Antibiotic Classification and Mechanisms – Click for full size

Group	Examples	Action	Side effects	Uses / Info	Resistance	Broad	G+	G-	Anaerobes Sulphonamides folic acid inhibitor	Sulfasalazine, sulfadiazine	Static	Nausea, vomiting headaches, hypersensitivity, bone marrow depression, hepatitis	Rarely used due to resistance. Allergic reactions common Useless in infections with ‘pus’	Widespread	?	?	?	? Trimethoprim folic acid inhibitor	Trimethoprim	Static	Nausea, vomiting, skin rashes, megoblastic anaemia resulting from folate deficiency (give supplements)	May be used in combination with sulphonamide (co-trimoxazole) – particularly in pneumonia. Used alone in RTI and UTI	Moderate	Y	Y	Y	? Penicillin β-lactam 	Penicillin, benzylpenicillin, amoxicillin, flucloxacillin	Cidal	Few. hypersensitivity (1-10%), nausea, vomiting, encephalopathy (rare – due to renal impairment)	Most effective when given IV, can still be given orally. Often given to treat an as-yet unidentified infection. Very short HL’s.	Varies (β-lactamase)	Y – very!	Y	Y	? Cephalosporins Modified β-lactam	Cefuroxime, cephalexin, cefotaxime	Cidal	Hypersensitivity, nephrotoxicity, diarrhoea, skin rashes, headache	These are synthesised. There are ‘3 generations’. 1st generation not very widely used (resistance). Of those allergic to penicillns, 10% show cross allergy to cephalosporins	Varies	Y	Y 	Y*	? Monobactam Modified β-lactam	Aztreonam	Cidal		Used against Gram negative bacteria in people with penicillin allergy. Must be given IV or IM	?	N	N	Y	N Carbapenems Modified β-lactam	Imipenem	Cidal	Same as penicillins. Neurotoxicity at high concentrations	Very wide spectrum	?	Y	Y	Y	Y Tetracyclines t-RNA inhibitor	Tetracycline, doxycycline	Static	GI upset if not taken with enough water.  Photosensitivity	used in renal impairment as an alrternative to β – lactams used a prophylaxis for malaria	Widespread 	Y	Y	Y	? Aminoglycosides Inhibit cell wall synthesis	Gentamycin, streptomycin, neomycin	Cidal	Can cause sensori-neuro deafness – both in the adult, and in the foetus if given to a pregnant mother. Can also effect balance	Resistance can be overcome if used with penicillin or vancomycin. Useful in treating serious gram-positive infections	Widespread	Y	Y	Y**	N Glycopeptides Inhibit cell wall synthesis	Vancomycin, teicoplanin	Cidal	Nephrotoxicity, rashes, blood disorders, nausea	Generally only used for serious staphylococcal infection or IE. Also effective against C. difficile 	Uncommon		Y	N	? Macrolides Inhibit translocation of proteins	Erythromycin, clarithromycin	Cidal / static	GI disturbance, hypersensitivity, skin rashes. 	Generally good against G+, but not against G-. exceptions include H. influenzae and legionella	Moderate	Y	Y	N**	? Fusidic Acid Inhibits protein synthesis	Fucidic acid		GI disturbance, skin eruptions, jaundice	Narrow spectrum, used mainly against staphylococci. Most commonly used topically on lesions and conjunctivitis. 	Occurs rapidly when drug is used alone	N	Y	N	? Quinolones Inhibits DNA transcription 	Ciprofloxacin, levofloxacin, ofloxacin	Cidal	Few. GI disorders, skin rashes. dizziness and headaches. Don’t use in conjunction with theophylline (asthmatics)!	These are useful against Gram-positive bacteria that are resistant to penicillins. Ciprofloxacin is also good against gram-negative cocci. Generally better against G-	Uncommon	Y (varies with drugs)	Y	Y	N Metronidazole Inhibits DNA synthesthis, breaks down DNA	Metronidazole, tindazole	Cidal	Nausea, vomiting, metallic taste, intolerance to alcohol, rashes	It is equally effective against dividing and non-dividing cells. mainly used to treat C. difficile – that has often been brought on by other AB use	Uncommon, but growing	?	Y	?	Y – not effective against aerobic bacteria! Nitrofurantoin Disrupts DNA	Nitrofurantoin	Cidal	Peripheral neuropathy, GI upset, long term use can cause lung fibrosis	Effective against most G+ cocci, and against E.coli (G-). Often used for LUTI’s	Uncommon		Y	N	 Tetra-cyclines Inhibit protein synthethesis	Doxycycline, minocycline, oxytetracycline	Static	Nausea, vomiting, diarrhoea, discolouration of the teeth in children, intracranial hypertension	They are very broad spectrum, and also often used in acne, chlamydia^, cholera, mycoplasma	G+ common G- moderate	Y	Y	Y	 Chlorampenicol Inhibits protein synthesis	Chloramphenicol	Static	Highly Toxic. Bone marrow toxicity, neuritis, headache, rashes, grey baby syndrome	Highly toxic – and thus generally reserved for life-threatening conditions. Also used topically for conjunctivitis 	Moderate	Y	Y	Y	? Lyncosamides Inhibit protein synthesis	Clindamycin	Cidal/static	Nausea, vomiting, rashes, jaundice, neutropaenia, thrombocytonpaenia (bone marrow suppression)	Used as prophylaxis for IE in penicillin allergy. Used for strep. Bone infections	Moderate	?	Y	Y	 •	*Gram-negative’s produces a different β-lactamase to Gram-positives; thus cephalosporins are still vulnerable to this (but not to the one produced by Gram-positives).  •	**only against some -	^chalmydia is not G+ or G-; it is its own thing, as is mycoplasma. Mycoplasma has no cell wall, and thus is unaffected by the β – lactams, as they inhibit cell wall synthesis

 

 

Gram Positive and Gram Negative Bacteria – Click for full size

Gram-Positive	Gram-negative Bacteria	Commonly found in	Common treatment	Bacteria	Commonly found in	Common treatment Staphylococci & streptococci	Skin and wound infections	Vancomycin, Teicoplanin, Gentamicin (staphylococci only).  Resistant to: Cephalosporins, metronidazole (except clostridia)	The Coliform bacteria; E. Coli, Klebsiella, enterobacter, salmonella	The Gut! UTI, also can cause ventilator assisted pneumonia, wound infection, biliary tract infection, septicaemia	Cephalosporins, gentamicin, ciprofloxacin, tazocin, imipenem, trimethoprim Resistant to: amoxicillin, Staph, Enterococci, corynebacteria	Line related infection		Pseudomonas	Moist environments – chronic leg ulcers. Catheters, pneumonia, septicaemia, CF/bronchiectasis	Aminoglycosides, cipro, tazocin, imipenem Resistant to: Most other AB’s Clostridia	Gangrenous wound infections, abdominal infections		Bacteroids – anaerobic bacteria	Intra-abdominal infections, soft tissue infection below the waist	Metronidazole, co-amoxiclav, imipenem, Tazocin, clindamycin Resistant to: Benzylpenicillin, amoxicillin, cefuroxime, gentamicin, quinolones, macrolides

 Drugs used in TB
Rifamycins
Inhibits DNA transcription
Rifamycin, rifabutin
Cidal
Nausea, anorexia, pseudomembranous colitis, hepatotoxicity, orange colouration of excreted bodily fluids, toxicity syndromes, drug interactions
Also used in mycobacterial infections – these most commonly occur in those with HIV. Resistance prevents more widespread use
Widespread – develops rapidly
Y
?
?
?
Isoniazid
Inhibits synthesis of cell wall
Isoniazid
Cidal / static
Nausea, vomiting, constipation, peripheral neuropathy, hepatitis, SLE-like-symptoms
Bactericidal on dividing organisms, static on resting. Only effective against myobacteria
Occurs rapidly if used alone
N
N
N
?
Pyrazinamide
Lowers intracellular pH, disrupting synthesis of fatty acids
pyrazinamide
Cidal
Hepatotoxicity, nausea, vomiting, arthralgia, sideroblastic anaemia
Only effective against myobacteria
Occurs rapidly if used alone
N
N
N
?
Ethambutol
Interferes with cell wall synthesis
Ethambutol
Static
Optic neuritis – resulting in red/green colourblindness. neuritis
Only effective against myobacteria
Uncommon
N
N
N
Myobacteria
This is its own genus of bacteria (like G+ or G-). The group include TB and leprosy. They are acid fast. They are also aerobic.
 
Acid fast
This basically means the organisms are difficult to stain using normal staining techniques. The name refers to the fact they can’t be stained by normal acid (ethanol) staining techniques. These bacteria are often particularly difficult to culture and identify; e.g. TB takes around 6-8 weeks
‘Sore Throat’
If you are going to give antibiotics, don’t give amoxicillin. If the infection is glandular fever, then the amoxicillin can cause a reaction, and the patient can come out in a rash.

 

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