Summaries the whole ama in pharmacology for me with impt points

Reading File

Asking for Preferences

Finding Sources

Reading File

Finding Sources

Reading File

I now have comprehensive content across all major antimicrobial classes from Katzung's Basic and Clinical Pharmacology (16th ed). Let me synthesize the complete summary now.

Antimicrobial Agents (AMA) - Complete Pharmacology Summary

Based on Katzung's Basic and Clinical Pharmacology, 16th Edition

1. BETA-LACTAM ANTIBIOTICS

Mechanism of Action

All beta-lactams inhibit bacterial cell wall synthesis by binding to and irreversibly inhibiting penicillin-binding proteins (PBPs) - the transpeptidases responsible for crosslinking the peptidoglycan layer. The result is cell lysis and bactericidal activity.

Structure

All share a 4-membered beta-lactam ring
Hydrolysis of this ring by bacterial beta-lactamases yields penicilloic acid - which is inactive

A. Penicillins

Subgroup	Drugs	Key Uses
Natural penicillins	Penicillin G (IV/IM), Penicillin V (oral), Benzathine PCN (long-acting IM)	Streptococcal infections, neurosyphilis, meningococcal infections
Antistaphylococcal penicillins	Nafcillin, Oxacillin (IV); Cloxacillin, Dicloxacillin (oral)	MSSA infections; resistant to staphylococcal beta-lactamase; biliary clearance
Aminopenicillins	Ampicillin (IV/oral), Amoxicillin (oral - better absorbed)	Otitis media, respiratory tract infections, Enterococcus, Listeria, H. influenzae
Extended-spectrum	Piperacillin/Tazobactam (IV)	Gram-negatives incl. Pseudomonas aeruginosa, anaerobes
Beta-lactam + inhibitor combinations	Amoxicillin/Clavulanate, Ampicillin/Sulbactam, Piperacillin/Tazobactam	Restores activity against beta-lactamase-producing organisms

Key Adverse Effects of Penicillins:

Hypersensitivity (most serious) - ~5-8% of patients report allergy, but only a small number have true reactions
Anaphylaxis (<0.05% of courses) - most feared
Rash, serum sickness
CNS toxicity (seizures) at very high doses

Cross-reactivity: Amoxicillin rash in the past does NOT automatically preclude use of cephalosporins; skin testing can clarify true IgE-mediated allergy.

B. Cephalosporins

All share the same mechanism as penicillins. Organized by "generation" based on spectrum:

Generation	Examples	Gram+	Gram-	Key Bugs
1st	Cefazolin (IV), Cephalexin (oral)	Excellent	Limited	Staph/Strep, surgical prophylaxis, UTIs
2nd	Cefuroxime, Cefoxitin, Cefaclor	Good	Moderate	H. influenzae, Moraxella, anaerobes (cefoxitin - Bacteroides)
3rd	Ceftriaxone, Cefotaxime, Ceftazidime	Moderate	Excellent	CNS infections (meningitis), gram-negative sepsis; Ceftazidime covers Pseudomonas
4th	Cefepime	Good	Excellent + Pseudomonas	Empiric hospital-acquired infections
Anti-MRSA	Ceftaroline	MRSA	Moderate	Active against MRSA via binding PBP2a
Siderophore	Cefiderocol	Limited	Extended-spectrum	Multi-drug resistant gram-negatives

Cross-reactivity with penicillins: About 1-2% (much lower than historically taught). Allergy to one does not prohibit use of the other in most cases.

Key ADRs: Hypersensitivity (less than penicillins), GI upset, Coombs-positive hemolysis, nephrotoxicity (esp. with aminoglycosides).

C. Carbapenems

Drugs: Imipenem/cilastatin, Meropenem, Ertapenem, Doripenem

Spectrum: Broadest of all beta-lactams - gram-positive, gram-negative, anaerobes. Imipenem and meropenem cover Pseudomonas. Ertapenem does NOT cover Pseudomonas or Enterococcus.

Special feature: The different stereochemical configuration of the beta-lactam ring makes carbapenems resistant to most common beta-lactamases.

Imipenem is inactivated by renal dehydropeptidase - co-formulated with cilastatin (enzyme inhibitor) to protect it
ADRs: Seizures (especially imipenem at high doses), GI upset

D. Monobactams

Drug: Aztreonam

Active ONLY against gram-negative aerobes (including Pseudomonas)
No gram-positive or anaerobic activity
Safe to use in penicillin-allergic patients (no cross-reactivity)

E. Beta-Lactamase Inhibitors

Drugs: Clavulanate, Sulbactam, Tazobactam, Avibactam (newer)

Have weak intrinsic antibacterial activity
Irreversibly bind beta-lactamases, protecting the parent penicillin
Avibactam is active against KPC-producing Klebsiella (used with ceftazidime)

2. OTHER CELL WALL-ACTIVE ANTIBIOTICS

Vancomycin

Mechanism: Binds D-Ala-D-Ala terminus of the peptidoglycan precursor, blocking transglycosylation and transpeptidation
Different mechanism from beta-lactams - no cross-resistance
Spectrum: Gram-positives only - MRSA, MRSE, Clostridium difficile (oral), penicillin-allergic streptococcal/enterococcal infections
Resistance: VRE modifies D-Ala-D-Ala to D-Ala-D-Lac (no longer binds vancomycin)
ADRs: "Red Man Syndrome" (rate-related histamine release - NOT allergy; prevented by slowing infusion), nephrotoxicity, ototoxicity

Daptomycin

Mechanism: Disrupts bacterial cell membrane by calcium-dependent insertion, causing rapid depolarization
Spectrum: Gram-positives only, including MRSA and VRE
Important: INACTIVATED by pulmonary surfactant - cannot be used for pneumonia
ADR: Myopathy - monitor CK levels

Fosfomycin

Inhibits MurA enzyme (first step in peptidoglycan synthesis)
Oral use for uncomplicated UTI (E. coli, Enterococcus faecalis)

Cycloserine

Structural analog of D-alanine; inhibits alanine racemase and D-Ala-D-Ala ligase
Used as a second-line agent for multi-drug resistant tuberculosis
ADR: CNS toxicity (seizures, psychosis) - serious and dose-related

3. PROTEIN SYNTHESIS INHIBITORS

A. Tetracyclines

Mechanism: Bind to the 30S ribosomal subunit, blocking attachment of aminoacyl-tRNA to the mRNA-ribosome complex. Bacteriostatic.

Drugs: Tetracycline, Doxycycline, Minocycline; newer: Tigecycline (glycylcycline), Omadacycline, Eravacycline

Spectrum:

Broad: gram-positives, gram-negatives, atypicals (Chlamydia, Mycoplasma, Rickettsia, Borrelia, Brucella)
Doxycycline: drug of choice for Lyme disease, rickettsial infections, community-acquired pneumonia (atypicals), malaria prophylaxis
Tigecycline: extremely broad; active against MRSA, VRE, MDR gram-negatives (NOT Pseudomonas or Proteus)

Resistance: Efflux pumps, ribosomal protection proteins - common for older tetracyclines. Tigecycline evades many of these mechanisms.

Key ADRs:

Chelate divalent metals (Ca2+, Mg2+, Fe2+) - take on empty stomach; avoid with dairy, antacids
Photosensitivity
Hepatotoxicity (high doses IV)
Contraindicated in pregnancy and children <8 years - cause permanent yellow-brown discoloration of teeth and retard bone growth (except doxycycline which has less chelation)

B. Macrolides, Azalides & Ketolides

Mechanism: Bind the 50S ribosomal subunit (23S rRNA), inhibiting translocation. Bacteriostatic (bactericidal at high concentrations).

Drugs: Erythromycin, Clarithromycin, Azithromycin (azalide - longer half-life/tissue penetration), Telithromycin (ketolide)

Spectrum: Gram-positives, atypicals (Mycoplasma, Chlamydia, Legionella), H. pylori (clarithromycin), MAC (clarithromycin/azithromycin)

Key Uses:

Community-acquired pneumonia (atypical coverage)
STIs (azithromycin for Chlamydia - single 1 g dose)
H. pylori eradication (clarithromycin triple therapy)
MAC prophylaxis/treatment in HIV

ADRs & DDIs:

GI upset (erythromycin is a motilin agonist - can use as a prokinetic)
QT prolongation - all macrolides; risk of torsades de pointes
Erythromycin and clarithromycin are strong CYP3A4 inhibitors - major drug interactions (statins, warfarin, cyclosporine)
Azithromycin has minimal CYP3A4 inhibition - preferred

C. Aminoglycosides

Mechanism: Bind 30S ribosomal subunit (16S rRNA), causing misreading of mRNA. Bactericidal. Require oxygen for uptake - inactive against strict anaerobes.

Drugs: Gentamicin, Tobramycin, Amikacin, Streptomycin, Neomycin

Key Points:

Concentration-dependent killing - once-daily dosing is preferred (maximizes peak/MIC ratio, reduces toxicity)
Synergy with beta-lactams against Pseudomonas, Enterococcus
Streptomycin: used for TB (first-line), plague, tularemia
Amikacin: most resistant to enzymatic inactivation by bacteria
Neomycin: oral/topical only (too toxic for systemic use)

ADRs (all nephrotoxic + ototoxic):

Nephrotoxicity (reversible) - accumulate in proximal tubule cells
Ototoxicity (irreversible) - damage to cochlear hair cells (auditory) and vestibular cells
Neuromuscular blockade (risk with general anesthetics, myasthenia gravis)
Monitor trough levels to minimize toxicity

D. Chloramphenicol

Mechanism: Binds 50S ribosomal subunit (23S rRNA), inhibits peptidyl transferase. Bacteriostatic.

Uses: CNS infections (excellent CSF penetration), rickettsial disease, typhoid in resource-limited settings

Now largely replaced by safer alternatives

ADRs:

Grey baby syndrome - in neonates, due to inability to conjugate chloramphenicol (immature UGT enzymes), leading to cardiovascular collapse
Aplastic anemia (idiosyncratic, irreversible) - limits use
Dose-related bone marrow suppression (reversible)

E. Clindamycin

Mechanism: Binds 50S ribosomal subunit, blocks peptide elongation. Bacteriostatic.

Spectrum: Excellent anaerobic coverage (including Bacteroides); gram-positive organisms (MSSA, streptococci)

No gram-negative coverage

Key Uses: Anaerobic infections, skin/soft tissue infections, necrotizing fasciitis (with penicillin), dental infections, bacterial vaginosis

ADRs:

C. difficile-associated diarrhea / pseudomembranous colitis (classic association)
GI intolerance

F. Linezolid (Oxazolidinone)

Mechanism: Unique - binds 30S-50S ribosomal complex junction, inhibiting formation of the 70S initiation complex. Bacteriostatic against most organisms (bactericidal against Strep).

Spectrum: MRSA, VRE, MDR streptococci - gram-positives only

ADRs:

Thrombocytopenia (monitor platelet count weekly)
Serotonin syndrome - inhibits MAO; avoid with SSRIs, SNRIs, tyramine-rich foods
Peripheral neuropathy, optic neuritis (prolonged use)
Avoid use >2 weeks if possible

G. Quinupristin/Dalfopristin (Streptogramins)

Two molecules act synergistically on the 50S ribosome - together bactericidal
Active against VRE faecium (NOT faecalis), MRSA
ADR: Injection site reactions, myalgia, CYP3A4 inhibitor

4. DNA/RNA SYNTHESIS INHIBITORS

A. Fluoroquinolones

Mechanism: Inhibit DNA gyrase (topoisomerase II) and topoisomerase IV - enzymes essential for DNA replication and repair. Bactericidal.

Generation	Drugs	Key Spectrum/Uses
1st	Nalidixic acid	Gram-negatives (urinary tract only)
2nd	Ciprofloxacin, Ofloxacin	Gram-negatives including Pseudomonas; UTIs, GI infections, anthrax
3rd	Levofloxacin	Gram-negatives + enhanced gram-positives + atypicals; CAP
4th	Moxifloxacin, Gemifloxacin	Enhanced gram-positive/anaerobic activity + atypicals; no Pseudomonas coverage

Resistance: Mutations in gyrA or parC genes; efflux pumps

ADRs:

QT prolongation (especially moxifloxacin)
Tendinopathy/tendon rupture (Achilles tendon) - especially in elderly + corticosteroid use
Phototoxicity
Cartilage toxicity in developing animals - avoid in children and pregnant women (relative contraindication)
Lower seizure threshold
Hyperglycemia/hypoglycemia (dysglycemia)

B. Sulfonamides & Trimethoprim

Mechanism:

Sulfonamides (sulfonamide structural analog of PABA) - block dihydropteroate synthase; inhibit folate synthesis
Trimethoprim - inhibits dihydrofolate reductase (DHFR)
TMP-SMX (Co-trimoxazole) - acts at TWO sequential steps in folate synthesis = synergistic bactericidal activity

Uses: UTIs (TMP-SMX), Pneumocystis jirovecii pneumonia (PCP) - prophylaxis and treatment, Toxoplasmosis (with pyrimethamine), Nocardia, MRSA skin infections

ADRs of Sulfonamides:

Hypersensitivity (rash, Stevens-Johnson syndrome)
Hemolytic anemia in G6PD deficiency
Kernicterus in neonates (displaces bilirubin from albumin)
Crystalluria - stay well hydrated
Bone marrow suppression (TMP-SMX with folate depletion)

C. Metronidazole (& Tinidazole)

Mechanism: Selectively reduced to reactive nitro-radical intermediates in anaerobic organisms/protozoa, causing DNA strand breakage

Spectrum: Strict anaerobes (Bacteroides, Clostridium), protozoa (Giardia, Trichomonas, Entamoeba, Cryptosporidium)

Uses:

C. difficile colitis (oral)
Bacterial vaginosis
Intra-abdominal infections (with a gram-negative agent)
Amebiasis, giardiasis, trichomoniasis
H. pylori eradication regimens

ADRs: Metallic taste, nausea, disulfiram-like reaction with alcohol (AVOID alcohol), peripheral neuropathy (prolonged use), neurotoxicity

D. Rifamycins (Rifampin/Rifampicin)

Mechanism: Inhibit bacterial DNA-dependent RNA polymerase (beta subunit), blocking mRNA synthesis

Uses:

Tuberculosis (essential first-line agent, always part of combination therapy)
Prophylaxis for meningococcal/H. influenzae type b exposure
Leprosy (with dapsone)
MRSA infections (always combined - resistance develops rapidly with monotherapy)

ADRs:

Orange-red discoloration of body fluids (urine, tears, sweat) - warn patients
Potent CYP450 inducer - major DDIs (reduces levels of warfarin, OCPs, antiretrovirals, cyclosporine, many others)
Hepatotoxicity
Flu-like syndrome (intermittent dosing)

5. ANTIFUNGAL AGENTS

A. Polyenes

Drugs: Amphotericin B, Nystatin

Mechanism: Bind ergosterol in the fungal cell membrane, forming pores that cause leakage of intracellular contents. Fungicidal.

Amphotericin B:

Broad spectrum (Candida, Aspergillus, Cryptococcus, endemic fungi - Histoplasma, Coccidioides, Blastomyces, Mucor)
Gold standard for severe/life-threatening fungal infections
Formulations: Conventional (AmBd) vs. lipid formulations (AmB liposomal = AmBisome, AmB lipid complex = ABLC) - lipid formulations have significantly less nephrotoxicity
ADRs: Infusion-related reactions ("shake and bake" - fever, chills, rigors; premedicate with acetaminophen, diphenhydramine, meperidine); nephrotoxicity (dose-limiting); hypokalemia, hypomagnesemia
Nystatin: Topical only (too toxic for systemic use); used for oral thrush, skin/vaginal candidiasis

B. Azoles

Mechanism: Inhibit lanosterol 14α-demethylase (CYP51) - a fungal CYP450 enzyme - blocking conversion of lanosterol to ergosterol; fungistatic (fungicidal for some Candida spp.)

Drug	Route	Key Features
Fluconazole	Oral/IV	Excellent for Candida (not krusei/glabrata), Cryptococcus meningitis maintenance; excellent CSF penetration; NO activity vs. Aspergillus or molds
Itraconazole	Oral/IV	Aspergillus, dimorphic fungi (Histo, Blasto, Sporothrix); poor CSF penetration
Voriconazole	Oral/IV	Aspergillus (DOC), many Candida spp., Fusarium; frequent ADRs
Posaconazole	Oral/IV	Aspergillus, Mucor/Rhizopus (coverage of Mucorales - unique among azoles), prophylaxis
Isavuconazole	Oral/IV	Aspergillus, Mucorales; better tolerated than voriconazole

Important ADRs:

Voriconazole: Visual disturbances (photopsia - transient), hallucinations, hepatotoxicity, skin squamous cell carcinoma (long-term), periostitis
All azoles: hepatotoxicity, strong CYP450 inhibitors (major DDIs - increase levels of cyclosporine, tacrolimus, statins, warfarin)
Fluconazole: relatively few ADRs, best-tolerated azole

Resistance: Candida krusei is intrinsically resistant to fluconazole. Candida auris (emerging) shows multi-azole resistance.

C. Echinocandins

Drugs: Caspofungin, Micafungin, Anidulafungin

Mechanism: Inhibit 1,3-beta-D-glucan synthase - blocks fungal cell wall synthesis (target does not exist in mammalian cells = excellent safety). Fungicidal vs. Candida, fungistatic vs. Aspergillus.

Uses:

Invasive candidiasis (including candidemia) - preferred first-line for most patients
Invasive aspergillosis (second-line or combination)
Empiric antifungal therapy in febrile neutropenia

ADRs: Generally very well tolerated

Mild elevation in liver enzymes
Histamine-like reactions (caspofungin)
NO significant renal toxicity, minimal drug interactions

Resistance: Rare; mutations in FKS1 gene encoding glucan synthase

D. Flucytosine (5-FC)

Mechanism: Converted by fungal cytosine deaminase to 5-fluorouracil, which inhibits thymidylate synthase (DNA synthesis) and is incorporated into RNA

Used almost ALWAYS in combination (never alone - resistance develops rapidly)
Classic use: Combined with amphotericin B for Cryptococcal meningitis
ADRs: Bone marrow suppression (especially with renal impairment or amphotericin B - monitor levels), hepatotoxicity, GI upset

E. Allylamine - Terbinafine

Mechanism: Inhibits squalene epoxidase, an early step in ergosterol synthesis (different from azoles)

Uses: Dermatophyte infections - onychomycosis (nail fungus), tinea corporis, tinea pedis - oral or topical

ADRs: GI symptoms, hepatotoxicity (rare), taste disturbance

6. ANTIVIRAL AGENTS

A. Anti-Herpesvirus Drugs (HSV/VZV)

Drug	Mechanism	Key Features
Acyclovir	Guanosine analog; activated by viral thymidine kinase → inhibits viral DNA polymerase	IV for severe HSV (encephalitis 10mg/kg q8h), HSV/VZV treatment; poor oral bioavailability
Valacyclovir	L-valyl ester prodrug of acyclovir; better oral bioavailability	Preferred oral agent for HSV/VZV
Famciclovir	Prodrug of penciclovir	Alternative oral agent for HSV/VZV
Penciclovir	Topical only	Cold sores
Docosanol	Topical	OTC cold sore treatment

Key Point: These drugs require activation by viral thymidine kinase - resistance develops when the virus loses TK activity (TK-negative mutants). In TK-deficient strains, use foscarnet or cidofovir.

B. Anti-CMV Drugs

Drug	Mechanism	Toxicity
Ganciclovir	Guanosine analog (activated by viral UL97 kinase); inhibits viral DNA polymerase	Myelosuppression (most significant - neutropenia, thrombocytopenia)
Valganciclovir	Oral prodrug of ganciclovir	Same toxicity as ganciclovir; easier administration
Foscarnet	Directly inhibits viral DNA polymerase (does NOT need activation)	Nephrotoxicity, electrolyte disturbances (hypocalcemia, hypomagnesemia), genital ulcers
Cidofovir	Nucleotide analog; inhibits viral DNA polymerase	Severe nephrotoxicity (co-administer probenecid + IV saline)
Letermovir	Inhibits CMV terminase complex (novel mechanism)	Well tolerated; used for CMV prophylaxis in HSCT recipients
Maribavir	Inhibits CMV UL97 protein kinase	Dysgeusia, nausea; used for refractory/resistant CMV

Note: Maribavir and ganciclovir are antagonistic (both need UL97 for activation) - do not co-administer.

C. Antiretroviral Agents (HIV)

Classes targeting different steps in the HIV lifecycle:

Class	Drugs (examples)	Mechanism
NRTIs (Nucleoside/tide RTIs)	Zidovudine, Tenofovir, Emtricitabine, Abacavir, Lamivudine	Incorporate into viral DNA as chain terminators; block reverse transcriptase
NNRTIs (Non-nucleoside RTIs)	Efavirenz, Rilpivirine, Doravirine, Nevirapine	Bind allosteric site on RT; do not need phosphorylation
Protease Inhibitors (PIs)	Darunavir, Atazanavir, Lopinavir (all boosted with ritonavir or cobicistat)	Inhibit HIV aspartyl protease; prevent maturation of virions
INSTIs (Integrase inhibitors)	Raltegravir, Elvitegravir, Dolutegravir, Bictegravir	Block integration of viral DNA into host genome
Fusion Inhibitors	Enfuvirtide (T-20)	Binds gp41; prevents viral-cell membrane fusion; SC injection only
CCR5 Antagonists	Maraviroc	Binds host CCR5 co-receptor; blocks entry of CCR5-tropic HIV
CD4-attachment inhibitors	Ibalizumab	Binds CD4 T-cell receptor
Capsid inhibitor	Lenacapavir	Inhibits HIV capsid; long-acting injectable

HAART/cART principle: Always use combination of ≥2 classes to prevent resistance. Current preferred regimens typically include 2 NRTIs + 1 INSTI (e.g., Bictegravir/Tenofovir AF/Emtricitabine - Biktarvy).

Key NRTI toxicities:

Zidovudine (AZT): anemia, neutropenia, myopathy
Tenofovir (TDF): nephrotoxicity, Fanconi syndrome, osteoporosis
Abacavir: hypersensitivity reaction (HLA-B*5701 testing required before use)
Class effect: mitochondrial toxicity, lactic acidosis, lipodystrophy

Key NNRTI toxicities:

Efavirenz: CNS effects (vivid dreams, dizziness, depression) - dose at bedtime; teratogenic (avoid in 1st trimester)
Nevirapine: hepatotoxicity, rash, Stevens-Johnson syndrome

Key PI toxicities:

Metabolic: hyperlipidemia, insulin resistance, lipodystrophy, "buffalo hump"
GI intolerance
All PIs are CYP3A4 inhibitors (ritonavir most potent - used as a "booster")

D. Anti-Influenza Drugs

Drug	Mechanism	Key Features
Oseltamivir (Tamiflu)	Neuraminidase inhibitor	Oral; active against Influenza A and B; must start within 48h
Zanamivir (Relenza)	Neuraminidase inhibitor	Inhaled; not for patients with asthma/COPD
Peramivir	Neuraminidase inhibitor	IV formulation
Baloxavir	PA endonuclease inhibitor (novel mechanism)	Single oral dose; active against influenza A and B
Amantadine/Rimantadine	M2 ion channel blockers	Only influenza A; high resistance rates - NOT recommended currently

E. Anti-Hepatitis Drugs

Hepatitis B (HBV):

Tenofovir (TDF or TAF), Entecavir - first-line oral antivirals; inhibit HBV DNA polymerase (reverse transcriptase activity)
Interferon-α (PEG-IFN): immune modulation; finite course; not for decompensated liver disease

Hepatitis C (HCV) - Direct-Acting Antivirals (DAAs):

Class	Drugs	Target
NS3/4A protease inhibitors	Glecaprevir, Grazoprevir, Voxelaprevir	HCV serine protease
NS5A inhibitors	Pibrentasvir, Elbasvir, Velpatasvir, Ledipasvir	Replication complex protein
NS5B polymerase inhibitors	Sofosbuvir (nucleotide), Dasabuvir	HCV RNA-dependent RNA polymerase

Current preferred regimens:

Glecaprevir/Pibrentasvir (Mavyret) - pangenotypic, 8-12 weeks
Sofosbuvir/Velpatasvir (Epclusa) - pangenotypic
Sofosbuvir/Ledipasvir - genotype 1
Voxelaprevir/Sofosbuvir/Velpatasvir - for NS5A-experienced failures

Serious DDI: Sofosbuvir combinations + amiodarone = life-threatening bradycardia

F. Anti-COVID-19 Drugs (Current)

Nirmatrelvir/Ritonavir (Paxlovid): 3CL protease inhibitor (nirmatrelvir) boosted with ritonavir; oral; for mild-moderate COVID-19 at high risk of progression; major DDIs due to ritonavir
Remdesivir: Nucleoside analog; inhibits RdRp; IV formulation; used in hospitalized patients
Molnupiravir: Nucleoside analog; induces RNA mutagenesis; oral; less effective than Paxlovid

7. KEY PHARMACOLOGY CONCEPTS

Bactericidal vs. Bacteriostatic

Bactericidal	Bacteriostatic
Beta-lactams, Vancomycin, Aminoglycosides, Fluoroquinolones, Metronidazole, Daptomycin	Tetracyclines, Macrolides, Clindamycin, Sulfonamides, Chloramphenicol, Linezolid

Important: In immunocompromised patients and bacterial endocarditis/meningitis, bactericidal drugs are preferred.

Mechanisms of Antibiotic Resistance

Mechanism	Example
Enzymatic inactivation	Beta-lactamases (penicillins, cephalosporins), aminoglycoside-modifying enzymes
Target modification	PBP mutations (MRSA/PRSP), ribosomal methylation (macrolides), gyrA/parC mutations (FQs), VRE (D-Ala-D-Lac)
Reduced permeability	Loss of outer membrane porins (gram-negatives)
Efflux pumps	Tetracyclines, macrolides, FQs
Metabolic bypass	Sulfonamide resistance (acquire exogenous folate)

Concentration-Dependent vs. Time-Dependent Killing

Type	Drugs	Dosing Implication
Concentration-dependent	Aminoglycosides, Fluoroquinolones	Maximize peak concentration - once-daily dosing
Time-dependent	Beta-lactams, Vancomycin	Maximize time above MIC - frequent dosing or continuous infusion

Antimicrobials in Special Situations

Pregnancy (avoid): Tetracyclines, Fluoroquinolones, Aminoglycosides (ototoxicity), Sulfonamides (3rd trimester), Metronidazole (1st trimester - relative), Efavirenz (1st trimester)
Renal impairment: Reduce doses of aminoglycosides, vancomycin, penicillins, most cephalosporins; Imipenem (seizure risk elevated); avoid nitrofurantoin (GFR <30)
Hepatic impairment: Reduce doses of metronidazole, chloramphenicol, clindamycin, nafcillin, rifampin

Source: Katzung's Basic and Clinical Pharmacology, 16th Edition, pp. 1236-1494

Which are bacteiocidal and bacteriostatic

Here's a clear, organized breakdown of bactericidal vs. bacteriostatic antimicrobial agents:

Bactericidal vs. Bacteriostatic Antimicrobials

Bactericidal = kills bacteria directly | Bacteriostatic = inhibits growth, relies on host immune system to clear

🔴 BACTERICIDAL Agents

Beta-Lactams

Drug	Class
Penicillins	Cell wall synthesis inhibitor
Cephalosporins	Cell wall synthesis inhibitor
Carbapenems	Cell wall synthesis inhibitor
Aztreonam	Cell wall synthesis inhibitor

Glycopeptides & Lipopeptides

Drug	Class
Vancomycin	Cell wall synthesis inhibitor
Daptomycin	Membrane depolarizer

Aminoglycosides

Drug	Note
Gentamicin, Tobramycin, Amikacin, Streptomycin	30S ribosome - concentration-dependent killing

Fluoroquinolones

Drug	Note
Ciprofloxacin, Levofloxacin, Moxifloxacin	DNA gyrase inhibitors

Others

Drug	Note
Metronidazole	Active against anaerobes/protozoa only
Rifampin	RNA polymerase inhibitor
Isoniazid	Mycobacteria only
TMP-SMX (Co-trimoxazole)	Synergistic dual folate blockade - bactericidal overall

🟡 BACTERIOSTATIC Agents

Protein Synthesis Inhibitors (50S blockers)

Drug	Class
Erythromycin, Azithromycin, Clarithromycin	Macrolides
Clindamycin	Lincosamide
Chloramphenicol	Peptidyl transferase inhibitor
Linezolid	Oxazolidinone (bactericidal vs. Strep only)
Quinupristin/Dalfopristin	Streptogramins (bactericidal when combined)

Protein Synthesis Inhibitors (30S blockers)

Drug	Class
Tetracycline, Doxycycline, Minocycline	Tetracyclines
Tigecycline	Glycylcycline

Others

Drug	Note
Sulfonamides alone	Folate synthesis inhibitor
Trimethoprim alone	DHFR inhibitor
Nitrofurantoin	Bacteriostatic at low conc, bactericidal at high conc

⚡ Exceptions & Tricks to Remember

Scenario	Note
Linezolid	Bacteriostatic against Staph & Enterococcus, but bactericidal against Streptococcus
Aminoglycosides + Beta-lactams	Synergistic - combination is bactericidal even against Enterococcus (which is only bacteriostatic with beta-lactam alone)
Quinupristin/Dalfopristin	Each component alone is bacteriostatic; combined = bactericidal
Azithromycin	Generally bacteriostatic, but can be bactericidal at high tissue concentrations
Daptomycin	Bactericidal - rapid membrane depolarization; but inactivated by lung surfactant (don't use for pneumonia)
Metronidazole	Bactericidal, but ONLY against strict anaerobes and certain protozoa

🧠 Mnemonics

Bacteriostatic = "CSTETL" (See Statins, Think Liver - they slow things down)

Chloramphenicol
Sulfonamides
Tetracyclines
Erythromycin (macrolides)
Trimethoprim
Linezolid / cLindamycin

Bactericidal = "BVAMFR" (Be Very Aggressive - Must Fight Rapidly)

Beta-lactams
Vancomycin
Aminoglycosides
Metronidazole
Fluoroquinolones
Rifampin / Daptomycin

Clinical Relevance

In these situations, always choose bactericidal drugs:

Infective endocarditis - vegetations impair immune access
Bacterial meningitis - poor immune penetration into CSF
Immunocompromised patients (neutropenic, HIV with low CD4) - host defenses can't finish the job
Bacteremia/sepsis - rapid kill needed

This is a shared conversation. Sign in to Orris to start your own chat.