Cardiovascular Drugs

Beta-1 selectivity is the detail the exam rewards. At standard doses metoprolol spares the beta-2 receptors in the lungs, so it is preferred over nonselective beta blockers (such as propranolol) for patients with asthma or COPD — but that selectivity fades at high doses, so caution still applies. Know the two salts, because they are dosed differently: immediate-release metoprolol tartrate is given twice daily for angina and after a myocardial infarction, while extended-release metoprolol succinate is given once daily and is the form used in chronic heart failure.

The most-tested teaching point is to never stop the drug abruptly — rebound tachycardia, hypertension, and even angina or MI can follow. Two classic traps round it out: metoprolol masks the tachycardia that normally warns a diabetic of hypoglycemia, and it can cause orthostatic hypotension, so patients should rise slowly. Before each dose, pair the apical-pulse check (hold for a rate below 60 bpm) with a blood-pressure parameter.

The exam loves the “-pril” suffix as the tell, then makes you pick the assessment that matters. The highest-yield trap is potassium direction: lisinopril raises K⁺, the mirror image of furosemide, which lowers it — so when the two run together their effects partly offset, and a “concerning lab” usually means K⁺ above 5.0–5.5 mEq/L. Teach patients to avoid potassium-sparing diuretics, salt substitutes (potassium chloride), and routine potassium supplements. When the dry, hacking cough becomes intolerable, the classic move is switching to an ARB (“-sartan”), which spares bradykinin.

The most-tested contraindications are pregnancy (stop as soon as pregnancy is detected; gravest fetal harm is 2nd–3rd trimester) and prior angioedema — facial, lip, or tongue swelling is an airway emergency and an absolute stop. Don’t confuse the pre-dose checks: metoprolol hinges on the apical pulse (hold below 60), while lisinopril hinges on blood pressure. Memory hook: ACE = “A Cough and Elevated potassium.”

Furosemide’s exam identity is its electrolyte fallout. By forcing sodium out it drags potassium, calcium, and magnesium along with it, so expect hypokalemia (the headline risk), along with hyponatremia, hypocalcemia, and metabolic alkalosis. The single most-tested link is furosemide plus digoxin: the low potassium furosemide causes sharply raises the risk of digoxin toxicity, which is why potassium is checked before either drug is given. (Contrast loop diuretics with thiazides, which retain calcium — “loops lose calcium.”)

Because furosemide is a sulfonamide, ask about sulfa allergies. Push IV doses slowly — rapid administration, high doses, or pairing with aminoglycosides risks ototoxicity (hearing loss). For monitoring, daily weights are the most reliable measure of fluid status; also track intake and output, blood pressure, and signs of dehydration or orthostatic hypotension. On the exam, a furosemide question is usually really a potassium question — watch for muscle weakness, cramps, and cardiac dysrhythmias that signal hypokalemia.

On the exam, digoxin is almost always a toxicity question. The therapeutic level is a razor-thin 0.5–2 ng/mL, and several conditions push a “normal” level into the toxic range — most importantly hypokalemia (so a patient taking both digoxin and furosemide is the classic high-risk pairing), along with hypomagnesemia, hypercalcemia, and the declining renal function of older adults, since digoxin is excreted by the kidneys.

Learn the toxicity timeline. The earliest signs are GI and visual — anorexia, nausea, vomiting, and the hallmark yellow-green halos or blurred vision — while serious toxicity shows up as bradycardia and AV block. The antidote is digoxin immune Fab (DigiFab). Before each dose, take the apical pulse for a full minute and hold for a rate below 60 bpm, then check the most recent potassium: correcting low potassium is often the first step when toxicity is suspected, because it relieves symptoms and helps prevent dysrhythmias.

On the NCLEX, warfarin questions hinge on matching the right lab to the right antidote: warfarin is followed by PT/INR, whereas heparin is followed by aPTT and reversed with protamine sulfate — swapping these pairs is the single most common trap. The classic “tell” is a bridging scenario: because warfarin’s effect is delayed, a patient is started on heparin or enoxaparin and the parenteral agent is stopped only once the INR has been therapeutic. Expect to act on a critical value — an INR above 4–5 with no bleeding usually means simply holding the dose, while active hemorrhage demands vitamin K plus 4-factor PCC (or FFP).

Unlike furosemide (hypokalemia) and lisinopril (hyperkalemia), where the watched lab is potassium, warfarin’s watched parameters are INR and signs of bleeding — don’t carry over electrolyte thinking. Flag warfarin as historically pregnancy category X (teratogenic, contraindicated), and remember the mantra “green = vitamin K = clotting” — so more greens blunt warfarin’s effect, which is why intake must stay steady, not zero.