definetly there is a difference in antibiotic concentration in different tissues anf fluids and you can estimate these difference by assaying of antibiotic in each organ or fluid .These differences due to metaboli reaction including absorption characteristic of each site of human body.

it is a good  question. Has anyone attempted such a comprehensive study of pulse chase experiments as was done on the route and incorporation of labeled amino acids/sugars in endoplasmic reticulum and Golgi network for cancer drugs?. Cancer drugs are normally directed to inhibit cell proliferation and division(mitotic) especially assembly/disassembly of microtubules/microfilaments/cytoskeleton or inhibition of DNA replication or protein synthesis. Cell signaling mechanism and metabolic pathways are also targeted. Therefore tools and methods are available and it is possible to estimate the occurrences of cancer drugs and  metabolites in fluids, tissues and cells after injection though such specific studies and reviews are rare to list them. It is worth pursuing the topic for further comprehensive research.

I think you can measure the blood level of drug and also in urine. I suggest you to measure plasma protein binding of drug and all its metabolites as well. As collection of samples (tissues/fluids) is difficult, this might give an indirect indication on the distribution of drug.

Distribution between blood and interstitial fluid can be monitored by microdialysis. Many papers about the topic can be found in the literature for different drugs including anticancer agents.