#7534 - Antibiotics Extended - Medical Finals & OSCEs Notes

Antibiotics (Extended Notes)

Cephalosporins

..Related to penicillins – similar coverage – affect cell wall synthesis – broad spectrum – allergies overlap with penicillins. 1-6% of people with a penicillin allergy have a cephalosporin allergy also. ..Renally excreted – watch out for dosing in renal failure. Recently fallen out of favour due to C. diff risk.

..Indications: meningitis for ceftriaxone. Severe pneumonia, peritonitis, second-line in sepsis, if you’re worried about a UTI in pregnancy. First line in ascending cholangitis and cholecystitis.

..3 generations:

1. Cefalexin – susceptible to beta-lactamases, UTIs in pregnancy

2. Cefuroxime – good against Haemophilus influenza and gonorrhoea

3. Ceftriaxone – usually used, salts can precipitate in gall bladder with calcium, careful in renal failure and when giving calcium

Quinolones – Ciprofloxacin (all quinolones have flox in the name)

Inhibitors of DNA making. Active against G+ve and G-ve, not good against Strep. pneumo, so not in pneumococcal pneumonia.

Five indications: (SCAN Ships)

S almonella

CA mpylobacter

N eisseria

Ships – Shigella and Pseudomonas

Most anaerobes are not susceptible. Many staphs are resistant.

Indications: RTIs if not pneumococcal, UTI, GI infection, bone & joint infections, gonorrhoea, septicaemia for sensitive organisms.

NOT safe in pregnancy. CAN use in penicillin allergy.

Generally a second-line agent due to an increased risk of C. diff.

Amoxifloxacin – second or third line in respiratory tract stuff

Adverse effects: Generally well tolerated. Increased risk of C. diff colitis. Tendon rupture. Increased risk if over sixty, should not use concurrently with corticosteroids or someone with a transplant has an increased risk of tendon rupture.

Contra-indications: pregnancy, breast-feeding, epilepsy.

Macrolides – erythromycin, azithromycin, clarithromycin (all have thromycin in the name)

(NOT clindamycin, NOT vancomycin, NOT streptomycin /neomycin /gentamicin /amikacin / tobramycin.)

Inhibit protein synthesis. Unlike other antibiotics, this is bacteria-static, not bactericidal.

They have similar spectrum to penicillins and are a good alternative in people who are allergic; they are good against a wide range of bugs and also some rare stuff; BUT each individual one has slightly different activity profiles, so are not as a class a good broad spectrum.

Clarithromycin is good because it has a high concentration in tissues therefore it is more potent and requires twice daily dosing which reduces GI side-effects.

Azithromycin is good against Haemophilus, unlike the other two.

Erythromycin is good for serious infections, but requires high doses and have GI side-effects in a dose-related manner.

Indications: moderate to severe CAP as an alternative or in addition to co-amoxiclav, Chlamydia, syphilis, H. pylori, campylobacter. Mostly clarithromycin is used.

Side-effects: diarrhoea & nausea are dose-related (can use as a laxative). Phlebitis in IV administration, so only oral, so use is limited. Cholestatic jaundice, prolonged QT.

Contra-indicated in liver failure; not renally excreted so safe in renal failure. Some are unsafe in pregnancy.

Clindamycin

Inhibitor of bacterial protein synthesis.

Active against G+ve cocci, including streptococci and penicillin-resistant staph. Also active against many anaerobes BUT metronidazole is better. Main indication is streps & staphs; it is useful because it is well-concentrated in bone, so recommended for osteomyelitis etc., and also intra-abdominal sepsis because it is also good against anaerobes. It is an alternative to macrolides, can be given when people cannot tolerate macrolides due to GI symptoms. Used as part of combination therapy for malaria. It is a second-line agent due to its C. diff probability.

Renally excreted.

10-30% of people get diarrhoea which isn’t C. diff related, but stop it anyway as 6% of people get C. diff colitis. Also get a mobiliform rash.

Metronidazole

We don’t know how it works, but it’s great against anaerobes, protozoa and H. pylori i.e. gut. THINK GUT. Indications are mostly GI: abdominal sepsis (with tazocin or co-amoxiclav), ascending cholangitis/cholecystitis (with ceftriaxone), diverticulitis, C. diff. Also PID/bacterial vaginosis, and in open fracture prophylaxis and human and animal bites as an add-in or as an...