There are many classes of antibiotics. It is useful to know at least a handful of antibiotics, and what they are useful for. Below we attempt to summarise the main types of antibiotics, their mechanisms and their common uses.
Antibiotic Classification and Mechanisms – Click for full size
Gram Positive and Gram Negative Bacteria – Click for full size
Drugs used in TB
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Rifamycins
Inhibits DNA transcription
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Rifamycin, rifabutin
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Cidal
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Nausea, anorexia, pseudomembranous colitis, hepatotoxicity, orange colouration of excreted bodily fluids, toxicity syndromes, drug interactions
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Also used in mycobacterial infections – these most commonly occur in those with HIV. Resistance prevents more widespread use
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Widespread – develops rapidly
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Y
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?
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?
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?
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Isoniazid
Inhibits synthesis of cell wall
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Isoniazid
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Cidal / static
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Nausea, vomiting, constipation, peripheral neuropathy, hepatitis, SLE-like-symptoms
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Bactericidal on dividing organisms, static on resting. Only effective against myobacteria
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Occurs rapidly if used alone
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N
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N
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N
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?
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Pyrazinamide
Lowers intracellular pH, disrupting synthesis of fatty acids
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pyrazinamide
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Cidal
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Hepatotoxicity, nausea, vomiting, arthralgia, sideroblastic anaemia
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Only effective against myobacteria
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Occurs rapidly if used alone
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N
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N
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N
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?
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Ethambutol
Interferes with cell wall synthesis
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Ethambutol
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Static
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Optic neuritis – resulting in red/green colourblindness. neuritis
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Only effective against myobacteria
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Uncommon
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N
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N
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N
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Mycobacteria
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 for a suspected tonsillitis, don’t give amoxicillin. If the infection is glandular fever, then the amoxicillin can cause a widespread skin reaction. The antibiotics of choice for tonsillitis is penicillin 500mg QID PO.