Antimicrobial synergism

Scarpignato C, Pelosini I Antisecretory drugs for eradication of Helicobacter pylori Antibacterial activity and synergism with antimicrobial agents. Progr Basic Clin Pharmacol 1999 11 136-180. 

If the organism undergoes simultaneous action of two antimicrobial drugs, it can result in an additive effect, synergism, or antagonism. 

Drugs are considered to act additively when the activity of drugs in combination are equal to the sum of their independent activity. The overall effect of two antimicrobial drugs can be less (antagonism) or more (synergism) than the sum effect. 

Other synergistic antimicrobial combinations have been shown to be more effective than monotherapy with individual components. Trimethoprim-sulfamethoxazole has been successfully used for the treatment of bacterial infections and Pneumocystis jiroveci (carinii) pneumonia. 3-Lactamase inhibitors restore the activity of intrinsically active but hydrolyzable 3-lactams against organisms such as S aureus and Bacteroides fragilis. Three major mechanisms of antimicrobial synergism have been established ... 

Certain combinations of antibiotics,such as (3-lactams and aminoglycosides, show synergism, that is, the combination is more effective than either of the drugs used separately. Because such synergism among antimicrobial agents is rare, they should only be used in special situations summarized in Figure 28.7)... 

In terms of bactericidal actions, the outcome of the combined use of two antimicrobials may be indifference, synergism, potentiation, or antagonism (see Chapter 61). Such actions are more readily demonstrated in vitro than at the clinical level. Some mechanisms that may account for synergism follow. 

C22H43N5O13 585.607 Aminoglycoside antibiotic. Semisyntheti-cally derived from Kanamycin A, K-3. Shows antimicrobial activity inch synergism with third-generation cephalosporins. Cryst. + 6H2O (MeOH/2-propanol). Sol. H2O, MeOH poorly sol. butanol, hexane. Mp 203-204° dec. [a] +99 (c, 1 in H2O). Log P -9.09 (uncertain value) (calc). 

Antimicrobial activities of many essential oils are well documented (Bakkali et ah, 2008). Such oils may be used singly or in combination with one or more oils. For the sake of synergism this may be necessary. 

A recent study has examined the antimicrobial activity of various aldehydes against M. tuberculosis [107]. Pentenal, benzaldehyde and phthalalde-hyde showed a kill greater than 10 cfu ml" in 5 minutes, though benzaldehyde was only active in the presence of 2% glutraldehyde. Substituents (nitro, chloro, methyl and methoxy) on the benzaldehyde ring reduced this synergism, but still showed increased activity over 2% glutaraldehyde alone [107]. 

However, few studies have analyzed the in vivo relevance of these findings. Overall, most of the data suggest that berberine is a weak antimicrobial per se, but its activity is strongly synergized by other drugs. 

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