Antibacterial Flashcards
Define Bacteriostatic
An antibacterial agent that inhibits the growth of bacteria
Define Bactericidal
An antibacterial agent that kills the bacteria
Define Antibiotic
A drug used to treat infections caused by microorganisms
Name 3 root causes of infection
- Viral
- Fungal
- Bacterial
Name the 4 stages of infection
Stage 1 - Exposure to pathogen
Stage 2 - Pathogen crosses protective barrier
Stage 3 - Pathogen multiplies
Stage 4 - Pathogens move around the body
What 3 things are looked at in bacteria classification
- Cell wall structure - Gram +ve / Gram -ve
- Shape - Cocci (Round) / Bacilli (Rod)
- Oxygen requirements - Aerobic / Anaerobic
Name 3 Gram positive organisms
- Staphylococcus aureus (Cocci)
- Streptococcus pneumonias (Diplococci)
- Clostridium Difficile (Rod)
Name 3 Gram negative organisms
- Eschrichia Coli (Rod)
- Klebsiella pneumoniae
- Pseudomonas aerguinosa
- Salmonella typi (rods)
- Neisseria Meningitidis (diplococci)
Name the 5 main targets for antibacterials
- Cell wall synthesis
- Protein synthesis
- Nucleic acid synthesis
- Metabolic pathways
- Cell membrane function
Name the three main classifications of antibacterial agents
- Bacteriostatic/Bactericidal
- By chemical structure
- Bacterial spectrum
Describe what is meant by high therapeutic index
A high therapeutic index is good ! The Therapeutic Index of a drug is the ratio of the toxic to the therapeutic dose. Drugs with a low therapeutic index may only require a small increase in dose to produce toxic effects
What 3 main factors would guide your antibiotic choice
- The presumed site of infection - suspected or know organisms, positive micro results
- Poperties of the antibiotic - Route/cost/spectrum/pharmacokinetics
- Patient status - Immunosuppression/allergies/renal or hepatic dysfunction/contraindications/response to treatment
Describe the mechanism of action of β-lactame antibiotics
Inhibit the synthesis of the bacterium cell wall by affecting synthesis of peptidoglycan
This results in the dividing cells not being able to maintain the osmotic gradient
net effect is cell swelling, rupture, and death of the bacterium
What is peptidoglycan
Peptidoglycan is the cell wall that surrounds most bacteria and is essential for their survival
Describe the pharmacokinetics of β-lactame antibiotics
Absorption - may vary depending on stability in acidic conditions - Penicillin tablets are acid stable (Labile) so ideally taken 1-2 hours before food. Absorption can be altered by absorption of food in the gut
Excretion - Rapidly excreted (90% renal route) and so relatively short half life.
Describe some side effects and cautions when using β-lactame antibiotics
Allergic reaction - Up to 10% of exposed individuals (anaphylaxis less common at 0.05%)
Minor hypersensitivity
GI disturbances such as diarrhoea and nausea
Describe how resistance can occur with β-lactame antibiotics
Inactivation of the β-lactame ring by an enzyme called β-lactamase. β-lactamase is produced by the bacteria itself. This splits open the β-lactame ring causing structural changes so unable to bind
Describe a Type A drug reaction
Type A Reactions Type A (augmented) reactions result from an exaggeration of a drug’s normal pharmacological actions when given at the usual therapeutic dose and are normally dose-dependent. Examples include respiratory depression with opioids or bleeding with warfarin. Type A reactions also include those that are not directly related to the desired pharmacological action of the drug, for example dry mouth that is associated with tricyclic antidepressants.
Describe a Type B drug reaction
Type B Reactions (bizarre) reactions are novel responses that are not expected from the known pharmacological actions of the drug. These are less common, and so may only be discovered for the first time after a drug has already been made available for general use. Examples include anaphylaxis with penicillin or skin rashes with antibiotics.
Describe the action of a β-lactamase inhibitor
β-lactamase inhibitors have no bacterial activity and are useful where resistance is due to β-lactamase enzyme.
Increases spectrum of activity to include bacteria that produces the β-lactamase enzyme.
Example - Clavulanic Acid is a β-lactamase-inhibitor
Augmenting = Amoxicillin + Clavulanic acid
Name members of the β-lactame group
Penicillins Cephalosporins Carbapenems Flucloxacillin Co amoxiclav
Describe Macrolides mechanism of action
Macrolides are protein synthesis inhibitors
They inhibit bacterial protein synthesis by binding to bacterial 50S subunit of the ribosome. These proteins are essential for the bacteria for functions such as growth, repair and reproduction. This action is considered bacteriostatic.
Macrolides are actively concentrated with leukocytes and are, therefore transported to the site of infection.
What is a macrolide
Erythromycin, clarithromycin, azithromycin
Similar antibacterial spectrum to penicillin agents
Bacteriostatic, useful in both Gram +ve and some -ve
Allows the body natural immune system to fight the infection
Can be effective agains unusual organisms (Mycoplasma pneumonia)
Describe the pharmacokinetics of Macrolides
Metabolised by the liver - Erythromycin and azithromycin are prepared for elimination - Clarithromycin is converted to an active metabolite.
Macrolides can inhibit cytochrome P450 leading to risk of toxicity/side effects
Variation in plasma half life - Erythromycin - 90mins, up to 24hours for Azithromycin
What is a Tetracycline
Tetracycline, Doxycycline, Minocycline
Broad spectrum antibiotics
Bacteriostatic
Issues with widespread resistance so limits use, good at treating intracellular infections.
Describe Tetracyclines mechanism of action
Inhibits bacterial protein synthesis by binding to bacterial 30S subunit.
Accumulates in cells by active transport and passive diffusion. Resistance occurs if efflux pump exists
Describe the side effects and cautions when using Tetracyclines
Oral absorption is effected by Calcium, magnesium, iron and food.
Should be avoided in pregnancy, breast feeding and children under 12 (Binds to calcium in growing bones and teeth causing discolouration)
May cause photosensitivity
GI upsets are common
What are Amino glycosides
Gentamicin, Streptomycin, Amikacin, Neomycin
Narrow spectrum (Gram -ve mainly) Reserved for serious Gram-ve infections e.g. pseudomonas
Bactericidal
Narrow therapeutic index (Requires close monitoring)
All given IV for systemic infections
Describe the mechanisms of action of Amino glycosides
Inhibit bacterial protein synthesis by binding to the 30S ribosomal subunit
This stops translation of mRNA into the proteins
They also cause transient holes in the cell membranes causing polysaccharide links to break (This is linked to bactericidal activity)
Describe the pharmacokinetics of Amino glycosides
Not absorbed in the GI tract so given IM or IV.
Half life is 2-3 hours
Excreted via renal glomerular filtration - in renal impairment accumulation occurs rapidly resulting in toxicity.
Regular plasma monitoring essential
Dose adjustment is essential in renal impairment
Describe cautions and side effects to consider when prescribing Amino glycosides
Ototoxicity - can lead to progressive damage to sensory cells, results can be irreversible including, vertigo, loss of balance, auditory disturbances, deafness.
Ototoxic effects are increased by the ototoxic drugs - i.e. loop diuretics
Nephrotoxic - Damage to kidney tubules
What is a Quinolone
Ciprofloxacin, Levofloxacin, Norfloxacin
Broad spectrum of activity
Bactericidal
Describe the mechanism of action of a Quinolone
Block the action of the enzyme DNA gyrate. DNA gyrate is responsible for forming DNA supercoils for replication and repair
Inhibition of the replication of bacterial DNA
