The pathophysiology varies by etiologic agent. Bacterial pneumonia is marked by an intraalveolar suppurative exudate with consolidation. Mycoplasmal and viral pneumonias produce interstitial inflammation with infiltrate in the alveolar walls; there is no accompanying exudate or consolidation. Pneumococcal and streptococcal pneumonia have four distinct stages: (1) congestion, characterized by serous exudate, vascular engorgement, and rapid proliferation of the pathogen; (2) red hepatization, when RBCs, fibrin, and polymorphonuclear cells fill the alveoli; (3) gray hepatization, when leukocytes and fibrin pack the alveoli; and (4) resolution, marked by lysis and resorption of exudate by macrophages.
The National Heart, Lung, and Blood Institute (NHLBI) recommended dosing for systemic prednisone, prednisolone, or methylprednisolone in pediatric patients whose asthma is uncontrolled by inhaled corticosteroids and long-acting bronchodilators is 1–2 mg/kg/day in single or divided doses. It is further recommended that short course, or "burst" therapy, be continued until the patient achieves a peak expiratory flow rate of 80% of his or her personal best or until symptoms resolve. This usually requires 3 to 10 days of treatment, although it can take longer. There is no evidence that tapering the dose after improvement will prevent a relapse.