Antibiotics Flashcards
An example of a broad spectrum penicillin?
Amoxicillin
An example of a narrow spectrum penicillin?
Benzylpenicillin (Pen G)
What diseases are penicillins used in?
Strep Infections
Endocarditis
Meningitis - meningoccal infections
Tetanus
What spectrum of bacteria do narrow and broad treat in penicillins?
Narrow spectrum is just gram positive
Broad spectrum is gram positive and negative
How do penicillins work?
Inhibit crosslinking of cells walls in bacteria
Weakens wall
Caused uncontrolled entry of water in many ways
Beta Lactam ring is responsible for this
What are penicillins ineffective against?
MRSA, Staph Aureus - have beta lactamase
What is so special about flucloxacillin?
Has a side chain which prevents bacteria beta lactamase from binding and having an effect
What are the side effects of Penicillins?
Hypersensitivity
GI disturbances
What are the contraindications of Penicillin?
History of allergy
Renal impairment
What are the important interactions of penicillins?
Reduce renal excretion of MTX - can cause toxicity
Name an example of a cephalosporin and give its spectrum?
Cephradine/Cefotazime - broad spectrum
What diseases are cephalosporins used in?
Urinary
RT organisms
Complicated infections - meningitis, septicaemia, pneumonia
Surgical prophylaxis
How do cephalosporins work?
Beta lactam ring, so same effect as penicillins
More resistant to beta lactamase though
What are the side effects of cephalosporins?
Hypersensitivity reactions
Antibiotic associated colitis
What are the contraindications of cephalosporins?
C.dif risk
Allergy to penicillins
What are the important interactions of cephalosporins?
Enhance warfarin effect by killing vit K gut bacteria
Can increase nephrotoxicity of aminoglycosides
Decrease effectiveness of OCP
What drug class is erythromycin?
Macrolide
What are macrolides indicated for?
Alternative to penicillin
Gram positive and some negatives
Mycoplasma pneumoniae (clarithromycin especially)
Eradication of H pylori
How do macrolides work?
Broad spectrum bacteriostatic
Inhibits protein synthesis
What are the side effects of macrolides?
GI irritant
Antibiotic associated colitis
Liver abnormalities
Ototoxicity at high doses
What are the contraindications of macrolides?
Renal/hepatic impairment
Allergy
What are the important drug interactions of macrolides
Erythromycin and Clarithromycin inhibit P450 enzymes
Statins increased chance of myopathy
Warfarin increased risk of bleeding
Drugs that prolong the QT interval - SSRIs, quinolones, amiodarone
What drug class is trimethoprim?
Trimethoprim
What is Trimethoprim indicated for?
Uncomplicated UTI Pneumocystis pneumonia (co-trimoxazole)
How does Trimethoprim work?
It interferes with folic acid absorption from host and therefore bacteria are unable to replicate DNA
What are the side effects of Trimethoprim?
GI disturbance
Pruritus
Rashes
Hyperkalaemia
What are the contraindications of Trimethoprim?
First trimester pregnancy Folate deficiency Renal impairment Neonates Elderly
What are the important drug interactions of Trimethoprim?
Potassium elevating drugs (ACEi, angiotensin blockers) - hyperkalaemia
MTX is a folate antagonist as well
Phenytoin increases folate metabolism - increase risk of haematological effects
What are Tetracyclines indicated for?
Acne LRTI Used in malaria prophylaxis Chlamydia Lyme disease Syphilis
How do Tetracyclines work?
Inhibits protein synthesis in bacteria - binds to 30s
What are the side effects of Tetracyclines ?
GI disturbance Allergy Oesophageal irritation Photosensitivity Discolouration and hypoplasia of tooth enamel in children
What are the contraindications of Tetracyclines ?
Renal impairment
Pregnancy
Breastfeeding
Children <12 yrs
What are the important drug interactions of Tetracyclines ?
Enhance warfarin effect due to Vit k bacteria killed
What drug class is Gentamicin?
Aminoglycosides
What are Aminoglycosides indicated for?
Aerobic gram negative Severe sepsis Pyelonephritis Biliary problems Endocarditis
How do Aminoglycosides work?
Inhibit protein synthesis
Irreversibly bind to 30s subunit
What are the side effects of Aminoglycosides ?
Nephrotoxicity
Ototoxicity - tinnitus (irreversible cochlear damage)
What are the contraindications of Aminoglycosides ?
Neonates and elderly susceptible to renal impairment
Myasthenia gravis - can impair neurotransmitter
What are the important drug interactions of Aminoglycosides ?
Loop diuretics increase chance of ototoxicty
Nephrotoxicity more likely with ciclosporin, cephalosporins, vancomycin, chemotherapy
What drug class is Ciprofloxacin?
Quinolones
What are Quinolones indicated for?
UTI
Severe GI infection
LRTI
Psuedomonas Aeruginosa
How do Quinolones work?
Kills bacteria by inhibiting DNA synthesis
What are the side effects of Quinolones?
GI upset Allergy Lowers seizure threshold Rupture of muscle tendons Prolong QT interval Colitis - antibiotic associated
What are the contraindications of Quinolones?
If at risk of seizures
Not in growing children due to risk of arthropathy
Cardiac Disease
What are the important drug interactions of Quinolones?
Increased toxicity of drugs metabolised by P450
In particularly theophylline
When given with NSAIDs increases risk of seizures
Prednisolone increases risk of tendon rupture
Problem in drugs that prolong QT interval - inc macrolides
What drug class is Nitrofurantoin?
Nitrofurantoin
What is Nitrofurantoin indicated for?
Uncomplicated lower UTI
Gram negative E. Coli
Gram positive Staph Saprophyticus
How does Nitrofurantoin work?
Is metabolised by bacterial cells
The active metabolite damages DNA
What are the side effects of Nitrofurantoin ?
GI upset Delayed hypersensitivity reactions Turn urine dark yellow or brown Chronic pulmonary reactions e.g. fibrosis Hepatitis Peripheral neuropathy Haemolytic anaemia
What are the contraindications of Nitrofurantoin ?
Pregnant women close to term
Babies in the first three months of life
Renal impairment
Chronic use causes adverse effects in elderly population
What are the important drug interactions of Nitrofurantoin ?
No significant ones
What is resistant to Nitrofurantoin?
Klebsiella
What drug class is Metronidazole?
Anaerobic antimicrobials
What is Metronidazole indicated for?
C.Dif infection (gram positive)
Gram negative anaerobes:
- oral infections: aspiration pneumonia
- surgical or gynaecological infections from colon
Protozoal infections - amoebic dysentery, giardiasis
How does Metronidazole work?
Enters bacterial cells via passive diffusion
Anaerobic bacteria reduce the metronidazole thus generating nitroso free radicals
Causes widespread damage
Aerobic bacteria are incapable of doing this
What are the side effects of Metronidazole?
GI upset Delayed hypersensitivity reaction Prolonged high dose course: -Optic neuropathy -Seizures -Peripheral neuropathy -Encephalopathy
What are the contraindications of Metronidazole?
Metabolised by P450, so if liver disease reduce dose
Do not drink alcohol - disulfiram like effect
What are the important drug interactions of Metronidazole?
Has an inhibitory effect on P450 enzymes as well
So will increase effect of warfarin and phenytoin
P450 inducers will reduce plasma conc of metronidazole though and therefore reduce efficacy
What drug class does Vancomycin belong to?
Glycopeptides
What is Vancomycin indicated for?
Gram positive endocarditis: MRSA
C. Dif
How does Vancomycin work?
Inhibits growth and cross linking of peptidoglycan chains
Inhibits synthesis of cell wall in Gram positive bacteria
Is inactive against most gram negative bacteria
What are the side effects of Vancomycin?
Thrombophlebitis: pain and inflammation of vein at IV site Anaphylatic reactions - redman syndrome IV Vancomycin: - Nephrotoxicty - Ototoxicity Delayed hypersensitivity reaction
What are the contraindications of Vancomycin?
Renal impairment
Ototoxicity in elderly
What are the important drug interactions of Vancomycin?
Aminoglycosides, diuretics, ciclosporin increase risk of nephrotoxicity or ototoxicity
