Hydroxypropyl methylcellulose, also known as HPMC, is a non-ionic cellulose ether mixture. It is a semi synthetic, inactive, viscoelastic polymer commonly used as a lubricant/thickener in ophthalmology. HPMC swells into clear or slightly turbid colloidal solution in cold water, and forms gel when the temperature rises to a certain extent; The solubility changes with viscosity, the lower the viscosity, the greater the solubility. There are certain differences in the properties of HPMC with different specifications, and its water solubility will decrease as the methoxy content decreases.

Note: Laboratory tests found that when the temperature was higher than 45 ℃, the HPMC solution became turbid, presumably due to the formation of gel by high temperature HPMC.

Filtration Solutions & Case Study

Due to the viscosity and adsorption characteristics of HPMC solution, sterile filtration process is difficult. If selected wrong filter, it is easy to have slow flow rate, rapid attenuation, and low loading. In this case, Cobetter conducted extensive testing with customers and in our own validation laboratory. Based on the results of the filterability test, we recommend Cobetter PP filter cartridges, sterilizing-grade low adsorption PES and PVDF filter cartridges for the filtration solution of eye products containing HPMC.

Case Study 1: Contact lens care solution for RGP

Main components of the material: HPMC, PHMB, PVP and other excipients

Recommended filters: HPP0.45+APP0.65+DLHPVDF(0.45+0.22)+DLHPVDF(0.45+0.22)

Filter performance as below, tested by Vmax(constant voltage):

Case Study 2：Multifunctional solution for hard contact lens

Main components of the material: 0.13% HPMC, Pluronic and other excipients

Recommended filters: APP0.65+PEHS+SLHS+SLHS
Filter performance as below, tested by Vmax(constant voltage):

Case Study 3：Azepine hydrochloride eye drops

Main components of the material: 0.1% HPMC, Azepine hydrochloride, Benzalkonium Chloride and other excipients
Recommended filters: PEHS+SLHS+SLHS
Filter performance as below, tested by Vmax(constant voltage):

Case Study 4：Compound dextran 70 eye drops

Main components of the material: 0.3% HPMC, Dextran, Benzalkonium Chloride and other excipients
Recommended filters: DLHPVNDR(1.0+0.45)+LHPVDF0.22+LHPVDF0.22
Filter performance as below, tested by Vmax(constant voltage):

Case Study 5：Contact lens care solutions

Main components of the material: 0.04% HPMC, Pluronic and other excipients
Recommended filters: APP0.65+LHPVDF0.45+LHPVDF0.22+LHPVDF0.22 
or APP0.65+PEHS+DSLES+DSLES
Filter performance as below, tested by Vmax(constant voltage):

Summary

Based on the above experimental results, for eye products containing HPMC, the filtration capacity of PES and PVDF membranes with low adsorption treatment is significantly better than that of conventional PES membranes. Cobetter PEHS/SLHS/DSLES and LHPVDF filters are recommended as a priority for the filtration of these products.