Penicillins

Key Points

• Penicillins are bactericidal antibiotics that kill bacteria by interfering with cell-wall protein synthesis.
• Commonly prescribed for Streptococcal, Pneumococcal, and Staphylococcal infections.
• Cross-sensitivity exists between penicillins and cephalosporins; assess allergy history before administration.
• Anaphylaxis is the most serious adverse reaction and requires emergency treatment with epinephrine.

Mechanism of Action

Penicillins are beta-lactam antibiotics that inhibit bacterial cell-wall synthesis. When the cell wall is impaired, the bacterial cell is rapidly broken down and destroyed. This bactericidal mechanism makes penicillins effective against actively growing organisms.

Indications

• Streptococcal infections (pharyngitis, skin infections).
• Pneumococcal infections.
• Staphylococcal infections (susceptible strains).
• Prophylaxis for rheumatic heart disease and valve replacement before invasive procedures.

Nursing Considerations

• Assess for penicillin and cephalosporin allergy history before administration (cross-sensitivity risk).
• Monitor for superinfection signs including C. difficile (bloody/foul-smelling stool) and candidiasis (vaginal itching/discharge).
• Penicillin contains significant potassium; monitor for Hyperkalemia in clients receiving potassium-sparing diuretics.
• Best absorbed on an empty stomach; may take with food if GI upset occurs but avoid citrus products that impede absorption.
• High-dose penicillin therapy may cause coagulation abnormalities; monitor bleeding parameters.

Side Effects and Adverse Effects

• Common: Nausea, vomiting, GI distress, diarrhea, black hairy tongue.
• Hypersensitivity: Rash (maculopapular to exfoliative dermatitis), urticaria, laryngeal edema.
• Serious: Anaphylaxis requiring emergency treatment with epinephrine and airway management.
• Superinfection: C. difficile colitis and candidiasis.

Anaphylaxis Risk

Discontinue penicillin immediately if allergic reaction occurs. Serious anaphylactic reactions require emergency epinephrine and airway support.

Health Teaching

• Take medication as prescribed around the clock; finish the full course as directed.
• Space doses evenly to maintain therapeutic drug levels.
• Report fever, bloody or mucus-containing diarrhea, rash, or signs of superinfection promptly.
• Female clients on oral contraceptives (especially with amoxicillin) should use an alternative contraception method during therapy.
• Never share medications with others.
• Chew chewable tablets thoroughly before swallowing.

Related Concepts

• cephalosporins - Related beta-lactam class with cross-sensitivity potential.
• infection-control - Antimicrobial therapy context within infection-prevention strategies.
• antibiotics - Broader antimicrobial therapy framework.

Self-Check

1. Why is cross-sensitivity between penicillins and cephalosporins clinically important?
2. What monitoring is essential during high-dose penicillin therapy with concurrent potassium-sparing diuretics?
3. What emergency interventions are required for penicillin-induced anaphylaxis?