Our ribosomes are different from bacterial ribosomes. We have a larger 80S particle and bacteria have a smaller 70S particle. We use this difference to create drugs that selectively target bacterial ribosomes.
The 70S bacterial ribosome has two subunits, the 50S and 30S subunits.
I remember anti-ribosomal antibiotics using the mnemonic CLEAT. If you want to remember also quinupristin/dalfopristin and spectinomycin, the mnemonic is TACKLE the ribosomes. K=Q for quinupristin/dalfopristin.
Anti-ribosomal antibiotics inhibit the ribosome and protein translation.
| Properties | Common Uses | |||
| 50S | Clindamycin, Chloramphenicol | Clindamycin is NOT useful against gram-negative bacteria. | -Anaerobes. Surgeons use Clinda + Aminoglycoside for penetrating wound infections of the abdomen, e.g. bullet or knife trauma. Aminoglycoside covers gram neg and clinda covers anaerobes. -Gram Positives (If patient has severe allergies to PCN and Cephalosporins) –MRSA (Community-acquired MRSA) outpatient -Toxoplasma gondii (use clinda + pyrimethamine) B/c of its coverage against anaerobes and gram positives, clinda is used in combination with another drug to treat female genital tract infections. -Treat aspiration PNA. |
Pseudomenbranous Colitis 2/2 to C. difficile proliferation. Dx with either stool culture or C. diff exotoxin. Note, all abx can cause pseudomembranous colitis, not just clinda. PCNs are the most common cause of it b/c they are used more frequently. |
| Chloramphenicol has an amazingly broad spectrum (like imipenem). It kills most clinically important bacteria. | It kills Gram pos, Gram neg, anaerobes. It is like pouring chlorine on the bacteria. Use: It is only used when no other abx is available. E.g. for -meningitis when pt has severe allergies to PCN including cephalosporins. It has great CSF penetration. -Also, kids and pregnant women with RMSF cannot be treated with tetracyclines. Chloramphenicol becomes the drug of choice. It developed countries, it is used widely since it is very cheap. |
Side effects: Bone marrow suppression (reversible & dose dependent) and Aplastic anemia (irreversible). Gray baby syndrome. | ||
| Linezolid | Avoid with antidepressants. | -HCAP -Complicated skin and soft tissue infections. -Staph aureus PNA -Resistant gram-positive bugs. Treats MRSA and Vancomycin Resistant enterococcus (VRE). Comes as IV and PO. |
Causes Bone marrow suppression, including thrombocytopenia, anemia, neutropenia. Can precipitate serotonin syndrome if used with SSRI antidepressants or MAO inhibitors. |
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| Erythromycin, and the Macrolides | Gram positives Some Gram Negatives Atypical bacteria (Chlamydia, Mycoplasma, Legionella) |
-Outpatient tx of URI & LRI. -Atypical organisms: Chlamydia, Mycoplasma, Legionella. Used in CAP, URI (such as sinusitis, otitis media, and bronchitis) to cover atypicals Azithromycin (or a newer quinolone) is the drug of choice for Legionnaires’ disease. |
Avoid telithromycin in patients with myasthenia gravis b/c they will develop acute respiratory failure. Macrolides, especially erythromycin stimulate peristalsis which can produce GI side effects. This side effect is put to good use as we prescribe erythromycin to pts with gastric dysmotility (e.g. diabetic gastroparesis). -Cause Cholestatic hepatitis (rare) -Prolong QT intervals. |
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| 30S | Aminoglycosides, Spectinomycin | Gentamicin is the most commonly in the family. | -Gram-negative enterics -Cover Pseudomonas. -Tularemia, Yersinia pestis, brucellosis, Mycobacterium tuberculosis. Gentamicin + PCN to tx in-hospital infections. Neomycin is so broad and toxic, it is used only for topical infections. |
Ototoxicity (8th CN toxicity: vertigo, hearing loss, ringing) Nephrotoxicity (it is cleared by the kidneys and injures the kidneys). |
| Tetracyclines | They chelate with cations in mild and mild products, aluminum hydroxide, Ca++, Mg++. B/c it chelates Ca++ in teeth and bones of babies, it causes discolored teeth and depressed bone growth. | -Rickettsia -Chlamydia -Mycoplasma pneumonia -Entamoeba histolytica -Spirochetes – Borrelia, Leptospira and Treponema pallidum (2nd choice behind PCN). -Brucella (2nd choice behind Bactrim) -Nocardia (2nd or 3rd choice) -Facial acne. **Demeclocycline is used to treat SIADH. |
GI irritation (N/V/D); Phototoxic dermatitis (skin inflammation on exposure to sunlight); Discolored teeth; Depressed bone growth. Don’t give this drug to pregnant women or the baby’s teeth will be discolored. |
Amp + Gent = Broad coverage.
Clinda + Aminoglycoside (Gentamicin) = Broad coverage if pt is allergic to penicillins and cephalosporins.
** The lung is the only organ that can have an abscess that doesn’t need surgical drainage.
Quinupristin/dalfopristin – works at 50S. It’s an antibiotic that is only used when all else fails. Helps to treat VRE. It causes hyperbilirubinemia, pain at infusion site, and arthralgias/myalgias.