Carbomer – Popular excipient for semi-solid dosage forms

1. Structure

High molecular weight polymer synthesized from acrylic acid monomers.
Has cross-links with allyl sucrose or allyl ether of pentaerythritol. 52% – 68% carboxylic acid functional groups create the acidity of carbomer.

2. Pharmacopoeia nomenclature

Carbomer (BP; PhEur; USP-NF).

3. Trade name

Carbomer (Lubrizol); Carbopol (Lurizol); Acrypol (Corel Pharma).

4. General properties

White powder, acidic (2.5 – 4.0 for 0.2% water dispersion), hygroscopic, with a characteristic mild odor. swells in water and glycerin, dispersed in water to form an acidic dispersion, forming a gel after neutralization with the base.
Impurities include residual solvents, unreacted monomers (acrylic acid), acetic acid, proprionic acid, and traces of heavy metals.

5. Classification(Grade)

Carbopol homopolymer: 71G NF, 971P NF, 974P NF, 980 NF, 981 NF, 5984 EP, 934 NF, 934P NF, 940 NF, 941 NF (usually used for controlled release or viscosity adjustment).
Carbopol copolymer: 1342 NF, TR-1, TR-2, TR-3 (commonly used as an emulsifier).
Carbopol interpolymer: ETD 2020 NF, Ultrez 10 NF (used as an adhesive agent (Bioadhesive agent) in skin patches, suspension agent).

6. Main application

Commonly used as a viscosity modifier in liquid or semi-solid dosage forms including: creams, gels, lotions, eye ointments, rectal or vaginal suppositories.
Some carbomer with low residual ethyl acetate content such as Carbopol 971P or Carbopol 974P NF can be used in oral products such as tablets, capsules, suspensions. In tablet formulations, carbomers are often used as binding or release control excipients.
Carbomer copolymer is commonly used as an emulsifier in oil-in-water topical emulsions. The proportion (%) in the dosage forms is as follows:
- Emulsifier: 0.1 – 0.5%
- Gelling agent: 0.5 – 2.0%
- Suspension agent: 0.5 – 1.0%
- Binder in tablets: 0.75 – 3.0%
- Controlled release excipient: 5.0 – 30.0 %

7. Original products that use carbomer

Twyneo (Tretinoin & Benzyl peroxide); Differin (Adapalene); Cloderm (Clocortolone); Xeglyze (Abametapir); Rowasa (Mesalamin); Hyftor (Sirolimus).

8. Incompatibility

Changes color due to resorcinol, which is incompatible with phenols, cationic polymers, strong acids and electrolytes.
Relatively stable to heat, can be heated at temperatures lower than 104 degrees Celsius for 2 hours. However, prolonged exposure to heat changes color and reduces stability. Carbomer hydrophilic gel can be autoclaved in an autoclave without affecting viscosity or pH.
Can reduce viscosity when exposed to light due to oxidation.

You can find out more about the technical characteristics in the Carbomer’s section of SEN Pharma’s excipient library.

9. Personal experience

Traditional carbomers use the synthetic solvent benzene. However, manufacturers are increasingly restricting benzene in the pharmaceutical industry. Some modern carbomer lines are synthesized from ethyl acetate or ethyl acetate and cyclohexane. Some typical non-benzene lines are: 71G NF, 971P NF, 974P NF, 980 NF, 981 NF, 5984 EP, ETD 2020 NF, Ultrez 10 NF.
Carbomer is added slowly to the solvent under constant stirring. It can then be sifted or sifted to break up clumps caused by electrostatic forces. Besides, it can be pre-dispersed in other co-solvents such as glycerin, propylene glycol to limit clumping before adding water. The use of homogenizers with high shear forces such as rotor-stators should be avoided because they can open the polymer and cause loss of fluid permeability. Carbopol 980 is less susceptible to mechanical damage than Carbopol 940.
Carbomer gel is physically stable at pH 6-9. If excess base (eg NaOH, triethanolamine) or electrolytes (NaCl) are added, the viscosity of the carbomer gel system decreases. Multivalent cations or cationic surfactants should be avoided with carbomers to limit the formation of complexes in the solubility.
Low viscosity carbomers are more effective in controlled release than high viscosity ones. In the wet granulation method, it can be combined with water, alcohol or a water-alcohol mixture to make a sticky solution. Talc can be added to prevent the wet granules from sticking to the high-speed mixing tank.
Carbomer is also used to mask the bitter taste of drugs. Carbomer 934 and 970 are commonly used for their masking effect.