random information on antibiotics usage

All cephalosporins have no activity against Enterococcus

Generally the higher the cephalosporin generation, the less Gram positive activity and the more Gram negative activity

Cephalosporins used to be spelt with “ph” but got changed to “f” → 1st generation cephalosporins are spelt with “ph” while the rest are spelt with “f”

Important oral cephalosporins are cephalexin, cefuroxime & cefaclor

Piperacillin, Ticarcillin, etc. (extended spectrum penicillins) are the only penicillins to have activity against Pseudomonas

Clavulanic acid, sulbactam & tazobactam are β-lactamase inhibitors that are combine with some penicillins to make them more effective

Amoxicillin + clavulanate = co-amoxiclav (Augmentin)

Ampicillin + sulbactam = Unasyn

Ticarcillin + clavulanate = Timentin

Piperacillin + tazobactam = Tazocin

Only oral penicillins are penicillin V, diclox/fluclox & amoxicillin

Common resistant bacteria

MRSA → methicillin resistant S. aureus (can be just methicillin resistant or multi-drug resistant)

MRSE → methicillin resistant S. epidermidis

Penicillin resistant Strep. pneumoniae & H. influenzae

VRE → vancomycin resistant Enterococcus

MRAB → multi-resistant Acinetobacter

ESBL bacteria → extended spectrum β-lactamase producing bacteria

GISA/VISA → glycopeptide/vancomycin intermediate S. aureus

Most resistance is acquired or inherent, not developed via mutation

Obviously you wouldn’t choose an antibiotic a bacteria is inherently resistant to

When an infection is exposed to the external environment, it is best to use multiple drugs to treat it so that resistance can’t be acquired from other bacteria

However, when the infection is “sterile”/closed off e.g. joint infections, abscesses, osteomyelitis, cellulitis, etc. there is less chance of acquiring resistance → a single antibiotic can be used e.g. only diclox/fluclox against osteomyelitis (unless MRSA)

Although most antibiotics have a short half life compared to other drugs, there is a post-antibiotic effect that is still inhibitory towards bacteria even when plasma levels of the antibiotic are sub-therapeutic → hence dosing is not needed as often as you may think




Antibiotic general uses
β-lactams → won’t go into here ‘cause it’s too much (see diagram)

Glycopeptides for MRSA

Aminoglycosides → used with β-lactams against Pseudomonas, used against Gram negatives

Tetracyclines → intracellular organisms, PID, CAP (especially atypical)

Macrolides → CAP (especially atypical including mycobacteria), chlamydia, some parasites, for people who are penicillin hypersensitive

Lincosamides → mixed anaerobic infections, some parasites, penicillin hypersensitivity

Streptogrammins → IV, glycopeptide resistant MRSA, VRE

Oxazolidinones → oral, VRE/MRSA/GISA

Fusidic acid + rifampicin → MRSA

Quinolones → Gram negatives, esp. Pseudomonas, intracellular organisms

Rifamycins → mycobacteria, MRSA, prophylaxis, good for all over skin action

Sulphamethoxazole + trimethoprim/ trimethoprim alone → UTIs

Nitroimidazoles → anaerobes, parasites

In general

Gram positives → penicillins

Staph skin/cone infections (without resistance) → di/fluclox, augmentin

Pseudomonas → extended spectrum penicillins, ceftazidime, cefepime, gentamicin, cipro

Anaerobes → metronidazole

Gram negatives → gentamicin, quinolones

Not much works against enterococcus