Antibiotics - Pt2

Question 1

What are some groups of antibiotics which target protein synthesis?

Answer 1

Aminoglycosides, tetracyclines, macrolides, lincosamides, oxazolidinones and chloramphenicol

Question 2

What are some types of aminoglycosides?

Answer 2

Gentamicin, streptomycin, kanamycin and neomycin

Question 3

What is the mechanism of action of aminoglycosides?

Answer 3

Binds 30S subunit of rRNA complex
Bacteriostatic
Irreversible binding of 30S subunit
Depolarises cell membrane - binds anionic cell membrane component which gives reduced membrane integrity

Question 4

When is streptomycin used?

Answer 4

TB
Given by IV

Question 5

When is kanamycin used?

Answer 5

Gentamicin - sepsis - IV and topical
Tobramycin - sepsis and CF - IV and inhaled
Amikacin - sepsis, TB, CF and nocardia - IV
Plazomicin - sepsis

Question 6

What is neomycin used for?

Answer 6

Intraluminal treatment
Giardia, amoebiasis, cryptosporidium and topical treatment leishmania
PO or topical route

Question 7

Describe nephrotoxicity of aminoglycosides

Answer 7

RF - age, cirrhosis, prolonged use and other nephrotoxins
Commoner after 7 day use
Reversible
Site is renal cortex

Question 8

Describe ototoxicity/ vestibulotoxicity by aminoglycosides

Answer 8

Mitochondrial toxicity - hair cell death
Dose independent and often irreversible
Deafness - high frequency initially and worse with furosemide

Question 9

Describe neuromuscular blockade by aminoglycosides

Answer 9

Blocks presynaptic ACh release/ postsynaptic receptors
Caution when concomitantly with neuromuscular blockade drugs

Question 10

Describe tetracyclines

Answer 10

Broad spectrum bacteriostatic antibiotics
Differ in pharmacological properties rather than spectrum of cover
High bioavailability - given orally
Inhibits bacterial protein synthesis - reversible binding to 30S subunit

Question 11

What are the types of tetracyclines?

Answer 11

Tetracycline, doxycycline and tigecycline

Question 12

Describe doxycycline spectrum and usage

Answer 12

SSTI, CAP and atypical, Genito-urinary infection, rickettsia, malaria prophylaxis and treatment and bone + joint

Question 13

What are the tetracycline side effects?

Answer 13

Photosensitivity and gastritis - oesophageal ulcer

Question 14

Why are tetracyclines not used for children and pregnancy?

Answer 14

Crosses placenta - maternal hepatotoxicity, foetal tooth discoloration and delay of long bones
High conc. in breast milk
Children under 8 - cause permanent tooth staining

Question 15

What are types of macrolides?

Answer 15

Erythromycin
Clarithromycin
Azithromycin

Question 16

What is erythromycin used for?

Answer 16

Skin and soft tissue infections (SSTI)
Community acquired pneumonia

Question 17

What is clarithromycin used for?

Answer 17

Skin and soft tissue infections
Community acquired pneumonia
Atypical pneumonia - listeria, mycoplasma and psticossis
H. pylori
Toxoplasma gondii

Question 18

What is azithromycin used for?

Answer 18

Typhoid fever - salmonella typhi and paratyphi
STI - gonorrhoea and chlamydia

Question 19

What are the side effects of macrolides?

Answer 19

Jaundice, ototoxicity, prolonged QT syndrome and GI disturbance

Question 20

Are macrolides used when pregnant or breastfeeding?

Answer 20

Erythromycin - not known to be harmful and only small amounts in breastmilk
Clarithromycin - avoid unless positives outweigh and present in breastmilk
Azithromycin - only use if alternative is mot available and present in breastmilk

Question 21

Describe metronidazole

Answer 21

Inhibition of DNA synthesis
Anaerobic organisms
Pro drug and activated intracellularly in anaerobic conditions
Widespread throughout all tissues
Metallic taste reported
Don’t take with alcohol

Question 22

What antibiotics can inhibit folic acid synthesis and what are the side effects?

Answer 22

Trimethoprim and co-trimoxazole
Side effects - renal impairment and bone marrow suppression

Question 23

When is trimethoprim used?

Answer 23

UTIs

Question 24

When is co-trimoxazole used?

Answer 24

Pneumocystis jiroveci pneumonia
Toxoplasmosis
Multidrug resistant organisms - mycobacterium species and stenotrophomonas

Question 25

How is susceptibility or resistance measured?

Answer 25

Disc diffusion (zone of inhibition seen on disc) and gradient strips

Question 26

What are some mechanisms of resistance?

Answer 26

Efflux pumps, decreased uptake, target alterations, alternative enzymes and inactivating enzymes

Question 27

What are some considerations for prescribing?

Answer 27

Formulation, source of infection, patient allergies, patient medications and likely organisms