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Question

Posted on: March 6 2013

Preparation of a mouthwash: Tetracycline HCl 1% NaCMC 1% Lidocaïme 0.5% Vit A 1.5 g Sirupus simplex 90cc Mint water AD 300 ml

NaCMC (-) is incompatible with TETRACYCL. and lidocaine (+) and is thus replaced Dr. Methyl cellulose...

Answer

  1. Lidocaine (and NOT Lidocaine HCl) is a base and will react with tetracyclineHCl with formation of tetracycline base, which precipitated. Tetracycline is an amphoteric product with three pkas: 3.7; 7.7 and 9.7. We take into account the two first, which then give as IEP 5.7. At this pH, the solubility of tetracycline is minimal. We therefore check the pH after precipitation and if not correct we apply with disodium phosphate (see Galenic Formularium,     Tetracycline suspension in HDST. Suspensions) Should the deviation be large.
  2. Vit A is naturally added as oil because it allows us to solubilize it with Tween 80. Of course we could also disperse the vitamin (emulsifying) into the mucus but this gives a less beautiful specimen.