Question 56

Doxycycline may have its therapeutic effect decreased by calcium interactions.

Doxycycline is known to interact with calcium, which can reduce its absorption and effectiveness. This interaction can lead to a decrease in the therapeutic effect of the antibiotic when taken concurrently with calcium-containing products.

A) Azithromycin

Azithromycin does not have a significant interaction with calcium that affects its therapeutic effect. It is generally well-absorbed regardless of calcium intake, making it an unsuitable choice for this specific interaction.

B) Doxycycline

Doxycycline is the correct answer because it binds with calcium, forming insoluble complexes that hinder its absorption in the gastrointestinal tract. This interaction can lead to decreased levels of the antibiotic in the bloodstream, thereby reducing its effectiveness in treating infections.

C) Doxylamine

Doxylamine is an antihistamine and does not interact with calcium in a way that would affect its therapeutic effect. As such, it is not relevant to this question, as the focus is solely on antibiotics.

D) Erythromycin

Erythromycin does not exhibit a significant interaction with calcium that decreases its therapeutic efficacy. It remains effective regardless of the presence of calcium, making it an incorrect choice for this question.

Conclusion

Doxycycline's interaction with calcium is well-documented, leading to reduced absorption and therapeutic efficacy. In contrast, azithromycin, doxylamine, and erythromycin do not demonstrate this interaction, which is why they cannot be considered correct answers in this context. Thus, option B is definitively the right choice, as it directly addresses the key concept of antibiotic efficacy affected by calcium interactions.