PTCB Guide to ACE Inhibitors
Also called Angiotensin-converting enzyme inhibitors · suffix -pril · updated
Quick answer
- Mechanism: ACE inhibitors block the conversion of angiotensin I to angiotensin II, relaxing blood vessels and lowering blood pressure.
- Top side effects: a dry, hacking cough (10% to 20%) plus dizziness and hypotension, with hyperkalemia (2% to 6%) and rare but dangerous angioedema (swelling of the face, lips, or tongue).
- Key point: every ACE inhibitor carries a boxed fetal toxicity warning and is treated as contraindicated in pregnancy, and the class can raise potassium, so watch potassium-sparing diuretics and salt substitutes.
What gets tested
- Recognizing the -pril suffix and matching brand to generic (Prinivil and Zestril are lisinopril)
- The mechanism: blocking angiotensin I to angiotensin II conversion in the RAAS
- The signature dry cough and the serious angioedema reaction
- Hyperkalemia risk and interactions that worsen it
- That ACE inhibitors carry a boxed fetal toxicity warning and are treated as contraindicated in pregnancy
- Common strengths, dosage forms, and routes (PTCE knowledge area 1.4 covers strengths and dose, dosage forms, routes of administration, special handling, and duration of therapy)
What is not tested
You do not need to know the full renin-angiotensin-aldosterone cascade biochemistry, receptor-level pharmacology, or the clinical judgment a prescriber uses when choosing an ACE inhibitor over an ARB. You are still expected to know common strengths, dosage forms, and routes: PTCE knowledge area 1.4 covers strengths and dose, dosage forms, routes of administration, special handling and administration instructions, and duration of drug therapy. The exam emphasis is on class recognition, the hallmark side effects, and the practical interaction and counseling points.
Why ace inhibitors matter
Lisinopril is the fourth most dispensed drug in the United States, with roughly 76 million prescriptions a year, and ACE inhibitors as a class are foundational blood-pressure and heart-failure medications you will see constantly.
ACE Inhibitors at a glance
| Generic | Brand | Primary indication |
|---|---|---|
| lisinopril | Prinivil (discontinued), Zestril | high blood pressure, heart failure |
| enalapril | Vasotec | high blood pressure, heart failure |
| ramipril | Altace (discontinued) | high blood pressure, cardiovascular risk reduction |
| benazepril | Lotensin | high blood pressure |
| quinapril | Accupril (discontinued) | high blood pressure, heart failure |
| captopril | Capoten (discontinued) | high blood pressure, heart failure |
| fosinopril | Monopril (discontinued) | high blood pressure, heart failure |
Mechanism of action
ACE inhibitors competitively block angiotensin-converting enzyme, the enzyme in the renin-angiotensin-aldosterone system (RAAS) that converts angiotensin I into angiotensin II. Angiotensin II is a potent vasoconstrictor that also triggers aldosterone release, so blocking its formation relaxes blood vessels, lowers blood pressure, and reduces fluid retention. ACE also breaks down bradykinin, so inhibiting it lets bradykinin build up, which is why a dry cough is a hallmark side effect. Captopril, approved in 1981, was the first ACE inhibitor.
Common and important side effects
- A dry, persistent cough (from bradykinin buildup), reported in about 10% to 20% of patients
- Dizziness and hypotension, which are as common as the cough
- Hyperkalemia (elevated potassium), about 2% to 6%
- Angioedema: swelling of the face, lips, tongue, or throat that can close the airway and is life-threatening
- First-dose hypotension and dizziness
- Acute kidney injury, especially in bilateral renal artery stenosis
- Fetal toxicity: boxed warning on every ACE inhibitor label, discontinue as soon as pregnancy is detected (treated as contraindicated in pregnancy)
Key interactions
- Potassium-sparing diuretics (spironolactone), potassium supplements, and salt substitutes can push potassium too high
- NSAIDs reduce the blood-pressure-lowering effect and raise the risk of kidney injury
- Lithium levels can rise, increasing lithium toxicity risk
- Aliskiren is contraindicated with an ACE inhibitor in patients with diabetes, and combining with ARBs (dual RAAS blockade) is avoided
- Sacubitril/valsartan (Entresto) is contraindicated with ACE inhibitors: 36 hours must pass between the two
Patient counseling notes
- Swelling of the face, lips, tongue, or throat, or any trouble breathing or swallowing, is a medical emergency: get emergency help (call 911) and do not take another dose
- A dry cough may develop; if it is intolerable, the prescriber may switch to an ARB
- Avoid potassium-based salt substitutes unless the prescriber approves
- Do not use during pregnancy, and call the prescriber right away if you become pregnant
- Rise slowly from sitting or lying down to limit dizziness
Practice questions
Then test the whole class in context with the drug class identification quiz and the brand and generic quiz.
1. Lisinopril (Prinivil, Zestril) belongs to which drug class?
- A. Angiotensin II receptor blocker (ARB)
- B. ACE inhibitor ✓
- C. Beta blocker
- D. Calcium channel blocker
Answer: B. Lisinopril is an ACE inhibitor. The -pril suffix is a reliable clue shared by enalapril, ramipril, and benazepril.
2. ACE inhibitors lower blood pressure by blocking the conversion of which substance?
- A. Renin to angiotensinogen
- B. Angiotensin I to angiotensin II ✓
- C. Aldosterone to cortisol
- D. Bradykinin to histamine
Answer: B. ACE inhibitors block angiotensin-converting enzyme, which normally converts angiotensin I to the vasoconstrictor angiotensin II. Less angiotensin II means relaxed vessels and lower blood pressure.
3. Which side effect is most characteristic of ACE inhibitors?
- A. A dry, persistent cough ✓
- B. Weight gain
- C. Constipation
- D. Blurred vision
Answer: A. ACE inhibitors let bradykinin accumulate, which causes a dry, hacking cough in roughly 10% to 20% of patients. If it is intolerable, prescribers often switch the patient to an ARB, which does not raise bradykinin.
4. A patient on an ACE inhibitor develops swelling of the lips and tongue. This serious reaction is called:
- A. Angioedema ✓
- B. Anaphylaxis to penicillin
- C. Stevens-Johnson syndrome
- D. Photosensitivity
Answer: A. Angioedema is a potentially life-threatening swelling of the face, lips, tongue, or throat that can occur with ACE inhibitors. It can close the airway, so the patient needs emergency care, the drug must be stopped, and the pharmacist and prescriber must be alerted.
5. ACE inhibitors are contraindicated in which of the following?
- A. Diabetes
- B. Pregnancy ✓
- C. Asthma
- D. Migraine
Answer: B. Every ACE inhibitor carries a boxed fetal toxicity warning telling prescribers to stop the drug as soon as pregnancy is detected, so the class is treated as contraindicated in pregnancy. ACE inhibitors can also raise potassium, so potassium-sparing diuretics and salt substitutes need caution.
Cheat sheet
- Suffix: -pril
- Class: ACE inhibitors (RAAS)
- Action: block angiotensin I to angiotensin II conversion
- Uses: high blood pressure, heart failure
- Watch: dry cough, dizziness, hyperkalemia, angioedema, boxed fetal toxicity warning
- Interactions: potassium-sparing diuretics, potassium supplements, NSAIDs, lithium, aliskiren, sacubitril/valsartan
- Brand note: Prinivil, Altace, Accupril, Capoten, and Monopril are discontinued US brands; the generics are still dispensed
Related drug-class guides
Official sources
- StatPearls: ACE Inhibitors (NBK430896)
- DailyMed: ZESTRIL (lisinopril) FDA label
- MedlinePlus: Lisinopril
- ClinCalc DrugStats: The Top 300 Drugs of 2023
PTCB Quiz Prep is an independent study resource, not affiliated with the Pharmacy Technician Certification Board. This guide is for exam preparation, not medical advice. See our editorial standards. Part of the PTCB Medications domain.