Tetracyclines, Tetracycline Derivatives, and Chloramphenicol

Tetracyclines, Tetracycline Derivatives
and Chloramphenicol

Russell E. Lewis, Pharm.D., FCCP
Associate Professor of Infectious Diseases (MEDS-10/B)

russelledward.lewis@unipd.it
https://github.com/Russlewisbo
Slides and course materials: www.idpadova.com

Introduction & Overview

Learning Objectives

After this presentation, you will be able to:

1. Describe the mechanism of action of tetracyclines
2. Compare pharmacokinetic properties of different tetracycline generations
3. Identify key clinical indications for each tetracycline
4. Recognize important adverse effects and drug interactions
5. Apply knowledge of newer derivatives (tigecycline, eravacycline, omadacycline)
6. Select the appropriate tetracycline for specific clinical scenarios

Historical Overview

Discovery & Development Timeline

1948: Benjamin M. Duggar discovers chlortetracycline

• He isolated from Streptomyces aureofaciens at age 76!
• Trade name “Aureomycin” from aureus (golden)

Era	Year	Agent	Significance
1st Gen	1948-1953	Chlortetracycline, Oxytetracycline, Tetracycline	Natural products
2nd Gen	1967-1972	Doxycycline, Minocycline	Improved PK
3rd Gen	2005-2018	Tigecycline, Eravacycline, Omadacycline	Resistance-active

Duggar’s discovery launched an entire antibiotic class. The 2018 approvals represented a renaissance driven by resistance concerns (Duggar, 1948).

But was he the first?- Egyptians drank tetracycline beer!

(Nelson et al., 2010)

The rise of resistance & classification

Resistance emerged quickly:

• First resistance: 1953 (Shigella dysenteriae)
• Non-clinical uses (animal feed) accelerated spread
• Led to 33+ resistance genes (“tetracycline resistome”)

Classification by half-life:

Category	Half-life	Examples
Short-acting	6-8 hours	Tetracycline, Oxytetracycline
Intermediate	12 hours	Demeclocycline
Long-acting	16-22 hours	Doxycycline, Minocycline
Very long-acting	37-67 hours	Tigecycline

Longer half-life agents allow for less frequent dosing and better compliance (Roberts, 2005; Thaker et al., 2010).

Structure & Mechanism of Action

Core structure

All tetracyclines share: Four-benzene ring structure (hydronaphthacene nucleus)

• Substitutions at C-5, C-6, C-7 determine properties

Cell Entry:

• Gram-negative: Mg²⁺-cation complex → OmpF/OmpC porins → accumulates in periplasm
• Gram-positive: Active transport through cytoplasmic membrane (ΔpH dependent)

The cation complex formation is essential for crossing gram-negative outer membranes - also explains why divalent cations interfere with absorption. (Schnappinger and Hillen, 1996)

Ribosomal binding & protein synthesis inhibition

Tetracyclines reversibly bind to the 30S ribosomal subunit → bacteriostatic…although clinical importance of bacteriostatic vs. cidal is debated. Free drug AUC/AUC is the PK/PD driver of activity- Killing (or growth suppression) depends on overall exposure, not peak concentration (Chopra and Roberts, 2001).

Pharmacokinetics

Absorption: key differences

Drug	Bioavailability	Food effect	Time to peak
Tetracycline	77-88%	↓50%	2-4 hours
Doxycycline	~100%	↓<20%	2-3 hours
Minocycline	~100%	↓<20%	2 hours

Clinical pearl

Important

Doxycycline can be taken with food to reduce GI upset without significantly affecting absorption!

This is a major practical advantage of doxycycline - patients with nausea can take it with meals (Cunha et al., 2000).

The critical cation interaction

Critical drug interaction

Divalent and trivalent cations reduce absorption by 50-90%

Problematic agents: Aluminum, magnesium, calcium (antacids), iron, zinc, multivitamins

Solution: Separate administration by 3 hours

Patient counseling:

• Take tetracycline 1 hour before OR 2 hours after meals
• Separate from antacids by 2-3 hours
• Dairy products (milk, yogurt, cheese) also chelate

One of the most important interactions to communicate. Many patients don’t realize their daily vitamin interferes (Chopra and Roberts, 2001).

Distribution & elimination

Half-life comparison:

Drug	Half-life	Protein Binding	Lipophilicity
Tetracycline	7 hours	24-65%	Baseline
Doxycycline	12-16 hours	82-93%	5× baseline
Minocycline	16-21 hours	70-80%	10× baseline
Tigecycline	37-67 hours	71-89%	Very high

Higher lipophilicity = better tissue penetration. Minocycline’s high lipophilicity explains its excellent CSF penetration (Moffa and Brook, 2024).

Tissue penetration

Doxycycline achieves excellent levels in:

• Bronchial secretions, pleural fluid
• Sinus, middle ear secretions
• Bone, prostate, testes
• Partically excreted in active form in urine

Minocycline uniquely penetrates:

• CSF (11-57% of serum levels)
• Saliva and tears
• Sebum (explaining efficacy in acne)

Tissue penetration drives clinical indications. Minocycline’s CNS penetration makes it useful for certain infections. Tetracyclines have high volume of distribution making them poor choices for bloodstream infection (Moffa and Brook, 2024).

Special populations

Renal impairment:

• Tetracycline: Avoid (accumulates, worsens azotemia)
• Doxycycline: No adjustment needed (Biliary secretion → fecal excretion)
• Minocycline: No adjustment needed

Hepatic impairment:

• All tetracyclines: Use with caution
• Tigecycline: Reduce dose in Child-Pugh C

Clinical Pearl

Doxycycline is the tetracycline of choice in renal failure!

This is a frequently tested point - Doxycycline’s unique elimination makes it safe in renal impairment (Moffa and Brook, 2024).

Antimicrobial Spectrum

Gram-positive coverage

Generally susceptible:

• Streptococcus pneumoniae (resistance varies: 20-40%)
• Streptococcus pyogenes
• Many Enterococcus faecalis
• MRSA (community-acquired strains often susceptible)
• Listeria monocytogenes
• Nocardia, Actinomyces

Note

Newer tetracyclines (tigecycline, eravacycline, omadacycline) have enhanced gram-positive activity including VRE

MRSA susceptibility to doxycycline makes it useful for community skin infections. However, resistance is increasing (Diekema et al., 2001).

Gram-negative coverage

Susceptible organisms:

• Haemophilus influenzae
• Brucella species
• Vibrio species (cholera)
• Yersinia pestis (plague)
• Francisella tularensis (tularemia)
• Pasteurella multocida (animal bites)

Limited or resistant:

• Pseudomonas aeruginosa - inherently resistant
• Proteus species - often resistant
• Enterobacterales - variable, increasing resistance

The gram-negative spectrum focuses on atypicals and specific pathogens. Not reliable for nosocomial gram-negatives (Chopra and Roberts, 2001).

Atypical pathogens

Clinical Pearl

Tetracyclines are first-line for many atypical pathogens!

Excellent activity against:

Organism	Clinical Syndrome
Chlamydia spp.	STIs, pneumonia, psittacosis
Mycoplasma pneumoniae	Atypical pneumonia
Rickettsia spp.	Rocky Mountain spotted fever, typhus
Borrelia burgdorferi	Lyme disease
Coxiella burnetii	Q fever
Ehrlichia/Anaplasma	Ehrlichiosis/Anaplasmosis

Doxycycline is often the drug of choice for tick-borne illnesses due to excellent activity against Rickettsia and related organisms (Moffa and Brook, 2024).

Anaerobes & other organisms

Anaerobic coverage:

• Moderate activity against many mouth anaerobes
• Bacteroides fragilis: variable (50-70% susceptible)
• Tigecycline: broader anaerobic coverage

Additional coverage:

• Treponema pallidum (syphilis - alternative to penicillin)
• Plasmodium spp. (malaria prophylaxis/treatment)
• Bacillus anthracis (anthrax)
• Actinomyces, Nocardia

Doxycycline’s activity against T. pallidum makes it the alternative of choice for penicillin-allergic patients with syphilis (Moffa and Brook, 2024).

Clinical indications

Respiratory tract infections

Community-Acquired Pneumonia (CAP):

Guideline Recommendation

Doxycycline is recommended as an alternative to macrolides for outpatient CAP in patients with comorbidities

• Covers atypicals (M. pneumoniae, C. pneumoniae, Legionella)
• Alternative when macrolide resistance is a concern
• Dose: 100 mg BID × 5-7 days

Other respiratory uses:

• Acute exacerbations of COPD
• Psittacosis (C. psittaci)

With rising macrolide resistance in S. pneumoniae, doxycycline has become an increasingly important alternative (Metlay et al., 2019).

Tick-borne diseases

Doxycycline is first-line for:

Disease	Pathogen	Duration
Lyme disease (early)	B. burgdorferi	10-14 days
Rocky Mountain Spotted Fever	R. rickettsii	5-7 days
Ehrlichiosis	Ehrlichia spp.	5-14 days
Anaplasmosis	A. phagocytophilum	10-14 days

Clinical Warning

For RMSF: Start doxycycline empirically - don’t wait for serologic confirmation! Delay increases mortality.

Empiric treatment of suspected RMSF can be lifesaving. Doxycycline is safe even in children for this indication (Lantos et al., 2021).

Sexually transmitted infections

Infection	Doxycycline Regimen
Chlamydia	100 mg BID × 7 days
Syphilis (penicillin allergy)	100 mg BID × 14 days (early) or 28 days (late)
PID (with ceftriaxone + metronidazole)	100 mg BID × 14 days
Epididymitis	100 mg BID × 10 days
LGV	100 mg BID × 21 days

Emerging Use

Doxy-PEP: Post-exposure prophylaxis (200 mg within 72h) reduces STI incidence by 66% in high-risk populations

Doxy-PEP is a major recent development - single dose within 72 hours of exposure significantly reduces gonorrhea, chlamydia, and syphilis(Centers for Disease Control and Prevention, 2021; Luetkemeyer et al., 2023).

Skin & soft tissue infections

Community-acquired MRSA SSTI:

• Doxycycline 100 mg BID or Minocycline 100 mg BID
• Duration: 5-10 days depending on severity

Acne vulgaris:

Agent	Dose	Notes
Doxycycline	40-100 mg daily	Lower doses for anti-inflammatory
Minocycline	50-100 mg BID	Risk of pigmentation, lupus-like
Sarecycline	60-150 mg daily	Narrow spectrum, fewer GI effects

Sub-antimicrobial doxycycline (40 mg) is effective for acne through anti-inflammatory mechanisms without promoting resistance (Garner et al., 2012; Ruhe and Menon, 2007).

Infections requiring combination therapy

Brucellosis:

• Doxycycline 100 mg BID × 6 weeks + Streptomycin (or Gentamicin) × 2-3 weeks
• OR Doxycycline + Rifampin × 6 weeks

Q Fever:

• Acute: Doxycycline 100 mg BID × 14 days
• Chronic/Endocarditis: Doxycycline + Hydroxychloroquine × 18-24 months

Anthrax (post-exposure):

• Doxycycline 100 mg BID × 60 days (with vaccine if available)

For brucellosis, the combination prevents relapse. Q fever endocarditis requires prolonged therapy (Garner et al., 2012; Ruhe and Menon, 2007).

Other important indications

Malaria prophylaxis:

• Doxycycline 100 mg daily (start 1-2 days before, continue 4 weeks after)
• Alternative to mefloquine or atovaquone-proguanil

Cholera:

• Single dose doxycycline 300 mg reduces duration

Periodontitis:

• Sub-antimicrobial doxycycline (20 mg BID) as adjunct to scaling

SIADH:

• Demeclocycline 600-1200 mg/day (induces nephrogenic DI)

Demeclocycline’s use for SIADH is a classic example of repurposing a side effect for therapeutic benefit (Centers for Disease Control and Prevention, 2023; Dahl et al., 2006; Forrest et al., 1978).

Adverse Effects

Gastrointestinal effects

Most common adverse effects:

• Nausea, vomiting, diarrhea (dose-related- peak concentration drive for IV tigecycline, can be reduced with splitting dosing- for oral doxycycline. GI effects are related to local irritation)
• Esophageal irritation and ulceration

Esophagitis Prevention

• Take with full glass of water
• Remain upright for 30 minutes after dose
• Doxycycline hyclate > doxycycline monohydrate for this risk

Management strategies:

• Take with food (doxycycline, minocycline)
• Use enteric-coated formulations
• Consider dose reduction if tolerating lower doses

Esophageal ulceration can be severe. The upright position and water are critical counseling points (Smith and Leyden, 2005).

Photosensitivity

Clinical Warning

Photosensitivity is dose-related and occurs in up to 20% of patients!

Risk ranking:

• Highest: Demeclocycline > Doxycycline > Tetracycline
• Lowest: Minocycline (rare)

Patient counseling:

• Avoid prolonged sun exposure
• Use SPF 30+ sunscreen
• Wear protective clothing
• Reaction occurs within minutes to hours of UV exposure

Photosensitivity is a phototoxic (not allergic) reaction. It can occur even through window glass with UVA (Smith and Leyden, 2005).

Dental & bone effects

Contraindication

Avoid tetracyclines in pregnancy and children under 8 years (except for life-threatening infections like RMSF)

Dental effects:

• Permanent yellow-brown staining
• Enamel hypoplasia
• Risk greatest during tooth development (in utero through age 8)

Bone effects:

• Deposit in calcifying tissues
• Reversible decrease in bone growth rate in fetus/young children
• Does not affect already-formed adult bone

The age 8 cutoff is when permanent teeth are largely formed. Doxycycline may have lower staining risk than older tetracyclines (Moffa and Brook, 2024).

CNS effects (Especially minocycline)

Vestibular effects (minocycline):

• Dizziness, vertigo, ataxia
• Occurs in 30-90% of patients
• More common in women
• Usually reversible within 48-72 hours of stopping

Other CNS effects:

• Benign intracranial hypertension (pseudotumor cerebri)
  • Headache, visual changes, papilledema
  • Risk increased with concurrent vitamin A, retinoids

Minocycline’s vestibular effects often limit its use. The combination with isotretinoin is particularly concerning for intracranial hypertension (Garner et al., 2012; Moffa and Brook, 2024).

Hepatotoxicity

Tetracycline-specific:

• Dose-related (usually with >2 g/day IV)
• Microvesicular fatty liver
• Historically seen in pregnant women with pyelonephritis
• Rarely reported with modern dosing

Tigecycline:

• Elevated LFTs in 5% of patients
• Cases of hepatic failure reported
• Contributes to FDA warnings

High-dose IV tetracycline is no longer used, but this historical toxicity is why the class carries pregnancy warnings (Moffa and Brook, 2024; US Food and Drug Administration, 2010).

Minocycline-specific effects

Unique adverse effects:

Effect	Incidence	Characteristics
Blue-gray skin pigmentation	Rare	Sun-exposed areas, may be permanent
Drug-induced lupus	Rare	ANA positive, arthritis
Hypersensitivity syndrome	Rare	DRESS syndrome
Autoimmune hepatitis	Rare	Often with long-term use
Eosinophilic pneumonitis	Rare	Occurs early in treatment

aside

Most minocycline-specific effects are associated with prolonged use (acne treatment)

The pigmentation can be disfiguring and may not fully resolve. Monitor for lupus-like symptoms in long-term users (Garner et al., 2012).

Drug interactions

Major drug interactions

Interacting Drug	Effect	Management
Antacids, iron, calcium	↓ Absorption 50-90%	Separate by 3 hours
Warfarin	↑ INR	Monitor closely
Oral contraceptives	Potential ↓ efficacy	Use backup method
Isotretinoin	↑ Intracranial pressure	Avoid combination
Methotrexate	↑ MTX levels	Monitor toxicity
Digoxin	↑ Digoxin levels (10%)	Monitor levels

The warfarin interaction is clinically significant - always check INR when starting/stopping tetracyclines in anticoagulated patients (Moffa and Brook, 2024).

Practical management

Clinical Pearl

When multiple interactions exist, consider alternative antibiotics rather than complex scheduling

Key counseling points:

1. Take tetracyclines 1 hour before or 2 hours after antacids
2. Separate from dairy products
3. Women on OCs should use backup contraception
4. Report signs of bleeding if on warfarin
5. Never combine with isotretinoin

Complex medication schedules reduce compliance. Sometimes switching to azithromycin or a fluoroquinolone is more practical(Moffa and Brook, 2024).

Resistance Mechanisms

Three major mechanisms

1. Efflux Pumps (most common):

• Tet(A), Tet(B), Tet(K), Tet(L), etc.
• Actively pump tetracycline out of cell
• Energy-dependent (proton motive force)
• Encoded on plasmids → easily transferable

2. Ribosomal Protection Proteins:

• Tet(M), Tet(O)
• GTPases that “rescue” ribosomes
• Release tetracycline from 30S binding site
• Dislodge drug without damaging ribosome

Efflux is the most common mechanism. Ribosomal protection is especially important in gram-positive organisms (Chopra and Roberts, 2001; Roberts, 2005).

Resistance mechanisms (continued)

3. Enzymatic Inactivation:

• Tet(X) - NADPH-dependent monooxygenase
• Inactivates tetracycline by adding hydroxyl group
• Rare but concerning (can affect tigecycline)
• Tet(X3), Tet(X4) emerging as threat

Current resistance landscape:

• 33+ resistance genes identified
• Often carried on mobile genetic elements
• Multiple mechanisms may coexist

Tet(X) enzymes are concerning because they can inactivate even the newer glycylcyclines. Surveillance is ongoing (Thaker et al., 2010).

How newer tetracyclines overcome resistance

Agent	Overcomes Efflux	Overcomes Ribosomal Protection
Doxycycline	Partially	No
Minocycline	Partially	No
Tigecycline	Yes	Yes
Eravacycline	Yes	Yes
Omadacycline	Yes	Yes

Key structural modifications:

• C-9 glycylamido group (tigecycline)
• Enhanced ribosomal binding affinity
• Steric hindrance prevents efflux pump recognition

The glycylcycline structure was specifically designed to evade common resistance mechanisms. However, Tet(X) can still inactivate some of these (Bergeron et al., 1996).

Newer Tetracycline Derivatives

Tigecycline (glycylcycline)

Key features:

• First glycylcycline (FDA approved 2005)
• IV only, 100 mg loading then 50 mg q12h
• Higher dose: 200 mg loading, then 100 mg daily (greater N&V)
• Broadest spectrum of tetracyclines

FDA-approved indications:

• Complicated skin/skin structure infections
• Complicated intra-abdominal infections
• Community-acquired bacterial pneumonia

FDA Black Box Warning

Increased mortality compared to other antibiotics in meta-analysis. Reserve for situations where alternatives are not suitable.

The mortality signal led to FDA warnings. Tigecycline should not be used for VAP or bacteremia due to low serum levels. Mortality difference was not seen with the higher dose (Babinchak et al., 2005; US Food and Drug Administration, 2010).

Tigecycline: Clinical considerations

Advantages:

• Active against MRSA, VRE, ESBL-producers
• Excellent tissue penetration (Vd = 7-10 L/kg)
• Good anaerobic coverage

Limitations:

• Low serum concentrations → avoid for bacteremia
• No Pseudomonas activity
• High rate of nausea/vomiting (30%)- can be reduced by splitting doses (activity AUC/MIC driven, N&V is peak related)
• Increased mortality signal

When to consider:

• MDR intra-abdominal infections
• MDR skin infections when oral options inadequate
• Not for VAP, bloodstream infections, or diabetic foot infections

The large volume of distribution means excellent tissue levels but inadequate serum concentrations for bacteremia (Babinchak et al., 2005; US Food and Drug Administration, 2010).

Eravacycline (fluorocycline)

Key features:

• Fluorocycline class (FDA approved 2018)
• IV only: 1 mg/kg q12h
• 2-4× more potent than tigecycline in vitro

FDA-approved indication:

• Complicated intra-abdominal infections

Advantages over tigecycline:

• More potent against Enterobacterales
• Similar spectrum but better MICs
• Better tolerability (less nausea)

Eravacycline was developed to improve on tigecycline’s limitations. It’s currently limited to cIAI (Solomkin et al., 2017; Solomkin et al., 2019).

Omadacycline (aminomethylcycline)

Key features:

• Aminomethylcycline class (FDA approved 2018)
• Both IV and oral formulations available
• Oral bioavailability: ~35%

FDA-approved indications:

• Community-acquired bacterial pneumonia
• Acute bacterial skin and skin structure infections

Clinical pearl

Omadacycline is the only newer tetracycline with oral availability - allows IV-to-oral switch!

The oral formulation is a major advantage. Loading dose of 450 mg day 1, then 300 mg daily (O’Riordan et al., 2019).

Omadacycline: Clinical use

Dosing:

Indication	Loading	Maintenance
CABP	200 mg IV or 300 mg PO × 2	100 mg IV or 300 mg PO daily
ABSSSI	200 mg IV or 450 mg PO	100 mg IV or 300 mg PO daily

Key advantages:

• Oral option for serious infections
• Activity against MRSA, atypicals
• Better tolerability than tigecycline
• No food effect on absorption (take on empty stomach)

The ability to complete therapy orally makes omadacycline practical for outpatient treatment or early discharge (Stets et al., 2019).

Sarecycline (Narrow-Spectrum)

Unique positioning:

• FDA approved 2018 for acne vulgaris only
• Specifically designed narrow spectrum
• Less impact on gut flora than other tetracyclines
• Weight-based dosing (60-150 mg once daily)

Not indicated for infections!

• Lower activity against typical respiratory pathogens
• Designed to target Cutibacterium acnes

Sarecycline represents a deliberate narrow-spectrum approach to minimize collateral damage and resistance selection (Moffa and Brook, 2024).

Comparing newer tetracyclines

Feature	Tigecycline	Eravacycline	Omadacycline
Route	IV only	IV only	IV and PO
Approved uses	cSSSI, cIAI, CABP	cIAI	CABP, ABSSSI
Pseudomonas	No	No	No
Black box warning	Yes (mortality)	No	No
Dosing frequency	q12h	q12h	Daily
Main limitation	Low serum levels	Limited indications	Cost

Selection depends on indication, need for oral therapy, and patient-specific factors (Moffa and Brook, 2024).

Chloramphenicol

Historical context & mechanism

History:

• Discovered 1947 from Streptomyces venezuelae
• First antibiotic to be manufactured synthetically (1949)
• Fell from favor due to aplastic anemia

Mechanism:

• Binds 50S ribosomal subunit (NOT 30S like tetracyclines)
• Inhibits peptidyl transferase activity
• Prevents peptide bond formation
• Bacteriostatic (bactericidal against some organisms)

Chloramphenicol’s toxicity limited its use in developed countries, but it remains important in resource-limited settings (Bennett et al., 2024).

Chloramphenicol: Spectrum & Uses

Broad spectrum coverage:

• Gram-positives (including many resistant organisms)
• Gram-negatives (including H. influenzae, N. meningitidis)
• Anaerobes
• Rickettsiae, spirochetes

Current uses:

• Rickettsial infections (when doxycycline contraindicated)
• Bacterial meningitis (resource-limited settings)
• Ophthalmic infections (topical)
• Alternative for serious infections in beta-lactam allergy

Oral chloramphenicol is still available for travelers to areas with limited alternatives (Bennett et al., 2024).

Chloramphenicol: Toxicity

Critical Toxicity

Aplastic anemia - idiosyncratic, not dose-related, often fatal (1 in 20,000-40,000)

Types of bone marrow toxicity:

Type	Mechanism	Reversibility	Risk
Dose-related suppression	Mitochondrial inhibition	Reversible	Common
Aplastic anemia	Idiosyncratic	Usually fatal	Rare (1:20,000-40,000)

Other toxicities:

• Gray baby syndrome: Cardiovascular collapse in neonates
  • Due to immature glucuronidation
  • Abdominal distension, cyanosis, shock
• Optic neuritis (prolonged use)

The risk of aplastic anemia, though rare, is the main reason chloramphenicol fell from widespread use in developed countries (Bennett et al., 2024).

Practical Prescribing

Tetracycline selection algorithm

This simple algorithm covers most clinical scenarios. Doxycycline is the most versatile choice.RMSF: Rocky mountain spotted fever

Available formulations

Drug	Formulations	Standard Dose
Doxycycline	PO (tabs, caps, syrup), IV	100 mg q12h
Minocycline	PO, IV, topical	100 mg q12h
Tigecycline	IV only	50 mg q12h (after 100 mg load)
Eravacycline	IV only	1 mg/kg q12h
Omadacycline	PO, IV	300 mg PO or 100 mg IV daily
Sarecycline	PO only	60-150 mg daily (weight-based)

Omadacycline’s dual formulation makes it unique among the newer agents.

Key counseling points

For all tetracyclines:

1. Avoid dairy and antacids (separate by 2-3 hours)
2. Take with full glass of water, stay upright 30 minutes
3. Use sun protection (especially doxycycline)
4. Complete full course even if feeling better

For specific agents:

• Minocycline: Report dizziness, skin discoloration
• Doxycycline: Can take with food if nauseated
• Tetracycline: Must take on empty stomach

Effective counseling improves adherence and reduces adverse effects.

Summary

Key Takeaways (Part 1)

1. Mechanism: Tetracyclines bind 30S ribosome, block protein synthesis (bacteriostatic)- activity is AUC/MIC driven, N&V with IV formulations is related to peak serum levels
2. Doxycycline is the workhorse: Best oral bioavailability, can take with food, safe in renal impairment
3. First-line for tick-borne diseases: Start empirically for suspected Rocky Mountain Spotted Fever - don’t wait for confirmation
4. Important for STIs: Chlamydia, syphilis (alternative), growing role in Doxy-PEP

Key Takeaways (Part 2)

5. Drug interactions are critical: Cations reduce absorption 50-90%, warfarin effect increased
6. Avoid in pregnancy/children <8: Dental staining and bone effects
7. Newer agents expand options: Tigecycline, eravacycline, omadacycline overcome resistance
8. Tigecycline limitations: Not for bacteremia, black box mortality warning

Clinical decision making

Bottom Line

Doxycycline remains the most versatile tetracycline for clinical practice, with excellent oral bioavailability, broad spectrum, and unique indications for atypicals and tick-borne diseases. Reserve newer agents for MDR infections or when oral therapy with omadacycline is preferred.

Appendix: Reference Tables

Spectrum of Activity Summary

Organism	TET	DOX	MIN	TIG	ERA	OMA
MSSA	S	S	S	S	S	S
MRSA	V	V	V	S	S	S
VRE	R	R	R	S	S	S
S. pneumoniae	V	V	V	S	S	S
Atypicals	S	S	S	S	S	S
Enterobacterales	V	V	V	S	S	V
P. aeruginosa	R	R	R	R	R	R
Anaerobes	V	V	V	S	S	V

S = susceptible, V = variable, R = resistant

MIC Reference Values

Organism	Doxycycline	Tigecycline
S. aureus (MSSA)	≤0.25	≤0.12
S. pneumoniae	≤1	≤0.06
E. coli	≤4	≤0.5
K. pneumoniae	≤4	≤1
Bacteroides fragilis	≤4	≤4

Values in μg/mL; breakpoints per CLSI

Dosing Quick Reference

Indication	Agent	Dose	Duration
CAP	Doxycycline	100 mg BID	5-7 days
Chlamydia	Doxycycline	100 mg BID	7 days
Lyme (early)	Doxycycline	100 mg BID	10-14 days
RMSF	Doxycycline	100 mg BID	5-7 days
MRSA SSTI	Doxycycline	100 mg BID	5-10 days
Malaria prophylaxis	Doxycycline	100 mg daily	Duration of exposure + 4 weeks
cIAI	Tigecycline	50 mg q12h*	5-14 days
CABP	Omadacycline	300 mg PO daily**	5-7 days

*After 100 mg loading dose; **After 300 mg × 2 loading

References

Babinchak T, Ellis-Grosse E, Dartois N, Rose GM, Loh E. The efficacy and safety of tigecycline for the treatment of complicated intra-abdominal infections: Analysis of pooled clinical trial data. Clinical Infectious Diseases 2005;41:S354–67. https://doi.org/10.1086/431676.

Bennett JE, Dolin R, Blaser MJ. Mandell, douglas, and bennett’s principles and practice of infectious diseases. 9th ed. Elsevier; 2024.

Bergeron J, Ammirati M, Danley D, et al. Glycylcyclines bind to the high-affinity tetracycline ribosomal binding site and evade tet(m)- and tet(o)-mediated ribosomal protection. Antimicrobial Agents and Chemotherapy 1996;40:2226–8.

Centers for Disease Control and Prevention. Guidelines for treatment of malaria in the united states 2023.

Centers for Disease Control and Prevention. Sexually transmitted infections treatment guidelines, 2021. MMWR Recommendations and Reports 2021;70:1–187.

Chopra I, Roberts MC. Tetracycline antibiotics: Mode of action, applications, molecular biology, and epidemiology of bacterial resistance. Microbiology and Molecular Biology Reviews 2001;65:232–60. https://doi.org/10.1128/MMBR.65.2.232-260.2001.

Cunha BA, Domenico P, Cunha CB. Pharmacodynamics of doxycycline. Clinical Microbiology and Infection 2000;6:270–3.

Dahl EL, Shock JL, Shenai BR, Gut J, DeRisi JL, Rosenthal PJ. Tetracyclines specifically target the apicoplast of the malaria parasite Plasmodium falciparum. Antimicrobial Agents and Chemotherapy 2006;50:3124–31. https://doi.org/10.1128/AAC.00394-06.

Diekema DJ, Pfaller MA, Schmitz FJ, et al. Survey of infections due to Staphylococcus species: Frequency of occurrence and antimicrobial susceptibility of isolates collected in the united states, canada, latin america, europe, and the western pacific region for the SENTRY antimicrobial surveillance program, 1997-1999. Clinical Infectious Diseases 2001;32:S114–32.

Duggar BM. Aureomycin: A product of the continuing search for new antibiotics. Annals of the New York Academy of Sciences 1948;51:177–81.

Forrest JN, Cox M, Hong C, Morrison G, Bia M, Singer I. Superiority of demeclocycline over lithium in the treatment of chronic syndrome of inappropriate secretion of antidiuretic hormone. New England Journal of Medicine 1978;298:173–7.

Garner SE, Eady A, Bennett C, Newton JN, Thomas K, Popescu CM. Minocycline for acne vulgaris: Efficacy and safety. Cochrane Database of Systematic Reviews 2012:CD002086.

Lantos PM, Rumbaugh J, Bockenstedt LK, et al. Clinical practice guidelines by the Infectious Diseases Society of America (IDSA), American Academy of Neurology (AAN), and American College of Rheumatology (ACR): 2020 guidelines for the prevention, diagnosis, and treatment of lyme disease. Clinical Infectious Diseases 2021;72:e1–48. https://doi.org/10.1093/cid/ciaa1215.

Luetkemeyer AF, Donnell D, Dombrowski JC, et al. Postexposure doxycycline to prevent bacterial sexually transmitted infections. New England Journal of Medicine 2023;388:1296–306. https://doi.org/10.1056/NEJMoa2211934.

Metlay JP, Waterer GW, Long AC, et al. Diagnosis and treatment of adults with community-acquired pneumonia: An official clinical practice guideline of the American Thoracic Society and Infectious Diseases Society of America. American Journal of Respiratory and Critical Care Medicine 2019;200:e45–67. https://doi.org/10.1164/rccm.201908-1581ST.

Moffa M, Brook I. Tetracyclines, tetracycline derivatives, and chloramphenicol 2024.

Nelson ML, Dinardo A, Hochberg J, Armelagos GJ. Brief communication: Mass spectroscopic characterization of tetracycline in the skeletal remains of an ancient population from Sudanese Nubia 350-550 CE. American Journal of Physical Anthropology 2010;143:151–4. https://doi.org/10.1002/ajpa.21340.

O’Riordan W, Green S, Overcash JS, et al. Omadacycline for acute bacterial skin and skin-structure infections. New England Journal of Medicine 2019;380:528–38. https://doi.org/10.1056/NEJMoa1800170.

Roberts MC. Update on acquired tetracycline resistance genes. FEMS Microbiology Letters 2005;245:195–203. https://doi.org/10.1016/j.femsle.2005.03.034.

Ruhe JJ, Menon A. Tetracyclines as an oral treatment option for patients with community onset skin and soft tissue infections caused by methicillin-resistant Staphylococcus aureus. Antimicrobial Agents and Chemotherapy 2007;51:3298–303.

Schnappinger D, Hillen W. Tetracyclines: Antibiotic action, uptake, and resistance mechanisms. Archives of Microbiology 1996;165:359–69.

Smith K, Leyden JJ. Safety of doxycycline and minocycline: A systematic review. Clinical Therapeutics 2005;27:1329–42.

Solomkin J, Evans D, Slepavicius A, et al. Assessing the efficacy and safety of eravacycline vs ertapenem in complicated intra-abdominal infections in the IGNITE1 trial: A randomized clinical trial. JAMA Surgery 2017;152:224–32. https://doi.org/10.1001/jamasurg.2016.4237.

Solomkin JS, Gardovskis J, Lawrence K, et al. IGNITE4: Results of a phase 3, randomized, multicenter, prospective trial of eravacycline vs meropenem in the treatment of complicated intra-abdominal infections. Clinical Infectious Diseases 2019;69:921–9.

Stets R, Popescu M, Gong S, et al. Omadacycline for community-acquired bacterial pneumonia. New England Journal of Medicine 2019;380:517–27. https://doi.org/10.1056/NEJMoa1800201.

Thaker M, Spanogiannopoulos P, Wright GD. The tetracycline resistome. Cellular and Molecular Life Sciences 2010;67:419–31. https://doi.org/10.1007/s00018-009-0172-6.

US Food and Drug Administration. FDA drug safety communication: Increased risk of death with Tygacil (tigecycline) compared to other antibiotics used to treat similar infections 2010.