👤 By the CinnaRN Clinical Content Team🕐 Updated 2026-08-23🏷️ Pharmacological Therapies🔖 Free to read, print, and share
Also known as: penicillin · amoxicillin · ampicillin · pen G · PCN · augmentin
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Use this quick-reference guide to spot, treat, and prevent Penicillins on the NCLEX. Keep it handy during review and on exam day!
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📒 The 1-minute cheat sheet
📌 Use
Strep, syphilis, gram + cocci
Cell wall inhibitor → bactericidal
📌 Allergy
Anaphylaxis risk → ask allergy first
Cross-allergy with cephalosporins
✅ Do
Observe 30 min after dose
Take full course, finish all
Some on empty stomach
🎓 Teach
↓oral contraceptive effectiveness
Report rash, wheeze, swelling
📚 Penicillins — full study notes
The cheat sheet above is your quick recall card. These notes go deeper — what it is, what to do first, what must be reported, and what to teach.
Penicillins are beta-lactam antibiotics that kill bacteria by disrupting cell wall synthesis, used for many gram-positive infections, strep throat, and syphilis. They are among the most common causes of drug allergy and anaphylaxis. The key safety principle is always screening for penicillin and cephalosporin allergy before giving.
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Key points
Understand these first
Penicillins are bactericidal and work by inhibiting bacterial cell wall synthesis.
Cross-sensitivity exists with cephalosporins, so a penicillin allergy raises caution with cephalosporins.
Take oral penicillins on an empty stomach (except amoxicillin) for best absorption.
A maculopapular rash is common with ampicillin, especially in patients with mononucleosis, and is not always a true allergy.
Penicillins can reduce the effectiveness of oral contraceptives.
Probenecid raises and prolongs penicillin blood levels by slowing renal excretion.
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Nursing priorities
What to do, in order
Ask about and document any prior penicillin or cephalosporin allergy before the first dose.
Keep epinephrine and emergency equipment available, especially with IV or IM doses.
Observe the patient for at least 30 minutes after a parenteral dose for allergic reaction.
Give the full prescribed course and emphasize completing all doses to the patient.
Monitor renal function and check that the dose is adjusted for kidney impairment.
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Red flags — report now
Escalate immediately
Stridor, wheezing, throat tightness, facial swelling, or hypotension signal anaphylaxis - stop the drug and get help immediately.
Never give a penicillin to a patient with a documented penicillin anaphylaxis history.
Severe or bloody diarrhea may indicate C. difficile colitis and must be reported.
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Labs & values
Numbers to know
WBC 5,000-10,000/mm3 (monitor response to infection)
Serum creatinine 0.6-1.2 mg/dL (dose adjustment in renal impairment)
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Patient teaching
What patients must know
Finish the entire prescription even if you feel better.
Use a backup birth control method while on the antibiotic and for the rest of that cycle.
Report any rash, hives, swelling, or trouble breathing right away.
Take most oral penicillins on an empty stomach with a full glass of water.
❓ Penicillins: NCLEX FAQs
What are the priority nursing interventions for Penicillins?
Ask about and document any prior penicillin or cephalosporin allergy before the first dose. Keep epinephrine and emergency equipment available, especially with IV or IM doses. Observe the patient for at least 30 minutes after a parenteral dose for allergic reaction. Give the full prescribed course and emphasize completing all doses to the patient.
What are the warning signs of Penicillins a nurse must report?
Stridor, wheezing, throat tightness, facial swelling, or hypotension signal anaphylaxis - stop the drug and get help immediately. Never give a penicillin to a patient with a documented penicillin anaphylaxis history. Severe or bloody diarrhea may indicate C. difficile colitis and must be reported.
What do I need to know about Penicillins for the NCLEX?
Penicillins are bactericidal and work by inhibiting bacterial cell wall synthesis. Cross-sensitivity exists with cephalosporins, so a penicillin allergy raises caution with cephalosporins. Take oral penicillins on an empty stomach (except amoxicillin) for best absorption. A maculopapular rash is common with ampicillin, especially in patients with mononucleosis, and is not always a true allergy.
What patient teaching is important for Penicillins?
Finish the entire prescription even if you feel better. Use a backup birth control method while on the antibiotic and for the rest of that cycle. Report any rash, hives, swelling, or trouble breathing right away. Take most oral penicillins on an empty stomach with a full glass of water.
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Quick Tip
Penicillins are bactericidal and work by inhibiting bacterial cell wall synthesis.