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MRCP Revision > Infectious Diseases > Flashcards

Infectious Diseases Flashcards

1
Q

Abx inhibiting cell wall formation

A

penicillins, cephalosporins, carbopenems
glycopeptides

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2
Q

Cephalosporins MOA

A

beta lactam, bactericidal, disrupt synthesis of bacterial cell walls by inhibiting peptidoglycan cross-linking

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3
Q

Cephalosporin resistance

A

changes to penicillin-binding-proteins, which are types of transpeptidases (cross-link peptidoglycan chains to form rigid cell walls)

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4
Q

Vancomycin MOA

A

Binding to D-Ala-D-Ala moieties, preventing polymerisation of peptidoglycans

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5
Q

Vancomycin resistance

A

alteration to terminal amino acid residues of NAM/NAG-peptide subunits

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6
Q

Vancomycin SE

A

nephrotpxic, ototoxic, thrombophlebitis, red man syndrome (with rapid infusion. Flushing, erythema, pruritis affecting face, neck, upper torso, due to mast cell and basophil histamine release. Resolves within 20 mins of stopping/slowing infusion)

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7
Q

50S protein synthesis inhibitors

A

Macrolides, chloramphenicol, clindamycin, linezolid, streptogrammins

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8
Q

Chloramphenicol

A

Inhibits peptidyl transferase
SE: aplastic anaemia

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9
Q

Clindamycin

A

Inhibits translocation
SE: C Diff

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10
Q

Macrolides

A

Inhibits translocation
SE: nausea (esp erythromycin), P450 inhibitor, prolonged QTc

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11
Q

Linezolid

A

Oxazolidinone, bacteriostatic + bacteriocidal
Highly active vs: MRSA, VRE, GISA
SE: thrombocytopenia (reversible), avoid tyramine (like MAOi)

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12
Q

30S protein synthesis inhibitors

A

aminoglycosides
tetracyclines

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13
Q

aminoglycosides

A

Gentamicin
Causes misreading of mRNA
SE: ototoxicity, nephrotoxicity (ATN). Contraindication: Myasthenia. Monitoring: peak + trough levels

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14
Q

Tetracyclines

A

Blocks binding of aminoacyl-tRNA
Resistance: increased efflux by plasmid-encoded transport pumps, ribosomal protection
SE: teeth discolouration, photosensitivity, angioedema, black hairy tongue
Contraix: pregnant, breastfeeding women, children <12yrs

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15
Q

DNA synthesis inhibitors

A

quinolones

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16
Q

Quinolones

A

cipro/levofloxacin.
Inhibits topoisomerase II (DNA gyrase) and IV.

Resistance with mutations to DNA gyrase, efflux pumps as well.

SE: lowers seizure threshold, tendon damage (increased with steroids), cartilage damage, long QTc.

Contraindicated in pregnancy/breastfeeding and G6PD

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17
Q

Metronidazole

A

damages DNA

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18
Q

Folic acid formation inhibitors

A

trimethoprim, sulphonamides

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19
Q

Trimethoprim

A

MOA: inhibits dihydrofolate reductase (may interact with methotrexate) → inhibits DNA synthesis

SE: myelosuppression, transient creatinine rise (due to competitive inhibition of tubular creatinine secretion, with creatinine rise by 40, reversible), Type 4 RTA (blocks ENaC channel in distal nephron), teratogenic

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20
Q

Rifampicin MOA

A

inhibits RNA synthesis

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21
Q

Bacteriocidal vs bacteriostatic abx

A

Bacteriocidal Abx: penicillins, cephalosporins, aminoglycosides, nitrofurantoin, metronidazole, quinolones, rifampicin, isoniazid

Bacteriostatic abx: chloramphenicol, macrolides, tetracyclines, sulphonamides, trimethoprim

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22
Q

Azoles

A

MOA: inhibits 14alpha-demethylase → reduces ergosterol production from lanosterol → reduces plasma membrane structural integrity/stability
SE: P450 inhibition, hepatotoxic

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23
Q

Terbinafine

A

MOA: inhibits squalene epoxidase → ultimately, reduced ergosterol production → reduces plasma membrane structural integrity/stability
SE: pancytopenia, agranulocytosis, hepatotoxic
Used orally to treat fungal nail infections

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24
Q

Echinocandins

A

(Gaspofungin/any -fungins)

MOA: beta-glucan synthase inhibition → prevents transport of beta glucans to cell wall to be used for its formation
SE: flushing

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25
Q

Amphotericin B

A

MOA: binds to ergosterol forming transmembrane channel makining little tears (AmphoTEARicin)→ leads to monovalent ion (K, Na, H, Cl) leakage + cell death
SE: nephrotoxicity, flu-like sx, hypoK, hypoMg, hepatotoxic, phlebitis
Used for systemic fungal infections

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26
Q

Nystatin

A

MOA: binds to ergosterol forming transmembrane channel makining little holes → leads to monovalent ion (K, Na, H, Cl) leakage + cell death
Very toxic, can only be used topically (e.g. for oral thrush)

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27
Q

Griseofulvin

A

MOA: interacts with microtubules, disrupts mitotic spindle
SE: CYP450 inducer, teratogenic

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28
Q

Flucytosine

A

MOA: converted by cytosine deaminase to 5-fluorouracil, inhibits thymidylate synthase → attacks DNA → disrupts fungal protein synthesis
SE: vomiting

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29
Q

DNA polymerase inhibitor antivirals

A

aciclovir, ganciclovir, foscarnet

30
Q

Aciclovir

A

MOA: guanosine analogue, phosphorylated by thymidine kinase, inhibits viral DNA polymerase
For HSV, VZV
SE: crystalline nephropathy

31
Q

Ganciclovir

A

MOA: guanosine analogue, phosphorylated by thymidine kinase, inhibits DNA polymerase
For CMV
SE: myelosuppression/agranulocytosis

32
Q

Foscarnet

A

MOA: pyrophosphate analogue, inhibits DNA polymerase
For CMV, HSV (2nd line)
SE: nephrotoxicity, hypoCa, hypoMg, seizures

33
Q

antiviral mRNA group

A

IFN alpha, ribavirin

34
Q

IFN alpha

A

MOA: inhibits mRNA synthesis
For HBV, HV, hairy cell leukaemia
SE: flu like sx, myelosuppression

35
Q

Ribavirin

A

MOA: guanosine analogue, inhibits IMP dehydrogenase, interferes with mRAN capping
For chronic HCV, RSV
SE: haemolytic anaemia

36
Q

M-group antivirals

A

amantadine, oseltamivir

37
Q

Amantadine

A

MOA: inhibits M2 protein and uncoating of virus, releases dopamine from nerve endings
For influenza, PD
SE: confusion, ataxia, slurred speech

38
Q

Oseltamivir

A

MOA: neuraminidase inhibitor
For influenza

39
Q

Cidofovir

A

MOA: acyclic nucleoside phosphonate, independent of phosphorylation by viral enzymes
For CMV retinitis in HIV
SE: nephrotoxicity

40
Q

E coli gastroenteritis

A

Cause: E Coli (facultative, anaerobic, lactose-fermenting, G-ve rod). ETEC produces toxins stimulating intestinal lining → excessive fluid. EHEC can cause bloody diarrhoea

Incubation period 12-48hrs

Sx: onset within 1st wk of travel. Commonest cause of traveller’s diarrhoea (at least 3 episodes within 24hrs). Watery diarrhoea, abdo cramps, nausea

41
Q

Giardiasis

A

Transmission: Giardia lamblia, faeco-oral.

RF: travel, swimming/drinking from river/lake, male-male sexual contact
Incubation period >7 days

Sx: prolonged non-bloody diarrhoea, steatorrhoea, bloating, abdo pain, lethargy, flatulence, weight loss, malabsorption, lactose intolerance

Ix: stool MCS for trophozoites, cysts (sensitivity 65%), stool antigen detection assay (greater sensitivity, faster), PCR assays.

Rx: metronidazole

42
Q

Cholera

A

Cause: vibrio cholerae (G -ve)
Sx: profuse, watery diarrhoea with severe dehydration, weight loss, hypoglycaemia
Rx: oral rehydration therapy. Abx: doxy, ciprofloxacin

43
Q

Shigella

A

Cause: S sonnei (mild), S flexneri, dysenteriae (severe)
Incubation period: 48-72hrs
Sx: bloody diarrhoea, vomiting, abdo pain
Rx: self limiting, but ciprofloxacin if severe, bloody or immunocompromised

44
Q

Salmonella

A

Cause: aerobic, G-ve rods of Salmonella group, are not gut commenals. Salmonella typhi and paratyphi (types A, B, C) cause enteric fevers. Faeco-oral transmission

Incubation period 12-48hrs

Sx: Enteric fever (headache, fever, arthralgia), relative bradycardia (Faget sign), abdo pain, distension, constipation (more common than diarrhoea), rose spots on trunk 40% (more common in paratyphoid)

Compl: osteomyelitis (esp in Sickle cell disease), GI bleed/perforation, meningitis, cholecystitis, chronic carriage (1%, more likely with adult F)

Ix: Large volume blood culture

Rx: Typhoid - ceftriaxone. Non-typhoid - ciprofloxacin

45
Q

S aureus gastroenteritis

A

Incubation period: 1-6hrs
Sx: severe vomiting

46
Q

Campylobacter

A

Cause: Campylobacter jejuni (G-ve bacillus), faeco-oral, undercooked poultry, unpasteurised milk
incubation period 1-6 days
Sx: prodrome (headache, malaise), bloody diarrhoea, abdo pain, mimics appendicitis
Rx: self-limiting. Clarithromycin if severe (high fever, bloody diarrhoea, >8 stools/day, >1wk) or immunocompromised. Alt: ciprofloxacin
Compl: GBS, reactive arthritis, septicaemia, endocarditis, arthritis

47
Q

Bacillus cereus

A

Cause: undercooked rice

Incubation period 1-6hrs

Sx: Vomiting within 6hrs or diarrhoeal after 6hrs

48
Q

Amoebiasis

A

Cause: entamoeba histolytica, faeco-oral. 10% chronically infected
Incubation period >7 days
Sx: can be asymptomatic, mild diarrhoea or gradual onset bloody diarrhoea, abdo pain, lasting several wks, can form liver/colonic abscesses
Amoebic dysentery:
Sx: profuse, bloody diarrhoea, long incubation period
Ix: Stool microscopy - trophozoites (examine within 15 mins or keep warm - ‘hot stool’)
Amoebic liver abscess:
Sx: fever, RUQ pain, systemic, hepatomegaly, ‘anchovy sauce’ contents of liver
Ix: ultrasound, serology >95%
Rx: oral metronidazole + luminal agent (e.g. diloxanide furoate

49
Q

S aureus pneumonia

A

post-influenza, cavitation lung lesions (esp with strains producing Panton-Valentine Leukocidin cytotoxin → necrotic, haemorrhagic pneumonia)

50
Q

S pneumoniae assx

A

herpes labialis

51
Q

Mycoplasma pneumoniae

A

Sx: younger pts, epidemic every 4 yrs, prolonged, gradual onset, flu-like sx then dry cough

Compl: cold agglutinins (IgM), haemolytic anaemia, thrombocytopenia, erythema multiforme, erythema nodosum, meningoencephalitis, GBS, bullous myringitis (painful vesicles on tympanic membrane), pericarditis/myocarditis, hepatitis, pancreatitis, acute glomerulonephritis

Ix: CXR b/l consolidation, dx by serology. +ve cold agglutination test, blood smear shows RBC agglutination
Rx: doxycycline/macrolide (lacks peptidoglycan cell wall)

52
Q

Legionella CAP

A

Cause: Legionella pneumophilia, intracellular bacterium, water tanks (dodgy air-conditioning, foreign travel)
Sx: flu-like 95%, dry cough, relative bradycardia, confusion
Ix: dx by urinary antigens, hypoNa, deranged LFTs, lymphopenia, CXR (mid-lower zone consolidation, pleural effusions 30%)
Rx: macrolide

53
Q

Pstitacosis

A

Cause: Chlamydia psittaci. An obligate intracellular bacterium. Via birds/bird secretions
Sx: flu-like + resp (dry cough). Sometimes hepatosplenomegaly
Ix: CXR consolidation, serology
Rx: 1. Doxy. 2. macrolides

54
Q

Klebsiella pneumonia

A

Cause: G -ve rod, part of normal gut flora. Common in alcoholics (due to ETOH-induced dysbiosis → intestinal immune response alterations). May occur following aspiration
Sx: ‘red-currant jelly’ sputum, often affects upper lobes. Cavitation lesions
Prognosis: commonly causes lung abscess formation + empyema, mortality 30-50%

55
Q

HAP Rx

A

<5 days of admission: co-amox/cefuroxime
>5 days post-admission: tazocin/broad-spectrum ceph/quinolone

56
Q

CURB65

A

confusion (AMTS<8), Urea >7, RR>30, BP <90/60, Age>65. Admit if 2 or more.

57
Q

LUTI causes

A

E Coli commonest (G -ve)
Staphylococcus saprophyticus 2nd most common in sexually active young women (G +ve, clusters, coagulase -ve)

58
Q

Rx for LUTI

A

Non-pregnant: if symptomatic, trimethoprim/nitrofurantoin 3 days

Pregnant: 1. Nitrofurantoin 2. amoxicillin/cefalexin. Avoid trimethoprim in 1st trimester. Treat for both asymptomatic + symptomatic

Men: 7 days trimethoprim/nitrofurantoin

Catheterised: treat only if symptomatic

59
Q

Pyelonephritis Rx

A

ceph/quinolones 10-14 days

60
Q

Meningitis causes

A

0-3months: Group B strep (esp neonates), E Coli, Listeria monocytogenes

3months - 6yrs: (NHS) N meningitidis, H Influenzae, S pneumoniae

6-60yrs: (-H to NHS) N meningitidis, S pneumoniae

> 60yrs: (replace H with L in NHS) N meningitidis, S pneumoniae, Listeria monocytogenes
Immunosuppressed: Listeria monocytogenes

Viral: non-polio enteroviruses (Coxsackie, echovirus), mumps, HSV, CMV, HZV, HIV, measles

61
Q

CSF in meningitis types

A

Bacterial: cloudy appearance, low glucose (<50% of plasma), high protein, WBC polymorphs

Viral: clear/cloudy, glucose 60-80% of plasma (low glucose in mumps, Herpes encephalitis), WBC lymphocytes

TB: slightly cloudy, fibrin web, low glucose (<50% of plasma), high protein, WBC lymphocytes. Zielh-Neelson stain only 20% sensitive, PCR more sensitive (75%)

Fungal: cloudy, low glucose, high protein, WBC lymphocytes

62
Q

Abx in meningitis

A

<3 months: cefotaxime + amoxicillin

3 months - 50 yrs: cefotaxime/ceftriaxone

> 50 yrs: cefotaxime/ceftriaxone + amoxicillin

Meningococcal: benzylpenicillin or cefotaxime/ceftriaxone

Pneumococcal: cefotaxime/ceftriaxone

Haemophilus influenzae: cefotaxime/ceftriaxone

Listeria: amoxicillin + gentamicin

Pen/ceph allergic: chloramphenicol

63
Q

When to avoid dex in meningitis

A

Avoid in septic shock, meningococcal septicaemia, immunocompromise, post-surgical meningitis

64
Q

Contacts Rx in meningitis

A

for those exposed to meningococcus (risk highest 1st 7 days, persists for 4 wks) oral ciprofloxacin/rifampicin (cipro just needs one dose), meningococcal vaccination when serotypes available, including boosters, no prophylaxis for pneumococcal

65
Q

Meningitis compl

A

sensorineural hearing loss (most common), seizures, focal neuro def, infective (sepsis, abscess), pressure (herniation, hydrocephalus), Waterhouse-Friderichsen syndrome (from meningococcal meningitis → adrenal haemorrhage → adrenal insufficiency

66
Q

Cellulitis causes

A

S pyogenes, S aureus (less common)

67
Q

Eron classification

A

I: no signs of systemic toxicity, no uncontrolled comorbidities
II: systemically unwell/ well + comorbidity (e.g. PAD, venous insufficiency, obese) that may complicate/delay resolution
III: significant systemic upset (confusion, tachycardia, tachypnoea, hypotension) or unstable comorbiditie
IV: sepsis with life-threatening infection such as nec fasc

68
Q

cellulitis rx

A

Oral fluclox if Eron I. Alt: clarithromycin, erythromycin, doxycycline. 2nd line: clindamycin
IV Abx if Eron II
admit if Eron III/IV, severe/rapidly deteriorating cellulitis, very young/frail, immunocompromised, significant lymphoedema, facial/periorbital cellulitis. Choice of abx: co-amox, clindamycin, cefuroxime, ceftriaxone

69
Q

Necrotising fasciitis causes

A

Type 1: mixed anaerobes, aerobes, often post-surgical, diabetics (most common)
Type 2: S pyogenes

70
Q

Nec fasc RF

A

skin factors (trauma, burns, soft tissue inf), DM, SGLT-2 inh use, IVDU, immunosuppression

71
Q
A

MRCP Revision (10 decks)

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