Question
Posted on: July 25 2013A dermatologist asks us to make Dalacin lotion.
Answer
I immediately make the comparison with Clindamycne 1.5% solution of the TMF. This preparation contains: Clindamycin phosphate 540 mg, propylene glycol 3 g, water 10 g and isopropyl alcohol up to 30 g
Dalacin Lotion contains 1% clindamycin in a mixture of propylene glycol, isopropyl alcohol, HCl, NaOH and water.
There is therefore a difference between the TMF formula and the speciality where the presence of HCl and NAOH indicate the setting of a certain pH.
This is confirmed by following information
Clindamycin phosphate is a water soluble ESTER of the semi-synthetic antibiotic produced by a 7 (S)-chloro-Substitution of the 7 (R)-hydroxyl group of the parent antibiotic lincomycin.
The solution contains isopropyl alcohol 50% v/V, propylene glycol, sodium hydroxide (to adjust The pH to between 4.0 – 7.0) and purified water. The structural formula is represented below:
By acidifying under the influence of the large amount of salicylic acid, the dissociation of the coupled phosphoric acid is reduced and the clindamycin phosphate becomes less soluble as the cloudy designates. Adding a small amount of base again brings the pH between pH 4 and 7. As base I would preferably use NaHCO3. Add small amounts (per 50 mg) to clear and note the added quantity for the following prescriptions.