What is the best method of monitoring therapeutic blood levels of vancomycin during therapy?

The correct method is C: By obtaining drug peak and trough levels. This is the most accurate way to monitor vancomycin levels as it allows for assessment of the highest (peak) and lowest (trough) concentrations in the blood, ensuring therapeutic levels are maintained without reaching toxic levels. Assessing temperature (A) or breathlessness (D) are not specific to monitoring vancomycin levels. Repeating culture and sensitivity tests (B) is not necessary for monitoring drug levels.