Penicillin

Class

• Beta-Lactam Antibiotic (Natural Penicillin)

Indications

• Treatment of bacterial infections caused by susceptible organisms, including:
  • Streptococcal infections (e.g., strep throat, rheumatic fever prophylaxis)
  • Pneumococcal infections (e.g., pneumonia)
  • Syphilis and other Treponema pallidum infections
  • Anthrax
  • Actinomycosis
  • Endocarditis (caused by susceptible bacteria)
  • Skin and soft tissue infections

Mechanism of Action

• Inhibits bacterial cell wall synthesis by blocking the transpeptidation step, leading to bacterial cell lysis.
• Effective against Gram-positive bacteria and some Gram-negative cocci.

Dosage and Administration

Forms and Typical Dosages

• Penicillin V (oral):
  • Mild to moderate infections: 250–500 mg every 6–8 hours.
  • Duration: 5–10 days depending on infection type.
• Penicillin G (intravenous or intramuscular):
  • Severe infections like syphilis or endocarditis: Dose depends on severity and organism; typically 1.2–4.8 million units/day divided every 4–6 hours.

Administration

• Oral penicillin should be taken on an empty stomach (1 hour before or 2 hours after meals) for better absorption.
• Intravenous or intramuscular forms are used for more severe infections or when oral administration is not feasible.

Forms Available

• Oral tablets: 250 mg, 500 mg (Penicillin V)
• Oral suspension: 125 mg/5 mL, 250 mg/5 mL (Penicillin V)
• Injectable: 1.2 million units, 2.4 million units (Penicillin G)

Brand Names and Manufacturers

• Pen-Vee K (Penicillin V)
• Pfizerpen (Penicillin G)
• Generic versions widely available.

Cost

• Generally affordable; a standard course costs $5–$30 depending on form and brand.

Contraindications

• Hypersensitivity to penicillin or other beta-lactam antibiotics.
• History of severe allergic reactions (e.g., anaphylaxis) to penicillin or cephalosporins.

Precautions

• Use with caution in patients with a history of mild allergies to beta-lactams.
• Adjust dosage in renal impairment to avoid toxicity.
• May cause superinfections with prolonged use, including fungal infections.

Side Effects

Common

• Nausea, vomiting
• Diarrhea
• Skin rash

Less Common

• Oral thrush or vaginal yeast infections
• Abdominal discomfort

Rare but Serious

• Severe allergic reactions (anaphylaxis): Difficulty breathing, swelling, hives.
• Stevens-Johnson syndrome or toxic epidermal necrolysis.
• Clostridioides difficile-associated diarrhea.
• Hemolytic anemia.

Drug Interactions

• Probenecid: Increases penicillin levels by reducing renal excretion.
• Methotrexate: May increase methotrexate toxicity; monitor closely.
• Oral Contraceptives: May reduce efficacy; use backup contraception.
• Tetracyclines: May reduce the effectiveness of penicillin.

Monitoring Parameters

• Symptom resolution (e.g., reduced fever, pain, or inflammation).
• Watch for allergic reactions, especially after the first dose.
• Kidney function in patients receiving high doses or those with pre-existing renal impairment.

Patient Counseling Points

• Take the medication exactly as prescribed and complete the full course, even if symptoms improve.
• Take oral penicillin on an empty stomach with a full glass of water.
• Report any rash, itching, or difficulty breathing immediately.
• Avoid skipping doses to prevent treatment failure or resistance.
• Use additional contraception methods while on penicillin if taking oral contraceptives.
• Store liquid suspensions in the refrigerator and shake well before each use; discard after 14 days.

FAQs About Penicillin

Q1: What types of infections does penicillin treat?

• Penicillin is effective for bacterial infections like strep throat, pneumonia, syphilis, and skin infections.

Q2: Can penicillin treat viral infections like colds or the flu?

• No, penicillin only works against bacterial infections, not viruses.

Q3: Can I take penicillin if I’m allergic to cephalosporins?

• Use with caution; consult your doctor as cross-reactivity may occur.

Q4: Is penicillin safe during pregnancy?

• Yes, penicillin is generally considered safe during pregnancy for treating bacterial infections.

Q5: What should I do if I miss a dose?

• Take it as soon as you remember unless it’s close to the next dose. Do not double doses.

Q6: Can I drink alcohol while taking penicillin?

• Alcohol does not directly interact with penicillin but may worsen side effects like nausea.

Q7: How quickly does penicillin work?

• Symptoms often improve within 24–48 hours, but complete the full course to ensure effectiveness.

Q8: What are signs of an allergic reaction to penicillin?

• Rash, itching, swelling, difficulty breathing, or severe dizziness. Contact a doctor immediately.

Q9: Can penicillin cause diarrhea?

• Yes, diarrhea is a common side effect. Persistent or severe diarrhea may indicate a more serious condition like C. difficile infection.

Q10: Does penicillin interact with other medications?

• Yes, interactions may occur with probenecid, methotrexate, oral contraceptives, and tetracyclines.

Q11: Can penicillin treat tooth infections?

• Yes, penicillin is often prescribed for bacterial tooth infections or abscesses.

Q12: What should I do if I develop a rash while on penicillin?

• Stop the medication and consult your doctor immediately; it may indicate an allergic reaction.

Q13: Is penicillin safe for children?

• Yes, it is commonly prescribed for pediatric bacterial infections; dosages are adjusted based on weight.

Q14: How should penicillin be stored?

• Tablets and capsules should be stored at room temperature, while liquid suspensions should be refrigerated.

Q15: Can bacteria become resistant to penicillin?

• Yes, overuse or misuse of penicillin can lead to antibiotic resistance; use only when prescribed

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