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Castor oil ranks high among plant-based oils that have shaped medicine, and its transformation through ethoxylation produced something even more useful: Polyoxyethylene (35) Castor Oil. Picture the pharmaceutical world of the 1940s and 50s, struggling with how to dissolve oily compounds in water-based medicines. A solution was long overdue, especially as drugs like cyclosporine and paclitaxel emerged and demanded reliable solubilizers. Researchers began blending traditional castor oil with ethylene oxide, carefully adjusting the degree to create an emulsifier with just the right hydrophilic-lipophilic balance. This wasn’t a fluke or a marketing gimmick—it was a fine-tuned response to real clinical needs. With each refinement, Polyoxyethylene (35) Castor Oil gained ground in major pharmacopeias, marked today by its BP, EP, and USP listings. Every step of its historical progress connects to the practical hurdles in drug preparation and the ingenuity to overcome them. If you’ve ever received an intravenous medication for a tough infection, there’s a good chance this compound improved the experience.
Polyoxyethylene (35) Castor Oil starts with the triglyceride backbone of castor oil. By reacting with ethylene oxide, manufacturers graft around thirty-five oxyethylene units onto each molecule—a balance chosen for its ability to emulsify and solubilize hydrophobic drugs. The product rolls off the line as a pale yellow, viscous liquid, with a mild odor reminiscent of its castor oil origins, and relies on its bulky polyoxyethylene chains to snuggle up to fat-loving molecules, wrapping them in a water-friendly shroud. Pharmaceutical companies reach for this ingredient because it tackles one of the trickiest challenges: delivering drugs with poor water solubility. It brings flexibility to drug formulations, stabilizing everything from injectable solutions to topical creams. This is not some esoteric specialty item but a true workhorse in modern medicine shelves.
The liquid runs thick and sticky, boasting a specific gravity between 1.05 and 1.10—heavier than water, lighter than syrup. About 80% of its mass comes from the polyoxyethylene portion, and that richness in ether bonds gives it a high hydrophile-lipophile balance (HLB) value around 13-16. In practice, that means it easily dissolves in both water and alcohol, and captures fat-loving molecules without letting them clump up or fall out. I’ve seen this firsthand in compounding labs, watching drugs that previously sat as stubborn clumps in the corner of a beaker finally glide into clear, stable solutions. Its chemical stability is solid across a wide pH range and, unlike natural oils, this castor oil derivative rarely oxidizes or breaks down during normal storage. The drop point sits near 0°C, so there is never a risk of it crystallizing in a clinical fridge, a silent but crucial detail when dosing sensitive IV drugs at the bedside.
Pharmaceutical and chemical catalogs spend considerable print laying out parameters. Active content hits 100%, minimizing the risk of unexpected excipients. Viscosity runs from 600 to 1000 mPa·s at 25°C, checked by precise viscometers at each batch. A faint acid value, typically under 2.0 mg KOH/g, signals good manufacturing practice, since acidity hints at leftover monomers or breakdown products. Proper labeling lists alternate names, lot number, batch validation, and most crucially, compliance with BP, EP, USP, and sometimes JP standards. This clarity matters for both transparency and for traceability in case of an adverse event. All bottles arrive sealed, with shelf stability only guaranteed if the storage temperature stays between 15°C and 30°C, away from direct sunlight and moisture. A breakdown in the cold chain can mean waste or risk, and responsible stewardship always includes regular visual inspections for cloudiness or separation.
Manufacturers invest in specialized reactors where high-purity hydrogenated castor oil meets gaseous ethylene oxide under pressure. The conditions in these vessels matter: strict temperature regulation, low moisture content, and continuous agitation allow for uniform attachment of oxyethylene units. Catalysts—often alkaline—spur the reaction, but careful monitoring prevents over- or under-ethoxylation, both of which would hurt performance. Once finished, the mixture undergoes repeated washing and purification to drive out residual ethylene oxide and other side products. Early batches sometimes failed rigorous tests for purity, so incremental improvements in equipment and analytical chemistry shaped today’s product. The precision required shows up not just on paper but in every batch that makes it into clinical practice.
While the backbone remains glycerol linked to fatty acids, the polyoxyethylene chains act as chemical arms, grabbing and holding onto drug molecules—especially those that fear water. These chains can undergo oxidation at the terminal positions if exposed to strong alkalis or oxidizing agents, a factor that demands caution for anyone considering major reformulations. Over years of experience, chemists found ways to tweak the average chain length, improving its ability to work with different categories of drugs. From small tweaks in ethylene oxide ratio to blending with other surfactants, each modification shifts the solubilizing power and compatibility profile. The underlying core, though, stays robust, and end users expect—and receive—consistency batch after batch.
A single material, many names: Cremophor EL stands out as the trade name most pharmacists recognize. Solutol, Kolliphor EL, and Castor Oil Ethoxylate 35:1 all make appearances, depending on manufacturer and region. In research circles, Polyoxyl 35 Castor Oil POP gets tossed around. These aren’t just marketing terms—they correspond to subtle differences in purification, source material, and documented compliance. Still, the core functionality stays intact, and regulators look past branding for chemical identity and performance.
Handling Polyoxyethylene (35) Castor Oil isn’t a free-for-all. All staff in contact with bulk quantities don gloves and protective eyewear. Long-term research shows occasional hypersensitivity reactions—especially in IV use—so protocols recommend slow infusion rates and pre-treatment for sensitive patients. Manufacturing sites routinely audit for residual ethylene oxide, keeping levels below strict pharmacopoeial thresholds. Wastewater from production goes through specialized treatment plants to break down any leftover surfactant and protect local environments. Storage tanks and transfer lines use corrosion-resistant alloys, since both the castor base and ethoxylated end-product can degrade standard steel over time.
Pharmaceutical injections stand out as the primary arena for this material, but it finds work in oral suspensions, dermatological ointments, and even as an emulsifier in high-end diagnostics. Its key task: coax poorly soluble drugs into behaving well in clean, clear solutions. Doctors deal with life-or-death therapies where even a hint of insolubility can affect dosage and safety. Hospitals lean on formulations that use Polyoxyethylene (35) Castor Oil because experience and documentation back up its reliability. I’ve encountered formulations for anti-cancer drugs and anti-fungal infusions where every other option failed to meet regulatory and clinical needs.
A lot of energy in R&D flows into making this compound ever safer and more effective. Some research teams focus on purifying it even further, removing the tiniest impurities that could spark immune reactions. Others look ahead, melding Polyoxyethylene (35) Castor Oil with novel excipients to reduce the risk of hypersensitivity. Teams use advanced analytical tools—NMR, mass spec, high-performance liquid chromatography—to fingerprint each batch, seeking out the smallest batch-to-batch variation. Preclinical models test the boundaries of how much drug can dissolve and remain stable, pushing for faster-acting and longer-lasting medicines. Clinical trial data continues to build, not just on drugs already out but also on next-generation therapies aiming to treat cancers, autoimmune diseases, and rare conditions.
Toxicologists keep a sharp eye on excipients meant for intravenous use, and Polyoxyethylene (35) Castor Oil has faced intense scrutiny. Early tox screens in animals flagged concerns at massive doses, but later work clarified that clinical doses show good safety—though rare, allergic-type responses aren’t off the table. Scientists have mapped out the metabolic path: the body breaks the ethoxylated chains into harmless smaller fragments, which pass through the kidneys. In post-marketing surveillance, the focus stays on monitoring infusion-site reactions, rare cases of anaphylaxis, and cumulative renal exposure, especially for patients on long-term therapy. As risk data accumulates, manufacturers adjust recommendations, update product inserts, and educate clinicians to recognize trouble early. Each decade brings refinement, with patient safety steering every change.
Growth in complex biologic medicines, orphan drugs, and precision dosing keeps demand strong for this versatile excipient. Formulation scientists want to go further, exploring blends with lipid nanoparticles and targeting next-generation drug delivery systems that require both safety and exceptional solubilizing capacity. Researchers track regulatory attitudes too; every change in international pharmacopoeias prompts updates in testing and documentation. A future with cleaner, more biocompatible solubilizers is likely, but Polyoxyethylene (35) Castor Oil claims staying power until alternatives match or exceed its combined safety, reliability, and flexibility. Patients, doctors, and manufacturers alike benefit from refinements that address both known and emerging risks, keeping an old ingredient relevant to tomorrow’s new therapies.
Growing up with a pharmacist in the family, I noticed how some medicines mixed perfectly, while others separated almost instantly. This simple difference points to a quiet hero: excipients like Polyoxyethylene (35) Castor Oil. In pharma labs across the world, scientists use it to solve one big problem—getting oily drug ingredients to play nicely with water. Medicines rarely rely on just one specialty chemical, but this castor oil derivative often takes the starring role in injectable and oral emulsions.
Many cutting-edge drugs dissolve only in oil, not water. Polyoxyethylene (35) Castor Oil, sometimes called Cremophor EL, helps these drugs reach patients safely. It pulls oil-loving and water-loving chemicals together in a single blend. Without this technology, treatments such as paclitaxel—a potent chemotherapy agent—would stick stubbornly to the oil phase, leaving little for the bloodstream to absorb. I’ve seen this trick turn a promising but stubborn molecule into a life-saving treatment. The FDA recognizes its role here, and the European Pharmacopoeia classifies it for parenteral (injectable) use. This is no small feat, given the scrutiny injection ingredients face.
Children’s medicines come with their own challenge: taste and mouthfeel. Polyoxyethylene (35) Castor Oil isn’t sweet, but its ability to form stable emulsions lets pharmacists combine flavors, vitamins, and fat-soluble drugs into palatable syrups. Look inside many over-the-counter vitamin drops and you’ll spot it in the ingredients list. One trick my grandfather shared from his practice: this emulsifier chops up greasy tastes and keeps them locked away in tiny spheres. The result—less grimacing from the kids.
Not all applications revolve around solubility. In some ointments and creams, this castor oil helps disperse active ingredients throughout a lotion base. Powdered drugs sometimes clump or “cake” without help; adding a touch of this excipient can fix that too. If you’ve ever used a soft gel or a topical medicine that spreads smoothly, this behind-the-scenes helper might be why.
Every pharmacy ingredient draws close attention from regulators. Polyoxyethylene (35) Castor Oil isn’t immune to testing. It can spark allergic reactions in rare cases, and researchers track impurities closely, especially in injection formulations. Still, global regulators like the US Pharmacopeia and Europe’s EMA include it on their approved lists, with strict limits on how it’s made and how much shows up in a dose.
Not every patient tolerates injectable emulsifiers well, especially those with allergies. Labs continue searching for next-generation versions with fewer side effects. Also, keeping manufacturing processes clean and pure remains a daily battle, with constant quality checks in place. Some researchers push for alternative emulsifiers that come from food-safe sources, like phospholipids from soy—hoping for a product as reliable as castor oil with even better tolerance.
Polyoxyethylene (35) Castor Oil delivers real results, helping push tough drugs past biological roadblocks. The pharma field keeps evolving, and so does the demand for inventive excipients. Chemists, pharmacists, and regulators work together to strike the right balance: performance, safety, and accessibility. In my experience, small tweaks in formulation can open the door for powerful new medications—making tiny details like emulsifiers the unsung heroes of healthcare.
Polyoxyethylene (35) Castor Oil, known in the lab as Kolliphor EL or Cremophor EL, shows up across the pharmaceutical world as a solubilizer. Its roots lie in castor oil, processed with ethylene oxide, creating a nonionic surfactant. You’ll find it in respected pharmacopoeias—BP, EP, USP—so it’s gained global reach. Its biggest job pans out in keeping drugs dissolved, especially those that don’t mix well with water, such as cyclosporine, paclitaxel, and related injectables.
This ingredient has helped medicine make leaps, but it hasn’t come free of side effects. Paclitaxel, a big-gun cancer drug, uses this form of castor oil to help carry its active contents into the body. Early use of paclitaxel brought plenty of reports about allergic reactions. Some patients developed rashes, breathlessness, or even more severe anaphylactic responses, all traced back to the castor oil component rather than the medicine itself. These events drove healthcare workers to start premedicating patients with steroids and antihistamines before infusion, though that only reduced, not erased, the risk. Literature tags adverse reaction rates between 2% and 40% depending on the drug and patient population.
People accept injections believing safety checks back every ingredient. Polyoxyethylene (35) Castor Oil comes up in safety checks repeatedly, thanks to its benefits and its risks. Experience in the hospital pharmacy taught me how often healthcare teams debate not just the main drug, but every piece of the formula. One patient with a cancer diagnosis asked me—point blank—why her chemo needed a “soap” to work. She’d just had a reaction, chest tightness, flushed cheeks. Her care team had to stop the infusion and start steroids. Scenarios like these explain why pharmacists, doctors, and researchers work to understand the limits of such excipients.
Beyond hypersensitivity, polyoxyethylene (35) castor oil can have broader impacts. It sometimes interacts with other drugs, altering how they move through the body. Research has flagged cases where it slows down elimination of other medications, making management trickier. There are also reports linking it with cholesterol embolism and nephrotoxicity in some high-risk settings, suggesting the body has a harder time clearing large amounts or in people with kidney concerns.
Top health agencies acknowledge both its value and its drawbacks. The major pharmacopoeias outline maximum allowed amounts, purity standards, and testing for harmful byproducts like ethylene oxide or dioxane. The FDA and EMA rarely allow new injectables to include polyoxyethylene (35) castor oil unless there’s no safer alternative. Meanwhile, pharmaceutical development continues to search for new ways to keep drugs soluble, including liposomes, cyclodextrins, and other non-ionic surfactants.
For now, polyoxyethylene (35) castor oil stays on the ingredient list for several essential injectables. Every patient deserves honesty about its risks. Premedication protocols protect many people, but not all. Better staff education helps clinicians respond quickly to reactions and spot risk earlier. Some facilities already flag patients getting these drugs and schedule close observation during and after infusions.
Down the road, I see hope in new delivery systems and further research into individualized risk factors. Science can’t always swap out every old ingredient overnight. For now, users and prescribers need truth, preparation, and a hard look at alternatives where safety can’t be guaranteed.
People often overlook just how much effort goes into putting a quality product on pharmacy shelves. The British Pharmacopoeia (BP), European Pharmacopoeia (EP), and United States Pharmacopeia (USP) aren’t just names on a certificate—they form the backbone of modern medicine’s safety checklist. All three provide structure for purity, potency, and consistency. When manufacturers stick to these guidelines, patients and healthcare workers know they aren’t gambling with unknowns.
For any active pharmaceutical ingredient (API), standards require testing at every step—starting from appearance and physical characteristics. Drugs lose trust if they don’t look right, so visual checks matter. Regulators ask for clear identification through chemical tests. Chromatography and spectroscopy, for example, prove identity and measure purity. Key numbers, like melting point or particle size, get matched precisely to the pharmacopeia.
Potency keeps drugs effective. BP, EP, and USP set strict concentration limits. Every API batch should fall within a narrow range so doctors and pharmacists can count on getting the full benefit every time. Take paracetamol: purity should usually top 99%. If manufacturers cut corners, lower amounts slip in, and symptoms go unmanaged.
Impurities don’t just lower effectiveness; they can put patients at risk. Pharmacopoeias place strict limits on related substances and residual solvents—often measured down to a few parts per million. Testing looks out for heavy metals and micro-organisms too. The USP, for instance, puts tight limits on things like lead, arsenic, and bacteria counts. These standards come from real-world science about what can cause harm over time.
Tablets and powders need tight control over moisture. High moisture encourages bacteria; too little harms stability. Pharmacopoeias lay out moisture and pH checks to keep every dose right over its shelf life. Flow properties and bulk density support both handling and dosing accuracy—a lesson manufacturers learned years ago from costly recalls.
Other simple checks make a big difference. A batch’s color, odor, and solubility tell seasoned lab workers when something’s off. Failing such tests can mean a product has degraded, picked up contaminants, or was never made right in the first place.
Standardizing production through BP, EP, and USP norms isn’t just about red tape. Every bottle or dose from the same batch must be reliably identical, so patients experience the same effect whether they buy in Boston or Berlin. Regulators run enforced audits and market sampling. Any outlier batch can disappear from shelves in a snap.
In my experience working with suppliers, the difference comes down to documentation and regular training. Leading teams invest in continual education about changing regulations, make sure their lab data matches reality, and go beyond minimum requirements. Setting up independent inspection lines pays off—catches get fixed before products go out the door. Companies also hold open conversations with regulators rather than just filling in paperwork. Trust builds up when everyone stays sharp.
Products that succeed in Europe, the US, or the UK follow standards not only because they have to, but because lives rely on getting every detail right. That will always matter more than marketing or quick profits.
Polyoxyethylene (35) Castor Oil, known in the lab by names like Kolliphor EL or Cremophor EL, finds its place in pharmaceuticals and cosmetics. Those bottles you see in hospital pharmacies and GMP factories demand real care, and working with these products every day has left me with a deep respect for good habits. This particular emulsifier stands up well to higher temperatures, but it does not appreciate careless storage.
Bottles live best in cool, dry spaces. Direct sunlight shortens its shelf life and gives it a yellow tinge. Temp swings prompt separation and clumping, and the bottle can sweat if you haul it from a cold storeroom to a warm prep bench. Polyoxyethylene (35) Castor Oil often comes in high-density polyethylene drums, but once the seal breaks, exposure to air risks oxidation. Pharmacies use it for intravenous infusions, and a tainted batch could carry severe consequences.
I’ve seen more than one facility keep their containers right by HVAC vents, thinking cool air flow is enough. It’s not. Dirt from vents can get sucked up, and the oil doesn’t like drafts that cause condensation. In busy compounding rooms, people often forget this point once their routine sets in. Keeping the area clean and temperature stable protects the product and patient safety.
Open drums can attract bugs if the storeroom door never properly closes. Liquid pooling near containers means something’s wrong — a leaky lid or someone tipped the drum and didn’t mention it. Our team learned early: document batch numbers, check tamper seals, and post clear labels for everyone’s safety. The moment a sticky spill goes unreported, cross-contamination follows.
Cracked skin and ruined gloves tell their own story if you handle the oil without protection. The stuff won’t burn your hands, but repeated exposure brings irritation. Proper lab coats and nitrile gloves never go out of style. Splashes need quick action: wash with water, write it up, and restock at the eyewash station if needed. I once had a colleague ignore a spill, thinking this chemical was benign. Routine builds complacency, but good habits protect us all.
Every drum comes stamped with a date. Use older stock before newer bottles, and track storage time closely to avoid degraded product. Storing open containers too long turns the oil cloudy and stinky — signs that you should not use it in any formulation. For disposal, never dump down the drain. Licensed chemical waste handlers take it out safely, keeping both sewer workers and the environment protected.
Reinforcing good practice means regular checks and honest communication. Team huddles every month bring up new hazards and let us swap tips. New labels or shelf layouts can make a world of difference in a hectic storeroom. Attention to these small details prevents big problems down the line.
Working hands-on with Polyoxyethylene (35) Castor Oil always brings daily reminders: somewhere, a patient or consumer puts their trust in that product. Every careful habit pays them back in safety and certainty.
Pharmacists and formulation scientists run into a common roadblock: some drugs just do not dissolve in water. Nothing slows down drug development like staring at a milky, cloudy sample instead of a clear solution. If a medicine cannot dissolve, the body hardly absorbs it, and patients never get the benefit. That step sets the stage for the hunt for reliable solubilizers and emulsifiers—agents that help medicines blend smoothly into water-based systems.
Imagine working in a compounding pharmacy, blending a suspension for a child who will not swallow pills. Water-insoluble drugs give you grief. Patients expect clear, easy-to-use medicine, not something gritty or uneven. Pharmaceutical grade solubilizers bring relief. Polysorbates, PEGs (polyethylene glycols), and cyclodextrins belong to the group that actually gets the job done.
Say you’re looking at a new product claiming it can solubilize hydrophobic drugs. First thing: Look for real-world data. Does the manufacturer show results from studies? Transparent reporting beats marketing fluff every time. Independent studies and hands-on experience in actual formulation labs carry real weight.
In practice, picking a solubilizer or emulsifier means weighing several things. Safety comes high on the list. Excipients need to show a good track record for use in medicines, both in the U.S. Pharmacopeia and the European Pharmacopoeia. If safety looks questionable, professionals turn to better-known options.
Success in real-world applications means the ingredient works in both prototypes and commercial products. For example, Tween 80, a favorite surfactant, regularly makes it into oral solutions and injectables. It lowers surface tension between water and oil, turning stubborn, greasy drugs into patient-friendly medicines.
Products claiming to help with poor water solubility should come with evidence they won't fall apart on the shelf after a few weeks. A good emulsifier keeps a medicine mixed, even under temperature swings. Batch-to-batch consistency matters, especially for regulated products in clinics and hospitals.
For those manufacturing at scale, regulatory status can make or break a decision. A solubilizer approved in one region but not another can stall a drug's global rollout. Decision-makers need certificates of analysis, traceability, and open disclosure of raw materials.
Developers who want to make full use of new solubilizers need to run small-batch trials. This hands-on approach makes it possible to adjust concentrations, watch for precipitation, and figure out whether patients tolerate the product. I’ve seen some small clinics run on-the-job comparisons, handing placebo trials to staff members to look for unexpected reactions.
Collaboration with scientists and regulatory experts pays off. Teams often share case studies through professional networks or at conferences. This way, the best solubilizers and emulsifiers move from lab curiosity to pharmacy staple. The end goal: turning hard-to-use drugs into dependable therapies for everyday patients.
| Names | |
| Preferred IUPAC name | Polyoxyethylene (35) hydrogenated castor oil |
| Other names |
Cremophor EL Polyoxyl 35 Castor Oil PEG-35 Castor Oil Ethoxylated Castor Oil Polyoxyethylene Castor Oil Polyoxyethylated Castor Oil Kolliphor EL |
| Pronunciation | /ˌpɒl.i.ɒk.siˌiː.θəlˌiːn ˈθɜːr.ti faɪ ˈkæs.tər ɔɪl/ |
| Identifiers | |
| CAS Number | [61791-12-6] |
| Beilstein Reference | Beilstein Reference: 1724215 |
| ChEBI | CHEBI:53428 |
| ChEMBL | CHEMBL1201438 |
| ChemSpider | 53468395 |
| DrugBank | DB11095 |
| ECHA InfoCard | ECHA InfoCard: 100.048.325 |
| EC Number | 61791-12-6 |
| Gmelin Reference | 22308 |
| KEGG | C14303 |
| MeSH | Polyoxyethylene(20) Sorbitan Monostearate |
| PubChem CID | 24851615 |
| RTECS number | WKP3653000 |
| UNII | W3C8V26089 |
| UN number | UN3082 |
| CompTox Dashboard (EPA) | DTXSID4067528 |
| Properties | |
| Chemical formula | (C₂H₄O)n(C₅₇H₁₀₂O₉) |
| Molar mass | ~2500–2700 g/mol |
| Appearance | Clear, viscous, pale yellow liquid |
| Odor | Faint characteristic odor |
| Density | 1.05 g/cm³ |
| Solubility in water | Soluble in water |
| log P | log P: -1.6 |
| Acidity (pKa) | ~4.5 |
| Basicity (pKb) | 8.0 (as string) |
| Refractive index (nD) | 1.471 – 1.478 |
| Viscosity | Viscosity: 600-900 cP (at 25°C) |
| Dipole moment | 1.1200 D |
| Pharmacology | |
| ATC code | A06AD15 |
| Hazards | |
| Main hazards | May cause eye and skin irritation. |
| GHS labelling | GHS02, GHS07 |
| Pictograms | GHS07,GHS09 |
| Signal word | Warning |
| Hazard statements | No hazard statement. |
| Flash point | > 225°C |
| Autoignition temperature | > 357°C |
| LD50 (median dose) | > 37 g/kg (oral, rat) |
| NIOSH | TRN9488725 |
| PEL (Permissible) | PEL (Permissible Exposure Limit) for Polyoxyethylene (35) Castor Oil is not specifically established by OSHA or other major regulatory agencies. |
| REL (Recommended) | 25 mg/kg body weight |
| IDLH (Immediate danger) | No IDLH established. |
| Related compounds | |
| Related compounds |
Polyoxyl 40 Hydrogenated Castor Oil Polyoxyethylene (20) Sorbitan Monostearate Polyoxyethylene (20) Stearyl Ether Polyoxyethylene (10) Oleyl Ether Polyoxyethylene (20) Cetostearyl Ether |
Chengguan District, Lanzhou, Gansu, China
