As with any antibiotic preparation, constant observation for signs of overgrowth of nonsusceptible organisms including fungi, is essential. Should superinfection occur, Viccillin-SX 1500 should be discontinued and/or appropriate therapy instituted. As with any potent systemic agent, it is advisable to check periodically for organ system dysfunction during extended therapy; this includes renal, hepatic and hematopoietic systems. This is particularly important in neonates, especially when premature, and other infants.