Antibiotics Flashcards
1) Name the main uses of penicillins.
2) What are the main uses of cephalosporins?
3) What are the main uses of macrolides?
4) What are the main uses of aminoglycosides?
5) Name the main uses of tetracyclines.
1) Antimicrobial chemotherapy of sensitive bacterial infections (e.g. community acquired pneumonia, bacterial endocarditis)
2) Antimicrobial chemotherapy of sensitive bacterial infections (e.g. community acquired pneumonia)
3) Antimicrobial chemotherapy of sensitive bacterial infections (e.g. community acquired pneumonia, atypical pneumonia)
4) Antimicrobial chemotherapy of sensitive bacterial infections (e.g. bacterial endocarditis, pyelonephritis, intra-abdominal infection)
5) Antimicrobial chemotherapy of sensitive bacterial infections (e.g. community acquired pneumonia, atypical pneumonia)
Name the 5 penicillin P-drugs.
Amoxicillin Benzylpenicillin Co-amoxiclav Flucloxacillin (staphylococci) Piperacillin-tazobactam
Name the 4 cephalosporin P drugs.
Cefaclor
Cefuroxime
Cefotaxime
Ceftriaxone
Name the 3 macrolide P drugs.
Azithromycin
Clarithromycin
Erythromycin
Name the 3 aminoglycoside P drugs.
Gentamicin
Streptomycin (TB)
Tobramycin
Name the 4 tetracycline P drugs.
Doxycycline
Tetracycline
Minocycline (acne)
Lymecycline (acne)
Give the 2 common clinical indications for the use of cephalosporins and carbapenems.
1) Oral cephalosporins are second and third line treatment for UTIs and RTIs.
2) IV cephalosporins and carbapenems are reserved for severe and complicated infections or antibiotic resistant organisms. They can be used for most indications due to their broad spectrum.
1) What are cephalosporins and carbapenems derived from?
2) What is their antimicrobial effect due to?
3) Describe the basic mechanism of action of cephalosporins and carbapenems.
1) Naturally occurring antimicrobials produced by fungi and bacteria.
2) Their beta lactic ring.
3) They inhibit enzymes responsible for cross-linking peptidoglycans in bacterial cell-wall synthesis during bacterial cell growth. This weakens the wall, preventing them from maintaining an osmotic gradient, resulting in bacterial cell swelling, lysis and death.
1) Describe the spectrum of action of cephalosporins and carbapenems.
2) What has progressive structural modification led to in cephalosporins?
3) Why are cephalosporins and carbapenems naturally more resistant to beta-lactamases?
1) They both have a broad spectrum of action.
2) Successive generations being created (1st to 5th) with increasing activity against gram negative bacteria and less oral activity.
3) Due to the fusion of the beta lactam ring with a dihydrothiazine ring (cephalosporins) or a unique hydroxyethyl side chain (carbapenems).
1) Give 2 common adverse effects of cephalosporins and carbapenems.
2) When might antibiotic-related colitis occur with use of cephalosporins/ carbapenems?
3) Why might cross-reactivity causing anaphylaxis occur in penicillin allergic patients when cephalosporins/ carbapenems are used?
4) When is there a particular risk of central nervous system activity using carbapanems and what might this cause?
1) GI upset: N+V.
2) When broad spectrum antibiotics kill gut flora, allowing overgrowth of toxin-producing C.Diff. Can be complicated by colonic perforation and death.
3) Because they share structural similarities with penicillins.
4) Particularly when carbapenems are used in higher doses or in patients with renal impairment, and this could cause seizures.
1) Who should cephalosporins and carbapenems be used with caution in?
2) What is the main contraindication for cephalosporins and carbapenems?
3) In which patients should a dose reduction of cephalosporins/ carbapenems be used?
1) People at risk of C.Diff infection (inpatients and the elderly).
2) Patients that have allergies to penicillins, cephalosporins or carbapenems, particularly with Hx of anaphylaxis.
3) In those with renal impairment.
1) How can cephalosporins enhance the anticoagulant effect of Warfarin?
2) Describe the interaction between cephalosporins and aminoglycosides.
3) Describe the interaction between carbapenems and Valproate.
1) By killing normal gut flora that synthesise vitamin K.
2) Cephalosporins may increase nephrotoxicity of aminoglycosides.
3) Carbapenems reduce plasma concentration and efficacy of valproate.
1) Name an orally active cephalosporin.
2) How are cephalosporins usually prescribed?
3) Describe how IV cephalosporins are used.
4) Describe how carbapenems are available.
1) Cefalexin.
2) For 6-12 hourly administration.
3) At high doses for severe infections (e.g. Cefotaxime 2g IV 6 hourly for bacterial meningitis).
4) They are only available for IV administration.
1) Describe the ways that cephalosporins can be administered.
2) Describe the ways that carbapenems can be administered.
3) Which carbapenem can facilitate the outpatient administration of antibiotics?
1) orally, IV by infusion or bolus and IM.
2) IV injection or infusion.
3) Ertapenem as it is administered OD.
1) In many hospitals, when/ who can prescribe cephalosporins/ carbapenems and why?
2) Why is use of second and third generation cephalosporins particularly restricted?
1) They can only be prescribed with the approval of a microbiologist in order to reduce the risk of the development of resistance.
2) Because antibiotic associated colitis seems to occur more commonly with these.
Give the 4 common clinical indications for the use of Tetracyclines.
1) Acne vulgaris, particularly where there are inflamed papule, pustules and/ or cysts (Proprionibacterium acnes).
2) LRTIs (infective exacerbations COPD/ atypical pneumonia - mycoplasma/ chlamydia psittaci).
3) Chlamydial infection including pelvic inflammatory disease.
4) Other infections such as anthrax, typhoid, malaria and Lyme disease (Borrelia Burgdoferi).
Name the 3 main clinical indications for the use of macrolides.
1) Treatment of respiratory and skin and soft tissue reactions as an alternative to penicillins when they are contraindicated by allergy.
2) In severe pneumonia added to a penicillin to cover atypical organisms including Legionella and mycoplasma pneumonia.
3) Eradication of H. Pylori in combination with a PPI and either amoxicillin/ metronidazole.
1) What do macrolides do?
2) Describe why inhibition of protein synthesis is useful.
3) Describe the spectrum of activity of erythromycin.
1) Inhibit bacterial protein synthesis by binding to ribosome 50S subunit of bacterial ribosomes to block translocation.
2) Because it is bacteriostatic, assisting the immune system in killing and removing bacteria from the body.
3) Relatively broad spectrum of action against Gr+ and some Gr- organisms.
1) Describe the spectrum of activity of synthetic macrolides (clarithromycin and azithromycin).
2) Why is bacterial resistance to macrolides common?
3) Adverse effects are most common and severe with which macrolide?
1) Increased activity against Gr- bacteria, particularly haemophilia influenzae.
2) Mainly due to ribosomal mutations preventing macrolide binding.
3) Erythromycin, although they can occur with any macrolide.
1) Describe the adverse effects of macrolides when taken orally.
2) Describe the main adverse effect of macrolides when given intravenously.
3) When should macrolides not be prescribed?
1) They are irritant when taken orally, causing nausea, vomiting, abdominal pain and diarrhoea.
2) Thrombophlebitis.
3) If there is a Hx of macrolide sensitivity
Aside from the specific oral and IV side effects of macrolides, name 5 other adverse effects.
1) Allergy
2) Antibiotic-associated colitis.
3) Liver abnormalities including cholestatic jaundice.
4) Prolongation of the QT interval (predisposing to arrhythmias)
5) Ototoxicity at high doses.
1) Why are macrolides useful when penicillins are contraindicated by allergy?
2) Describe macrolide elimination by the body and describe where caution might be needed.
3) Which macrolides inhibit cytochrome P450 enzymes?
4) Describe the effect of CYP450 enzyme inhibition.
1) Because there is no cross-sensitivity between the drug classes.
2) Mostly hepatic with renal contribution so caution is required in hepatic impairment and dose reduction may be required in severe renal impairment.
3) Erythromycin and Clarithromycin.
4) Increases plasma concentrations and risk of adverse effects in drugs metabolised by CYP450 enzymes.
1) Which other drugs should macrolides be prescribed with caution in?
2) Describe the interaction between macrolides and warfarin.
3) Describe the interaction between macrolides and statins.
1) Drugs that can prolong the QT interval or cause arrhythmias (amiodarone, antipsychotics, quinine, quinolones, SSRIs).
2) Increased risk of bleeding.
3) Increased risk of myopathy.
1) What is the most commonly prescribed macrolide in the UK and why?
2) How is clarithromycin usually prescribed?
3) When would clarithromycin be administered intravenously?
4) What is the usual dosage for clarithromycin?
1) Clarithromycin as it is more stable and causes fewer side effects than erythromycin and is cheaper than azithromycin.
2) For oral administration as it is absorbed readily in the intestine and has good bioavailability.
3) Where patients are unable to take or absorb drugs via the GI tract (e.g. due to vomiting).
4) 250-500mg BD for 7-24 days.
1) How do you reduce the risk of thrombophlebitis when administering clarithromycin IV?
2) If there is evidence of pneumonia, how should macrolides be prescribed?
3) In which situations might macrolides be required to treat LRTIs?
1) Dilute IV clarithromycin withNaCl then infused into a large proximal vein over at least 60 minutes to reduce the risk.
2) They should generally be added to penicillin treatment
3) They may be required to cover penicillin-resistant atypical organisms that cause pneumonia but do not cause other LRTIs (Legionella/ mycoplasma pneumoniae).
Give the 4 common clinical indications for the use of metronidazole.
Treatment of infections caused by anaerobic bacteria in:
1) Antibiotic associated colitis caused by C. Diff which is a gram positive anaerobe.
2) Oral infections or aspiration pneumonia caused by gram negative anaerobes from the mouth.
3) Surgical and gynaecological infections caused by gram negative anaerobes from the colon.
4) Effective treatment of protozoal infections including trichomonal vaginal infection, amoebic dysentery and giardiasis.
1) How does metronidazole enter bacterial cells?
2) Describe how metronidazole works in anaerobic bacteria.
3) Why does metronidazole not work in aerobic bacteria?
1) By passive diffusion.
2) Reduction of metronidazole generates a intros free radical > this binds to DNA, reducing synthesis and causing widespread damage, DNA degradation and cell death.
3) Because aerobic bacteria are not able to reduce metronidazole in this way.
Describe 2 mechanisms of bacterial resistance to metronidazole.
1) Reduced uptake of metronidazole.
2) Reduced generation of intros free radicals.
State the 2 main adverse effects which can occur with metronidazole that can occur with most antibiotics.
1) GI upset (N+V)
2) Immediate and delayed hypersensitivity reactions.
Describe 4 neurological adverse effects that can occur when metronidazole is used at high doses.
1) Peripheral neuropathy
2) Optic neuropathy
3) Seizures
4) Encephalopathy
1) How is metronidazole metabolised?
2) In whom should the dose of metronidazole used be reduced?
3) Why should alcohol not be drunk whilst taking Metronidazole?
1) By hepatic CYP450 enzymes
2) Those with severe liver disease.
3) Because it inhibits the enzyme acetaldehyde dehydrogenase so can cause a Disulfiram-like reaction (the flush reaction).
1) Why does metronidazole reduce metabolism of Warfarin and Phenytoin?
1a) What are the effects of this?
2) Describe the interaction between metronidazole and lithium.
3) Describe the interaction between CYP450 inducers and Metronidazole.
1) Because it has some inhibitory effect on CYP450.
1a) Increased risk of bleeding with Warfarin and increased risk of toxicity, including impaired cerebellar function with Phenytoin.
2) Metronidazole increases the risk of toxicity with lithium.
3) They can cause reduced plasma concentrations of Metronidazole, which can cause impaired antimicrobial efficacy.
1) When is oral administration of metronidazole used?
2) When is Metronidazole used via IV administration?
3) Describe another administration route that can be used for nil by mouth patients.
4) When might Metronidazole be used as a gel for topical administration?
1) For GI infection or where the patient is not systemically unwell.
2) For severe infections where patients cannot take treatment by mouth.
3) Rectal metronidazole is another administration route.
4) To treat vaginal infection (bacterial vaginosis) or to reduce the odour from an infected skin ulcer.
1) What must you warn the patient not to drink when they are taking Metronidazole?
2) Why are anaerobic bacteria often resistant to penicillins?
3) Which type of penicillin is useful for anaerobic bacterial infections?
1) Alcohol during or for 48 hours after treatment.
2) Due to the production of beta lactamases.
3) Co-amoxiclav has good efficacy against anaerobes.
Name the 3 main indications for the use of penicillins.
1) Streptococcal infections - tonsillitis, pneumonia, endocarditis and skin and soft tissue infections.
2) Clostridial infection (e.g. tetanus)
3) Meningococcal infection.
