Question
Posted on: March 6 2013Question about erythromycin 4% in Beeler Basis.
In the preparation erythromycin 4% in Beeler Basis we obtain the best STABILITY at a pH of about 8, while the ACTIVITY of erythromycin is optimal at a pH of about 5. How do we solve this dilemma: do we choose the stability by Alkalinisation of the creme by using e.g. NaOH or do we opt for the activity by weighing an extra amount of erythromycin to compensate for the degradation of erythromycin or can you offer us a better proposal?
Answer
I think we prefer the pH of maximum stability. For what benefit a preparation with so-called maximum activity if it is not stable. Preparations for external use, which contain erythromycin, are set to a pH = 8. Dissolved in water gives Erythromycin a pH between 8 and 10.5. So there may be a little acidified to set a pH = 7.5 à 8.