Which medication requires close monitoring of digoxin levels when initiated?

The correct choice is albuterol. When initiating therapy with albuterol, particularly in patients who are already on digoxin, close monitoring of digoxin levels may be warranted due to potential interactions. Albuterol, a beta-agonist used primarily for asthma and other respiratory issues, can lead to hypokalemia (low potassium levels), which can consequently increase the risk of digoxin toxicity. Digoxin has a narrow therapeutic range, and any significant changes in potassium levels can affect its efficacy and safety. Therefore, in patients taking digoxin, the initiation of albuterol requires careful monitoring to ensure that digoxin levels remain within the therapeutic range, minimizing the risk of adverse effects.

In contrast, loratadine and diphenhydramine are antihistamines primarily used for allergy relief and do not have significant interactions with digoxin that would necessitate close monitoring of digoxin levels. Ipratropium is an anticholinergic medication used for respiratory conditions, but similar to the antihistamines, it does not typically require monitoring of digoxin levels. Thus, among the given options, albuterol stands out as the medication that necessitates careful oversight in the context of digoxin therapy.