Initial therapy is usually empirical; and the regimen is ad-justed according to the results of culture and sensitivity testing. Physicians must select a drug, administration route, dosage, and dosing interval. These may be changed several times during therapy. For example, severe nausea and high severity of illness may necessitate initial par-enteral antibiotic administration. Several days later, when the nausea has abated and the patient is clinically stable, the patient may be switched to oral chemotherapy. Such an adjustment of therapy reduces the length of hos-pital stay while providing effective, safe treatment.
Once a chemotherapy regimen has been selected, the next step in managing chemotherapy is to define the outcome measures that will define therapeutic success and those that will define unacceptable toxicity and ne-cessitate discontinuation of the chosen drugs. For exam-ple, resolution of fever and purulent sputum produc-tion, normalization of the white blood cell count, reversal of tachypnea and hypoxia, and improvement of constitutional signs and symptoms may be selected as measures that will be used to evaluate whether treat-ment of pneumonia is successful.
Often treatment must be continued for several days after objective signs and symptoms of infection have re-solved. Patients should be instructed to continue antibi-otics for the full duration indicated, even if they feel better. If the patientâ€™s recovery is delayed from what is reasonably expectable, the diagnosis should be recon-sidered.
Many patients receive lengthy courses of antibiotics that probably should not have been started. More than half of courses of antimicrobial chemotherapy are inap-propriate. Influenza pneumonia and viral upper respira-tory infections, for example, are impervious to assault by antibiotics, although many patients with these ill-nesses receive such antibiotics. Of course, influenza may be complicated by postinfluenzal staphylococcal pneu-monia, for which antibiotics are indicated. Careful se-quential evaluation of seriously ill patients for whom antibiotics are deferred is as important as in patients for whom antibiotics are prescribed.