Antibacterials

Question 1

Mechanism of action of amoxicillin ?

Answer 1

Inhibits cell wall synthesis by preventing cross linking between peptidoglycan chains, leads to cell lysis (bactericidal)

Question 2

Indications for amoxicillin

Answer 2

• Gram +ve: streptococci e.g. Pneumoniae
• Gram -ve: H. Influenzae, N Gonorrhoeae
• H pylori eradication
• infective endocarditis prophylaxis before dental surgery

Question 3

Contraindications for amoxicillin ?

Answer 3

• hypersensitivity to penicillins or cephalosporin

- suspected/confirmed Infectious mononucleosis (develop generalised itchy rash)

Question 4

Common side effects of amoxicillin ?

Answer 4

• nausea, vomiting, diarrhoea
• skin rash
• vaginal thrush
• hypersensitivity (rare)

Question 5

Elimination of amoxicillin ?

Answer 5

Kidneys

Question 6

What type of antibiotic is trimethoprim ?

Answer 6

Anti folate

Question 7

Mechanism of action if trimethoprim ?

Answer 7

Decreases bacterial folate production by inhibiting dihydrofolate reductase which inhibits sequential enzymes in purine synthesis thus inhibiting DNA synthesis (bacteriostatic)

Question 8

Indications for trimethoprim ?

Answer 8

• UTI (e. Coli, p. Mirabilis)
• acute or chronic bronchitis
• pneumocystic pneumonia

Question 9

Contraindications of trimethoprim ?

Answer 9

• blood dyscrasias
• pregnancy (1st trimester)
• caution in severe renal impairment

Question 10

Side effects of trimethoprim

Answer 10

• nausea, vomiting, diarrhoea
• blood dyscrasias
• rash (e.g. TEN)
• hypersensitivity

Question 11

Interactions of trimethoprim

Answer 11

• cyclosporins - increase risk of nephrotoxicity

- pyrimethamine - increase anti folate effects

Question 12

What drug class is doxycycline ?

Answer 12

Tetracycline antibiotic

Question 13

Mechanism of action if doxycycline ?

Answer 13

Inhibits ribosome (30s) and thus protein synthesis - bacteriostatic

Question 14

Indications of doxycycline ?

Answer 14

• malaria prophylaxis
• pneumonia
• resp infections caused by: staph, strep, H influenzae (inc sinusitis)
• skin & soft tissue: acne, rosacea, cellulitis, abscess
• syphilis, chlamydia
• chronic protatitis

Question 15

Contraindications of doxycycline

Answer 15

• children

Question 16

Elimination of doxycycline

Answer 16

Kidneys

Question 17

Side effects of doxycycline ?

Answer 17

• nausea, vomiting, diarrhoea
• oesophagitis
• photosensitivity
• rash
• hypersensitivity

Question 18

Interactions of doxycycline

Answer 18

• carbamazepine/phenytoin - increased doxycycline metabolism

- methotrexate- increased risk of methotrexate toxicity

Question 19

What drug class is cephalexin?

Answer 19

Cephalosporin - broad spectrum

Question 20

Mechanism of action if cephalexin “

Answer 20

Inhibits cell wall synthesis, leads to cell lysis (bacteriocidal)

Question 21

Side effects of cephalexin ?

Answer 21

• diarrhoea, nausea, vomiting
• dyspepsia
• hypersensitivity

Question 22

How are cephalosporins excreted ?

Answer 22

Mostly renal

Question 23

Contraindications of cefalexin ?

Answer 23

• cephalosporin hypersensitivity

- immediate hypersensitivity to penicillins

Question 24

Side effects of cephalosporins ?

Answer 24

• diarrhoea, nausea, vomiting
• rash
• rarely: antibiotic associated colitis

Question 25

Indication for cephalosporins ?.

Answer 25

- septicaemia - pneumonia - meningitis - biliary tract infections - UTI - peritonitis Susceptible gram positive and negative

Question 26

What drug class is meropenem ?

Answer 26

Carbapenem - beta lactam antibacterial, broad spectrum activity

Question 27

Are carbapenems active against MRSA ?

Answer 27

No

Question 28

Indications for meropenem ?

Answer 28

Aerobic and anaerobic gram positive and negative infections

Question 29

What are aminoglycosides ? What do they work against ?

Answer 29

Bactericidal antibiotics active against mainly gram negative bacteria e.g. Pseudomonas aeruginosa

Question 30

Why must aminoglycosides be injected for systemic infections ?

Answer 30

As are not absorbed through the gut

Question 31

Side effects of aminoglycosides

Answer 31

- ototoxicity - nephrotoxicity * most commonly in elderly and renal failure *

Question 32

Where are aminoglycosides excreted ?

Answer 32

Kidney

Question 33

Which drug class is gentamicin ?

Answer 33

Aminoglycoside

Question 34

What is gentamicin inactive against ?

Answer 34

- Anaerobes | - poor activity against haemolytic streptococci and pneumococci

Question 35

What is the blind therapy for serious illness ?

Answer 35

Gentamicin + penicillin or metronidazole - serious unidentifiable infection

Question 36

Indications for gentamicin ?

Answer 36

- septicaemia - CNS infections - acute pyelonephritis

Question 37

Contraindications in gentamicin ?

Answer 37

- myasthenia gravis | - pregnancy

Question 38

Side effects of gentamicin ?

Answer 38

- vestibular and auditory damage | - nephrotoxicity

Question 39

Interactions of gentamicin

Answer 39

- Cyclosporins: potentiate nephrotoxic effect | - loop diuretics (furosemide): potentiate ototoxicity

Question 40

Why is erythromycin usually used as an alternative for penicillin allergic patients ?

Answer 40

Has a similar but not identical spectrum

Question 41

What drug class is erythromycin ?

Answer 41

Macrolide

Question 42

Indications for erythromycin

Answer 42

- resp infections e.g. Pharyngitis, tonsillitis (caused by strep) - whooping cough - legionnaires disease - campylobacter enteritis - penicillin resistant staphylococci - CAP

Question 43

What class of drug is amoxicillin ?

Answer 43

Broad spectrum penicillin, b-lactam

Question 44

Contraindications of erythromycin ?

Answer 44

Macrolide hypersensitivity

Question 45

Side effects of erythromycin ?

Answer 45

Common: GI disturbance, rash Uncommon: reversible ototoxicity, cholestatic jaundice

Question 46

Elimination of erythromycin ?

Answer 46

Biliary ? | - hepatic ?

Question 47

What drug class is ciprofloxacin ?

Answer 47

Quinolone - broad spec antibiotic

Question 48

Mechanism of action of erythromycin ?

Answer 48

Binds to 5s subunit of bacterial ribosomes, inhibiting bacterial protein synthesis

Question 49

Mechanism of action of ciprofloxacin

Answer 49

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

Question 50

Side effects of ciprofloxacin

Answer 50

- diarrhoea - CNS effects: dizziness, confusion, tremor - seizures - QT prolongation - tendonitis

Question 51

Indications for ciprofloxacin ?

Answer 51

- 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

Question 52

Contraindications of ciprofloxacin

Answer 52

- hypersensitivity to any quinolones | - concurrent treatment with tizanidine (muscle relaxant)

Question 53

Elimination of quinolones ?

Answer 53

Renal

Question 54

What class of antibiotic is metronidazole ?

Answer 54

Nitroimidazole

Question 55

Indications for metronidazole

Answer 55

Anaerobic organisms e.g. - intra abdo infections: c diff, h pylori - bacterial vaginosis - protozoal infections

Question 56

Mechanism of action of metronidazole

Answer 56

Broken down within anaerobic organism into toxic metabolites -> kills microbes by interfering with nucleic acid function and synthesis

Question 57

Side effects of metronidazole ?

Answer 57

- GI disturbance - elevation in liver enzymes - CNS effects: dizziness, confusion, tremor

Question 58

Contraindications for metronidazole

Answer 58

- hypersensitivity | - caution: pregnancy and hepatic impairment

Question 59

Interactions with metronidazole

Answer 59

- alcohol: flushing, abdo pain, hypotension (disulfiram-like reaction) - phenytoin: increased plasma conc of phenytoin - warfarin: increased plasma conc of warfarin

Question 60

Main route of elimination for metronidazole

Answer 60

Kidney