ID

🦠 1. The Body’s Defenses

Your body has “defense systems” against germs:

  • Skin & mucous membranes = walls and shields.

  • White blood cells (WBCs) = soldiers that attack invaders.

  • Antibodies = smart weapons that remember past enemies.

  • Spleen & lymph nodes = headquarters where soldiers train and fight.

👉 If someone doesn’t have a spleen, they’re more at risk for certain “armored” bacteria (like Strep pneumo).

🔍 2. How Do We Know Someone Has an Infection?

Doctors check for:

  • Symptoms: pain, swelling, pus, burning with urination, cough.

  • Fever: usually above 100.4°F.

  • Lab tests:

    • WBC count (normal = 4,500–11,000).

      • High = infection.

      • Low = weak immune system.

    • ESR/CRP = markers of inflammation (like smoke detectors).

    • Procalcitonin (PCT) = more specific for bacterial infection.

🧪 3. Figuring Out the Bug

Doctors collect samples → blood, urine, sputum, wound pus.

  • Gram stain: quick test, shows if bacteria are Gram+ (purple) or Gram– (pink).

  • Culture: grow the bug in the lab → takes days, tells exactly which antibiotic works.

  • MIC (Minimum Inhibitory Concentration): lowest dose of a drug that stops the bacteria from growing.

👉 S = sensitive (drug works), R = resistant (drug won’t work), I = in-between.

💊 4. Picking the Right Antibiotic

Doctors think of Host, Bug, Drug:

  • Host (patient): allergies, kidney function, immune system strength.

  • Bug (germ): what bacteria is causing the infection?

  • Drug (antibiotic): does it reach the infection site? Is it strong enough?

3 stages of treatment:

  1. Prophylaxis = prevent infection (like before surgery).

  2. Empiric therapy = best guess based on symptoms & common germs.

  3. Definitive therapy = switch to targeted drug once cultures come back.

⚔ 5. Static vs Cidal Drugs

  • Bacteriostatic = freeze bacteria (stop growth, immune system finishes the job).

  • Bactericidal = kill bacteria directly.

👉 Cidal drugs are better for really sick patients or hard-to-reach infections (like brain or bone).

📈 6. Drug Action (Pharmacodynamics)

Two main styles:

  • Time-dependent killers: work best if drug levels stay above MIC for most of the time.

    • Examples: Beta-lactams (penicillins, cephalosporins).

  • Concentration-dependent killers: stronger the peak, the better.

    • Examples: Aminoglycosides, Quinolones.

Post-Antibiotic Effect (PAE): Some drugs keep working even after the levels drop (like a “shadow punch”).

🧭 7. Monitoring Treatment

Doctors watch for:

  • Improvement: fever goes down, WBCs normalize, less pain.

  • Failure: wrong drug, resistant bug, weak immune system.

  • Toxicity: side effects (rash, diarrhea, kidney damage, C. diff infection).

🦠 8. Common Bacteria (The “Players”)

Gram Positive

  • Staph aureus: skin infections, abscesses, can be MRSA.

  • Strep pyogenes: strep throat, skin infections.

  • Strep pneumoniae: pneumonia, meningitis, ear infections.

  • Enterococcus: UTIs, gut infections, some resistant (VRE).

Gram Negative

  • E. coli, Klebsiella, Proteus: UTIs, belly infections.

  • H. influenzae, Moraxella: respiratory infections.

  • Pseudomonas: hospital bug, pneumonia, UTIs, wound infections.

Atypicals

  • Mycoplasma, Chlamydia, Legionella → don’t have normal walls, need special drugs.

Anaerobes

  • Bacteroides, Clostridium → gut infections, abscesses, C. diff colitis.

🧩 9. Case Example

👵 A 72-year-old woman has burning when she pees, WBC is high, no fever.

  • Probably a UTI.

  • Next steps: urine culture, choose empiric antibiotic, adjust once results return.

💊 What are Beta-Lactams?

  • A huge family of antibiotics (medicines that kill bacteria).

  • Includes:

    • Penicillins

    • Cephalosporins

    • Carbapenems

    • Monobactams

They are some of the most used antibiotics in the world.

⚙ How They Work (Mechanism)

  • Bacteria have a cell wall that keeps them alive (like armor).

  • Beta-lactams break the wall-building machine (PBPs).

  • If the wall can’t be built → the bacteria burst and die.

  • That’s why they are bactericidal (kill, not just slow down).

🛡 How Bacteria Fight Back (Resistance)

Bacteria can survive by:

  1. Making scissors (β-lactamases) that cut the drug.

  2. Changing the lock (PBPs) so the drug can’t fit.

  3. Blocking the door (closing porins or pushing drug out).

⚠ Side Effects

  • Most common: allergic reaction (rash, itching, sometimes serious).

  • Stomach upset (nausea, vomiting, diarrhea).

  • Rare but serious:

    • Kidney problems

    • Low blood counts

    • Seizures (if too much drug builds up).

🚨 Penicillin Allergy

  • About 10% of people say they’re allergic, but most aren’t.

  • Serious reaction (anaphylaxis) is very rare (<0.05%).

  • Some related drugs are usually still safe (tiny chance of cross-reaction).

📊 The Beta-Lactam Families

🟢 Penicillins

  • First discovered, oldest antibiotics.

  • Different types:

    • Natural penicillin (Penicillin G, VK): strep throat, syphilis.

    • Aminopenicillins (Amoxicillin, Ampicillin): ear infections, strep throat, UTIs.

    • Antistaph penicillins (Nafcillin, Oxacillin): kill Staph (MSSA).

    • Antipseudomonal (Piperacillin): strong drug for hospital infections, usually mixed with a helper.

    • Penicillin + helper (β-lactamase inhibitor):

      • Augmentin (Amox + Clav): sinus/ear infections, bite wounds.

      • Zosyn (Pip + Tazo): very sick patients (pneumonia, belly infections).

🔵 Cephalosporins (5 generations = like 5 “eras”)

  • 1st Gen: Keflex, Ancef → skin infections, surgery prevention.

  • 2nd Gen: Ceftin, Cefaclor, Cefoxitin → ear infections, strep throat, belly surgery.

  • 3rd Gen: Rocephin, Omnicef → pneumonia, meningitis, gonorrhea, UTIs.

  • 4th Gen: Cefepime → very sick patients, hospital infections.

  • 5th Gen: Ceftaroline → special, only one that kills MRSA.

⚡ Remember: None fight atypical bacteria (like Mycoplasma).

🔴 Carbapenems

  • SUPER strong antibiotics.

  • Kill almost everything: Gram+ bacteria, Gram– bacteria, anaerobes.

  • Used when bacteria are resistant to other drugs.

  • Examples: Imipenem, Meropenem, Ertapenem.

  • ⚠ Imipenem may cause seizures.

🟠 Monobactam

  • Aztreonam.

  • Works only on Gram– bacteria (including Pseudomonas).

  • Safe in penicillin allergy.

📌 Quick Pearls

  • All kill by breaking the wall.

  • All can cause allergy.

  • All need kidney dose adjustments.

  • None fight atypicals (like Chlamydia, Mycoplasma, Legionella).

🌀 Fluoroquinolones (FQ)

Examples:

  • Ciprofloxacin (Cipro)

  • Levofloxacin (Levaquin)

  • Moxifloxacin (Avelox)

  • Delafloxacin (Baxdela)

How they work (MOA):
They mess up bacterial DNA by blocking DNA gyrase & topoisomerase → bacteria can’t copy themselves → they die.

  • Bactericidal = they kill, not just freeze.

  • Concentration-dependent = need a big punch (high peak).

Special features:

  • Taken by mouth and absorbed super well (almost like IV).

  • Spread into almost all tissues.

  • Dose adjustment in kidney problems (except moxi).

Downside: lots of safety problems ⚠

🚨 Side Effects (FDA Warnings)

  • Tendons can snap (especially >60 yrs or on steroids).

  • Brain effects: confusion, dizziness, hallucinations.

  • Nerve damage (tingling, numbness).

  • Muscle weakness in myasthenia gravis.

  • Heart risks: QT prolongation, aortic problems.

  • Other: stomach upset, insomnia, sugar swings, C. diff infection, photosensitivity.

👉 FDA says: don’t use for simple infections if other options exist.

🔗 Drug Interactions

  • Cipro blocks CYP1A2 → ↑ levels of theophylline, warfarin.

  • Don’t take with calcium, magnesium, iron, milk, antacids, multivitamins → they block absorption.

  • If you must, separate by 2+ hours.

🦠 Spectrum

  • Cipro: Strong for Gram-negative rods + Pseudomonas, some atypicals. Bad for Strep.

  • Levo: Better at Strep (respiratory), also Gram– and atypicals, covers Pseudomonas.

  • Moxi: Like Levo but no Pseudomonas, adds anaerobes.

  • Dela: Covers almost everything, including MRSA + Pseudomonas + anaerobes.

🩺 Uses

  • Pneumonia (Levo, Moxi, Dela).

  • UTIs (Cipro, Levo).

  • Skin infections (Levo, Moxi, Dela).

  • Intra-abdominal (Cipro/Levo + anaerobe coverage, or Moxi alone).

  • Eye infections (topical drops).

  • Avoid unless necessary!

🎯 Aminoglycosides

Examples: Gentamicin, Tobramycin, Amikacin, Streptomycin, Neomycin.

MOA: Bind the 30S ribosome, cause misreading → broken proteins → bacteria die.

  • Cidal, concentration-dependent.

  • Work even better with beta-lactams (synergy).

Side Effects:

  • Kidney damage (reversible).

  • Hearing loss (sometimes permanent).

  • Monitor drug levels carefully!

Uses:

  • Serious Gram– infections.

  • Often hospital-only (IV).

  • Neomycin = topical (like skin, eye, ear).

🎯 Macrolides

Examples: Azithromycin (Z-Pak), Clarithromycin, Erythromycin.

MOA: Block the 50S ribosome, stopping protein chain growth.

  • Usually static (freeze bacteria).

Spectrum:

  • Respiratory bugs (Strep pneumo, H. flu, M. catarrhalis).

  • Atypicals (Mycoplasma, Chlamydia, Legionella).

  • Some STIs, H. pylori.

Side Effects:

  • GI upset (worst with erythro).

  • QT prolongation (heart risk).

  • Clarithro = metallic taste, liver issues.

Uses:

  • Respiratory infections (pneumonia, bronchitis).

  • Strep throat, ear infections.

  • Some STIs.

  • H. pylori (with other drugs).

🎯 Clindamycin

MOA: Stops protein synthesis (50S ribosome).

Spectrum:

  • Gram+ (Staph, Strep, MRSA).

  • Anaerobes.

  • Suppresses toxin production.

Side Effects:

  • High risk of C. diff diarrhea!

  • Metallic taste, rash.

Uses:

  • Skin infections, acne (topical).

  • Oral/IV for resistant Gram+.

🎯 Tetracyclines

Examples: Doxycycline, Minocycline, Tetracycline, Tigecycline.

MOA: Block 30S ribosome, stop protein synthesis.

Spectrum:

  • Atypicals, MRSA, tick diseases (Lyme, RMSF), H. pylori, acne bugs.

Side Effects:

  • Tooth discoloration (avoid <8 yrs).

  • Photosensitivity.

  • GI upset.

  • Don’t take with dairy, calcium, magnesium, iron.

Uses:

  • Pneumonia (outpatient).

  • Chlamydia STI.

  • Tick diseases.

  • Acne.

🎯 TMP/SMX (Bactrim)

MOA: Blocks folic acid pathway (bacteria can’t make DNA).

Spectrum:

  • Gram– rods (not Pseudomonas).

  • MRSA.

  • Pneumocystis (PCP).

Side Effects:

  • Rash (can be severe SJS).

  • High potassium.

  • Crystals in urine.

  • ↑ INR with warfarin.

Uses:

  • UTIs.

  • Skin infections (MRSA).

  • PCP pneumonia in HIV.

🎯 Nitrofurantoin

MOA: Makes radicals that destroy DNA.

Spectrum: Mostly E. coli, Enterococcus (urine only).

Side Effects:

  • Not for kidney failure (CrCl <30).

  • Headache, dizziness.

Uses:

  • Uncomplicated UTI only.

🎯 Metronidazole (Flagyl)

MOA: Damages DNA.

Spectrum:

  • Anaerobes (Bacteroides, C. diff).

  • Protozoa (Trichomonas).

  • H. pylori.

Side Effects:

  • Metallic taste, nausea.

  • Neuropathy (long-term).

  • Red-brown urine.

  • Don’t drink alcohol (disulfiram-like reaction).

Uses:

  • C. diff.

  • Trichomoniasis.

  • Intra-abdominal infections (anaerobes).

🎯 Rifampin

MOA: Blocks RNA polymerase.

Spectrum:

  • Gram+ (Staph, Strep, MRSA).

  • Mycobacteria (TB).

Side Effects:

  • Red-orange fluids (urine, sweat, tears).

  • Liver damage.

  • Many drug interactions (induces CYPs).

Uses:

  • TB.

  • Add-on for MRSA infections with prosthetics.

🎯 Vancomycin (Glycopeptide)

MOA: Blocks cell wall (different site than beta-lactams).

Spectrum:

  • Gram+ only (MRSA, Strep, Enterococcus).

  • C. diff (oral only).

Side Effects:

  • Kidney damage.

  • Ototoxicity.

  • “Red Man Syndrome” if infused too fast.

Uses:

  • MRSA infections.

  • C. diff (oral).

🎯 Lipoglycopeptides (Daptomycin, Dalbavancin, Oritavancin)

  • Like vancomycin, but longer-acting.

  • Dapto: Not for pneumonia (inactivated in lungs).

  • Side effects: muscle breakdown (check CK).

  • Uses: MRSA, skin infections.

🎯 Linezolid (Oxazolidinone)

MOA: Blocks 50S ribosome → no initiation complex.

Spectrum: MRSA, VRE.

Side Effects:

  • Low platelets.

  • Neuropathy if long use.

  • Serotonin syndrome with SSRIs.

Uses:

  • Resistant Gram+ infections.

📌 Super-Simple Summary

  • FQs = DNA killers, strong but dangerous, avoid unless needed.

  • Aminoglycosides = protein killers, toxic to kidney/ear.

  • Macrolides = protein blockers, good for respiratory bugs.

  • Clinda = MRSA + anaerobes, high C. diff risk.

  • Tetracyclines = MRSA, atypicals, ticks, no kids.

  • TMP/SMX = MRSA, UTIs, PCP.

  • Nitrofurantoin = UTI only.

  • Metronidazole = anaerobes, parasites, no alcohol.

  • Rifampin = TB, red fluids, drug interactions.

  • Vanco = MRSA, C. diff (oral).

  • Linezolid = MRSA, VRE, serotonin issues.