This occurs when the action or effect of a drug modulates that of another drug, producing a clinical response that differs from that anticipated from either drug when taken individually. In acute care, careful selection of drugs and meticulous monitoring maximize the treatment benefit and prevent untoward effect arising from the combination strategy. Not uncommonly, drugs given in combination intentionally for clinical benefits turn harmful either by over-amplifying a drug’s effect or by reducing its efficacy. These interactions, beneficial or harmful, are summarized, with representative examples, in Table 10.2.