Using in-vitro models to analyse the efficacy of antibiotics such as fluoroquinolones is not a novel idea. Various systems can be used to mimic the pharmacokinetic profiles in-vivo in order to simulate drug clearance.

The relationship between concentration or exposure and bactericidal effects can then be described in order to calculate dosing regimens and pharmacodynamic values such as the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC). MIC is defined as the minimum concentration of antibacterial agent that inhibits pathogen growth in-vitro. The MIC is commonly used to measure changing antibiotic resistance in bacterial strains and, as such is widely understood. Minimum bactericidal concentration (MBC) is defined as the minimum concentration of antibiotic that kills a pathogen in-vitro.

There are clear advantages and disadvantages to in-vivo studies such as lower costs, greater degree of control, wider dose ranges, evaluation against a broader selection of bacterial species and ability to mimic human conditions. Overuse of antibiotics has led to a shift in the application of in-vitro pharmacodynamic models from focusing on antibiotic effect, to focusing on prevention of resistance. The rapid rise of Staphylococcus aureus resistance to fluoroquinolones such as ciprofloxacin is a fantastic example of evolution in action. In 2004 up to 89% of S. aureus isolates were resistant to ciprofloxacin in some parts of the world(Oonishi et al., 2007). In-vitro methods are now being used to calculate optimum dosage regimes in order to help restrict bacterial resistance to antibiotics and preserve the effectiveness of existing drugs.