Antibacterial Agents Flashcards
Drugs that inhibit cell metabolism (1 example)
Sulfonamides (antimetabolites)
Drugs that inhibit cell wall synthesis (3)
Penicillin Cephalosporins Vancomycin
Drugs that affect the plasma membrane (2)
Polymyxins Tryothricin
Drugs that disrupt protein synthesis (4)
Chloramphenicol Aminoglycosides Rifamycins Tetracyclins
Drugs that inhibit NA transcription and replication (2)
Nalidixic acid Proflavine
Sulfonamides were discovered from this compound
Prontosil (a prodrug converted to sulfanilamide)
Sulfonamide SARS
- All groups are essential for activity
- Should be para-substituted only
- Nitrogen must only be primary or secondary
- R1 must be unsubstituted unless it’s an amide (which can be metabolized)
*
Long lasting sulfonamide
Sulfadoxine
(taken only once a week)
Sulfonamide combination for malaria
Sulfadoxine + Pyrimethamine
(Fansidar)
Sulfonamides MOA
- Mimic p-aminobenzoic acid (PABA) to inhibit dihydropteroate synthetase
- Block tetrahydrofolate synthesis, a cofactor for pyrimidine synthesis (for DNA)
Trimethoprim (antimetabolite) MOA
Sulfone (antimetabolite) indication
Leprosy
Baterial cell wall sugars (2)
- N-Acetylmuramic acid (NAM)
- N-Acetylglucosamine (NAG)
Succesfully isolated penicillin using processes such as freeze-drying and chromatography
Florey and Chain
Enzyme inhibited by penicillin
Transpeptidase
Penicillin action (G+ or G-)
- G+ since although they have a thicker cell wall, G- have a lipopolysaccharide barrier impervious to water and polar molecules
- Futhermore, most G- have b-lactamases
- G- activity if there are porins (allow hydrophilic, zwitterions to cross)
- A G+ bacteria may be immune if it has b-lactamases
Penicillin SARS
- Bicyclic system: the greater the strain the greater the activity
- All are essential EXCEPT sulfur
Adding an electron withdrawing group to the acyl side chain of the penicillin structure will render the drug:
Resistant to acid hydrolysis
What is the effect of steric shields to the penicillin structure?
- It will give beta lactamase protection
First effective semi-synthetic penicillin with resistance to S. aureus b-lactamase enzymes
- Methicillin (but it is not acid resistant)
- Whereas, Nafcillin is resistant to both b-lactamase and acid
Examples of isoxazolyl penicillins (isoxazolyl group acts as an e- withdrawing group and stearic shield)
Give the 3 classes of broad-spectrum penicillins
- aminopenicillins (amino group)
- caboxypenicillins (carboxylic acid group)
- ureidopenicillins (urea)
Aminopenicillin drugs (2)
- Ampicillin
- Amoxicillin
Acid resistant but susceptible to b-lactamase
Carboxypenicillin drugs (2)
- Carbenicillin (phenyl group)
- Ticarcillin (thiophene ring)
Ureidopenicillin drugs (3)
- Azlocillin
- Mezlocillin
- Piperacillin
Drug synergistic to penicillin
Probenecid (increase penicillin effect)
- block excretion
- compete with albumin binding
Aminoacid precurors of penicillins (2)
- Cysteine
- Valine
Cephalosporin C SARS
- Six-membered ring fused to b-lactam
- Presence of acetyloxy group
Carbapenem structure
- Absent supfur atom in the bicyclic ring
- No acyl amino side chains
Combination of b-lactamase inhibitors + penicillins (4)
- Augmentin (Clavulanic acid + Amoxicillin)
- Timentin (Clavulanic acid + Ticarcillin)
- Unasyn (Sulbactam + Ampicillin)
- Tazocin/Zosyn (Tazobactam + Piperacillin) *broadest spectrum combinaiton
Antibiotic from S. garyphalus which inhibits bacterial cell wall synthesis by mimicking the structure of D-Alanine and inhibiting the enzymes L-alanine racemase and D-Ala-D-Ala ligase
D-Cycloserine
An antibiotic composed of 16 amino acids that is described as a tunelling molecule that act on the plasma membrane and result in the uncontrolled movement of ions across cell membrane leading to cell death
Gramicidin A
An ionophore antibiotic with a cyclic structure btained from Streptomyces fermentation that acts on the plasma membrane structure by allowing the uncontrolled movement of ions across the cell membrane. This ionophore is specific for potassium ions over sodium ions.
Valinomycin
A cyclic lipopeptide derived from a bacterial strain of S. roseosporus and works by disrupting multiple functions of the bacterial cell membrane
Daptomycin
A bactericidal protein synthesis inhibitor that was isolated from S. griseus. This antibiotic contains a carbohydrate and basic amine groups in the structure.
Streptomycin
A bacteriostatic antibiotic which inhibits protein synthesis by binding to the 30S subunit of ribosomes and preventing aminoacyl tRNA from binding. This drug was isolated from S. aureofasciens.
Chlortetracycline
Antibiotic which has a large lactone ring, a ketone group, and a glycosidically linked amino sugar in its structure.
Erythromycin
Antibiotics that inhibit the 30s subunit
- Aminoglycosides (gentamicin)
- Tetracyclines
Antibiotics that inhibit the 50s subunit
- Macrolides
- Chloramphenicol
- Clindamycin
- Linezolid
- Streptogramins (Quinupristin & Dalfopristin)
An aminoacridine agent used topically to treat deep surface wounds. It can interact directly with bacterial DNA by intercalation
Proflavine
The antibiotic isolated from S. mediterranei which inhibits G+ bacteria and works by binding noncovalently to DNA-dependent RNA polymerase and inhibiting the start of RNA synthesis.
Rifamycin B
A nitroimidazole structure introduced as an anti-protozoal agent and later became an antibacterial agent. Its MOA involves the drug entering the bacterial cell wall where the nitro group is reduced and free radicals are formed and act on DNA.
Metronidazole
A drug used to treat UTI where it degrades in acid conditions to give formaldehyde as the active agent.
Methenamine
Chloramphenicol SAR
- Which part is NOT essential?
- Which part is reponsible for the toxic effect?
- Dichloroacetamide group is not essential
- Nitro group is reponsible for the toxic effect
Bacteriostatic agent with a 14-membered macrocyclic lactone ring
Erythromycin
- acid instability due to ketone and alcohol groups
- acid stability can be achieved by adding hydroxy groups (Clarithromycin) or by increasing the ring size to 16-members
- will be LESS effective if combined with Chloramphenicol (same 50s binding site)
