Antibiotics Notes | BP403T Pharmacology II
Subject: Pharmacology
Subject: Pharmacology
| Year | Discovery/Event | Significance |
|---|---|---|
| 1928 | Discovery of Penicillin by Alexander Fleming | First true antibiotic, accidentally discovered from Penicillium notatum. |
| 1940 | Development of Penicillin for therapeutic use by Florey and Chain | Paved the way for clinical use of antibiotics, saving millions of lives. |
| 1944 | Discovery of Streptomycin by Selman Waksman | First effective treatment for tuberculosis; coined the term "antibiotic." |
| Mechanism of Action | Examples of Antibiotic Classes |
|---|---|
| Inhibition of Cell Wall Synthesis | Beta-lactams (Penicillins, Cephalosporins, Carbapenems, Monobactams), Glycopeptides, Bacitracin, Fosfomycin, Cycloserine |
| Inhibition of Protein Synthesis (30S Ribosomal Subunit) | Aminoglycosides, Tetracyclines |
| Inhibition of Protein Synthesis (50S Ribosomal Subunit) | Macrolides, Lincosamides (Clindamycin), Chloramphenicol, Streptogramins, Linezolid |
| Inhibition of Nucleic Acid Synthesis | Quinolones (DNA gyrase), Rifamycins (RNA polymerase) |
| Inhibition of Folic Acid Synthesis | Sulfonamides, Trimethoprim |
| Disruption of Cell Membrane Function | Polymyxins, Daptomycin |
| Spectrum | Description | Examples |
|---|---|---|
| Narrow-Spectrum | Effective against a limited range of bacteria (e.g., primarily Gram-positive or primarily Gram-negative). | Penicillin G (mostly Gram-positive), Isoniazid (Mycobacteria), Polymyxin B (mostly Gram-negative). |
| Extended-Spectrum | Effective against Gram-positive bacteria and a significant portion of Gram-negative bacteria. | Ampicillin, Amoxicillin (amino-penicillins). |
| Broad-Spectrum | Effective against a wide range of Gram-positive and Gram-negative bacteria. May also target atypical bacteria. | Tetracyclines, Chloramphenicol, Carbapenems, Third-generation Cephalosporins. |
| Type | Effect | Examples (Mnemonic: F-L-A-T-T for Bacteriostatic) |
|---|---|---|
| Bactericidal | Directly kill bacteria. Preferred in immunocompromised patients and serious infections (meningitis, endocarditis). | Beta-lactams, Aminoglycosides, Vancomycin, Fluoroquinolones, Metronidazole, Polymyxins, Daptomycin, Rifampicin. |
| Bacteriostatic | Inhibit bacterial growth, relying on the host's immune system to clear the infection. | Fosfomycin (at lower doses), Linezolid, Azithromycin (at lower doses), Tetracyclines, Trimethoprim, Sulfonamides, Chloramphenicol, Clindamycin, Erythromycin (at lower doses). |
Bacterial cell walls, particularly peptidoglycan, are unique to bacteria, making them excellent targets for selective toxicity. These drugs interfere with the synthesis or cross-linking of peptidoglycan polymers.
Characterized by a beta-lactam ring, essential for their activity. They act by inhibiting transpeptidases (also known as Penicillin-Binding Proteins, PBPs), which are enzymes involved in the final stages of peptidoglycan synthesis, leading to cell lysis.
Derived from Penicillium chrysogenum. Resistance often due to beta-lactamase (penicillinase) enzymes.
| Class | Key Drugs | Spectrum & Features | Adverse Effects |
|---|---|---|---|
| Natural Penicillins | Penicillin G (IV), Penicillin V (Oral) | Narrow spectrum; primarily Gram-positive cocci (Streptococci). Sensitive to beta-lactamase. | Hypersensitivity (rash, anaphylaxis), Jarisch-Herxheimer reaction. |
| Antistaphylococcal Penicillins | Methicillin (obsolete), Nafcillin, Oxacillin, Cloxacillin, Dicloxacillin | Resistant to staphylococcal beta-lactamase. Used for penicillinase-producing Staph. aureus (MSSA). | Interstitial nephritis (Methicillin), hepatotoxicity (Oxacillin). |
| Aminopenicillins (Extended Spectrum) | Ampicillin, Amoxicillin | Broader Gram-negative activity (H. influenzae, E. coli, Proteus, Salmonella) due to better penetration of outer membrane. Susceptible to beta-lactamase. | Rash (especially in mononucleosis), pseudomembranous colitis (less common). Often combined with beta-lactamase inhibitors. |
| Antipseudomonal Penicillins (Extended Spectrum) | Piperacillin, Ticarcillin, Carbenicillin | Very broad spectrum, including Pseudomonas aeruginosa. Susceptible to beta-lactamase. | Platelet dysfunction (Ticarcillin, Piperacillin), sodium overload. Usually combined with beta-lactamase inhibitors. |
| Beta-Lactamase Inhibitors | Clavulanic Acid, Sulbactam, Tazobactam, Avibactam, Vaborbactam, Relebactam | Irreversibly bind and inhibit bacterial beta-lactamases, protecting the co-administered penicillin from hydrolysis. | Generally well-tolerated; often increase incidence of GI side effects. |
| Combinations | Amoxicillin-clavulanate, Ampicillin-sulbactam, Piperacillin-tazobactam, Ceftazidime-avibactam | Broaden spectrum against beta-lactamase producing strains. | Side effects of individual components. |
Broad-spectrum, bactericidal beta-lactams, generally more resistant to beta-lactamases than penicillins. Classified into generations based on spectrum and resistance patterns.
| Generation | Key Drugs | Spectrum & Features | Adverse Effects |
|---|---|---|---|
| First-Gen | Cefazolin (IV), Cephalexin (Oral), Cefadroxil | Good Gram-positive (Staphylococci, Streptococci). Modest Gram-negative (PEcK: Proteus, E. coli, Klebsiella). Surgical prophylaxis. | Hypersensitivity, GI upset. |
| Second-Gen | Cefuroxime, Cefoxitin, Cefotetan | Extended Gram-negative activity (HENS: H. influenzae, Enterobacter, Neisseria, Serratia) compared to 1st gen. Some anaerobic activity (Cefoxitin, Cefotetan). | Cefotetan/Cefamandole can cause disulfiram-like reaction and hypoprothrombinemia (due to methylthiotetrazole side chain). |
| Third-Gen | Ceftriaxone, Cefotaxime, Ceftazidime | Excellent Gram-negative activity (including Pseudomonas for Ceftazidime). Penetrates CNS (meningitis). Less Gram-positive than 1st/2nd gen. | Biliary sludge (Ceftriaxone), pseudomembranous colitis, vitamin K deficiency. |
| Fourth-Gen | Cefepime | Broad spectrum, active against Pseudomonas and many Gram-positive bacteria (similar to 1st gen for Gram-pos). Good CNS penetration. Resistant to many beta-lactamases. | Neurotoxicity (encephalopathy, seizures) at high doses. |
| Fifth-Gen | Ceftaroline fosamil | Unique activity against MRSA (Methicillin-Resistant Staphylococcus aureus) and penicillin-resistant S. pneumoniae. Broad Gram-negative. | Similar to other cephalosporins. |
Broadest spectrum beta-lactams, often used for severe, multi-drug resistant infections. Resistant to most beta-lactamases (including ESBLs).
| Drug | Key Features | Adverse Effects |
|---|---|---|
| Imipenem | Very broad spectrum (Gram-positive, Gram-negative, anaerobes). Co-administered with Cilastatin (a renal dipeptidase inhibitor) to prevent its inactivation in the renal tubules and reduce nephrotoxicity. | Seizures (especially in renal impairment), GI upset. |
| Meropenem | Similar spectrum to imipenem but with less seizure risk. Does not require cilastatin. | Less seizure risk than imipenem. |
| Ertapenem | Narrower spectrum than Imipenem/Meropenem; lacks activity against Pseudomonas aeruginosa and Acinetobacter. Long half-life (once daily dosing). | Well tolerated. |
| Doripenem | Similar spectrum to meropenem, good against Pseudomonas. | Well tolerated. |
| Drug | Key Features | Adverse Effects |
|---|---|---|
| Aztreonam | Narrow spectrum; active ONLY against Gram-negative aerobes (including Pseudomonas). RESISTANT to most beta-lactamases. No activity against Gram-positive or anaerobes. Safe in penicillin-allergic patients (minimal cross-allergenicity). | Phlebitis, skin rash, GI upset. |
Inhibit cell wall synthesis by binding to the D-Ala-D-Ala terminus of the peptidoglycan precursor, preventing transglycosylation and transpeptidation.
| Drug | Key Features | Adverse Effects |
|---|---|---|
| Vancomycin | Primarily Gram-positive spectrum, including MRSA, C. difficile (oral route for CDAD). Administered IV for systemic infections due to poor oral absorption. | Red Man Syndrome (histamine release with rapid IV infusion), Nephrotoxicity, Ototoxicity (rare), Phlebitis. |
| Teicoplanin | Similar to vancomycin but with longer half-life (once daily) and less nephrotoxicity/ototoxicity. Can be given IM. | Similar to vancomycin, but generally better tolerated. |
| Dalbavancin, Oritavancin | Newer long-acting lipoglycopeptides. Single dose or weekly dosing due to very long half-lives. Active against Gram-positives, including MRSA. | Nausea, diarrhea. Oritavancin can interfere with coagulation tests. |
| Drug | MOA | Key Features | Adverse Effects |
|---|---|---|---|
| Bacitracin | Inhibits dephosphorylation of lipid pyrophosphate carrier, essential for peptidoglycan synthesis. | Too nephrotoxic for systemic use. Topical only (Gram-positive). | Nephrotoxicity (systemic). |
| Fosfomycin | Inhibits UDP-N-acetylglucosamine enolpyruvyl transferase, an early step in peptidoglycan synthesis. | Broad spectrum, used for uncomplicated UTIs (single oral dose). | GI upset. |
| Cycloserine | D-Alanine analogue; inhibits alanine racemase and D-alanine ligase, preventing D-Ala-D-Ala formation. | Second-line drug for multidrug-resistant tuberculosis. Neurotoxic. | CNS effects (seizures, psychosis). |
These drugs exploit differences between prokaryotic (70S) and eukaryotic (80S) ribosomes. They target either the 30S or 50S ribosomal subunit.
Bactericidal. Irreversibly bind to the 30S subunit, leading to misreading of mRNA and premature termination of protein synthesis. Oxygen-dependent uptake, thus inactive against anaerobes. Post-antibiotic effect (PAE).
| Drug | Key Features | Adverse Effects |
|---|---|---|
| Gentamicin, Tobramycin, Amikacin, Streptomycin, Neomycin (topical/oral for bowel prep) | Broad Gram-negative (including Pseudomonas for Tobramycin, Amikacin). Synergistic with beta-lactams for Gram-positive endocarditis. | Ototoxicity (vestibular and cochlear, irreversible), Nephrotoxicity (reversible acute tubular necrosis), Neuromuscular blockade (contraindicated in myasthenia gravis). |
Bacteriostatic. Reversibly bind to the 30S subunit, preventing attachment of aminoacyl-tRNA to the A-site, thus inhibiting protein elongation. Broad spectrum, including atypical bacteria (Rickettsiae, Mycoplasma, Chlamydia).
| Drug | Key Features | Adverse Effects |
|---|---|---|
| Tetracycline, Doxycycline, Minocycline, Tigecycline | Doxycycline (long-acting, eliminated by non-renal routes, preferred in renal failure), Minocycline (good CNS penetration, vestibular toxicity), Tigecycline (Glycylcycline, active against MRSA, VRE, ESBL-producing bacteria; higher mortality risk for certain severe infections). | GI upset, Photosensitivity (especially Doxycycline), Tooth discoloration (in children < 8 yrs, pregnancy), inhibition of bone growth, Fanconi syndrome (outdated tetracyclines), pseudotumor cerebri. Chelate with divalent/trivalent cations (milk, antacids, iron). |
Bacteriostatic (bactericidal at higher doses). Bind to the 50S subunit, inhibiting translocation and preventing peptide chain elongation.
| Drug | Key Features | Adverse Effects |
|---|---|---|
| Erythromycin Clarithromycin, Azithromycin | Erythromycin (oldest, good against Gram-positive, atypical, CYP inhibitor, GI motility stimulator). Clarithromycin (better oral absorption, H. pylori, CYP inhibitor). Azithromycin (longer half-life, less CYP inhibition, less GI side effects, used for URTI/LRTI, STIs). | GI upset (Erythromycin), QT prolongation (risk of Torsades de Pointes), Cholestatic hepatitis (Erythromycin estolate), CYP3A4 inhibition (Erythromycin, Clarithromycin). |
| Drug | Key Features | Adverse Effects |
|---|---|---|
| Clindamycin | Bacteriostatic. Binds to 50S subunit. Good against anaerobes (Bacteroides fragilis) and Gram-positive cocci (including some MRSA). Does not penetrate CNS. | Pseudomembranous colitis caused by Clostridioides difficile (most common side effect), diarrhea. |
Bacteriostatic (bactericidal for some organisms). Binds to 50S subunit, inhibiting peptidyl transferase. Broad spectrum, good CNS penetration.
| Drug | Key Features | Adverse Effects |
|---|---|---|
| Chloramphenicol | Used for serious infections (meningitis, rickettsial diseases) where less toxic alternatives are unsuitable due to severe toxicity profile. | Bone marrow suppression (dose-dependent reversible anemia; dose-independent irreversible aplastic anemia), Gray Baby Syndrome (in neonates due to deficient glucuronidation). |
| Drug | Key Features | Adverse Effects |
|---|---|---|
| Linezolid | Bacteriostatic. Inhibits initiation of protein synthesis by binding to 23S rRNA of 50S subunit, preventing formation of 70S initiation complex. Active against MRSA, VRE, drug-resistant S. pneumoniae. | Myelosuppression (thrombocytopenia, anemia), Peripheral and optic neuropathy (with prolonged use), Serotonin Syndrome (due to MAO inhibition, with SSRIs). |
| Drug | Key Features | Adverse Effects |
|---|---|---|
| Quinupristin/Dalfopristin | Bactericidal. Synergistic combination. Binds to 50S subunit. Used for vancomycin-resistant Enterococcus faecium (VRE). Not active against E. faecalis. | Arthralgia/Myalgia, Infusion-related reactions, CYP3A4 inhibition. |
These drugs interfere with DNA replication or RNA transcription.
Bactericidal. Inhibit bacterial DNA gyrase (topoisomerase II) and topoisomerase IV, crucial for DNA replication, transcription, repair, and recombination.
| Class/Drug | Key Features | Adverse Effects |
|---|---|---|
| First-Gen: Nalidixic Acid | Urinary tract infections (UTIs) only. | Photosensitivity. |
| Second-Gen: Ciprofloxacin, Ofloxacin | Broad spectrum (excellent Gram-negative, including Pseudomonas, some Gram-positive). Used for UTIs, GI infections, respiratory infections. | GI upset, CNS effects (headache, dizziness, seizures), Tendonitis/Tendon Rupture (especially Achilles, contraindicated in children/pregnancy due to cartilage damage risk), QT prolongation, Photosensitivity, Peripheral neuropathy, Dysglycemia. Chelate with divalent/trivalent cations. |
| Third-Gen: Levofloxacin | "Respiratory Quinolone." Enhanced activity against Gram-positive (S. pneumoniae), good Gram-negative. | |
| Fourth-Gen: Moxifloxacin, Gemifloxacin | Broadest spectrum, good Gram-positive (S. pneumoniae), Gram-negative, anaerobes. Moxifloxacin not used for UTIs (poor urinary excretion). |
| Drug | MOA | Key Features | Adverse Effects |
|---|---|---|---|
| Rifampicin (Rifampin) | Inhibits bacterial DNA-dependent RNA polymerase, thus blocking RNA synthesis. | Bactericidal. Broad spectrum, but resistance develops rapidly if used alone. Key drug for Tuberculosis (always used in combination). Used for prophylaxis of meningitis (N. meningitidis, H. influenzae). | Red-orange discoloration of body fluids (urine, tears, sweat), Hepatotoxicity, Flu-like syndrome, Potent CYP450 enzyme inducer (many drug interactions). |
Bacteria must synthesize their own folic acid, unlike humans who obtain it from diet. These drugs target different steps in this pathway.
Bacteriostatic. Structurally similar to para-aminobenzoic acid (PABA). Competitively inhibit dihydropteroate synthase, preventing bacterial folic acid synthesis.
| Drug | Key Features | Adverse Effects |
|---|---|---|
| Sulfamethoxazole, Sulfadiazine, Sulfacetamide (topical) | Broad spectrum. Used for UTIs, Nocardiosis, Toxoplasmosis (Sulfadiazine). | Hypersensitivity reactions (rashes, Stevens-Johnson Syndrome, Toxic Epidermal Necrolysis), Crystalluria (renal damage), Photosensitivity, Hemolytic anemia (in G6PD deficiency), Kernicterus in neonates. |
| Drug | MOA | Key Features | Adverse Effects |
|---|---|---|---|
| Trimethoprim | Bacteriostatic. Inhibits bacterial dihydrofolate reductase (DHFR), blocking the conversion of dihydrofolate to tetrahydrofolate. | Used for UTIs. | Megaloblastic anemia, leukopenia, granulocytopenia (folate deficiency), Hyperkalemia. |
A synergistic combination where two sequential steps in the folic acid pathway are inhibited, resulting in a bactericidal effect.
| Combination | Key Features | Adverse Effects |
|---|---|---|
| TMP-SMX | Broad spectrum, bactericidal. Used for UTIs, PCP (Pneumocystis jirovecii pneumonia) in HIV patients, Nocardiosis. | Combined adverse effects of both drugs, but can be more severe. Rash, GI upset, photosensitivity, bone marrow suppression, hyperkalemia. |
These drugs increase cell membrane permeability, leading to leakage of intracellular components and cell death.
Cationic detergents that disrupt the outer and inner membranes of Gram-negative bacteria. Active against Pseudomonas, Acinetobacter, Klebsiella.
| Drug | Key Features | Adverse Effects |
|---|---|---|
| Polymyxin B, Colistin (Polymyxin E) | Often last-resort drugs for multidrug-resistant Gram-negative infections. Colistin is a prodrug that gets activated. | Nephrotoxicity (dose-dependent), Neurotoxicity (paresthesias, weakness, apnea due to neuromuscular blockade). |
| Drug | MOA | Key Features | Adverse Effects |
|---|---|---|---|
| Daptomycin | Bactericidal. Inserts into the bacterial cell membrane, causing depolarization and inhibition of protein, DNA, and RNA synthesis. Not active against Gram-negatives. | Used for MRSA, VRE. NOT for pneumonia (inactivated by pulmonary surfactant). | Myopathy (monitor CPK), Eosinophilic pneumonia. |
The ability of bacteria to withstand the effects of an antibiotic. A major global health concern.
| Mechanism | Description | Examples |
|---|---|---|
| Enzymatic Inactivation | Bacteria produce enzymes that inactivate the antibiotic. | Beta-lactamases (destroy beta-lactam ring), Aminoglycoside-modifying enzymes. |
| Alteration of Target Site | Mutation or modification of the drug's target site, reducing drug binding. | PBP alteration (MRSA), Ribosomal mutation (Linezolid, Aminoglycosides), D-Ala-D-Lac substitution (Vancomycin resistance). |
| Decreased Permeability | Modification of outer membrane porins, reducing drug entry. | Carbapenem resistance in Gram-negatives. |
| Efflux Pumps | Active transport systems that pump antibiotics out of the bacterial cell. | Tetracyclines, Macrolides, Fluoroquinolones. |
| Bypass Pathway | Bacteria develop an alternative metabolic pathway not targeted by the drug. | Resistance to Sulfonamides/Trimethoprim. |
Used to:
Administering antibiotics to prevent infection (e.g., surgical prophylaxis, prevention of recurrent UTIs, dental procedures in high-risk cardiac patients).
A new infection arising during antimicrobial therapy, often due to disruption of normal microbiota, allowing overgrowth of resistant organisms (e.g., C. difficile colitis with Clindamycin, oral candidiasis with broad-spectrum antibiotics).
| Category | Risk | Examples |
|---|---|---|
| Safe (Category B) | Generally safe. | Penicillins, Cephalosporins, Erythromycin (avoid estolate), Azithromycin, Clindamycin. |
| Avoid/Contraindicated (Category C/D/X) | Known or suspected fetal risk. | Tetracyclines (D: tooth discoloration, bone growth inhibition), Aminoglycosides (D: ototoxicity), Fluoroquinolones (C: cartilage damage), Chloramphenicol (C: Gray Baby Syndrome), Sulfonamides (C: kernicterus, late pregnancy), Trimethoprim (C: folate antagonism). |
Dosage adjustments are often necessary for renally or hepatically excreted/metabolized drugs to prevent accumulation and toxicity. Doxycycline (tetracycline) is notable for non-renal elimination, making it safer in renal failure. Ceftriaxone is primarily biliary excreted, making it useful in renal impairment.