Poloxamer 188 and tromethamine in eye drops

Poloxamer 188 is a nonionic block copolymer, a long molecule built from alternating blocks of polyoxyethylene and polyoxypropylene. Tromethamine is a small organic amine, also called tris or trometamol, widely used as a buffer. Both are inactive ingredients in Quell; the label spells the first “Polaxamer 188.” Neither carries a claim on the label, which ties the product’s uses to its three actives.

Where they appear on Quell’s label

The full inactive list reads: Caprylyl Glycol, Dead Sea Salt (Sodium Chloride), Emu Oil, Glyceryl Laurate, Glyceryl Undecylenate, Manuka Honey, Polaxamer 188, Sterile Water, Terminalia Chubula and Tromethamine. Under federal labeling rules for OTC drugs, 21 CFR 201.66, inactive ingredients go in alphabetical order without amounts. That puts the poloxamer in the middle of the list and tromethamine at the very end. Their places tell you the first letter of each name and nothing about quantity.

What is poloxamer 188?

The National Library of Medicine’s MeSH vocabulary, which indexes biomedical literature, defines poloxamer as a nonionic polyoxyethylene-polyoxypropylene block copolymer. In plainer terms, it’s a chain made of three segments: a middle block of one repeating unit with a block of a different repeating unit on each end. The two kinds of block behave differently around water, which is what makes the molecule useful to formulators.

MeSH adds that poloxamers come in grades ranging from liquids to solids, and that in pharmaceuticals they’re used as emulsifiers, solubilizers and wetting agents. Poloxamer 188 is one specific grade. MeSH lists Pluronic F-68 and Pluronic F68 among its entry terms, so you may see those trade names in technical writing about the same material.

Why the label says “Polaxamer”

The standard spelling, used by MeSH and in pharmacy references, is poloxamer, with two o’s. Quell’s label prints it with an a. It’s the same ingredient; we reproduce the label wording exactly as it appears on the carton rather than editing it. If you look the ingredient up, search the standard spelling.

What is tromethamine?

MeSH describes tromethamine as an organic amine proton acceptor, used in making surface-active agents and pharmaceuticals, as an emulsifying agent, as a biological buffer and as an alkalizer. PubChem, the NIH chemistry database, files it as tris(hydroxymethyl)aminomethane and describes it as a compound widely used as a biological buffer substance. Its structure is a central carbon carrying an amine group and three hydroxymethyl arms.

• Tris and Tris buffer, the names most lab scientists use.
• Trometamol, the international nonproprietary name.
• Tris(hydroxymethyl)aminomethane, the descriptive chemical name.
• Trisamine and Trizma, older and trade names MeSH also lists.

Buffers, in general terms

A buffer is a substance that resists changes in pH, the measure of how acidic or alkaline a solution is. Chemists add buffers to all kinds of water-based products so the pH stays within a set range during storage. That’s the general chemistry. Quell’s label doesn’t state a role for tromethamine or give the product’s pH, so we won’t assign one. If you want that level of detail, Aurora Pharmaceuticals, LLC can be reached at 615.465.6041, M–F 9AM–5PM CST.

What the label does tell you

The product’s uses are tied to its actives, Glycerol (1.0%), Polysorbate 80 (1.0%) and Light Mineral Oil (0.5%). The Uses line reads: For use as a protectant against further irritation or to relieve dryness of the eye. The directions are: Apply 1 drop 3 times per day in each eye. Quell is designed to reinforce the tear film’s oil layer to help reduce moisture loss. That’s a statement about the formula, not about any one inactive ingredient, and nothing on the label singles out the poloxamer or tromethamine.

You’ll also notice that Quell describes itself as preservative-free. Neither of these ingredients is described on the label as a preservative. What preservative-free means explains the term, and why the tip rule matters for every bottle: Do not touch tip of bottle to any surface to avoid contamination.

Synthetic ingredients next to natural ones

Quell’s inactive list mixes ingredients with obvious natural sources, such as emu oil, manuka honey, Dead Sea salt and a plant extract, with laboratory-made ones like these two. That’s common in drug products. Being synthetic doesn’t make an ingredient suspect, and being natural doesn’t make one harmless; what counts is the finished, sterile product used as labeled. The natural ingredients in Quell covers the other side of the list.

Questions to bring to a pharmacist

• Whether any ingredient on the list has caused you trouble in another product.
• Whether Quell fits with other eye drops or medicines you use; the label doesn’t cover combining drops.
• What the label’s caution means for you: Caution should be used in those with egg or bird allergies — For use in the eyes only.

The complete panel is on our Drug Facts page. If any drop leaves your eyes painful or your vision changed, stop using it and see a doctor.