Cefuroxime (Zinacef) versus co-amoxiclav (Augmentin) in dogs and cats
In my experience Zinacef and Augmentin are far and away the most widely used intravenous antibiotics in small animal practice in the UK -despite both being unlicensed. Marbofloxacin (as Marbocyl SA) does have a license for intravenous use but is less commonly used -perhaps because fluoroquinolones are (understandably) not seen as first-line agents, concern about inducing blindness in cats (although my belief is that this phenomenon is specific to enrofloxacin) or lack of efficacy against anaerobes -please correct me if I’m wrong: it’s an interesting discussion.
Both cefuroxime and co-amoxiclav are relatively safe (excepting allergic patients), broad-spectrum, with efficacy against many beta-lactamase producing strains and wide distribution (except CNS).
I suspect that there may be a bit of a ‘convention’ in UK small animal practice that Zinacef is often used peri-operatively, especially in orthopaedics.
Zinacef is somewhat cheaper -especially in smaller patients where the smallest size Augmentin vial incurs a lot of wastage. But I’m more interested in the clinical decision-making.
As regards spectrum of activity, co-amoxiclav is highly effective against most anaerobes. Cefuroxime less so (e.g Bacteroides species may be relatively resistant). Both are effective against a wide range of Gram-positive bacteria. MICs for Gram-negative Enterobacteriaceae tend to be higher for cefuroxime (e.g. MIC90 for E. coli typically around 4 ug/ml for human E.coli isolates). Neither would be a good choice in circumstances where MRSA/MRSP are suspected. Staphylococcal drug sensitivity generally is quite unpredictable: knowledge of local susceptibility patterns is useful.
Obviously, in real life we can have an educated guess at which pathogens might be involved. If a single agent is to be used then I think it is arguable that co-amoxiclav would be a better choice where anaerobes may be involved: e.g. peritonitis, pyothorax, bite wounds, periodontitis, cholecystitis. This being reinforced by the chances that the practice has oral co-amoxiclav on the shelf to continue with afterwards. Cephalexin is much less effective against anaerobes than cefuroxime and would be a poor substitute in such circumstances. Obviously one could add in (unlicensed, potentially neurotoxic, potentially carcinogenic and bad-tasting) metronidazole but that’s another story.
Pharmacokinetics:
Happily for cefuroxime we have a brand new pharmacokinetic study to help us:
http://www.ncbi.nlm.nih.gov/pubmed/25982523
These authors reported that twice daily i.v. cefuroxime would likely be effective for relatively susceptible pathogens (mostly Gram-positives) but that q8hrs might be required where Enterobacteriaceae were involved.
8 hourly dosing is probably also appropriate for amoxicillin where administered intravenously since the half life is short.
Is there any direct evidence to support the use of one over the other in any specific conditions in cats or dogs? No.
How about in human medicine? There’s a little bit more to go at here. Even some direct comparisons between the two agents:
http://www.ncbi.nlm.nih.gov/pubmed/3582135
http://www.medscimonit.com/download/index/idArt/502528
Both demonstrate equivalence in treating human URT infections.
Summary:
- Ideally, base decisions on culture and sensitivity.
- Empirically, where anaerobes may be involved then co-amoxiclav is probably preferable
- Empirically, where anaerobes are improbable (UTI, respiratory infections, endocarditis) then the use of either agent may be defensible. If treating serious infections intravenously then both should be given 8 hourly.
