Antibacterials Flashcards
Mechanism of action of amoxicillin ?
Inhibits cell wall synthesis by preventing cross linking between peptidoglycan chains, leads to cell lysis (bactericidal)
Indications for amoxicillin
- Gram +ve: streptococci e.g. Pneumoniae
- Gram -ve: H. Influenzae, N Gonorrhoeae
- H pylori eradication
- infective endocarditis prophylaxis before dental surgery
Contraindications for amoxicillin ?
- hypersensitivity to penicillins or cephalosporin
- suspected/confirmed Infectious mononucleosis (develop generalised itchy rash)
Common side effects of amoxicillin ?
- nausea, vomiting, diarrhoea
- skin rash
- vaginal thrush
- hypersensitivity (rare)
Elimination of amoxicillin ?
Kidneys
What type of antibiotic is trimethoprim ?
Anti folate
Mechanism of action if trimethoprim ?
Decreases bacterial folate production by inhibiting dihydrofolate reductase which inhibits sequential enzymes in purine synthesis thus inhibiting DNA synthesis (bacteriostatic)
Indications for trimethoprim ?
- UTI (e. Coli, p. Mirabilis)
- acute or chronic bronchitis
- pneumocystic pneumonia
Contraindications of trimethoprim ?
- blood dyscrasias
- pregnancy (1st trimester)
- caution in severe renal impairment
Side effects of trimethoprim
- nausea, vomiting, diarrhoea
- blood dyscrasias
- rash (e.g. TEN)
- hypersensitivity
Interactions of trimethoprim
- cyclosporins - increase risk of nephrotoxicity
- pyrimethamine - increase anti folate effects
What drug class is doxycycline ?
Tetracycline antibiotic
Mechanism of action if doxycycline ?
Inhibits ribosome (30s) and thus protein synthesis - bacteriostatic
Indications of doxycycline ?
- malaria prophylaxis
- pneumonia
- resp infections caused by: staph, strep, H influenzae (inc sinusitis)
- skin & soft tissue: acne, rosacea, cellulitis, abscess
- syphilis, chlamydia
- chronic protatitis
Contraindications of doxycycline
- children
Elimination of doxycycline
Kidneys
Side effects of doxycycline ?
- nausea, vomiting, diarrhoea
- oesophagitis
- photosensitivity
- rash
- hypersensitivity
Interactions of doxycycline
- carbamazepine/phenytoin - increased doxycycline metabolism
- methotrexate- increased risk of methotrexate toxicity
What drug class is cephalexin?
Cephalosporin - broad spectrum
Mechanism of action if cephalexin “
Inhibits cell wall synthesis, leads to cell lysis (bacteriocidal)
Side effects of cephalexin ?
- diarrhoea, nausea, vomiting
- dyspepsia
- hypersensitivity
How are cephalosporins excreted ?
Mostly renal
Contraindications of cefalexin ?
- cephalosporin hypersensitivity
- immediate hypersensitivity to penicillins
Side effects of cephalosporins ?
- diarrhoea, nausea, vomiting
- rash
- rarely: antibiotic associated colitis
Indication for cephalosporins ?.
- septicaemia
- pneumonia
- meningitis
- biliary tract infections
- UTI
- peritonitis
Susceptible gram positive and negative
What drug class is meropenem ?
Carbapenem - beta lactam antibacterial, broad spectrum activity
Are carbapenems active against MRSA ?
No
Indications for meropenem ?
Aerobic and anaerobic gram positive and negative infections
What are aminoglycosides ? What do they work against ?
Bactericidal antibiotics active against mainly gram negative bacteria e.g. Pseudomonas aeruginosa
Why must aminoglycosides be injected for systemic infections ?
As are not absorbed through the gut
Side effects of aminoglycosides
- ototoxicity
- nephrotoxicity
- most commonly in elderly and renal failure *
Where are aminoglycosides excreted ?
Kidney
Which drug class is gentamicin ?
Aminoglycoside
What is gentamicin inactive against ?
- Anaerobes
- poor activity against haemolytic streptococci and pneumococci
What is the blind therapy for serious illness ?
Gentamicin + penicillin or metronidazole
- serious unidentifiable infection
Indications for gentamicin ?
- septicaemia
- CNS infections
- acute pyelonephritis
Contraindications in gentamicin ?
- myasthenia gravis
- pregnancy
Side effects of gentamicin ?
- vestibular and auditory damage
- nephrotoxicity
Interactions of gentamicin
- Cyclosporins: potentiate nephrotoxic effect
- loop diuretics (furosemide): potentiate ototoxicity
Why is erythromycin usually used as an alternative for penicillin allergic patients ?
Has a similar but not identical spectrum
What drug class is erythromycin ?
Macrolide
Indications for erythromycin
- resp infections e.g. Pharyngitis, tonsillitis (caused by strep)
- whooping cough
- legionnaires disease
- campylobacter enteritis
- penicillin resistant staphylococci
- CAP
What class of drug is amoxicillin ?
Broad spectrum penicillin, b-lactam
Contraindications of erythromycin ?
Macrolide hypersensitivity
Side effects of erythromycin ?
Common: GI disturbance, rash
Uncommon: reversible ototoxicity, cholestatic jaundice
Elimination of erythromycin ?
Biliary ?
- hepatic ?
What drug class is ciprofloxacin ?
Quinolone - broad spec antibiotic
Mechanism of action of erythromycin ?
Binds to 5s subunit of bacterial ribosomes, inhibiting bacterial protein synthesis
Mechanism of action of ciprofloxacin
Quinolone:
- inhibits bacterial enzyme DNA gyrase, an enzyme that cuts and reseals DNA, allowing it to be unwound and read
- quinolones inhibit the resealing, leading to fragmentation of DNA -> cell death
Side effects of ciprofloxacin
- diarrhoea
- CNS effects: dizziness, confusion, tremor
- seizures
- QT prolongation
- tendonitis
Indications for ciprofloxacin ?
- acute exacerbation of chronic bronchitis - H influenzae, M catarrhalis
- acute pneumonia - enterbacter, H influenzae, E Coli etc
- sinusitis
- upper and lower UTI
- skin and soft tissue infections - staph A + E and strep p
- typhoid
- N Gonorrhoeae
Contraindications of ciprofloxacin
- hypersensitivity to any quinolones
- concurrent treatment with tizanidine (muscle relaxant)
Elimination of quinolones ?
Renal
What class of antibiotic is metronidazole ?
Nitroimidazole
Indications for metronidazole
Anaerobic organisms e.g.
- intra abdo infections: c diff, h pylori
- bacterial vaginosis
- protozoal infections
Mechanism of action of metronidazole
Broken down within anaerobic organism into toxic metabolites -> kills microbes by interfering with nucleic acid function and synthesis
Side effects of metronidazole ?
- GI disturbance
- elevation in liver enzymes
- CNS effects: dizziness, confusion, tremor
Contraindications for metronidazole
- hypersensitivity
- caution: pregnancy and hepatic impairment
Interactions with metronidazole
- alcohol: flushing, abdo pain, hypotension (disulfiram-like reaction)
- phenytoin: increased plasma conc of phenytoin
- warfarin: increased plasma conc of warfarin
Main route of elimination for metronidazole
Kidney
