What are the common antibiotics and their potential side effects?

Comprehensive List of Antibiotics and Their Side Effects

Antibiotics cause a spectrum of adverse effects ranging from mild gastrointestinal symptoms to life-threatening reactions, with approximately 150,000 unplanned medical visits annually in children alone for antibiotic-related adverse events. 1

Common Antibiotics by Class and Their Side Effects

Beta-Lactam Antibiotics (Penicillins)

Amoxicillin

• Gastrointestinal effects: Diarrhea (most common), nausea, vomiting, black hairy tongue, hemorrhagic/pseudomembranous colitis 2
• Dermatologic reactions: Rash (>1% incidence), pruritus, urticaria, erythema multiforme 2
• Severe cutaneous reactions: Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), drug reaction with eosinophilia and systemic symptoms (DRESS), acute generalized exanthematous pustulosis (AGEP) 2
• Hypersensitivity: Anaphylaxis/anaphylactoid reactions including shock, angioedema, serum sickness-like reactions, hypersensitivity vasculitis 2
• Hepatic: Moderate rise in AST/ALT, cholestatic jaundice, hepatic cholestasis, acute cytolytic hepatitis 2
• Hematologic: Anemia (including hemolytic), thrombocytopenia, thrombocytopenic purpura, eosinophilia, leukopenia, agranulocytosis (usually reversible) 2
• Renal: Crystalluria 2
• Central nervous system: Reversible hyperactivity, agitation, anxiety, insomnia, confusion, convulsions, behavioral changes, aseptic meningitis, dizziness 2
• Dental: Tooth discoloration (brown, yellow, or gray staining), particularly in pediatric patients 2
• Infectious complications: Mucocutaneous candidiasis, Clostridioides difficile-associated diarrhea (CDAD) 2

Amoxicillin-Clavulanate

• Gastrointestinal effects: Significantly higher rates of diarrhea and dermatitis compared to amoxicillin alone 1
• Adverse event rate: 44% in patients treated with high-dose amoxicillin-clavulanate versus 14% in placebo group for sinusitis, including rash, diarrhea, vomiting, and abdominal pain 1
• All other side effects: Similar to amoxicillin 2

Macrolide Antibiotics

Azithromycin

• Cardiac: Sudden death risk in adults, likely related to QT interval prolongation 1
• Severe cutaneous reactions: Stevens-Johnson syndrome, toxic epidermal necrolysis, pruritus, erythema multiforme 3
• Gastrointestinal effects: Diarrhea, nausea, vomiting, abdominal pain 1
• Note: Not first-line for any pediatric upper respiratory infection and most likely to be used inappropriately 1

Erythromycin

• Severe cutaneous reactions: Stevens-Johnson syndrome 3
• Gastrointestinal effects: Nausea, vomiting, abdominal cramping 3

Fluoroquinolones (Respiratory)

Levofloxacin

• Musculoskeletal: Tendon disorders including pain, swelling, inflammation, rupture (higher risk in patients >60 years, on corticosteroids, or with kidney/heart/lung transplants) 4
• Neurologic: Peripheral neuropathy (may be irreversible), including pain, burning, tingling, numbness, weakness; convulsions; dizziness; lightheadedness; increased intracranial pressure; persistent headache 4
• Cardiac: QT interval prolongation, heart palpitations, loss of consciousness 4
• Hypersensitivity: Skin rash, hives, rapid heartbeat, difficulty swallowing/breathing, angioedema (swelling of lips, tongue, face, throat tightness, hoarseness) 4
• Hepatotoxicity: Severe hepatotoxicity including acute hepatitis and fatal events; loss of appetite, nausea, vomiting, fever, weakness, tiredness, right upper quadrant tenderness, itching, jaundice, light-colored bowel movements, dark urine 4
• Gastrointestinal: Diarrhea (including C. difficile-associated diarrhea occurring up to 2+ months after treatment) 4
• Dermatologic: Photosensitivity/phototoxicity 4
• Neuromuscular: Exacerbation of myasthenia gravis, muscle weakness, respiratory difficulties 4
• Metabolic: Hypoglycemic reactions when used with insulin or oral hypoglycemic agents 4
• Hematologic: Increased INR/prothrombin time and bleeding episodes when used with warfarin 4
• Pediatric-specific: Musculoskeletal disorders, joint-related problems 4
• Renal: Crystal formation in urine if inadequate fluid intake 4

Moxifloxacin

• Similar adverse effects to levofloxacin including tendinopathy, QT prolongation, peripheral neuropathy 5
• FDA boxed warning: Against use for acute bacterial exacerbation of chronic bronchitis due to disabling and potentially permanent side effects affecting tendons, muscles, joints, peripheral neuropathy, and central nervous system effects 1

Tetracyclines

Doxycycline

• Gastrointestinal effects: Nausea, vomiting, diarrhea 1
• Dermatologic: Photosensitivity 1
• Dental: Tooth discoloration in children 1
• Bacterial failure rates: 20-25% for respiratory infections 5

Sulfonamides

Trimethoprim-Sulfamethoxazole (TMP-SMX)

• Severe cutaneous reactions: Crude relative risk of 172 for Stevens-Johnson syndrome and toxic epidermal necrolysis, particularly in HIV-positive patients 3
• Gastrointestinal effects: Nausea, vomiting, diarrhea 1
• Hematologic: Bone marrow suppression 1
• Bacterial failure rates: 20-25% for respiratory infections due to high resistance rates (50% for S. pneumoniae, 27% for H. influenzae) 1, 5

Lincosamides

Clindamycin

• Gastrointestinal: Clostridioides difficile colitis (significant risk) 1
• Limited coverage: Ineffective against Haemophilus influenzae 5

Cephalosporins (Third-Generation Oral)

Cefixime, Cefpodoxime, Cefdinir

• Clinical efficacy: 84-87% for respiratory infections 5
• Gastrointestinal effects: Diarrhea 5
• Cross-reactivity: May be used in non-Type I penicillin hypersensitivity reactions 5

Nitroimidazoles

Metronidazole

• Neurologic: Peripheral neuropathy, seizures 1
• Gastrointestinal: Metallic taste, nausea 1

Carbapenems

Meropenem

• Neurologic: Seizures (particularly in patients with renal impairment or CNS disorders) 1
• Gastrointestinal: Diarrhea, nausea 1

Penicillin/Beta-Lactamase Inhibitor Combinations

Piperacillin-Tazobactam

• Similar to other beta-lactams: Hypersensitivity reactions, rash, diarrhea 1
• Hematologic: Thrombocytopenia 1

Universal Antibiotic-Related Adverse Effects

Immediate and Short-Term Effects

• Hypersensitivity reactions: Range from mild rash to life-threatening anaphylaxis 1, 6
• Gastrointestinal disturbances: Diarrhea and rash occur in approximately 5% more patients receiving antibiotics versus placebo 1
• Drug fever: Beta-lactams and sulfonamides are most common causes among antimicrobials 6

Infectious Complications

• Clostridioides difficile colitis: Incidence has increased substantially in hospitalized children over the past decade; can occur up to 2+ months after antibiotic exposure 1, 4, 2
• Fungal superinfections: Mucocutaneous candidiasis, vaginal moniliasis 1, 2
• Resistant organism overgrowth: Secondary infections more difficult to treat 7

Long-Term and Systemic Effects

• Microbiome disruption: Growing evidence that early-life antibiotic exposures contribute to inflammatory bowel disease, obesity, eczema, and asthma 1, 8
• Antimicrobial resistance: Well-established relationship at individual patient and community levels; antibiotic-resistant infections associated with poor clinical outcomes 1, 7
• Enhanced pathogenicity: Molecular changes in organisms exposed to antibiotics may enhance virulence 7

Risk Stratification by Severity

Mild Adverse Effects (Common)

• Diarrhea, nausea, vomiting, abdominal pain, rash, headache 1

Moderate Adverse Effects (Less Common)

• Severe diarrhea, dermatitis, photosensitivity, drug interactions 1, 4

Severe Adverse Effects (Rare but Serious)

• Stevens-Johnson syndrome, toxic epidermal necrolysis, DRESS, AGEP 1, 3, 2
• Anaphylaxis 1, 2
• Tendon rupture (fluoroquinolones) 4
• Peripheral neuropathy (may be irreversible) 4

Life-Threatening Adverse Effects (Very Rare)

• Sudden cardiac death (azithromycin) 1
• Fatal hepatic necrosis 6
• Severe C. difficile colitis requiring colectomy 2

Special Population Considerations

Pediatric Patients

• Highest risk group: Antibiotics responsible for >150,000 unplanned medical visits annually for medication-related adverse events in children 1, 8
• Tooth discoloration: With amoxicillin and tetracyclines 2
• Long-term effects: Microbiome disruption potentially contributing to chronic diseases 1, 8
• Musculoskeletal effects: Particularly with fluoroquinolones 4

Elderly Patients (>60 years)

• Tendon disorders: Higher risk with fluoroquinolones, especially if on corticosteroids 4
• Dehydration risk: Greater susceptibility with diarrheal illnesses 1

Immunocompromised Patients

• C. difficile colitis: Greatest risk in hospitalized patients with comorbid conditions 1
• Opportunistic infections: Higher risk of fungal superinfections 2

Duration-Dependent Effects

• Shorter courses (5-7 days) versus longer courses (10 days): Adverse events reduced with shorter duration (odds ratio 0.79), with similar efficacy for most respiratory infections 1
• Single-dose regimens: Likely minimize risks of microbiome disruption, ESBL-PE acquisition, and C. difficile infection, though data are limited 1

Clinical Pitfalls to Avoid

• Prescribing for viral infections: Exposes patients to harm without benefit, particularly for nonspecific URI and common cold 1
• Inappropriate antibiotic selection: Azithromycin most likely to be used inappropriately with inadequate coverage for common pathogens 1
• Ignoring resistance patterns: Macrolide resistance >40% for S. pneumoniae in the United States; TMP-SMX resistance 50% for S. pneumoniae and 27% for H. influenzae 1
• Prolonged courses without indication: Increases adverse events without improving outcomes for most conditions 1
• Fluoroquinolone overuse: Should be reserved for patients with true allergies to first-line agents due to serious adverse effect profile 5