I'm not an expert either, but combinations are apparently used. For example, you mention amoxicillin, which is often combined with something called clavulanic a

I'm not an expert either, but combinations are apparently used. For example, you mention amoxicillin, which is often combined with something called clavulanic acid [1]. Another combination drug is Trimethoprim/sulfamethoxazole [2]. Some diseases, like resistant tuberculosis, are sometimes treated with antibiotic "cocktails". The problem is that combinations of antibiotics may have cytotoxic effects even at doses lower than normally harmful. Those two combinations above are used because they are known to work in synergy, with few side effects. Some antibiotics are not used except as a last resort precisely because they are so toxic to the human body that they might kill the host in the process of eradicating the target bacteria. In fact, antibiotics are found in nature all the time, but they tend to be too toxic to use. [1] http://en.wikipedia.org/wiki/Amoxicillin/clavulanic_acid http://en.wikipedia.org/wiki/Amoxicillin/clavulanic_acid [2] http://en.wikipedia.org/wiki/Trimethoprim/sulfamethoxazole http://en.wikipedia.org/wiki/Trimethoprim/sulfamethoxazole