Question
Posted on: June 4 2018Are cetyl and Cetomacrogol cream suitable for erythromycin?
Answer
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 GCitric acid 0.5%
8.0 g 12.0 g 14.0 gCream base up to
100 g 100 g 100 gPreparation 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)