Final answer:
Synergistic drug interactions occur when two or more drugs are used together and their combined effect is greater than the sum of their individual effects. Antagonistic drug interactions occur when two or more drugs are used together and their combined effect is less than the sum of their individual effects.
Step-by-step explanation:
Synergistic drug interactions occur when two or more drugs are used together and their combined effect is greater than the sum of their individual effects. This means that the drugs work together to enhance the therapeutic outcome. For example, the combination of trimethoprim and sulfamethoxazole (Bactrim) provides a synergistic interaction that is bactericidal, whereas individually they only provide bacteriostatic inhibition of bacterial growth.
On the other hand, antagonistic drug interactions occur when two or more drugs are used together and their combined effect is less than the sum of their individual effects. This means that the drugs work against each other, resulting in decreased efficacy or harmful effects. An example of antagonistic interaction is the effect of two pancreatic hormones, insulin, and glucagon, where insulin decreases blood glucose levels by increasing liver glycogen storage, while glucagon increases blood glucose levels by stimulating glycogen breakdown.