Which of the following statements aligns with additive effects across drug classes?

• A. They are independent and do not affect each other's efficacy
• B. They can be additive when used together
• C. They always yield the same reduction
• D. They negate each other

Answer: (B)

Additive effects across drug classes occur when combining medications yields a total effect that roughly equals the sum of each drug’s individual effect. In glaucoma, different drug classes lower intraocular pressure through distinct mechanisms, so using them together can stack their effects and produce a greater overall reduction than either would alone. For example, one drug might reduce aqueous humor production while another increases outflow; used together, the overall IOP drop is about the sum of their separate effects, though the exact amount can vary due to ceiling effects and individual response. This is why the idea that they can be additive when used together best fits. The other statements describe no interaction or even opposing effects, which don’t align with the additive concept.