Which of the following medications should not be initiated if potassium is greater than 5.5?

The medication that should not be initiated if potassium levels are greater than 5.5 is an ACE inhibitor. This is important because ACE inhibitors can increase potassium levels by inhibiting the renin-angiotensin-aldosterone system. Normally, aldosterone promotes the excretion of potassium, so when an ACE inhibitor prevents the formation of angiotensin II, which stimulates aldosterone release, it can lead to hyperkalemia—elevated potassium levels in the bloodstream.

In patients with a potassium level greater than 5.5, the risk of developing severe hyperkalemia increases significantly if ACE inhibitors are initiated. This can result in various complications such as cardiac arrhythmias, muscle weakness, or even life-threatening conditions.

Other options, such as thiazide diuretics, while they can help lower potassium levels, are generally not contraindicated at elevated potassium levels but should be used cautiously. Beta-blockers and calcium channel blockers do not have a direct contraindication related to potassium levels, although they are also involved in various metabolic processes. Hence, the initiation of ACE inhibitors in the presence of elevated potassium is particularly concerning due to its potential for exacerbating hyperkalemia.