Tetracyclines: Overview
Tetracyclines are a class of broad-spectrum antibiotics effective against a wide range of bacteria, including Gram-positive, Gram-negative, and atypical organisms. They are used to treat infections ranging from respiratory infections to skin and soft tissue infections. Resistance is a concern in some cases, but newer agents like Tigecycline and Eravacycline address this issue.
Common Tetracyclines:
- Doxycycline
- Minocycline
- Tigecycline (Glycylcycline subclass)
- Eravacycline (Fluorocycline subclass)
Spectrum:
Doxycycline:
- Gram-positive: Covers MSSA, MRSA (CA-MRSA), Streptococcus
- Gram-negative: Limited, effective against H. influenzae, Moraxella, Brucella, Vibrio
- Atypicals: Good coverage, including Legionella, Chlamydia, Mycoplasma, Bartonella, Rickettsia
- Anaerobes: Limited
Minocycline:
- Gram-positive: MSSA, *MRSA (CA-MRSA)
- Gram-negative: Limited, similar to Doxycycline with better coverage against Acinetobacter
- Atypicals: Legionella, Chlamydia, Mycoplasma
- Anaerobes: Limited
Tigecycline (Glycylcycline):
- Gram-positive: Broad, covers MSSA, MRSA, Streptococcus, VRE (Vancomycin-resistant Enterococcus)
- Gram-negative: Broad, including Enterobacteriaceae, Acinetobacter, but NO Pseudomonas
- Anaerobes: Good anaerobic coverage
- Atypicals: Covers Legionella, Chlamydia, Mycoplasma
Eravacycline (Fluorocycline):
- Gram-positive: Covers MSSA, MRSA, Streptococcus, VRE
- Gram-negative: Broad, including Carbapenem-resistant Enterobacteriaceae (CRE), Acinetobacter, but NO Pseudomonas
- Anaerobes: Good anaerobic coverage
- Atypicals: Effective against Legionella, Chlamydia, Mycoplasma
Key Uses:
Doxycycline:
- Skin and soft tissue infections: Particularly effective against CA-MRSA.
- Respiratory infections: Useful for community-acquired pneumonia caused by atypical organisms (Legionella, Chlamydia, Mycoplasma).
- Tick-borne diseases: First-line for Lyme disease, Rocky Mountain spotted fever, and Ehrlichiosis.
- STIs: Treats Chlamydia infections and pelvic inflammatory disease (PID).
Minocycline:
- Acne vulgaris: Frequently used for moderate to severe acne.
- Skin infections: Effective against CA-MRSA and skin/soft tissue infections.
- Respiratory infections: Occasionally used for respiratory infections caused by atypical organisms.
Tigecycline:
- Complicated intra-abdominal infections: Used in resistant cases involving polymicrobial infections.
- Complicated skin and soft tissue infections: Effective in infections involving MRSA and VRE.
- Multidrug-resistant infections: Effective against Acinetobacter and Enterobacteriaceae, but no Pseudomonas coverage.
Eravacycline:
- Complicated intra-abdominal infections (cIAI): Approved for use in complicated intra-abdominal infections, particularly with multidrug-resistant organisms, including CRE.
- Resistant infections: Effective against VRE, MRSA, Acinetobacter, and CRE infections.
- Broad-spectrum alternative: A newer option for infections resistant to traditional antibiotics, with better safety and tolerability compared to Tigecycline.
Key Notes:
- Doxycycline is versatile, covering a wide range of infections from tick-borne diseases to respiratory infections and skin infections caused by MRSA.
- Minocycline is commonly used for acne and skin infections with good penetration into tissues.
- Tigecycline offers broad-spectrum coverage, especially for complicated intra-abdominal infections and resistant Gram-negative organisms, but has no Pseudomonas coverage.
- Eravacycline is a newer agent with broad coverage against resistant organisms, particularly CRE and VRE, making it ideal for complicated intra-abdominal infections and resistant cases where Tigecycline may not be effective.
- Resistance concerns: While Doxycycline and Minocycline are widely used, increasing resistance is a concern, particularly with Gram-negative organisms.
- GI side effects: Both Tigecycline and Eravacycline can cause significant gastrointestinal side effects, particularly nausea and vomiting.
- Photosensitivity: All tetracyclines, including Doxycycline, can cause photosensitivity, so patients should avoid excessive sun exposure.
Summary:
- Doxycycline: Widely used for respiratory infections, skin infections, and tick-borne diseases.
- Minocycline: Effective for acne and skin infections.
- Tigecycline: Great for complicated infections, including VRE and MRSA, but no Pseudomonas coverage.
- Eravacycline: Newer alternative for complicated intra-abdominal infections and resistant organisms, including CRE.
Tetracyclines: Overview
Tetracyclines are broad-spectrum antibiotics effective against a variety of Gram-positive, Gram-negative, and atypical bacteria. They are commonly used for skin, respiratory, and soft tissue infections, as well as certain atypical infections. However, these antibiotics come with notable side effects, including vestibular toxicity and phototoxicity.
Common Tetracyclines:
- Doxycycline
- Minocycline
- Tigecycline (Glycylcycline subclass)
- Eravacycline (Fluorocycline subclass)
Spectrum:
Doxycycline:
- Gram-positive: Covers MSSA, MRSA (CA-MRSA), Streptococcus
- Gram-negative: Limited, effective against H. influenzae, Moraxella, Brucella, Vibrio
- Atypicals: Good coverage, including Legionella, Chlamydia, Mycoplasma, Rickettsia
- Anaerobes: Limited
Minocycline:
- Gram-positive: MSSA, *MRSA (CA-MRSA)
- Gram-negative: Limited, similar to Doxycycline with better coverage against Acinetobacter
- Atypicals: Legionella, Chlamydia, Mycoplasma
- Anaerobes: Limited
Tigecycline (Glycylcycline):
- Gram-positive: Broad, covers MSSA, MRSA, Streptococcus, VRE (Vancomycin-resistant Enterococcus)
- Gram-negative: Broad, including Enterobacteriaceae, Acinetobacter, but NO Pseudomonas
- Anaerobes: Good anaerobic coverage
- Atypicals: Covers Legionella, Chlamydia, Mycoplasma
Eravacycline (Fluorocycline):
- Gram-positive: Covers MSSA, MRSA, Streptococcus, VRE
- Gram-negative: Broad, including Carbapenem-resistant Enterobacteriaceae (CRE), Acinetobacter, but NO Pseudomonas
- Anaerobes: Good anaerobic coverage
- Atypicals: Effective against Legionella, Chlamydia, Mycoplasma
Key Uses:
Doxycycline:
- Skin and soft tissue infections: Effective for community-acquired MRSA.
- Respiratory infections: Useful for community-acquired pneumonia caused by atypical organisms (Legionella, Chlamydia, Mycoplasma).
- Tick-borne diseases: First-line for Lyme disease, Rocky Mountain spotted fever, and Ehrlichiosis.
- STIs: Treats Chlamydia infections and pelvic inflammatory disease (PID).
Minocycline:
- Acne vulgaris: Frequently used for moderate to severe acne.
- Skin infections: Effective against CA-MRSA and skin/soft tissue infections.
- Respiratory infections: Occasionally used for respiratory infections caused by atypical organisms.
Tigecycline:
- Complicated intra-abdominal infections: Effective against resistant Gram-negative bacteria, including Acinetobacter (except Pseudomonas).
- Complicated skin and soft tissue infections: Effective for infections involving MRSA and VRE.
- Polymicrobial infections: Used for mixed infections where resistance is a concern.
Eravacycline:
- Complicated intra-abdominal infections (cIAI): Effective for complicated intra-abdominal infections, especially with multidrug-resistant organisms like CRE.
- Resistant infections: Effective against VRE, MRSA, Acinetobacter, and CRE infections.
- Broad-spectrum alternative: Used in resistant cases where Tigecycline may not be suitable.
Key Side Effects:
- Phototoxicity: Common with all tetracyclines, particularly Doxycycline. Patients should avoid prolonged sun exposure and use sunscreen to prevent severe sunburn.
- Vestibular toxicity: Notably seen with Minocycline, which can cause dizziness, vertigo, and nausea, especially with prolonged use.
- GI upset: Tigecycline and Eravacycline are associated with gastrointestinal side effects, particularly nausea and vomiting.
- Tooth discoloration: Tetracyclines can cause permanent tooth discoloration if used in children under 8 or during pregnancy.
Summary:
- Doxycycline: Versatile, used for respiratory infections, tick-borne diseases, and skin infections (including MRSA).
- Minocycline: Commonly used for acne but can cause vestibular toxicity.
- Tigecycline: Broad-spectrum, effective against multidrug-resistant infections, including MRSA and VRE, but lacks Pseudomonas coverage.
- Eravacycline: Newer option for complicated intra-abdominal infections and resistant Gram-negative bacteria, including CRE.
Below is a broad, but clinically useful catalogue of organisms that may be susceptible to minocycline.
Activity is of course strain‑ and site‑dependent, so always confirm your local susceptibility data before pulling the trigger.
1. Gram‑positive bacteria
Staphylococcus aureus (MSSA & MRSA)
Coagulase‑negative staphylococci (e.g. S. epidermidis, S. haemolyticus)
Nocardia spp. (particularly N. asteroides complex)
Cutibacterium acnes (formerly Propionibacterium)
Enterococci (E. faecalis > E. faecium; variable, salvage role only)
Bacillus anthracis (adjunct/alternative in anthrax regimens)
2. Gram‑negative bacteria
Haemophilus influenzae, Moraxella catarrhalis
Acinetobacter baumannii (including many MDR isolates)
Stenotrophomonas maltophilia
Burkholderia cepacia complex
Brucella spp.
Vibrio vulnificus & V. parahaemolyticus
Pasteurella multocida
Yersinia pestis, Francisella tularensis (alternative options)
Neisseria meningitidis (pen‑allergic or prophylaxis back‑up)
Enteric GNRs (E. coli, Klebsiella, Enterobacter, Salmonella, Shigella) – activity is species/strain‑specific and not routinely relied upon
3. “Atypical” & intracellular pathogens
Mycoplasma pneumoniae, Ureaplasma urealyticum
Chlamydia trachomatis, Chlamydophila pneumoniae/psittaci
Rickettsia rickettsii (RMSF), R. typhi; Orientia tsutsugamushi (scrub typhus)
Ehrlichia chaffeensis, Anaplasma phagocytophilum
Coxiella burnetii (Q fever)
Bartonella henselae (cat‑scratch) & B. quintana
Tropheryma whipplei (Whipple disease)
4. Mycobacteria & related acid‑fast organisms
Rapid‑growers: Mycobacterium abscessus, M. chelonae, M. fortuitum
Slow‑growers: M. marinum, M. kansasii
Mycobacterium leprae (component of multi‑drug therapy)
5. Spirochaetes
Borrelia burgdorferi (Lyme disease – alt. to doxycycline)
Leptospira interrogans (when doxy unavailable/contra‑indicated)
6. Anaerobes
Cutibacterium acnes (re‑listed here for device/implant infections)
Selected Clostridium spp. (excludes C. difficile)
7. Protozoa & miscellaneous
Plasmodium species – minocycline is an accepted alternative to doxycycline for malaria prophylaxis/treatment when needed
Balamuthia mandrillaris (limited case reports)
Practical pearls
Minocycline earns its keep in the hospital mainly for difficult Gram‑negatives (MDR A. baumannii, Stenotrophomonas, Burkholderia) and for NTM/Nocardia work‑ups.
Check CSF levels: it penetrates the CNS better than doxycycline, which is handy for Steno or Acinetobactermeningitis.
Don’t forget classic tetracycline cautions – dental staining in kids, vestibular side‑effects, and interaction with divalent cations.
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