Which drugs may interact with calcium when used concurrently with Vitamin D?

The correct choice highlights that certain medications may interact with calcium when taken concurrently with Vitamin D.

Digitalis and verapamil are known to have interactions with calcium. Digitalis can increase the risk of toxicity when serum calcium levels are elevated, as both digitalis and calcium can have effects on cardiac function. Verapamil, a calcium channel blocker, may also interact with calcium levels in the body, especially since it affects muscle contraction and has implications for heart health. Vitamin D enhances calcium absorption from the gut, so the combination with these drugs has clinical significance regarding calcium homeostasis.

The other choices contain medications that are less commonly associated with direct interactions with calcium in the context of Vitamin D. Hydralazine and isoniazid do not specifically have well-documented interactions related to calcium dynamics. Similarly, phenytoin, an anticonvulsant, and penicillamine, which is used to treat conditions like rheumatoid arthritis and Wilson's disease, are not primarily linked to calcium interactions in the context provided. Therefore, the specificity of the interaction between digitalis and verapamil with calcium when used alongside Vitamin D marks it as the significant choice in this scenario.