Final answer:
Synergism is the term for the situation where two antimicrobial agents have a greater combined effect than the sum of their individual effects, whereas antagonism refers to drug interactions that reduce efficacy or increase toxicity. The correct option is c.
Step-by-step explanation:
The term that denotes a situation in which the effect of two antimicrobial agents together is greater than the sum of the effects of either drug alone is known as synergism. Synergistic drug interactions are beneficial for the patient, providing a more potent effect against microbes than when the drugs are used separately.
For example, the combination of trimethoprim and sulfamethoxazole (Bactrim) is known to be synergistic; each drug alone provides only bacteriostatic effects, but together, they become bactericidal.
On the other hand, antagonism occurs when the interaction between antimicrobials or with other nonantimicrobial drugs results in reduced efficacy or increased toxicity.
An example of antagonism is when antibacterials that require an acidic stomach environment for absorption are taken with antacids, which raise stomach pH and inhibit their effectiveness. The correct option is c.