Description

Hydroxypropyl Methyl cellulose (HPMC)is globally known as “Hypromellose” and is manufactured by chemically made polymer cellulose. Hydroxypropyl methylcellulose is identified with the single Chemical Abstracts Service (CAS) number 9004-65-3 and the European Inventory of Existing Chemical Substances (EINECS) number 232-674-9. It is manufactured by reacting partially depolymerized cellulose with methyl groups and containing a small degree of hydroxypropyl substitution. Since cellulose is a high molecular weight linear polysaccharide of indeterminate mass and its degree of substitution will depend on the conditions of manufacture, a unique mass and structure cannot be specified[1]. HPMC is in the form of white to off-white powder.

Chemical property

Hydroxypropyl methylcellulose is an odorless and tasteless, white to slightly off-white, fibrous or granular, free-flowing powder that is a synthetic modification of the natural polymer cellulose. Specifically, it is a modification of alkali cellulose produced when purified wood pulp is treated with an 18% sodium hydroxide solution. Methyl and hydroxypropyl ether groups are introduced into the molecule by reacting the alkali cellulose with methyl chloride and propylene oxide, respectively. The degree of substitution (DS) of commercial HPMC with these methoxy and hydroxypropoxy groups will vary depending on the commercial use and properties desired. These added groups confer on the molecule its unique properties of being cold-water soluble while at the same time exhibiting reversible gelation when heated and recooled.

Toxicity

Acute oral and dermal toxicity studies with hydrophobically modified HPMC were conducted in rats. HPMC containing approximately 1.1% C16–C18 alkoxyhydropoxyl content was administered orally via gavage to Crj: CD (SD) rats (5/sex/dose) in single doses of 0, 300, 600, or 900 mg/kg body weight, after which the animals were monitored for 14 days. The dermal toxicity study employed the same dosing groups, with the dose applied to the shaved backs of the rabbits for 24 h under occlusion. One animal in the high-dose oral group exhibited loose stools 30 min after dosing. Otherwise, no abnormalities or deaths were observed in any treatment group, oral or dermal. A six-month repeated-dose dermal toxicity study with 30-day recovery was conducted in SD rats with hydrophobically modified HPMC. HM-HPMC containing approximately 1.1% C16–C18 alkoxyhydropoxyl content was applied daily as an aqueous paste to the shaved backs of the animals (25/sex/dose) at doses of 0, 20, 40, or 60 mg/kg body weight/day. Five animals of each sex from each dosing group were maintained for 30 days to assess the reversibility of any observed effects. Parameters evaluated included clinical signs, urinalysis, hematology, ophthalmology, and histopathology. The authors report that no toxic effects attributable to test article administration were found. Comparing the NOAEL of 5000 mg/kg/day from a 90-day feeding study in rats and estimated consumption of 0.047 mg HPMC/kg body weight/day, a theoretical safety factor of >100,000 exists. These data indicate that at the current intake level, HPMC does not pose a health risk to humans[2].

Side effects

Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat. Change in eyesight, eye pain, or terrible eye irritation.

References

[1] Additives, EFSA Panel on and Products or Substances used in Animal Feed (FEEDAP). “Safety and efficacy of hydroxypropyl methyl cellulose for all animal species.” EFSA Journal 18 7 (2020). [2] Burdock, George A. “Safety assessment of hydroxypropyl methylcellulose as a food ingredient.” Food and Chemical Toxicology 45 12 (2007): Pages 2341-2351.