Introduction to Antibiotics Flashcards
What type of bacteria react more to things that attack the cell wall?
- Gram positive due to peptidoglycan
What type of organisms require different antibiotics?
- Intracellular
- E.g. Borrelia and chlamydia
Which antibiotic acts against the cell wall and what is its action?
- Penicillin, glycopeptides and cephalosporins (beta lactams)
- Binding and inhibiting of cell wall synthesis
Which antibiotic acts against nucleic acids and what is its action?
- Metronidazole and Rifampicin (used for TB)
- Interference with nucleic acid synthesis and function
Which antibiotic acts against DNA gyrase and what is its action?
- Fluoroquinolones (around 20 minutes)
- Stops the function of this enzyme (coiling of DNA)
Which antibiotic acts against ribosomes and what is its action?
- Aminoglycosides (gentamycin), Tetracyclines (doxycycline), Macrolides (erythromycin) and Chloramphenicol
- Inhibits ribosomal translation so proteins cannot be made
Which antibiotic acts against folic acid and what is its action?
- Sulphonamides and Trimethoprim
- Inhibition of folate synthesis and carbon unit metabolism
Describe the action of penicillins
- Inhibits staphylococci
- Benzylpenicillin- gram positive killer
(only IV) - Modified oral product
– Phenoxymethyl penicillin (penicillin V)- narrow spectrum - Short half-lives and restrictive
- Class: Beta lactam ring, penicillin allergy results in anaphylactic shock reaction to any drug with this ring
Describe the action of aminopenicillins
- Modified penicillins
- Beta lactam ring + amino group
- Increased grip on peptidoglycan, works on gram negative as well
Describe Amipicillin and Amoxycillin as examples of Aminopenicillins
- IV and oral
- Amino group means well-absorbed
- Broad spectrum
- Do not treat staph
- MRSA- staph resistant to methicillin
- Gram pos and neg
Describe fluxloacillins as examples of aminopenicillins
- Prototype methicillin
- IV and oral, staphylococcal activity
- Gram pos only
Describe extended-spectrum penicillins
- E.g. piperacillin
- IV only, active against Pseudomonas
- Gram positive and negative
- Not very potent
Describe cephalosporins
- Used for very severe infections
- Oral and IV
- Very broad spectrum
- Higher potency and safe in pregnancy
- Cefotraxime and ceftriaxone (3rd generation)
- Ceftriaxone used in children once a day
- High half life
Describe carbopenems
- Gram pos and neg
- Semi- synthetic product (related to cephalosporins)
- Factory produced
- Very high potency and broad spectrum
- Imipenem and Ertapenem
- Meropenem- last resort drug (although clones of gram negative resistant bacteria emerging from India and China)
What is the problem with the beta lactam ring?
- All antibiotics have roughly similar core structue (like ring)
- Some bacteria can alter the cell wall- not recognisable
- Bacteria can also make enzymes that destroy antibiotics like beta-lactamase
- Extended spectrum beta-lactamases (ESBL)
- Resistant to sephalosporins
- Carbapenem substitute
Describe beta-lactam/beta-lactamase inhibitors
- Oral and IV
- Very broad-spectrum and highly potent
- Co-Amoxiclav (Amoxicillin and clavulanate)
- Tazocin (piperacullin- broad spectrum and tazobactam- beta-lactamase inhibitor)
Describe macrolides
- Oral and IV
- Broad spectrum
- Safe
- E.g. erythromycin, clarithromycin, azithromycin
- Also works against intracellular organisms, e.g. chlamydia
- Against gram positive (skin and soft tissue)
Describe tetracyclines
- Caution for pregnant women
- Broad spectrum
- Oral
- Doxycycline
- Active against plasmodia (also anti-malarial)
- However, may cause tooth discolouraiton in children and phototoxicity
- Gram pos, neg and intracellular organisms
Describe trimethoprim
- Oral
- Broad spectrum
- Excreted in urine
- Not safe in pregnancy (folic acid target)
- Used for coliforms
- UTIs (gram positive and negative)
Describe co-trimoxazole (Septrin)
- Trimethoprim and sulphamethoxazole
- Oral and iV
- Broad spectrum
- Quite potent and penetrates tissue
- May not be safe in pregnancy
- Works against some fungi
- E.g. pneumocystis in HIV
- Treats difficult pneumonia
Describe fluoroquinolones
- Oral and IV
- Safe and highly potent
- E.g. Ciprofloxacin (only gram neg like in kidney infections
- Moxifloxacin active against gram positive as well
What are the two classes of antibiotics that hit the cell wall?
- Beta lactam
- Glycopeptides
Describe Vancomycin
- Glycopeptide
- For those with high MRSA
- IV as orally not absorbed
- Adverse renal effects
- Must monitor plasma concentrations
- Not as good as flucloxacillin
- Only against gram positive
Describe Aminoglycosides
- E.g. Gentamicin
- IV
- Stays in bloodstream, good for bacteraemia
- Synergises with beta-lactam
- Ear and kidney toxicity- requires monitoring
- Long half-life
What antibiotic is used for anaerobes?
- Metronidazole
What causes ear infections?
Haemophilus influenzae
