Antibiotics Flashcards
(24 cards)
Beta-lactam antibiotics
Antibiotic drugs that contain the beta-lactam ring functional unit.
Includes:
Penicillin
Cephalosporins
Monobactams
Beta lactam binds to transpeptidase in the cell wall of bacteria, and prevents the further synthesis of the cell wall.
However not all bacteria use the same transpeptidase- like pseudomonas.
Penicillin G
Benzylpenicillin, contains the benzene ring as its R group.
This antibiotic can only been administered intravenously.
It has rapid renal clearance so it does not stay in the blood for very long.
It is mainly effective against Gram negative bacteria and some Gram - bacteria.
Penicillin
Beta-lactam antibiotic that help destroy bacteria by binding to transpeptidase.
Transpeptidase is the enzyme involved in synthesising peptidoglycan.
Penicillin inhibits the cell wall formation by inhibiting transpeptidase.
Good at targeting:
Staphs, Streps, and Neisseria
Penicillin V
Phenoxymethylpenicillin
Type of penicillin that can be taken orally but is rapidly excreted.
Has to be taken 6 times a day.
Aminopenicillin
Beta-lactam penicillin with a positively charged amino group as its ‘R group’.
Includes:
Amoxicillin
Ampicillin
Bacampicillin
Amoxicillin
Aminopenicillin that is orally administered. More effective against gram negative bacteria that penicillin V
Has a longer half life than penicillin V, so can be taken three times a day.
Action:
Inhibits bacterial cell wall production.
Interaction:
Can increase levels of other protein bound drugs.
Adverse effects:
Allergies
Destruction of the commensal flora.
Diseases treated:
S.pyogenes infections- sore throat, skin infections
Pneumococcal- respiratory tract
Coliform- urinary tract
Antibiotic administered to treat S.pyogenes infections
Amoxicillin.
Clarythromycin (if allergic to penicillin)
Vancomycin (non-penicillin)
Treatment against pseudomonas
Antipseudomonal penicillin
Normal penicillins are ineffective against pseudomonas as they have a different transpeptidase enzyme to synthesise their cells walls.
Antipseudomonals include:
Piperacillin
Bacterial antibiotic resistance mechanism
4 main methods of resistance: Enzymatic degradation of drug Target modificiation Efflux pumps Reduced penetration of cell wall
Certain strains of bacteria synthesise enzyme beta lactamase which hydrolyzes the beta-lactam ring in beta-lactam antibiotics.
S.aureus and E.coli can develop resistance through this mechanism
Drugs synthesised resistant to staphylococcal beta-lactamase
Methicillin- not used clinically. Used in labs to determine antibiotic sensitivity of bacteria (seen in MRSA)
Flucloxacillin: used clinically, mainly for S.aureus
Beta lactamase inhibitors
Drugs developed to target bacteria that are resistant to beta lactam drugs, especially penicillin.
The inhibitors bind to beta lactamase produced by the bacteria, preventing it from hydrolysing the beta lactam ring.
Includes:
Clavulanic acid
Co-amoxiclav
Beta-lactamase inhibitor composed of amoxicillin bound to clavulanic acid.
This prevents amoxicillin from being degraded by beta lactamase enzymes produced by the bacteria.
MRSA
Methicillin-resistant S. aureus
Strain of S. aureus resistant to all beta-lactam antibiotics.
This is tested by testing its sensitivity to methicillin, hence its name.
This strain contains a different transpeptidase to make peptidoglycan, coded by mecA gene.
mecA gene
Gene possessed by MRSA and other bacteria Streps reisistant to all beta-lactam antibiotics.
The gene codes for penicillin binding protein 2A (PBP2A) used to synthesise the cell wall.
PBP2A is a transpeptidase that cannot bind to penicillin, so penicillins are infective in removing bacteria with this gene.
Efflux pumps
Active transport protein pumps that are present in many Gram negative bacteria with antibiotic resistance:
E. coli
The pump allows antibiotics to be moved out of the cell, preventing it from having an effect.
The gene to make this protein is coded in mobile genetic elements, like plasmid and transposons, which allow the spread of resistance across species.
Mycoplasma resistance to penicillin
Has no cell well, so penicillin are infective.
Examples:
M. pneumoniae
Cephalosporins
Beta-lactam antibiotic made from cephalosporium acremonium
Contains two R groups which gives many different antibiotics and properties:
Altered water solubility
Delayed secretion
Action against transpeptidases of different species
Resistance to degradation of beta-lactamase
The higher generations affect Gram negative bacteria and are administered IV
Macrolide
Non bata-lactam penicillin that targets protein synthesis in bacteria.
Macrolides binds to the 50s subunit in ribosome.
Effective against Gram positives, many Gram negatives and bacteria without cell walls.
HOWEVER, some Streps are resistant due to target site mutations
Examples:
Clarythromycin
Clarythromycin
Macrolide antibiotic taken orally used for patients allergic to penicillin.
Used to treat: S. pyogenes Pneumococcal infections Coliform infections Chlamydia
Has high affinity to proteins
Metabolism:
Hepatic, excreted via liver. Excreted in the bile.
Half life:
1-6 hours
Adverse effects:
Nausea
Diarrhoea
Arrhythmia
Interactions:
Can bind to other proteins involved in drug metabolism, like cytochrome p450
Reasons why some patients may not get better with antibiotics
Poor tissue penetration: could be due to oedema or poor blood flow.
Patients may not take adhere to treatment plans
Patient could be resistant to antibiotics
Patient risk factor, like obesity.
Antibiotic could select out commensals and cause another infection
Vancomycin
Glycopeptide that inhibits peptidoglycan production, hence cell wall production.
Has to be taken IV as it is very big.
Only active against Gram positive bacteria and the very resistant strains like MRSA.
Half life:
4-8 hours
Excretion:
Via the urine, not metabolised
Adverse effects:
Ototoxic
Nephrotoxic
Also interacts with other ototoxic and nephrotoxic drugs
Narrow therapeutic window
Bacteria species that most commonly causes cellulitis
S. pyogenes
Organism that commonly causes thrush
Candida albicans (orally)
Candidal vulvovaginitis (vagina)
Genetic mechanisms of antibiotic resistance
- Acquisition of a resistant genes like mecA, gene for beta lactamase, from mobile genetic elements
Patient is usually infected with resistant strain, it is rare for bacteria to acquire this during infection. - Mutation:
Occurs spontaneously in bacteria.
The mutations are selected for if they cause resistance
