Final answer:
Drug interactions are called synergistic when the combined effect is greater than the individual effects, and antagonistic when one drug reduces the effect of another.
Step-by-step explanation:
When two drugs interact, it is known as a drug interaction. Drug interactions can be synergistic or antagonistic. A synergistic interaction occurs when two drugs produce an effect that is greater than the sum of their individual effects, such as the combination of trimethoprim and sulfamethoxazole (Bactrim), which together, provide bactericidal action rather than just bacteriostatic inhibition.
On the other hand, an antagonistic interaction is when the drugs' effects are diminished or reduced, which can decrease therapeutic levels, cause loss of activity, or increase potential toxicity, exemplified when antacids decrease the effectiveness of certain antimicrobials by altering stomach ph.