Is it necessary for an antimicrobial solution to be prepared with its natural pH, in order to avoid any loss of efficacy? Or, as the performance standards in the guides such as CLSI say, can I prepare a solution adding alkaline - acidic compunds or buffers to completely solve the antibiotic? WHY?
Hi there,
Antimicrobial activity of antibiotics is based on some structural features of the molécules. Any parameter susceptible to affect these structural features would be decreasing the antimicrobial activity of the molécules. pH is an essential parameter : it may promote acid hydrolysis or alkaline hydrolysis of molécules. For instance, ampicillin is highly unstable at pH over 7 whereas it is more stable at moderatly acidic pH. Chloramphenicol will be degraded both at acidic and basic pH.
There is no golden rule about pH effect on antibiotics activity so each molecule has to be considered as a peculiar case and specific protocols for solution preparation have to be used.
I agree completely with Dominique's excellent summary. I would add though that some antibiotics do have fairly extreme pH requirements for solubility. For example, some fluoroquinolones and nisin are stable at acidic pH (~2) and require acidic pH for aqueous solubility. In most cases, however, antibiotics can be reconstituted in unbuffered or weakly-buffered solutions (although "shelf life" can vary significantly).
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