No improvement in ventilatory status, defined as no change or a decrease in arterial or alveolar difference ((A-a) DO2) in the 72 hours prior to entry. (A-a) DO2 should be determined on room air, or receiving an FiO2 of 100 percent for 10 minutes via a tightly fitting non-rebreathing mask, or at an FiO2 of 100 percent for 10 minutes if the patient is being ventilated. Intolerance to TMP / SMX is defined as one or more of the following: