Final answer:
The veterinarian should choose amoxicillin to maintain high concentrations of the drug in the urine for a dog with a suspected urinary tract infection, as it is excreted primarily through the kidneys and concentrates in the urine.
Step-by-step explanation:
To maintain high concentrations of the drug in the urine for a dog with a suspected urinary tract infection (UTI), the veterinarian should choose an antibiotic that is known to be excreted primarily through the kidneys and thus concentrates in the urine. Among the options provided, amoxicillin is a commonly used antibiotic for UTIs and has good urinary excretion; therefore it tends to maintain high concentrations in the urine. Doxycycline could also be a good choice due to its broad spectrum of activity and its concentration in the urine but is not as typically preferred for early stage UTI treatments when compared to amoxicillin. Lincomycin and erythromycin are not the first line of treatment for UTIs, and while they may achieve urinary concentrations, they are not as specifically targeted towards urinary pathogens as amoxicillin is. Furthermore, literature indicates that drugs such as fluoroquinolones and cephalexins can also be effective in treating UTIs, particularly when the infection is caused by bacteria like E. coli, Klebsiella pneumoniae, or common urinary tract pathogens.