Classify penicillin
Reading File
Finding Sources
Finding Sources
Reading File
Reading File
Reading File
I now have comprehensive information. Let me compile the full classification of penicillin.
Classification of Penicillins
Penicillins are beta-lactam antibiotics. Their core structure consists of a thiazolidine ring connected to a beta-lactam ring, with a variable side chain (R group) attached. Modifications to the side chain alter antimicrobial spectrum, acid stability, resistance to beta-lactamase, and route of administration.
Mechanism of Action (shared by all penicillins)
All penicillins inhibit the transpeptidation (cross-linking) step of bacterial peptidoglycan cell wall synthesis. They bind covalently to penicillin-binding proteins (PBPs), which are transpeptidases. This leads to cell lysis and death. They are bactericidal and are most effective against actively dividing bacteria.
Classification
1. Natural Penicillins
Derived directly from Penicillium mold fermentation.
| Drug | Route | Key Features |
|---|---|---|
| Penicillin G (benzylpenicillin) | IV / IM | Narrow spectrum; acid-labile (not oral); drug of choice for syphilis (T. pallidum), streptococcal infections, meningococcal disease, gas gangrene, actinomycosis |
| Penicillin V (phenoxymethylpenicillin) | Oral | Acid-stable; narrower use - minor streptococcal infections only; low bioavailability |
Penicillin G preparations:
- Aqueous crystalline Pen G - IV for serious infections
- Procaine Pen G - IM depot; prolonged low levels; once used for pneumococcal pneumonia and gonorrhea
- Benzathine Pen G - IM; very prolonged low levels; 1.2 MU single dose for streptococcal pharyngitis; 2.4 MU weekly x 1-3 wk for syphilis; every 3-4 weeks for rheumatic fever prophylaxis
2. Penicillinase-Resistant Penicillins (Anti-staphylococcal Penicillins)
Semisynthetic; bulky side chains protect the beta-lactam ring from staphylococcal beta-lactamase. Used specifically for beta-lactamase-producing (methicillin-susceptible) Staphylococcus aureus (MSSA). Ineffective against MRSA, enterococci, and Listeria.
| Drug | Route |
|---|---|
| Methicillin | IM/IV (historical; withdrawn due to nephritis) |
| Nafcillin | IV / IM |
| Oxacillin | IV |
| Cloxacillin | Oral / IV |
| Dicloxacillin | Oral (acid-stable; 0.25-0.5 g every 4-6 h) |
| Flucloxacillin | Oral / IV |
3. Aminopenicillins (Extended-Spectrum Penicillins - Group I)
Addition of an amino group extends gram-negative coverage but retains susceptibility to beta-lactamase. Used for susceptible gram-negative bacilli (E. coli, H. influenzae, Proteus, Salmonella, Shigella) and gram-positives. Inactivated by beta-lactamases - often combined with a beta-lactamase inhibitor.
| Drug | Route | Notes |
|---|---|---|
| Ampicillin | Oral / IV / IM | Food reduces absorption; broader than Pen G |
| Amoxicillin | Oral | Better oral bioavailability than ampicillin; can be taken with food |
| Amoxicillin-clavulanate | Oral | Beta-lactamase inhibitor added; covers beta-lactamase producers |
| Ampicillin-sulbactam | IV / IM | Parenteral combination |
4. Antipseudomonal Penicillins (Extended-Spectrum - Group II)
Further extended spectrum to include Pseudomonas aeruginosa and other resistant gram-negative bacilli. All are parenteral and beta-lactamase-susceptible (used with inhibitors).
a. Carboxypenicillins
| Drug | Notes |
|---|---|
| Ticarcillin | Available as ticarcillin-clavulanate |
| Carbenicillin | Largely historical |
b. Ureidopenicillins
| Drug | Notes |
|---|---|
| Piperacillin | Available as piperacillin-tazobactam (Pip-Tazo); broadest spectrum penicillin; covers Pseudomonas, many gram-negatives, and anaerobes |
| Mezlocillin | Largely historical |
| Azlocillin | Largely historical |
Summary Table
| Group | Spectrum | Key Drugs | Beta-lactamase? |
|---|---|---|---|
| Natural penicillins | Narrow (gram+, spirochetes) | Pen G, Pen V | Susceptible |
| Penicillinase-resistant | Gram+ (MSSA) | Nafcillin, Oxacillin, Dicloxacillin | Resistant |
| Aminopenicillins | Broad (gram+ and limited gram-) | Ampicillin, Amoxicillin | Susceptible |
| Carboxypenicillins | Broad + Pseudomonas | Ticarcillin | Susceptible |
| Ureidopenicillins | Broadest + Pseudomonas | Piperacillin | Susceptible |
Resistance Mechanisms
- Beta-lactamase production - enzymatic hydrolysis of the beta-lactam ring (most common)
- Altered PBPs - as in MRSA (PBP2a encoded by mecA gene has low penicillin affinity)
- Reduced permeability - loss of outer membrane porins in gram-negatives
- Active efflux pumps
Adverse Effects (class-wide)
- Hypersensitivity reactions - most important; range from rash (maculopapular, ~5%) to anaphylaxis (0.01-0.05%). Mediated by IgE (immediate/Type I) to the penicilloyl hapten. About 1-10% cross-reactivity with cephalosporins exists, though this is lower with modern cephalosporins
- GI intolerance (ampicillin, amoxicillin)
- Neurotoxicity / seizures - at very high doses (especially Pen G)
- Electrolyte disturbances - some formulations contain Na+ or K+
- Neutropenia / hemolytic anemia - with prolonged high-dose therapy
- Jarisch-Herxheimer reaction - when treating syphilis (not a drug side effect per se)
Sources: - Goodman & Gilman's Pharmacological Basis of Therapeutics, Chapter 58 | - Katzung's Basic and Clinical Pharmacology, 16th Ed., Chapter 43
This is a shared conversation. Sign in to Orris to start your own chat.