Antimicrobials Flashcards
Four classes of beta lactams
Penicillins
Monobactams
Cephalosporins
Carbapenems
Narrow spectrum penicillins
Penicillin is mainly used for the treatment of Gram-positive pathogens such as streptococci, enterococci and anaerobes such as Clostridium spp
Phenoxymethylpenicllin V, oral
Benzylpenicillin, penicillin G, IV
Benzathine penicillin, IM, IV in system for 4 weeks
Procaine penicillin, IV
Anti-staphylcoccal penicillins
Members include: flucloxacillin, dicloxacillin. These drugs are stable to beta - lactamase produced by staphylococci and are therefore particularly useful against most strains of S. aureus.
Moderate spectrum penicillins
These agents, the aminopenicillins (amoxycillin and ampicillin), have greater activity than benzylpenicillin against common Gram-negative pathogens such as E. coli and H.influenzae.
Among patients with acute Epstein Barr virus infection (glandular fever), both drugs are similarly associated with the production of a prominent erythematous rash - however this does not indicate true allergy.
Broad spectrum antibiotics
Piperacillin and ticarcillin are active against Pseudomonas aeruginosa, but are generally administered in combination with a second anti-pseudomonal drug such an aminoglycoside.
Ticarcillin is generally inferior to piperacillin in its coverage of Klebsiella species, as well as enterococci. Both drugs are reasonably expensive, especially piperacillin.
Penicillin/beta-lactamase inhibitor combinations
amoxycillin (amoxycillin + clavulanate; Augmentin®)
ticarcillin (ticarcillin + clavulanate; Timentin®)
piperacillin (piperacillin + tazobactam; Tazocin®)
These have extended the spectrum of these drugs to include activity against S. aureus, anaerobes (e.g. B. fragilis) and strains of Gram-negative pathogens such as E. coli, Neisseria gonorrhoea and H. influenzae that are resistant to each of these penicillins alone.
First generation cephalosporins
Cephalothin
Cephazolin
Cephalexin
Good gram positive activity
Gram negative activity against enterobacteriacae, klebsiella
Second generation cephalosporins
Cefaclor and cefuroxime
Cefoxitin and cefotetan
Good gram positive cover
Improved gram negative cover, covers haemophilus, enterbacteriacae, klebsiella
Only cephalosporin group to cover anaerobes
Third generation cephalosporins
Cefotaxime and ceftriaxone
Ceftazidime
No MSSA cover
Ceftazidime does not cover MSSA or streptococci
Cefotaxime and ceftriaxone will have good gram negative coverage as does second generation
Ceftazidime will cover pseudomonas
Fourth generation cephalosporins
cefepime and cefpirome
Wider coverage than third generation
Will cover most gram positives including MSSA
Will cover most gram negatives including pseudomonas and ESCAPPM group
Fifth generation cephalosporin
Ceftaroline
MRSA and penicillin non-susceptible Strept. pneumoniae activity (PNSP)
Wide gram negative and gram positive activity
Carbapenems
Meropenem, ertapenem and imipenem
Action on wide spectrum of gram positive and negative bacteria
pseudomonas, ESCAPPMs, MRSA, Burkholderia cepacia and Stenotrophomonas maltophilia.
Meropenem has good CSF penetration
Glycopeptides
Vancomycin and Teicoplanin
Glycopeptides include vancomycin and teicoplanin, both of which are active against a wide range of Gram-positive organisms including MRSA and methicillin-resistant S. epidermidis (MRSE).
Aminoglycosides
Aminoglycosides (gentamicin, tobramycin, netilmicin, amikacin, streptomycin, neomycin and framycetin) are active against most Gram-negative pathogens including Pseudomonas aeruginosa, but have no substantive Grampositive activity as monotherapy.
Macrolides
Macrolides include erythromycin, roxithromycin, azithromycin and clarithromycin. They have a wide spectrum of activity including Gram-positive cocci such as streptococci and staphylococci, as well as so-called “atypical” pathogens such as Legionella, Mycoplasma and Chlamydia spp.
They are also active against Bordetella pertussis (whooping cough), Corynebacteria and some strains of H. influenzae. Notably, they have no activity against enteric Gram-negative bacilli and resistance among S. pneumoniae and S. aureus is increasing.
Azithromycin and clarithromycin are newer agents and have longer half lives
Clarithromycin has Mycobacterium avium activity
Tetracyclines
Tetracyclines have a broad range of activity against many Gram-positive and Gram-negative bacteria, mycoplasma, chlamydia, rickettsia and some spirochaetes.
Bacteriostatic
Emergence of resistance has limited the role of tetracyclines for treating some infections.
Photosensitive skin rash
IV tigecycline only efficicaous for MRSA, VRE, resistant mycoplasma (m. abscessus), poor choice for sepsis
Anaerobe and atypical activity, not pseudomonas activity
Anti-folate agents
Trimethoprim and sulfamethoxazole both have anti-folate activity that impairs satisfactory DNA production. Except in combination with trimethoprim as cotrimoxazole,
sulphonamides used in the treatment of cerebral toxoplasmosis
Cotrimoxazole is a useful antibiotic for a broad range of indications, but especially for the treatment and prophylaxis of Pneumocystis carinii, the treatment of Listeria monocytogenes, Nocardia spp. and Stenotrophomonas maltophilia infections, and as an alternative for the treatment of infections due to “ESCAPPM” organisms.
Stevens-Johnson syndrome is one extreme of this allergic spectra, with marked muco-cutaneous desquamation and potentially fatal outcome. Patients with a history of sulpha allergy should not be given cotrimoxazole.
Fluroquinolone
Fluoroquinolones (ciprofloxacin, norfloxacin, ofloxacin and enoxacin) broad range of activity against most Gramnegative bacteria (including Pseudomonas aeruginosa).
In addition, however, ciprofloxacin has excellent intra- cellular penetration and good oral availability, such that oral ciprofloxacin provides similar serum concentrations to intravenous ciprofloxacin.
Moxifloxacin extended Gram-positive spectrum to include activity against S. pneumoniae have recently been developed. Anaerobic, MSSA and atypical activity. No pseudomonas activity.
Side effects to fluoroquinolones include photosensitive skin rash, CNS toxicity (e.g. nightmares) and some agents interact with theophylline and caffeine.
Fluoroquinolones have been shown to damage the joints of immature animals and are therefore recommended to be used with caution in children under the age of 14 years.
Rifamycins
Rifabutin and rifampicin
Largely active against gram positive species including MRSA and mycobacterium
Inducers of P450
Rifampicin needs to be used in combination with fusidic acid or ciprofloxacin to avoid resistant emergence
Nitroimidazoles
Effective against gram positive and gram negative anaerobes
Anaerobic protozoa - trichomonas, giardia, entamoeba
C. diff infections
Effective in combination for intra-abdominal sepsis
Do not use with alcohol, disulfram-like activity occurs
Lincosamides
Clindamycin
Most anaerobes and gram positive aerobes
Toxoplasma gondii activity
Chloramphenicol and nitrofurantoin
Chrlorampenicol causes aplastic anaemia and dental issues in for unborn children
nitrofuratoin causes pulmonary fibrosis, polyneuropathy and acute hepatitis. Only used for UTIs
Linezolid
Binds to the 50S subunit of bacterial ribosomes
Its main indication is treatment of methicillin-resistant Staph aureus, vancomycinresistant Staph aureus and vancomycin-resistant Enterococcus.
Adverse reactions include: myelo-suppression, polyneuropathy taste perversion and abnormal liver function.
