A gel formulation includes a gelling agent—carbomers, hydroxyethyl cellulose, and hydroxypropyl cellulose are the most widely used—and solubilizers. Depending on the excipients used, a gel can be transparent (most common), translucent, or opaque.
The challenge when developing a gel is to keep the drug in a solubilized state and to identify the right gelling agent. Thus the selection of appropriate solubilizer is very important and must be compatible with the gelling agent.
Transcutol® P is compatible with all types of gelling agents and can be used at a very high concentration in the gel without altering its structure. Clear gels are obtained.
Labrasol® is compatible with all types of gelling agents. Depending on the concentration, clear or opaque gels are obtained.
Capryol™ PGMC produces an opaque gel when used at <6% with hydroxypropyl cellulose.
Transcutol® P is widely used as solubilizer in gels with many drugs, including capsaicin, dapsone, diclofenac, estradiol, ibuprofen, ketoprofen, lidocaine, menthol, methyl salicylate, nimesulide, oxybutynin, piroxicam, and tetracaine HCl.