Antibiotics Flashcards
What is the antibiotic treatment for a community acquired pneumonia?
Amoxicillin
Doxycycline or clarithromycin for penicillin allergic
What is the basic mechanism of penicillins?
Cell wall synthesis inhibitors
They inhibit transpeptidase so remodelling of NAM + NAG chains can’t occur
If penicillin allergic, which other antibiotics should be avoided?
Cephalosporin (also beta-lactams)
When should you not give amoxicillin?
Sore throat in children - if it is EBV it will cause a rash
What are some indications for penicillins?
- Gram positive bacteria e.g. staph + strep
- Meningococci
- Pneumococcal infections
- Tetanus
What drug do penicillins interact with?
They reduce renal excretion of methotrexate which is a folate antagonist
What is generally used for skin infections?
Flucloxacillin
Erythromycin if allergic
Name some cephalosporins
Ceftriaxone
Cefazolin
Cefuroxime
How do cephalosporins work?
They inhibit enzymes involved in cross-linking the cell wall
What are cephalosporins used for?
UTIs
More severe infection
Antibiotic-resistant infections
What is the main risk of cephalosporins
C. difficile infection
What are the C. difficile causing antibiotics
Cephalosporins
Ciprofloxacin
Clarithromycin
What drug do cephalosporins interact with?
Warfarin - they kill the gut flora that synthesises vitamin K so the effect of warfarin is increased
Name some macrolides
Erythromycin
Clarithromycin
Azithromycin
How is azithromycin different to the other macrolides?
It is not a CYP450 inhibitor
What are the main indications for macrolides
LRTIs - particularly mycoplasma pneumoniae
Skin infections when penicillin allergic
Eradication of H. Pylori with amoxicillin and PPI
Describe the mechanism of macrolides
They bind to 50S ribosomal subunit to inhibit protein synthesis
What are the QT interval prolonging drugs
Amiodarone Lithium SSRIs Quinolones Macrolides Antipsychotics e.g. lithium Antihistamines
What drugs do macrolides interact with and why?
They are CYP450 inhibitors
Increase the concentration of warfarin, statins, antidepressants
Name 2 quinolones
Ciprofloxacin
Levofloxacin
What are the indications for quinolones
UTI
GI infection - salmonella, shigella, campylobacter
HAP - pseudomonas aeroginosa
What is the other antibiotic used to treat pseudomonas aeroginosa?
IV gentamicin
What are some important side effects of quinolones?
- C. difficile
- Prolonged QT interval
- Rupture of achilles tendon
- Seizures
What condition can also cause rupture of achilles tendon?
Cushing’s (weak tendons)
How do quinolones interact with other drugs?
They are CYP450 inhibitors
Name the CYP450 inhibitors
Some Certain Silly Compounds Annoyingly Inhibit Enzymes, Grr
Sodium valproate Ciprofloxacin Sulphonamide Cimetidine/omeprazole Antifungals, amiodarone Isoniazid Erythromycin/clarithromycin Grapefruit juice
What antibiotic is used for serious gram negative aerobe infections?
Gentamicin
Name some indications for gentamicin
Endocarditis
Pyelonephritis/complicated UTI
Sepsis
Pseudomonas aeroginosa LRTI
What drug class is gentamicin in? How do they work?
Aminoglycosides
Enter cells via oxygen transport system
Bind to 30S subunit of ribosomes and inhibit protein synthesis
What antibiotics is gentamicin often used with and why?
Beta-lactams
To weaken the cell wall and make it more effective
What are the 2 main side effects of gentamicin?
Ototoxicity
Nephrotoxicity
When is gentamicin contraindicated?
Myasthenia gravis - it impairs neuromuscular transmission
What other drugs cause ototoxicity?
Loop diuretics
Macrolides at high doses
Gentamicin
Vancomycin
Which drugs would increase risk of nephrotoxicity if given with gentamicin?
Ciclosporin
Chemotherapy
Cephalosporins
How is co-amoxiclav effective against anaerobes?
Penicillins aren’t effective against anaerobes.
However, the acid component (clavulanic acid) breaks down the beta-lactamases that make bacteria anaerobic
Name a tetracycline
Doxycycline
What are tetracyclines used for?
- Acne vulgaris - Propionibacterium acnes
- LRTIs - Chlamydia pneumoniae
- Chlamydia
- Typhoid
- Anthrax
- Malaria
- Lyme disease
What are the main side effects of tetracyclines
Photosensitivity
Discolouration of teeth
Who should you not give tetracyclines to?
Pregnant women and children
Harms teeth, bones and liver
Blue/black discolouration
What decreases absorption of tetracyclines?
Divalent cations e.g. calcium, antacids, iron
What gram bacteria is vancomycin only effective against?
Gram positive
Name some indications for vancomycin
- MRSA
- Severe C. difficile infection when metronidazole could not treat it
- Endocarditis
What kind of reaction can occur due to vancomycin?
Anaphylactoid reaction -> Red man syndrome
What other side effects can vancomycin cause?
- Thrombophlebitis if given IV
- Ototoxicity
- Nephrotoxicity
- Neutropenia
- Thrombocytopenia
What drug class is vancomycin in ?
Glycopeptides
Name an anaerobic antimicrobial. How do they work
Metronidazole
They enter bacteria and are reduced, which releases a free radical that prevents DNA synthesis
What is the main contraindication for metronidazole?
Alcohol - it inhibits acetyldehydrogenase
What are the main indications for metronidazole
- Bacterial vaginosis
- C. difficile
- Dental abscesses
- Endocarditis
- H. Pylori eradication with amoxicillin + PPI
What side effects might you get with metronidazole?
Metallic taste
Dark urine
Peripheral neuropathy
Seizures
What drug does metronidazole particularly interact with?
Lithium
Which antibiotic inhibits folate synthesis? What should you not give it with?
Trimethoprim
Don’t give with methotrexate (folate antagonist)
What is trimethoprim used for?
- UTIs
2. Pneumocystis pneumonia - co-trimoxazole (trimethoprim + sulfamethoxazole)
What is an important interaction with trimethoprim?
It enhances the effect of warfarin
What are the main side effects of trimethoprim?
Hyperkalaemia
Impaired haematopoiesis - folate deficiency
Who should you not give trimethoprim to?
- Pregnant women particularly in first trimester
- Folate deficiency
- Renal impairment
- Neonates, elderly, HIV
Which antibiotic is used in long term UTIs or UTI prophylaxis?
Nitrofurantoin
Which organisms is nitrofurantoin particularly effective against?
E. Coli
Staphylococcus saprophyticus
Who should not be given nitrofurantoin?
Pregnant women and neonates - risk of haemolytic anaemia in the baby
People with renal impairment
Name some side effects of nitrofurantoin?
- Dark brown urine
- Peripheral neuropathy
- Pulmonary reactions - acute and chronic
