More On Antibiotics: Antibiotic Classes – Comprehensive Review Notes

1. Penicillins (-cillin)

Examples: Penicillin, Amoxicillin
Targets: Primarily Gram-positive, some Gram-negative (broad-spectrum types)
Mechanism: Inhibits bacterial cell wall synthesis → bactericidal
Treats: Strep throat, syphilis, ear infections

Key Points (PCNS):

• P: Penicillin allergy common → rash, hives, anaphylaxis

• C: Cross-sensitivity with cephalosporins

• N: Nausea → take with food if GI upset

• S: Superinfection (C. diff, oral/vaginal yeast)

2. Cephalosporins (Cef-/Ceph-)

Examples: Ceftriaxone, Cephalexin
Targets: Broad-spectrum → Gram+ (early gens), Gram– (later gens)
Mechanism: Inhibits cell wall synthesis → bactericidal
Treats: Pneumonia, UTI, skin infections, meningitis, surgical prophylaxis

Key Points (CEPHAL):

• C: Creatinine/BUN – nephrotoxic

• E: Ethanol intolerance → disulfiram-like reaction

• P: Pseudomembranous colitis (C. diff)

• H: Hypersensitivity (cross with penicillin)

• A: Administration → IV (phlebitis) / IM (large muscle)

• L: Lower prothrombin → monitor PT/INR

3. Aminoglycosides (-mycin / -micin)

Examples: Gentamicin, Tobramycin, Neomycin
Targets: Gram-negative (sepsis, respiratory, intra-abdominal infections)
Mechanism: Inhibits 30S ribosomal subunit → bactericidal
Route: IV or IM (Neomycin oral for gut decontamination or hepatic encephalopathy)

Key Points (AMINO):

• A: Assess peak & trough (narrow therapeutic range)

• M: Monitor kidneys → nephrotoxic

• N: Neuromuscular blockade (esp. in myasthenia gravis)

• O: Ototoxicity (hearing loss, tinnitus, vertigo)

4. Fluoroquinolones (-floxacin)

Examples: Ciprofloxacin, Levofloxacin
Targets: Broad → Gram– and some Gram+
Mechanism: Inhibits DNA gyrase & topoisomerase IV → bactericidal
Treats: UTI, respiratory, GI, skin infections

Key Points (FLOCKIN):

• F: Fluids to prevent crystalluria

• L: Long QT interval → monitor ECG

• O: Older adults → Achilles tendon rupture risk

• C: Calcium/antacids/iron ↓ absorption

• K: Kids & pregnancy → contraindicated

• I: Increased sun sensitivity

• N: Neuro effects (dizziness, confusion)

5. Macrolides (-thromycin)

Examples: Azithromycin, Erythromycin, Clarithromycin
Targets: Mainly Gram+, some Gram–
Mechanism: Inhibits 50S ribosomal subunit → bacteriostatic
Treats: Respiratory infections, STIs (Chlamydia), H. pylori, ear infections

Key Points (LIDES):

• L: Liver toxicity → monitor LFTs

• I: Increased QT interval

• D: Drug interactions (CYP450 inhibitors → ↑ warfarin, statins, theophylline toxicity)

• E: Eat with food if GI upset

• S: Superinfection (C. diff, thrush, yeast)

6. Sulfonamides (Sulfa-)

Examples: Sulfamethoxazole + Trimethoprim (Bactrim), Sulfadiazine
Targets: Broad → Gram+, Gram–, some protozoa
Mechanism: Inhibits folic acid synthesis → bacteriostatic
Treats: UTI, MRSA, toxoplasmosis, bowel/ear/lung infections

Key Points (SULFA):

• S: Sensitivity → allergy, Stevens-Johnson syndrome

• U: Use sunscreen → photosensitivity

• L: Liver toxicity → monitor LFTs

• F: Folic acid blocked → avoid in pregnancy (1st & 3rd trimesters) & folate deficiency

• A: Adequate fluids → prevent crystalluria

Extra: ↑ effects of warfarin, phenytoin, sulfonylureas → monitor INR & glucose

7. Tetracyclines (-cycline)

Examples: Doxycycline, Tetracycline
Targets: Broad (Gram+, Gram–, protozoa)
Mechanism: Inhibits 30S ribosomal subunit → bacteriostatic
Treats: Acne, chlamydia, syphilis, Lyme, Rocky Mountain spotted fever, malaria prevention

Key Points (TETRA):

• T: Teratogenic → avoid in pregnancy & kids <8 yrs (tooth discoloration, bone growth delay)

• E: Empty stomach with water (no dairy/antacids/iron)

• T: Take upright → esophagitis risk

• R: Risk of photosensitivity

• A: Avoid under 8 years → affects bone/teeth

8. Glycopeptides (no prefix/suffix)

Example: Vancomycin
Targets: Gram+ (MRSA, C. diff, pneumonia, endocarditis)
Mechanism: Inhibits cell wall synthesis → bactericidal

Key Points (VANCO):

• V: Very toxic → narrow range; trough before 4th dose (10–20 µg/mL)

• A: Administer slowly (>60 mins) → prevent Red Man Syndrome

• N: Nephrotoxic → monitor BUN, creatinine

• C: C. diff → oral route

• O: Ototoxic → hearing loss, tinnitus, vertigo

9. Carbapenems (-penem)

Examples: Imipenem, Meropenem
Targets: Very broad (Gram+, Gram–, anaerobes, ESBL)
Mechanism: Inhibits cell wall synthesis → bactericidal
Treats: Serious resistant infections (final-line use)

Key Points (FINAL):

• F: For resistant infections

• I: IV/IM only

• N: Neuro risk → seizures (esp. with imipenem)

• A: Allergy potential (cross with penicillins/cephalosporins)

• L: Labs → monitor renal function

10. Lincosamides (no common suffix)

Example: Clindamycin
Targets: Gram+, anaerobes
Mechanism: Inhibits 50S subunit → bacteriostatic or bactericidal (dose-dependent)
Treats: MRSA skin, dental infections

Key Points (LINCO):

• L: Liver toxicity (monitor LFTs)

• I: IV, PO, topical; take with full glass of water

• N: Nausea → take with food if needed

• C: C. diff risk (major concern)

• O: Option for penicillin-allergic patients

11. Oxazolidinones (-zolid)

Examples: Linezolid, Tedizolid
Targets: Gram+ (MRSA, VRE)
Mechanism: Inhibits 50S subunit → bacteriostatic
Treats: Complicated skin, blood, lung infections

Key Points (ZOLID):

• Z: Zaps bone marrow → myelosuppression (↓ WBC, RBC, PLT)

• O: Oral = IV dose (great bioavailability)

• L: Long use → neuropathy (peripheral, optic)

• I: Interacts with serotonin drugs → serotonin syndrome

• D: Diet → avoid tyramine foods (aged cheese, cured meats)

12. Nitroimidazoles (-dazole)

Example: Metronidazole
Targets: Anaerobes (Gram–, Gram+), protozoa
Mechanism: Damages DNA → bactericidal
Treats: C. diff, trichomoniasis, giardiasis

Key Points (DAZOLE):

• D: Disulfiram-like reaction → no alcohol (during & 3 days after)

• A: Avoid in 1st trimester; caution later

• Z: Zaps anaerobes & protozoa

• O: Oral, IV, topical, vaginal forms

• L: Leaves metallic taste, dark urine, GI upset; monitor for neuro effects (rare seizures, neuropathy)