and conditions prevents uncontrolled by-products. Continuous testing and purification guarantee the product leaves little unreacted castor oil, minimal free polyoxyethylene chains, and negligible trace toxins. This gives formulators confidence, dose after dose, in the product’s consistency.
The core ethoxylated structure lets EL35 undergo further chemical tweaks, though in pharma, most stick close to the standard. In theory, modifications could tailor the number of ethylene oxide groups or add end-capping groups for special purposes, but such change always triggers new safety and regulatory review. EL35’s robust ether linkages hold up under a wide range of pH conditions, and few routine reactions in a compounding lab damage its surfactant power.
Anyone in the business should recognize a string of names for this same excipient: Cremophor EL and Kolliphor EL top the list, especially in the context of injectable drugs from the ’80s onward. Elsewhere on paperwork and packaging, manufacturers might list PEG-35 Castor Oil, Polyoxyl 35 Castor Oil, or Polyethylenglykolricinusöl 35. Pharmacopoeias sometimes use slightly different naming but reference the same product type, tied back to its physical-chemical identity.
No excipient gets as much scrutiny as EL35, because its widespread use in injectables puts it one step from the bloodstream. Anyone handling bulk material in a plant wears full PPE—gloves, goggles, lab coats—and follows protocols for spill response due to the sticky, absorbent nature of the oil. GMP compliance dictates room air quality, raw material origin, and verification of the absence of microbial or pyrogenic contaminants. Packaging always warns against ingestion or contact with skin until diluted and specifies correct storage—sealed containers, away from strong oxidizers, out of direct sunlight. Only approved methods handle disposal of waste batches, since glycol ethers can be tough on water systems.
EL35 has become a backbone excipient in medicines that deliver water-repelling drugs—think cancer therapeutics like paclitaxel, where nothing else can keep the compound stable and ready for infusion. Its reach goes past oncology to include vitamins, fat-soluble hormones, and experimental anti-inflammatories. Because EL35 ensures these actives stay mixed with water for injection, pharmacists can focus on clinical utility and not on the challenges of clumping or separation. Topical creams, especially those meant for fast absorption, often rely on EL35’s gentle skin interaction and powerful solubilizing effect. Even in veterinary medicine and food supplements, you’ll find this molecule smoothing out complicated blends.
Over the last fifty years, journals have filled with papers exploring how EL35 enhances drug absorption, stabilizes protein suspensions, and interacts with cell membranes. Formulation teams at pharmaceutical companies look for even better ways to control how EL35 interacts with actives—trying to ward off unwanted precipitation during storage and administration. Recent R&D focuses on combining EL35 with other surfactants for improved injection tolerability and on finding reliable plant-based feedstocks to guarantee supply without sky-high prices. Analytical chemists keep pushing for ever-more-sensitive detection of impurities or breakdown products, given regulatory focus on patient safety.
Toxicologists track both short-term and chronic exposure risks of EL35, especially since cases of hypersensitivity and anaphylactoid reactions have turned up in some chemotherapy patients. Rodent and in vitro studies support dosage limits and help drug developers know where caution matters most—especially for IV infusions. Regulatory agencies mandate systemic toxicity data, allergenic potential, and evaluation of metabolites. The literature regularly points to a need for close clinical monitoring, not due to any mystery of EL35’s chemistry but because surfactant-excipient interactions with actives can be unpredictable. Hospitals now pre-medicate with antihistamines during high-profile EL35-containing drug infusions.
EL35 stands at a crossroads. As demand for injectable biotech drugs rises, excipient makers face new pressure to clean up residual impurities even further and document every step in the supply and testing chain. Companies invest in greener processes for synthesis and purification, knowing regulators want both sustainability and safety. Work is underway on more biodegradable versions of nonionic surfactants, but for now, few candidates match EL35’s blend of price, performance, and regulatory acceptance. At the same time, digital QA and supply-chain tracking promise fewer counterfeits and tighter control for hospital and clinic buyers. With personalized and targeted medicine on the rise, EL35 just keeps proving its worth, so long as industry keeps working to minimize known risks and maximize quality.
Polyoxyethylene 35 Castor Oil, often called EL35, comes from ordinary castor oil, turning the thick vegetable product into something far more versatile through a process called ethoxylation. The outcome looks nothing like raw castor oil. This new form dissolves in water easily and can carry substances that aren't fond of mixing with water on their own. Picture a stubborn oil droplet—EL35 wraps around it and brings it along into the watery world of a medication or infusion.
EL35 steps in any time a medicine needs an oily ingredient to stay dissolved in water-based solutions. Vitamin preparations, injectable drugs like certain painkillers, and anti-cancer treatments all run into this hurdle. EL35 acts much like a middleman—bridging the gap that oil and water so rarely cross on their own. This quality has big impacts on patient care. If something only dissolves in oil, without EL35 or similar helpers, some treatments would only come as painful or impractical shots or oily mixtures.
In my time reading ingredient lists as a patient and looking into drug safety for my family, EL35 pops up every now and then, especially in hospital-grade medications. It helps doctors dose drugs accurately and safely, giving patients medicine that the body can take up in the right way. For example, paclitaxel, an important cancer drug, uses EL35 to keep the medicine stable until it reaches the cells that need it most. The alternative could mean fewer drugs, tougher side effects, or treatment delays.
Anyone who’s sat with a loved one through chemo probably knows the long infusion routines. The focus lands on the medicine, not what else rides along in the IV. EL35 isn’t the hero anyone talks about, but its role matters. It lowers pain at the injection site, avoids lumps or clogs in lines, and lets tough drugs reach their target. Without helpers like EL35, treatments could hurt more or work less predictably.
The story isn’t all good. Like many helpers, EL35 has caused allergic reactions in rare cases. Some folks run fevers, some get rashes, and in very rare situations, patients may face anaphylaxis. The medical world keeps an eye on these risks, adjusting doses or testing for allergies before using solutions with EL35. Paclitaxel infusions now often include pre-treatments with antihistamines or steroids to head off allergic responses.
Manufacturers also tackle purity. Manufacturing EL35 right, and testing for impurities, can prevent many problems. Some countries set tougher guidelines than others. Pharmaceutical brands have had to recall products when impurity levels turned up higher than allowed. This pushes the industry to keep improving how EL35 is made and monitored.
Researchers continue hunting for ingredients that work like EL35, but cause fewer side effects or allergic reactions. Some new products promise to blend things more gently, or biodegrade better once they’ve done the job in the body. EL35 stays important for now, though, simply because it works so well for its main purpose. For families relying on modern medication, that means more safe and comfortable treatments, so long as monitoring and quality control stick to strict standards.
Pharmaceuticals live and die by their ingredients. Not just the drugs, but the carriers, solvents, and emulsifiers. Polyoxyethylene 35 Castor Oil—marketed as El35 or by other names—plays a big part in formulating intravenous medicines. It helps dissolve drugs that don’t like water. Even a small deviation from formula can tip the balance from safe to risky.
BP (British Pharmacopoeia), EP (European Pharmacopoeia), and USP (United States Pharmacopeia) set rules, not suggestions. Strict standards keep impurities, toxins, and contamination out of the bloodstreams of patients. Every batch of El35 must hit specific marks; it’s tested for ethylene oxide, diethylene glycol, heavy metals, and residues from raw castor oil.
If El35 fails any of these checks, it can lead to severe, even life-threatening, reactions. I’ve seen hospitals recall batches of drugs when a batch of excipient failed on one point alone. Even a change in fragrance or color—a sign of potential oxidation or contamination—triggers investigation. These rules aren’t just bureaucratic hurdles. They are lifelines for children needing chemotherapy, for elderly patients with heart disease, for anyone who can't afford a single shortcut.
Every batch marked as Pharmaceutical Grade El35 must show clear test results. The BP, EP, and USP standards demand traceability from raw materials all the way to the finished excipient. Testing involves chromatography, spectroscopy, and tests for peroxide content and pH. If a supplier fails on one specification, drug companies dump the lot.
One crucial requirement involves the amount of polyethoxylation. Every molecule has to fall within a narrow average of ethylene oxide units. Go outside this range, and the excipient performs differently—leading to solubility issues or reactions with the active ingredient. Pharmaceutical producers run their own quality control labs to double-check. Regulators inspect facilities, review paperwork, and sometimes demand process changes if repeated failures emerge.
Experience tells me a trusted material one year could miss the mark the next. Source quality shifts with climate, with new suppliers, and with old equipment falling out of calibration. A few years ago, I worked with a manufacturer who swapped to a cheaper, lower-grade castor oil. Batch results failed for rancidity levels. The cost saving turned into a massive recall, legal fees, and lost trust.
Close collaboration among suppliers, manufacturers, and regulators forms the strongest defense. Suppliers who share batch data openly make it easier to spot problems early. Drug makers who validate and stress-test excipients beyond basic specifications expedite fail-safe drugs reaching patients. Regulators who provide feedback and allow dialogue keep materials safe without slowing innovation.
Trust grows when everyone in the chain refuses shortcuts. If a batch of El35 claims to comply with BP, EP, and USP, show me the paperwork, the data, and the plant tour. Anything less, and patients pay the cost.
Polyoxyethylene 35 Castor Oil, better known to those in labs and pharmaceutical production as El35, plays a key role as a nonionic surfactant. Pharmacies, compounding centers, and manufacturing plants rely on it for its ability to dissolve drugs that do not play well with water. Despite its everyday use, this oily liquid comes with its quirks, and storing it the wrong way brings more trouble than most realize. Leaks, product breakdown, safety hazards—all of these tie to simple mistakes that crop up during storage and handling.
From experience, crowded storage rooms often become dumping grounds for everything liquid, including El35. But this stuff benefits from some careful attention. Store it in a place that keeps temperatures steady, away from extremes. Even though El35 remains stable under normal conditions, cold temperatures cause cloudiness and even solidification, making the liquid tough to work with. Heating brings it back to clear, but keep the heat gentle—too much risks chemical changes. Too cold and you waste time thawing out containers when production can’t wait.
Light matters, too. Extended exposure to strong sunlight gradually degrades El35, especially if the container sits near windows or skylights. Translucent bottles seem convenient, but light creeps in, so it’s worth sticking with containers that keep UV rays out. I’ve seen discolored product from months of leaving drums near loading bays—workers notice the change, and batches get rejected. The lesson is simple: dark, closed spaces offer the protection El35 needs.
Genuine problems start with poor containers. El35 tends to absorb moisture from humid air if left open, leading to bacterial growth or changes in chemical makeup. Tight, resealable lids cut down on risk. Stainless steel or high-density polyethylene (HDPE) containers stop chemical reactions that eat away less robust plastics. Metal drums with proper linings become standard in many bulk facilities. Over time, leaks from flimsy packaging cause safety scares, waste money, and increase cleanup work.
One overlooked difference between a slick operation and chaos? Label everything. It’s easy to lose track of which drum is which without labels, especially with floor workers changing shifts. Clear, durable labels that resist oil stains cut down on mix-ups and confusion. Proper labeling also keeps accidental misuse to a minimum, especially if near flammable products or concentrates meant for topical use.
Spills create a mess and bring risk. Slippery floors send workers to the emergency room, and nobody wants to wrangle a half-used drum of spilled surfactant. Besides hazard risks, El35 has a mild odor and can irritate skin on prolonged exposure. Basic personal protective equipment goes a long way: gloves and social distancing from active pumps work wonders. Spill kits with absorbents should live close to storage locations, not locked away where nobody knows to look.
Proper ventilation serves double duty: protecting workers from fumes that accumulate in sealed rooms and cutting down risk from accidental splashes that might otherwise linger in the air. A well-ventilated store room, paired with good housekeeping, solves most problems before they even begin.
Routine checks make all the difference. Containers need to be inspected for cracks, brittle plastic, or signs of chemical breakdown. Outdated or poorly maintained drums become liabilities, spilling contents or letting in contaminants. Take care during transfers between containers to avoid introducing dust or dirt, and always document who moved what—accountability matters with any chemical, even one as familiar as El35.
Respecting expiration dates avoids headaches with failing products and loss of trust down the supply chain. It’s tempting to squeeze another few months from aging stock, but taking shortcuts usually ends with product recalls or regulatory trouble. Simple logbooks or digital inventory apps cut down on expired stock hiding on shelves.
Handling Polyoxyethylene 35 Castor Oil safely calls for a little diligence, some practical storage habits, and trust in clear procedures. Spaces matter. Containers matter. The everyday routines of checking, labeling, and cleaning pay off by reducing risk and waste. Fine-tuning storage plans can seem tedious, but in industries where margins and safety are tight, there’s simply no better approach.
Many people never hear about excipients like Polyoxyethylene 35 Castor Oil during a pharmacy visit. Still, this surfactant helps drugs dissolve, mix, or stabilize in a liquid. Drug developers often lean on it in intravenous, oral, and ophthalmic products, mainly for its ability to keep active ingredients stable and improve absorption.
Nobody likes to think an ingredient in their medication could trigger a reaction. With Polyoxyethylene 35 Castor Oil—often called EL35—reports have piled up linking it to hypersensitivity issues. In my time reviewing safety briefs, I’ve noticed acute allergic responses don’t sneak up just on patients with lots of allergies; almost anybody can experience reactions like itching, hives, or even breathing difficulty. Cases connected to intravenous drugs, most famously the chemotherapy agent paclitaxel (Taxol), turned up enough stories of severe allergic reactions to push the FDA and drug companies to implement strict premedication routines using steroids and antihistamines.
This castor oil derivative goes through the body’s detox system, getting processed by the liver and kidneys. A handful of research papers point to possible kidney and liver workload increases, especially in patients with organ challenges beforehand. Since hospital stays or treatments can already push these organs hard, anything stacking the odds further needs attention.
Pharmacists mixing and matching medicines every day have found trouble when EL35 meets certain materials. Reports detail harmful changes if it comes into contact with materials like PVC tubing or syringes, possibly releasing plasticizers or leaching the drug out of solution. Sometimes people notice cloudiness, color changes, or precipitation. I’ve spoken with hospital pharmacists who double-check their IV setups, swapping out PVC for polyolefin or glass to dodge these possible hiccups.
EL35 can also play rough with other drugs. There have been cases where it altered the stability or absorption of medicines blended into the same formulation—this includes some antivirals and antifungals. Nothing takes the wind out of a treatment more than drug levels dropping or causing an unexpected spike in toxicity.
Solving these issues means more than just putting out fires as they pop up. Drug makers run batch safety trials that focus on excipient reactions in at-risk patients. Product labels for EL35-containing drugs include strong warnings and dosing advice, especially for people with a track record of allergies or organ struggles.
Flagging product bags and syringes as “non-PVC” and running training for hospital and pharmacy staff changed how drugs travel from the lab to the bedside. In my own experience listening to roundtable talks among compounding pharmacists, nearly everyone has a war story about avoiding or mitigating EL35 issues with good teamwork and regular updates on materials and protocols.
No single excipient covers every base, and Polyoxyethylene 35 Castor Oil draws heavy attention for good reasons. Careful choice of device materials, open label warnings, and close monitoring stand out as ways scientists, clinicians, and pharmacists keep drug therapies safe—especially for those who already walk a tightrope with their health.
The small print on pharmaceutical excipients often gets overlooked. Polyoxyethylene 35 Castor Oil, or EL35, isn’t a household name, but those who handle it know: packaging and shelf life can set off a chain of problems if ignored. In an industry pushing for quality and safety, skipping over these details doesn’t just invite regulatory headaches—it can risk patient safety.
Having spent time in GMP manufacturing, you start to see packaging not as an afterthought, but as the real front line. For EL35 pharma grade, the usual suspects are tight-sealed, high-density polyethylene (HDPE) drums—typically around 50 to 200 liters. Some manufacturers go with stainless steel or epoxy-lined steel drums, mostly for bulk shipments. This isn’t just for convenience. HDPE blocks out moisture and oxygen, which matters because even a slow drip of humidity can turn a stable raw material into a source of contamination. Metal drums add muscle in case of rough handling or storage changes, though they come with extra cost and occasionally, cleaning challenges.
In smaller-scale labs or pilot plant scenarios, I’ve seen EL35 packed in dark amber glass or smaller PE canisters—5 liters or less. That setup ends up handy for clinical-scale operations or pre-formulation work, where risk from light and oxidation gets more attention. Some suppliers will go above and beyond: adding tamper-evident seals, secondary shrink wrapping, or nitrogen blankets to extend shelf stability.
The shelf life stamped on EL35 drums—usually two to three years—carries more weight than many realize. It’s not just about “still usable” product; it’s about polymer chain length, peroxide buildup, and even changes in viscosity. Analytical chemists know a drum sitting out past its prime can fail critical tests like HPLC purity and microbiological specs. Real-world incidents—like failed batch releases—traced back to old excipient lots underscore how shelf life isn't an empty claim.
Major pharmacopeias and regulatory filings often back up a 24-month shelf life, stored between 15°C and 30°C, away from direct sunlight and heat sources. Some suppliers advertise up to 36 months, but few risk going beyond that without new stability data. Degradation isn’t always visible, so trust in documentation, and regular inventory rotation (FIFO) becomes more than nice-to-haves—it’s operational discipline.
In many facilities I’ve visited, excipient rooms end up as afterthoughts—overloaded, poorly labeled, missing tracking logs. Product recalls in years past show how bad inventory management links to shelf life risks. I’ve seen quality audits flag open-drum EL35 “topped up” across batches, leaving shelf stability in limbo. Even worse, staff sometimes ignore manufacturer recommendations altogether, storing EL35 outside the recommended temperature range, causing phase separation or gelling.
Solutions exist. Semi-automated inventory logs with expiry notifications have saved batches from being reworked. Simple steps—like regular drum inspections, proper segregation, and regular refresher training on excipient handling—pay off in real improvements. Dual-check receipt logs ensure that expired drums get removed before blending teams pull the wrong lot. Some companies use barcode-driven track-and-trace, a step that slashes human error and fraud.
Polyoxyethylene 35 Castor Oil doesn’t make headlines, but mistakes in handling and storage reverberate through every level of manufacturing. When regulatory agents ask about traceability, or a formulation fails release testing, the answers often lead back to overlooked basics: packaging, shelf life, and attention to detail in the stockroom. Relying on routine, clear processes and evidence-backed specs gives confidence not just for compliance, but—more importantly—for patient safety.
| Names | |
| Preferred IUPAC name | Polyoxyl 35 Hydrogenated Castor Oil |
| Other names |
Cremophor EL Polyoxyl 35 Castor Oil Polyoxyethylene Castor Oil Polyoxyl Castor Oil 35 Ethoxylated Castor Oil Cremophor EL 35 PEG-35 Castor Oil Solubilizer EL Kolliphor EL EL35 |
| Pronunciation | /ˌpɒliˌɒksɪˌiːθiːlˈiːn θɜːti faɪv ˈkæs.tə ˈɔɪl/ |
| Identifiers | |
| CAS Number | 9005-64-5 |
| Beilstein Reference | 1711266 |
| ChEBI | CHEBI:53428 |
| ChEMBL | CHEMBL1201582 |
| ChemSpider | 33365741 |
| DrugBank | DB11062 |
| ECHA InfoCard | 03d7e184-7bcd-4c81-9890-87e71c883d6d |
| EC Number | 61791-12-6 |
| Gmelin Reference | Gmelin Reference: 84692 |
| KEGG | C34832 |
| MeSH | Polysorbates |
| PubChem CID | 68527 |
| RTECS number | WK8250000 |
| UNII | ZI045T2NH8 |
| UN number | UN3082 |
| Properties | |
| Chemical formula | (C₂H₄O)ₓ·C₅₇H₁₀₀O₉ |
| Molar mass | ~2500–3500 g/mol |
| Appearance | Clear yellow oily liquid |
| Odor | Characteristic odor |
| Density | 1.06 g/cm³ |
| Solubility in water | Soluble in water |
| log P | 1.98 |
| Vapor pressure | Negligible |
| Acidity (pKa) | ~2.5 |
| Basicity (pKb) | 7.0 (pKb) |
| Refractive index (nD) | 1.471 – 1.473 |
| Viscosity | Viscosity (25°C): 400 – 600 cP |
| Dipole moment | 3.15 D |
| Thermochemistry | |
| Std enthalpy of combustion (ΔcH⦵298) | -2426 kJ/mol |
| Pharmacology | |
| ATC code | A06AD15 |
| Hazards | |
| Main hazards | May cause eye and skin irritation. Harmful if swallowed or inhaled. |
| GHS labelling | GHS07, Warning, H315, H319, P264, P280, P305+P351+P338, P337+P313 |
| Pictograms | GHS07,GHS08,GHS09 |
| Signal word | No signal word |
| Hazard statements | Hazard statements: "Causes serious eye irritation. |
| Precautionary statements | Precautionary statements: P261, P264, P280, P305+P351+P338, P337+P313, P301+P312, P501 |
| NFPA 704 (fire diamond) | Health: 1, Flammability: 1, Instability: 0, Special: - |
| Flash point | > 220°C |
| Autoignition temperature | 300°C |
| Lethal dose or concentration | LD50 (Rat, Oral): > 5,000 mg/kg |
| LD50 (median dose) | LD50 (oral, rat): > 59,000 mg/kg |
| NIOSH | RN: 61791-12-6 |
| PEL (Permissible) | PEL (Permissible Exposure Limit) for Polyoxyethylene 35 Castor Oil (EL35) is not specifically established by OSHA or other regulatory agencies. |
| REL (Recommended) | REL (Recommended): 10 mg/m³ |
| Related compounds | |
| Related compounds |
Polyoxyethylene Castor Oil Polyoxyethylene 40 Hydrogenated Castor Oil (PEG-40 Hydrogenated Castor Oil) Polyethylene Glycol (PEG) Castor Oil Polyoxyethylene Sorbitan Esters (Polysorbates) PEG-35 Castor Oil |
Chengguan District, Lanzhou, Gansu, China
