Question
Posted on: March 6 2013Creams containing the combination chlorhexidine and zinc oxide. Compatible or incompatible?
The Martindale teaches us that chlorhexidine is incompatible with anionic components and the activity of chlorhexidine decreases in the presence of cations such as Zn 2 + .
since the Excipi ë NS is usually a CETOMACROGOLCR è me, no visible incompatibilities occur, which rely on reactions between opposite loads. But what about the zinc oxide? It is suggested that the chlorhexidine be taken out during preparation.
dermatologists do not follow us here and therefore we are looking for the correct answer.
since the Excipi ë NS is usually a CETOMACROGOLCR è me, no visible incompatibilities occur, which rely on reactions between opposite loads. But what about the zinc oxide? It is suggested that the chlorhexidine be taken out during preparation.
dermatologists do not follow us here and therefore we are looking for the correct answer.
Answer
(in collaboration with Apoth. P. Declercq)
since the incompatibility of chlorhexidine with zinc oxide was not clear to me (there is no load difference!) , I have consulted the literature. I seem to conclude that combining chlorhexidine with zinc ions is not desirable because apparently chlorhexidine and the zinc ions are in competition for the same points of engagement. This has been researched mainly for mouthwash agents. Here we are still in dermatological field where zinc oxide mainly has a covering function. Not only. For Chlorhexidine, two pKa & #039; s can be recovered: pKa1 = 2.2 and pKa2 = 10.3
tests have shown that the average pH of the supernatant of a zinc oxide suspension = 7.25. This means that chlorhexidine will not occur in its diprotonated but monoprotonated form. Apparently, the latter is the most active of the two seen as pH area of maximum activity a pH of 5 à 7 is specified. A higher pH of 8 is out of the question because from this pH, precipitation of the unprotonated form can occur, of course depending on the concentration of chlorhexidine. It can therefore be concluded that matter of activity the preparation has a good pH. And therefore there is no reason to remove the chlorhexidine from its composition.
since the incompatibility of chlorhexidine with zinc oxide was not clear to me (there is no load difference!) , I have consulted the literature. I seem to conclude that combining chlorhexidine with zinc ions is not desirable because apparently chlorhexidine and the zinc ions are in competition for the same points of engagement. This has been researched mainly for mouthwash agents. Here we are still in dermatological field where zinc oxide mainly has a covering function. Not only. For Chlorhexidine, two pKa & #039; s can be recovered: pKa1 = 2.2 and pKa2 = 10.3
tests have shown that the average pH of the supernatant of a zinc oxide suspension = 7.25. This means that chlorhexidine will not occur in its diprotonated but monoprotonated form. Apparently, the latter is the most active of the two seen as pH area of maximum activity a pH of 5 à 7 is specified. A higher pH of 8 is out of the question because from this pH, precipitation of the unprotonated form can occur, of course depending on the concentration of chlorhexidine. It can therefore be concluded that matter of activity the preparation has a good pH. And therefore there is no reason to remove the chlorhexidine from its composition.