Which of the following should not be taken within 48 hours of flying?

Antihistamines should not be taken within 48 hours of flying due to their sedative effects, which can impair cognitive function and reaction time. This is particularly important for pilots, as any medication that can lead to drowsiness or decreased alertness poses significant safety risks during flight operations. While some antihistamines are considered less sedating than others, their ability to cause varying degrees of sedation means they can still affect performance, especially in the context of flying, where alertness is critical.

Other medications listed, such as Sudafed and non-sedating analgesics, are generally acceptable to use prior to flying, as they do not carry the same level of risk regarding drowsiness. Over-the-counter vitamins typically do not have sedative properties and are therefore not known to interfere with flight performance.