Protein I Inhibitors Overview

Protein Synthesis Inhibitors: A Cheatsheet

These antibiotics target bacterial protein synthesis, a crucial process for their survival, aiming for selective toxicity by exploiting differences between bacterial and mammalian ribosomes.

• The goal is to kill bacteria without harming the patient.

• Bacterial ribosomes are 70S (composed of 30S and 50S subunits).

• Mammalian ribosomes are 80S (composed of 40S and 60S subunits).

• These drugs are generally bacteriostatic, meaning they stop bacterial growth.

• In high doses, these drugs can harm host mitochondria, which have 70S ribosomes similar to bacteria.

Tetracyclines (TeAm 30)

• Mechanism: Binds to the 30S ribosomal subunit, blocking tRNA binding.

• Key Examples: Tetracycline, Doxycycline, Minocycline, Demeclocycline.

• Uses:

  • Acne (especially doxycycline)

  • Chlamydia (doxycycline)

  • Lyme disease (doxycycline)

  • Helicobacter pylori (tetracycline)

  • Minocycline: high levels in saliva/tears, good for meningococcal carrier state.

• Adverse Effects:

  • Discoloration of teeth and bones: Binds to calcifying tissues (avoid in children < 8 years, pregnancy, breastfeeding).

  • Phototoxicity

  • Vestibular dysfunction

  • Pseudotumor cerebri

• Important Interaction: Do NOT take with dairy products, antacids, or iron supplements (chelation reduces absorption).

• Not recommended for: Pregnancy, breastfeeding, children < 8 years.

Aminoglycosides (N.O.T. Harmless)

• Mechanism: Binds to the 30S ribosomal subunit, causing "misreading" of the genetic code.

• Effect: Bactericidal.

• Key Examples: Amikacin, Gentamicin, Neomycin, Streptomycin, Tobramycin.

• Uses:

  • Serious aerobic Gram-negative infections (e.g., Pseudomonas, Klebsiella pneumoniae, Enterobacter spc.).

  • Often requires O to work; ineffective against anaerobes.

• Adverse Effects: Aminoglycosides are NOT harmless!

  • Nephrotoxicity: Kidney damage (require careful monitoring of levels).

  • Ototoxicity: Hearing loss and vertigo (can be irreversible, teratogenic for fetus - deafness).

  • Neuromuscular block: Can exacerbate myasthenia gravis.

Macrolides (Best Alternative for Penicillin)

• Mechanism: Binds to the 50S ribosomal subunit, inhibiting translocation.

• Key Examples: Azithromycin, Clarithromycin, Erythromycin, Telithromycin. (Note: Fidaxomicin is similar but acts on RNA polymerase).

• Uses:

  • Respiratory infections (pneumonia)

  • Chlamydia

  • Great alternative for patients with Penicillin allergies.

  • Erythromycin: Can stimulate smooth muscles, sometimes used for gastroparesis.

• Adverse Effects:

  • Heart: Can prolong QT interval (risk of arrhythmia).

  • Common GI upset.

  • Inhibits P450 system (especially Erythromycin/Clarithromycin), increasing levels of Warfarin, Statins, Digoxin.

Fidaxomicin (Specialist for C. diff)

• Mechanism: Acts on the sigma unit of RNA polymerase, disrupting transcription and inhibiting protein synthesis (structurally similar to macrolides but different target).

• Unique Use: Clostridium difficile infection (minimal systemic absorption, stays in GI tract).

• Advantages: Minimal adverse effects, minimal resistance due to unique action.

• Adverse Effects (rare): Allergic response if macrolide allergy, GI distress, anemia, neutropenia.

Chloramphenicol (Grey Baby Syndrome)

• Mechanism: Binds to the 50S ribosomal subunit, inhibiting the peptidyl transferase reaction.

• Use: Last resort drug for serious infections when other options have failed.

• Adverse Effects:

  • Bone marrow toxicity (in high concentrations).

  • Grey Baby Syndrome: Due to underdeveloped kidney function in infants, leading to poor excretion, cardiovascular collapse, cyanosis, and death.

• Avoid in: Breastfeeding mothers.

Lincosamide: Clindamycin (C. diff Risk)

• Mechanism: Binds to the 50S ribosomal subunit (same site as macrolides).

• Uses:

  • Anaerobic infections (abscesses, abdominal wounds).

  • Skin infections (MRSA).

  • Osteomyelitis (penetrates bones well).

  • Not good for UTIs due to low urinary excretion.

• Adverse Effect: Highest risk antibiotic for causing pseudomembranous colitis (severe diarrhea) due to C. difficile overgrowth.

Linezolid (The Big Gun)

• Mechanism: Binds to the 23S rRNA of the 50S subunit, preventing the formation of the 70S initiation complex.

• Effect: Generally bacteriostatic, but bactericidal against streptococci.

• Uses:

  • Resistant Gram-Positives: MRSA, VRE (Vancomycin-Resistant Enterococci), Penicillin-resistant strep.

  • First-line treatment for MRSA bacteremia.

  • Moderately active against Mycobacterium tuberculosis.

• Adverse Effects:

  • Thrombocytopenia (if used > 10 days).

  • Optic Neuritis/Neuropathy (if used > 28 days).

  • Nonselective MAO inhibitor activity: Avoid SSRIs and Tyramine-rich foods due to risk of serotonin syndrome ormhypertensive crisis.

Summary Table