drug synergism
an enhancement of efficacy occurring when two or more drugs are administered concurrently, so that their combined pharmacological or clinical effects are greater than those occurring when the drugs are administered individually. Drug synergism can be metabolic, when the administration of one agent interferes with the metabolism of another, or it can be pharmacological, when the administration of two or more agents results in enhanced receptor binding or other activity at target sites. The enhanced antimicrobial activity of two antibiotics administered together is an example of positive synergism; negative synergism can be seen when the administration of a nontoxic agent with a toxic drug worsens the toxicity of the latter.