Are cetyl and Cetomacrogol cream suitable for erythromycin?

There is indeed not immediately a classical incompatibility of the type anionic-cationic or phenol-polyoxyethyleenketen visibly. Since erythromycin is not completely insoluble in water, the water phase of your cream will be a solution saturated to erythromycin. This solution has a pH between 8.5 and 10 which is unfavorable to the stability of erythromycin. After all, the pH of maximum stability is situated at +/-8. To lower the pH we use 0.5% citric acid solution.  

Table below shows the values of the various raw materials, which can be used for the preparation of an erythromycin cream with cetyl-or unbuffered cetomacrogol cream. The buffered Cetomacrogol cream is not eligible!  

 

Erythromycin 1%

Erythromycin 2%

Erythromycin 4%

 

 

erythromycin 1.1 g erythromycin   2.2 g erythromycin   4.4 g

Neutral oil

1 g 2 G 4 G

Citric acid   0.5%

8.0 g 12.0 g 14.0 g

Cream base   up to

100 g 100 g 100 g

Preparation Method

A round bottom scale or light mortar with pestle and note the tare weight (T)

The erythromycin is rubbed with the neutral oil into a homogeneous paste in which a portion of the cream base is mixed. Then the citric acid solution is gradually added under stirring.

Place the container with pestle on the balance and apply weight (T + 100) with the rest of the cream base and mix to homogenous. Packaging.  

Note: erythromycin is overdosed for stability reasons by 10% (see TMF)