Pharmacology for Nurses · Antihypertensive and Antianginal Drugs
Angiotensin-Converting Enzyme (ACE) Inhibitors
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In 30 seconds
ACE The enzyme that converts angiotensin I to angiotensin II Full entry → inhibitors are among the most widely used blood pressure medications — you will recognize them by the -pril ending (captopril, lisinopril, enalapril, ramipril). They work inside the renin-angiotensin-aldosterone system (RAAS), the body's main long-term blood pressure control loop.
The RAAS story: when the kidneys sense falling pressure, they release renin, which converts a liver protein into angiotensin I. Angiotensin-converting enzyme (ACE) — found mainly in the lungs — then clips angiotensin I into Angiotensin II The active hormone that constricts vessels and releases aldosterone Full entry →, a powerful molecule that constricts blood vessels and triggers aldosterone release, making the kidneys hold onto sodium and water. Angiotensin II raises pressure twice over: it squeezes the pipes and adds volume.
ACE inhibitors interrupt the loop by blocking the enzyme. Less angiotensin II means relaxed vessels, less aldosterone, and less sodium and water retention — pressure falls. But the enzyme also breaks down a chemical called Bradykinin A peptide that dilates vessels and irritates airways Full entry →, and that detail explains the class's two famous effects: a dry cough (common, annoying) and angioedema (rare, dangerous). Understanding the pathway makes the whole profile predictable.
Why this matters
- ACE inhibitors are first-line agents for hypertension, heart failure, and post-MI care, and are valued in chronic kidney disease, especially with diabetes.
- The mechanism explains the monitoring: less aldosterone can raise potassium, and relaxing the kidney's outflow vessel can shift creatinine — so potassium and renal function are standard checks (per orders/reference).
- Pregnancy is a hard contraindication — ACE inhibitors are Teratogenic Capable of harming a developing fetus Full entry → — a classic safety point.
- The ACE versus ARB comparison (enzyme blocker vs receptor blocker) is a favorite exam question.
The college version
Core Concepts
The RAAS pathway, step by step
Pressure falls → kidneys release renin → renin converts angiotensinogen (from the liver) into angiotensin I → ACE (mostly in the lungs) converts it into angiotensin II → angiotensin II constricts arterioles and triggers aldosterone release → the kidneys retain sodium and water. Net effect: pressure rises. The pathway is a thermostat with several points where drugs can intervene.
Mechanism: blocking the enzyme, not the receptor
ACE inhibitors bind and inactivate the converting enzyme, so angiotensin I cannot become angiotensin II. The consequences cascade: vessels dilate, aldosterone falls, and pressure drops via resistance and volume. Because ACE also degrades bradykinin, blocking it leaves more bradykinin around — dilating vessels further (a small added benefit) but irritating the airways (the cough) and, rarely, driving angioedema. The next topic, ARBs, blocks the angiotensin II receptor instead of the enzyme — why ARBs cause less cough with similar blood pressure effects.
Hemodynamic and kidney effects
By dilating arterioles, ACE inhibitors lower afterload (the resistance the heart pumps against), which is why they help in heart failure and after a heart attack. In the kidney, they dilate the Efferent arteriole The vessel leaving the kidney's filtering unit Full entry → (the vessel leaving the glomerulus), lowering pressure inside the filtering units. That reduced pressure is protective in diabetic kidney disease but can also produce a modest creatinine rise, especially with dehydration or significant kidney artery narrowing. Teaching point: small creatinine changes are common when starting and are followed by the prescriber; large changes warrant review (educational — thresholds verified against references).
The electrolyte story: potassium
Aldosterone makes the kidneys excrete potassium. With less aldosterone, potassium is retained — so ACE inhibitors can raise serum potassium, especially with potassium supplements, potassium-sparing drugs, or potassium-containing salt substitutes. Hyperkalemia is the complication to watch; potassium and renal function are the standard baseline and follow-up labs (per orders and reference ranges).
Adverse effects to recognize
- Dry cough: the most common reason people stop an ACE inhibitor; a persistent, tickling, nonproductive cough from bradykinin buildup. Not dangerous, but it disrupts sleep and resolves when the drug is stopped or switched to an ARB (per prescriber).
- Angioedema: rapid swelling of the face, lips, tongue, or throat with airway risk — a medical emergency; anyone with new facial swelling needs immediate evaluation. Rare, but possible at any time, even years into therapy.
- First-dose hypotension: because the drug relaxes vessels, the first dose can cause dizziness, especially in people who are volume-depleted or on other pressure-lowering drugs.
- Pregnancy: ACE inhibitors are teratogenic — they can injure the developing fetus — so they are contraindicated in pregnancy; counseling follows guidelines.
Nursing considerations
- Baseline and monitoring: blood pressure, potassium, and renal function are assessed before starting and during therapy per prescriber orders; report significant potassium rises or large creatinine changes.
- Education: teach the person to report a persistent dry cough, dizziness, or — urgently — any facial, lip, or tongue swelling or difficulty breathing; advise against potassium supplements and salt substitutes without prescriber approval.
- Interactions: NSAIDs can reduce the blood pressure benefit, and potassium-raising combinations (some diuretics, supplements) are reviewed with the pharmacist; never adjust therapy independently.
- Adherence: as with all silent-disease medications, reinforce that the drug protects heart and kidneys over years though it causes no daily sensation.
- Scope note: monitoring intervals, lab parameters, and counseling requirements vary by institution and jurisdiction — verify against the current formulary, references, and prescriber orders.
Common Confusions
| Do not confuse | With | Difference |
|---|---|---|
| ACE inhibitor (blocks the enzyme) | ARB (blocks the receptor) | Both lower angiotensin II activity; ARBs act downstream and cause far less cough |
| Dry cough (common, benign) | Angioedema (rare, emergency) | Cough is annoying but safe; facial/lip/tongue swelling or breathing difficulty is urgent |
| ACE inhibitors raise potassium | Diuretics lower potassium | Less aldosterone = potassium retention; volume-depleting diuretics do the opposite |
| "Safe in pregnancy" | Contraindicated (teratogenic) | They can injure the fetus — pregnancy is a hard contraindication |
Eli explains
The same idea, in plain words
Explain it like I’m 10
Your body has a chain — kidneys to a molecule that squeezes blood vessels and holds onto water — that raises blood pressure. ACE inhibitors turn off the middle step, the enzyme that makes the squeezing molecule. With the chain broken, vessels relax and pressure comes down. The side effect: a tickly dry cough for some people, and in very rare cases sudden facial swelling — an emergency.
Worked example
A person with type 2 diabetes and hypertension is started on an ACE inhibitor. The nurse walks through the rationale aloud: "Your kidneys released renin; renin made angiotensin I; the enzyme in your lungs converted it to angiotensin II, which squeezes your vessels and holds salt and water. This pill blocks that conversion, so your vessels relax and you lose less fluid — that's how your pressure comes down and your kidneys are protected long-term." Before the first dose, the nurse checks the latest potassium and creatinine results and reviews the list for supplements, salt substitutes, and NSAIDs. The person is taught to expect possible mild dizziness at first, to report a persistent dry cough, and — most emphatically — to seek help immediately for any facial or lip swelling. Pregnancy status is confirmed per policy. Every lab value, interval, and counseling point comes from orders and current references; the nurse connects mechanism to monitoring so nothing surprises the team.
Key takeaways
- ACE inhibitors end in -pril and block the enzyme converting angiotensin I to angiotensin II. Less angiotensin II → vasodilation + less aldosterone → lower resistance and less sodium/water retention → lower pressure.
- Used for hypertension, heart failure, post-MI care, and kidney protection (especially diabetic kidney disease).
- Dry cough (bradykinin) is common and benign; angioedema (facial/lip/tongue swelling) is rare and an emergency.
- Potassium rises because aldosterone falls — hyperkalemia is the electrolyte to watch, especially with supplements or salt substitutes.
- Pregnancy is a contraindication (teratogenic); first-dose dizziness is possible; NSAIDs can blunt the effect. All parameters verified against current references, formulary, and prescriber orders.
Check yourself
6 review questions from the chapter. Try each one, then open the answer.
Where in the RAAS pathway do ACE inhibitors act, and what two pressure-raising effects of angiotensin II are lost?
Show answer
They block the converting enzyme, so angiotensin I cannot become angiotensin II; lost effects are vasoconstriction and aldosterone-driven sodium/water retention.
Why do ACE inhibitors cause a dry cough, and why do ARBs cause less of one?
Show answer
Blocking ACE leaves bradykinin undegraded, and it irritates the airways. ARBs leave ACE intact, so bradykinin is still broken down normally.
Why can ACE inhibitors raise serum potassium, and what drug combinations increase that risk?
Show answer
Less aldosterone means less potassium excretion; risk rises with potassium supplements, potassium-sparing drugs, and potassium-containing salt substitutes.
Why is angioedema a priority recognition skill?
Show answer
Facial, lip, tongue, or throat swelling can compromise the airway rapidly and can occur at any time, even after years — immediate recognition and escalation save lives.
Why are ACE inhibitors valued in diabetic kidney disease despite a possible small creatinine rise?
Show answer
Lowering pressure inside the glomerulus reduces kidney damage over time; a modest creatinine rise is common and followed by the prescriber, while large changes trigger review.
What is the pregnancy-related safety point for this class?
Show answer
ACE inhibitors are teratogenic and contraindicated in pregnancy; pregnancy status is assessed per policy and counseling provided.
Study tools & related lessonsKey vocabulary · Related
Key vocabulary
- Angiotensin II
- The active hormone that constricts vessels and releases aldosterone
- ACE
- The enzyme that converts angiotensin I to angiotensin II
- Bradykinin
- A peptide that dilates vessels and irritates airways
- Efferent arteriole
- The vessel leaving the kidney's filtering unit
- Teratogenic
- Capable of harming a developing fetus
Sources & references
This lesson was adapted from the open educational references above; their licenses and attributions are preserved. See Copyright & Licensing.
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