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BASIC - INFECTIOUS DISEASES Flashcards

1
Q

Indications of phenomethylpenicillin?

A

o Oral infections, tonsillitis, otitis media, cellulitis, erysipelas
o Prevention of pneumococcal in asplenia/sickle cell disease
o Prevention of recurrence of rheumatic fever
o Acute sinusitis

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2
Q

Indications of benzylpenicillin?

A

o Throat infections, otitis media, cellulitis, pneumonia, endocarditis, anthrax
o Intrapartum prophylaxis of Group-B strep
o Meningitis, meningococcal disease

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3
Q

Mechanism of action of penicillin?

A
  • Inhibit enzyme responsible for cross-linking peptidoglycan in bacterial cell walls
  • Weakens cell walls, preventing maintenance of osmotic gradient
  • Cell swells, lysis and dies
  • Penicillins contain B-lactam ring
  • Bacteria resist actions of penicillins by making B-lactamase, limiting intracellular concentration of penicillin or change target enzyme to prevent binding
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4
Q

Side effects of penicillins?

A
  • Diarrhoea, nausea, vomiting
  • Allergy in 1-10% of people
    o Skin rash 7-10 days after first exposure or 1-2 days after repeat exposure (IgG subacute)
    o IgE anaphylactic reaction (0.05%) – hypotension, bronchial and laryngeal spasm, angioedema
  • CNS toxicity in high doses or renal impairment
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5
Q

Contraindications in penicillins?

A
  • History of allergy
  • Renal impairment
    o Dose reduction in benzylpenicillin
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6
Q

Interactions of penicillins?

A
  • Reduce renal excretion of methotrexate – risk of toxicity
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7
Q

Routes of phenoxymethylpenicillin and benzylpenicillin?

A
  • Benzylpenicillin – only IV/IM as hydrolysis by gastric acid prevents absorption
    o Severe infections at high dose only
  • Pen V – orally taken
  • Short half-life so given every 4-6 hours
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8
Q

Indications of amoxicillin & co-amoxiclav?

A
  • CAP, acute bronchiectasis, acute exacerbation of COPD, acute otitis media, sinusitis
  • UTI (other alternatives)
  • Combination for hospital-acquired infection or intra-abdominal sepsis
  • H.pylori eradication
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9
Q

Mechanism of amoxicillin & what addition does co-amoxiclav have?

A
  • Inhibit enzyme responsible for cross-linking peptidoglycan in bacterial cell walls
  • Weakens cell walls, preventing maintenance of osmotic gradient
  • Cell swells, lysis and dies
  • Penicillins contain B-lactam ring
    o Addition of amino group – increases activity against aerobic Gram-negative bacteria – broad spectrum
    o Addition of B-lactamase inhibitor clavulanic acid increases spectrum of antimicrobial activity further (S.aureus and gram-negative anaerobes)
  • Bacteria resist actions of penicillins by making B-lactamase, limiting intracellular concentration of penicillin or change target enzyme to prevent binding
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10
Q

Side effects of amoxicillin/co-amoxiclav?

A
  • Diarrhoea, nausea, vomiting
  • Antibiotic-associated colitis
    o Broad spectrum antibiotics kill normal gut flora and C.diff grows
    o Debilitating and can cause colonic perforation
  • Cholestatic jaundice (co-amoxiclav)
  • Allergy in 1-10% of people
    o Skin rash 7-10 days after first exposure or 1-2 days after repeat exposure (IgG subacute)
    o IgE anaphylactic reaction (0.05%) – hypotension, bronchial and laryngeal spasm, angioedema
  • CNS toxicity in high doses or renal impairment
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11
Q

Dose changes in renal impairment in amoxcillin/co-amoxiclav?

A

o Dose reduction (crystalluria)

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12
Q

Interactions of amoxicillin/co-amoxiclav?

A
  • Reduce renal excretion of methotrexate – risk of toxicity
  • Enhance anticoagulant effect of warfarin by killing gut flora that synthesise vitamin K
  • DO NOT GIVE IN EBV
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13
Q

Dose of amoxicillin?

A
  • IV should be switched to oral after 48h if indicated

- Oral amoxicillin usually 500mg 8-hourly for 7-14 days

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14
Q

Indications of flucloxacillin?

A
  • Otitis externa, impetigo, cellulitis, endocarditis, osteomyelitis, surgical prophylaxis
  • Prevention of S.aureus infection in cystic fibrosis
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15
Q

Mechanism of flucloxacillin?

A
  • Inhibit enzyme responsible for cross-linking peptidoglycan in bacterial cell walls
  • Weakens cell walls, preventing maintenance of osmotic gradient
  • Cell swells, lysis and dies
  • Penicillins contain B-lactam ring
    o Acyl side chain protect B-lactam ring from B-lactamases
     Effective against B-lactamase producing staphylococci
     MRSA resists flucloxacillin action by reducing penicillin binding affinity
  • Bacteria resist actions of penicillins by making B-lactamase, limiting intracellular concentration of penicillin or change target enzyme to prevent binding
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16
Q

Side effects of flucloxacillin?

A
  • Liver toxicity – cholestasis and hepatitis
  • Allergy in 1-10% of people
    o Skin rash 7-10 days after first exposure or 1-2 days after repeat exposure (IgG subacute)
    o IgE anaphylactic reaction (0.05%) – hypotension, bronchial and laryngeal spasm, angioedema
  • CNS toxicity in high doses or renal impairment
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17
Q

Contraindications of flucloxacillin?

A
  • History of allergy

- Prior flucloxacillin-related hepatotoxicity

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18
Q

Dose changes in renal impairment of flucloxacillin?

A

o Dose reduction if <10eGFR

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19
Q

Interactions of flucloxacillin?

A
  • Reduce renal excretion of methotrexate – risk of toxicity
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20
Q

Dose of flucloxacillin?

A
  • IV high dose 1-2g 4-6 hourly for severe infections
  • Osteomyelitis and endocarditis require 6 weeks of high-dose IV
  • Oral flucloxacillin 250-500mg 4 times a day
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21
Q

Indications of Tazocin?

A
  • For severe infections
    o HAP, sepsis, acute COPD/bronchiectasis
    o Complicated UTI, skin, soft-tissue infections
  • Neutropenic sepsis
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22
Q

Mechanism of Tazocin?

A
  • Inhibit enzyme responsible for cross-linking peptidoglycan in bacterial cell walls
  • Weakens cell walls, preventing maintenance of osmotic gradient
  • Cell swells, lysis and dies
  • Penicillins contain B-lactam ring
    o Side chain of broad-spectrum antibiotics converted to form urea
     Increases affinity including pseudomonas aeruginosa
    o B-lactamase inhibitor tazobactam confers activity against S.aureus and Gram-neg anaerobes
  • Bacteria resist actions of penicillins by making B-lactamase, limiting intracellular concentration of penicillin or change target enzyme to prevent binding
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23
Q

Side effects of Tazocin?

A
  • Diarrhoea, nausea, vomiting
  • Antibiotic-associated colitis
    o Broad spectrum antibiotics kill normal gut flora and C.diff grows
    o Debilitating and can cause colonic perforation
  • Allergy in 1-10% of people
    o Skin rash 7-10 days after first exposure or 1-2 days after repeat exposure (IgG subacute)
    o IgE anaphylactic reaction (0.05%) – hypotension, bronchial and laryngeal spasm, angioedema
  • CNS toxicity in high doses or renal impairment
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24
Q

Dose changes in renal impairment of Tazocin?

A

o Max 4.5g every 8 if eGFR 20-40

o Max 4.5g every 12 hours if eGFR <20

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25
Q

Cautions of Tazocin?

A

o Risk of C.diff infection

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26
Q

Interactions of Tazocin?

A
  • Reduce renal excretion of methotrexate – risk of toxicity

- Enhance anticoagulant effect of warfarin by killing gut flora that synthesise vitamin K

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27
Q

Dose of Tazocin?

A
  • IV infusion only

- Usual dose of 4.5g, given every 6-8 hours

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28
Q

Names of carbapenems?

A

Meropenem

Ertapenem

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29
Q

Indications of carbapenems?

A
  • IV reserved for severe infections
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30
Q

Mechanism of carbapenems?

A
  • Naturally occurring antimicrobials produced by fungi and bacteria
  • B-lactam ring
  • Inhibit enymes responsible for cross-linking peptidoglycans in bacterial cell walls
  • Weakens walls and causes bacterial cell swelling, lysis and death
  • Broad spectrum
  • Hydroxyethyl Ring – resistant to B-lactamases
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31
Q

Side Effects of carbapenems?

A
  • Diarrhoea, nausea, vomiting
  • Antibiotic-associated colitis
    o Broad spectrum antibiotics kill normal gut flora and C.diff grows
    o Debilitating and can cause colonic perforation
  • Allergy in 1-10% of people
    o Skin rash 7-10 days after first exposure or 1-2 days after repeat exposure (IgG subacute)
    o IgE anaphylactic reaction (0.05%) – hypotension, bronchial and laryngeal spasm, angioedema
  • CNS toxicity in high doses or renal impairment
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32
Q

Cautions of carbapenems?

A

o Risk of C.diff infection

o Epilepsy

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33
Q

Dose changes in renal impairment of carbapenems?

A

o Dose reduction

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34
Q

Interactions of carbapenems?

A
  • Enhance anticoagulant effect of warfarin by killing gut flora that synthesise vitamin K
  • Reduce plasma concentrations and efficacy of valproate
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35
Q

Dose of meropenems?

A
  • IV only

- Meropenem 1-2g IV 8-hourly

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36
Q

Names of cephalosporins?

A

Cephalexin, cefuroxime, cefotaxime, ceftriaxone, ceftazidime and ceftaroline

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37
Q

Indications of cephalosporins?

A
  • 2nd and 3rd line treatment for urinary and respiratory tract infections
  • IV reserved for severe infections
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38
Q

Mechanism of cephalosporins?

A
  • Naturally occurring antimicrobials produced by fungi and bacteria
  • B-lactam ring
  • Inhibit enymes responsible for cross-linking peptidoglycans in bacterial cell walls
  • Weakens walls and causes bacterial cell swelling, lysis and death
  • Broad spectrum
  • Dihydrothiazine Ring – resistant to B-lactamases
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39
Q

Side effects of cephalosporins?

A
  • Diarrhoea, nausea, vomiting
  • Antibiotic-associated colitis
    o Broad spectrum antibiotics kill normal gut flora and C.diff grows
    o Debilitating and can cause colonic perforation
  • Allergy in 1-10% of people
    o Skin rash 7-10 days after first exposure or 1-2 days after repeat exposure (IgG subacute)
    o IgE anaphylactic reaction (0.05%) – hypotension, bronchial and laryngeal spasm, angioedema
  • CNS toxicity in high doses or renal impairment
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40
Q

Contraindications and cautions of cephalosporins?

A

Contraindication
- History of allergy to penicillins, cephalosporins or carbepenems

Caution
o Risk of C.diff infection

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41
Q

Dose changes in renal impairment of cephalosporins?

A

o Half dose in eGFR <5

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42
Q

Interactions of cephalosporins?

A
  • Enhance anticoagulant effect of warfarin by killing gut flora that synthesise vitamin K
  • Increase nephrotoxicity of aminoglycosides
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43
Q

Dose of cefotaxime?

A
  • Usually over 6-12 hourly

- Cefotaxime 2g IV 6-hourly for bacterial meningitis

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44
Q

Names of aminoglycosides?

A

Gentamicin, amikacin

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45
Q

Indications of aminoglycosides?

A
  • Severe infections, particularly Gram-negative aerobes
    o Severe sepsis
    o Pyelonephritis and complicated UTI
    o Biliary and other intra-abdominal sepsis
    o Endocarditis
    o Bacterial eye infections
  • Lack activity against streptococci and anaerobes
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46
Q

Mechanism of aminoglycosides?

A
  • Bind irreversibility to bacterial ribosomes (30S subunit) and inhibit protein synthesis
  • Bactericidal
  • Enters bacterial cells via oxygen-dependent transport system
  • Spectrum – gram-negative aerobic bacteria, staphylococci and mycobacteria
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47
Q

Side effects of aminoglycosides?

A
  • Nephrotoxicity and ototoxicity
    o Accumulate in renal tubular epithelial cells and cochlear hair cells triggering cell death
  • Tinnitus
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48
Q

Contraindications of aminoglycosides?

A
  • Impair neuromuscular transmission so avoid in Myasthenia gravis
  • Caution
    o Elderly, neonates, renal impairment
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49
Q

Interactions of aminoglycosides?

A
  • Ototoxicity increases with loop diuretics or vancomycin

- Nephrotoxicity increases with ciclosporin, platinum, cephalosporins or vancomycin

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50
Q

Prescription of gentamicin?

A
  • IV only given over an hour
  • Dose calculated using patients’ weight and renal function (IBW = 7mg/kg)
    o Use patient’s height to select IBW, if ABW less than IBW – use dose according to ABW
  • Dose interval determined by drug level monitoring, usually 24 hours but longer in renal impairment
  • Often single dose course
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51
Q

Initial monitoring in gentamicin?

A

o One 10ml blood sample between 6-14 hours after start of first infusion
o Plain tube (clotted blood) – record exact time taken
o Plot of normogram
o Dose interval according to value given off graph – if 24,36 or 48h
o If level is over 48h dosing interval STOP treatment and take daily levels – gentamicin can be restarted once below 2mg/L

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52
Q

Repeat monitoring in gentamicin?

A

o U&Es and creatinine daily
 If creatinine rising >20% and still between 6-14 hours – measure gentamicin levels
 If not between 6-14 hours – contact microbiology

o Repeat Gentamicin levels according to dosage interval:
 Dosage level - 24 hours = 3 days
 Dosage level - 36 hours = 3 days
 Dosage level - 48 hours = 2 days

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53
Q

Names of macrolides?

A

Clarithromycin, Erythromycin, Azithromycin

54
Q

Indications of macrolides?

A
  • Treatment of respiratory and soft tissue infections as alternative to penicillin
  • Severe pneumonia (added to cover atypicals like Legionella, Mycoplasma)
  • Eradication of H.pylori
55
Q

Mechanism of macrolides?

A
  • Inhibit bacterial protein synthesis – bind to 50S subunit and block translocation
  • Bacteriostatic
56
Q

Side effects of macrolides?

A
  • Irritant – causing nausea, vomiting, abdominal pain and diarrhoea when taken orally, thrombophlebitis if IV
  • Antibiotic-associated colitis (C.diff)
  • Cholestatic jaundice
  • Prolongation of QT interval
  • Ototoxicity at high doses
57
Q

Contraindications of macrolideS?

A
  • Hepatic elimination mostly – caution in severe hepatic impairment and dose reduction in severe renal impairment
58
Q

Interactions of macrolides?

A
  • Erythromycin and Clarithromycin inhibit CYP450 enzymes
  • Caution with drugs that prolong QT
    o Amiodarone, antipsychotics, quinine, quinolone, antibiotics and SSRIs
59
Q

Common dose of macrolides?

A
  • Oral dosage 250-500mg BDS for 7-14 days
60
Q

What class of drug is clindamycin?

A

Semisynthetic Lincosamide

61
Q

Indications of clindamycin?

A
  • Treatment of staphylococcal bone and joint infections
  • Peritonitis
  • Intrabdominal sepsis
  • Falciparum malaria
  • Bacterial vaginosis
  • Acne Vulgaris
62
Q

Mechanisms of clindamycin?

A
  • Inhibit bacterial protein synthesis – bind to 50S subunit and block translocation
  • Bacteriostatic
63
Q

Side effects of clindamycin?

A
  • Skin reactions
  • Abdominal pain
  • Antibiotic-associated colitis
  • Diarrhoea
64
Q

Contraindications of clindamycin?

A
  • Diarrhoeal states
65
Q

Interactions of clindamycin?

A
  • Increases effects of actracurium, mivacurium, pancuronium, rocuronium, suxamethonium so caution
66
Q

Dose of clindamycin?

A
  • Oral dosage 150-300mg QDS up to 450mg
67
Q

Important patient information given in clindamycin?

A

o Damages latex condoms with vaginal use

68
Q

Names of glycopeptides?

A

Vancomycin, Teicoplanin

69
Q

Indications of glycopeptides?

A
  • Treatment of Gram-positive infections – bone, joint, CAP, HAP, meningitis, endocarditis if penicillins can’t be used
  • Antibiotic associated colitis (C.diff)
70
Q

Mechanism of glycopeptides?

A
  • Inhibits growth and cross-linking of peptidoglycan chains, inhibiting synthesis of cell wall of Gram-positive bacteria
71
Q

Side effects of glycopeptides?

A
  • Thrombophlebitis at infusion site
  • Anaphylactoid reactions
    o Red man syndrome – generalised erythema, hypotension and bronchospasm
    o Not true allergy but due to non-specific degranulation of mast cells
  • Allergy
  • IV Vancomycin
    o Nephrotoxic (renal failure and interstitial nephritis)
    o Ototoxic (tinnitus and hearing loss)
    o Neutropenia and thrombocytopenia
72
Q

Caution of glycopeptides?

A
  • Monitoring of plasma concentrations and dose adjustment
  • Caution
    o Renal impairment (serial renal function monitoring)
    o Elderly
73
Q

Interactions of glycopeptides?

A
  • Ototoxicity/nephrotoxicity increases with aminoglycosides, loop diuretics or ciclosporin
74
Q

Dose of glycopeptides?

A

o Initial loading dose determined by actual body weight (in glucose 5% or NaCl 0.9%)
 <60kg = 1g
 60-90kg = 1.5g
 >90kg = 2g

75
Q

Monitoring of vancomycin?

How is maintenance level calculated?

A

o Maintenance dose & dosing interval calculated using patient’s creatinine clearance (keeps trough levels of 10-15mg/L)
o Monitor pre-dose trough levels at 36-48 hours (should be between 10-20mg/L)

76
Q

How to adjust maintenance dose of vancomycin?

A

 If <5 – move up to two dosing levels from current dosing schedule

 If 5-10 – move up 1 or 2 levels depending on target (10-15 or 15-20)

 If 10-20 – continue at current dose

 If 20-25 – Move down one dosing level

 IF >25 – omit next dose & decrease by two dosing levels

 If >30 – seek pharmacy advice

77
Q

Monitoring during vancomycin levels?

A

o Daily U&Es and creatinine

o Regular FBC during prolonged therapy

78
Q

Common dose for vancomycin?

A
  • IV only given

- For C.diff – 125mg 6-hourly for 10-14 days

79
Q

Indications of metronidazole?

A
  • Anaerobic infections in:
    o Antibiotic-associated colitis (C.diff)
    o Oral infections (dental abscess) or aspiration pneumonia
    o Surgical and gynaecological infections
    o Protozoal infections (BV, trichomonas, giardiasis)
    o H.pylori eradication
80
Q

Mechanism of metronidazole?

A
  • Enter bacterial cells via passive diffusion
  • In anaerobic bacteria, reduction of metronidazole generates nitroso free radicals that bind to DNA and cause DNA degradation and cell death
81
Q

Side effects of metronidazole?

A
  • Dry mouth, metallic taste
  • Nausea and vomiting
  • Diarrhoea
  • Immediate or delayed hypersensitivity reactions
  • High doses/prolonged course
    o Peripheral or optic neuropathy
    o Seizures
    o Encephalopathy
82
Q

Cautions of metronidazole?

A

o Renal impairment (serial renal function monitoring)

o Elderly

83
Q

Interactions of metronidazole?

A
  • Metabolised by CYP450 enzymes – dose reduction in severe liver impairment
  • Some inhibitory effect on CYP450 enzymes
  • Inhibits acetaldehyde dehydrogenase – responsible for clearing alcohol so no alcohol when on metronidazole
    o Gives disulfiram reaction (flushing, nausea, headache, vomiting)
  • Increased risk of lithium toxicity
84
Q

Typical dose of metronidazole?

A
  • Oral typical and starting dose is 400mg 8-hourly

- Can be prescribed IV, rectally, topical, vaginal

85
Q

Monitoring of metronidazole?

A

o If treatment >10 days measure:

 FBC and LFTs

86
Q

Important communication to patients of metronidazole?

A

o No alcohol during or 48 hours after metronidazole treatment

87
Q

Indications of nitrofurantoin?

A
  • Uncomplicated UTI

- Prophylaxis in recurrent, catheter-associated or surgical prophylaxis of UTI

88
Q

Mechanism of nitrofurantoin?

A
  • Metabolised (reduced) in bacterial cells by nitrofuran reductase
  • Active metabolite damages bacterial DNA and causes cell death
89
Q

Side effects of nitrofurantoin?

A
  • N & V, diarrhoea
  • Immediate or delayed hypersensitivity reactions
  • Turn urine dark yellow/brown
  • Pneumonitis, hepatitis, peripheral neuropathy
  • Neonates – haemolytic anaemia
90
Q

Contraindications of nitrofurantoin?

A

o Porphyria, G6PD deficiency
o Infants <3m
o Pregnancy 3rd trimester
o Renal Impairment

91
Q

Dose change in renal impairment of nitrofurantoin?

A

o Avoid if <45 eGFR

92
Q

Typical dose in UTI of nitrofurantoin? And dose of prophylactic?

A
  • Acute UTI – 50-100mg QDS either 3 day (uncomplicated women) or 7 days (men or more complicated women)
  • Prevention of recurrent UTI – single nightly dose of 50-100mg
93
Q

Monitoring of nitrofurantoin?

A

o Long term therapy: LFT, pulmonary symptoms

94
Q

Names of quinolones?

A

Ciprofloxacin, Moxifloxacin, Levofloxacin

95
Q

Indications of quinolones?

A
  • 2nd or 3rd generation due to resistance and C.diff
    o UTI
    o Severe GI infection – Shigella, campylobacter
    o LRTI
96
Q

Mechanism of quinolones?

A
  • Inhibit DNA synthesis

- Rapid resistance can develop though

97
Q

Side effects of quinolones?

A
  • N&V, diarrhoea
  • Oesophageal irritation
  • Lower seizure threshold
  • Hallucinations
  • Rupture of muscle tendons
  • Prolong QT interval
  • C.diff Colitis
98
Q

Contraindications of quinolones?

A

o Hx of tendon disorders

o Pregnancy

99
Q

Cautions of quinolones?

A

o Risk of seizures

o Risk factors for QT prolongation

100
Q

Dose changes in renal impairment of quinolones?

A

o Reduce dose if eGFR <60

101
Q

Interactions of quinolones?

A
  • Drugs containing divalent cations reduce absorption of quinolones
  • Inhibits CYP450 enzymes
  • Avoid in drugs that prolong QT:
    o Amiodarone, antipsychotics, quinine, macrolides, SSRIs
102
Q

Typical dose of ciprofloxacin?

A
  • Ciprofloxacin typically 250-750mg orally 12-hourly or 400mg IV 12-hourly
103
Q

Names of tetracyclines?

A

Doxycycline, lymecycline, Tigecycline

104
Q

Indications of tetracyclines?

A
  • Acne vulgaris and rosacea
  • LRTIs including exacerbation of COPD, pneumonia and atypical pneumonia
  • Chlamydia, Syphilis, and PID
  • Typhoid anthrax, malaria and Lyme Disease
105
Q

Mechanism of tetracyclines?

A
  • Inhibits bacterial protein synthesis by binding to ribosomal 30S subunit
  • Prevents transfer of tRNA to mRNA – bacteriostatic
106
Q

Sides effects of tetracyclines?

A
  • N, V and diarrhoea
  • Oesophageal irritation
  • Photosensitivity
  • Discolouration and/or hypoplasia of tooth enamel in children
  • Intracranial hypertension
107
Q

Contraindications of tetracyclines?

A

o Pregnancy
o Breastfeeding
o Children <12 years old

108
Q

Dose changes in renal impairment of tetracyclines?

A

o Avoid – raise plasma urea

109
Q

Interactions of tetracyclines?

A
  • Bind to divalent cations
    o Do not give within 2 hours of Ca, antacids, iron
  • Enhance anticoagulant effect of warfarin
110
Q

Dose of doxycycline?

A
  • Oral typically 100-200mg daily
111
Q

Indications of trimethoprim?

A
  • Uncomplicated UTI

- Co-trimoxazole (trimethoprim and sulfamethoxazole) - PCP in HIV

112
Q

Mechanism of trimethoprim?

A
  • Inhibits bacterial folate synthesis, bacteriostatic

- However, widespread resistance in areas of UK

113
Q

Side effects of trimethoprim?

A
  • Nausea and vomiting
  • Diarrhoea
  • Hypersensitivity reactions – anaphylaxis, drug fever, erythema multiforme
  • Megaloblastic anaemia, leukopenia and thrombocytopenia
  • Hyperkalaemia and elevate creatinine concentrations
114
Q

Contraindications of trimethoprim?

A

o Blood dyscrasias

o 1st trimester of pregnancy (folate antagonist associated with foetal abnormalities (CV defects, oral cleft))

115
Q

Dose change in renal impairment of trimethoprim?

A

o Dose reduction – half dose after 3 days if eGFR 15-30, half dose if <15 eGFR

116
Q

Interactions of trimethoprim?

A
  • Elevates potassium in conjunction with:
    o Aldosterone antagonists, ACE inhibitors, ARBs
  • Risk of haematological effects increased with:
    o Methotrexate, phenytoin
  • Enhance anticoagulant effect of warfarin
117
Q

Usual dose of trimethoprim? And prophylactic dose?

A
  • Acute UTI – 200mg BDS either 3 day (uncomplicated women) or 7 days (men or more complicated women)
  • Prevention of recurrent UTI – single nightly dose of 100mg
118
Q

Monitoring of trimethoprim?

A

o Long term therapy: FBC

119
Q

Names of common antifungals?

A

Clotrimazole (Nystatin), Fluconazole

120
Q

Indications of azoles?

A
  • Local fungal infections of oropharynx, vagina or skin (topical or oral)
  • Systemic treatment of invasive fungal infections
121
Q

Mechanism of azoles?

A
  • Antifungals bind to ergosterol in fungal cell membranes, creating polar pore which allows intracellular ions to leak out
  • Imidazole (clotrimazole) and triazole (fluconazole) inhibit ergosterol synthesis, impairing cell membrane synthesis and replication
122
Q

Side effects of topical azoles and fluconazole?

A
  • Topical – local irritation where applied
  • Fluconazole
    o GI upset (nausea, vomiting, diarrhoea, abdominal pain)
    o Headache
    o Hepatitis
    o Hypersensitivity causing skin rash
  • Rarely:
    o Severe hepatic toxicity
    o Prolonged QT interval
123
Q

Contraindications of fluconazole?

A

o Pregnancy

124
Q

Cautions in fluconazole?

A

o Risk factors for QT prolongation

o Hepatic Impairment

125
Q

Dose changes in renal impairment in fluconazole?

A

o Reduce dose if eGFR <50

126
Q

Interactions with fluconazole?

A

o Inhibits CYP450 enzymes
o Reduce antiplatelet actions of clopidogrel
o Risk of arrhythmias in drugs that prolong QT
 Amiodarone, antipsychotics, quinine, quinolone, macrolides and SSRIs

127
Q

Prescriptions of nystatin, clotrimazole & fluconazole?

A

o Nystatin – topical or oral – thrush - 100,000 units QDS for 7 days or 48h after lesions resolve

o Clotrimazole – 1% cream applied BDS/TDS

o Fluconazole – Oral 150mg single dose

128
Q

Indications of aciclovir?

A
  • Herpes Simplex Infection
  • VZV
  • Herpes Zoster Virus
129
Q

Mechanism of aciclovir?

A
  • Converted by thymidine kinase to acyclovir monophosphate which inhibits HSV-specific DNA polymerases and prevents synthesis
130
Q

Side effects of aciclovir?

A
  • Oral – abdominal pain, diarrhoea, headache, nausea and vomiting
    o Rarely encephalopathy, neutropenia, leukopenia, thrombocytopenia
  • Topical – dry skin, stinging sensation
131
Q

Dose changes in renal impairment of aciclovir?

A

o Maintain adequate hydration

o Dose reduction if eGFR <10

132
Q

Interactions of aciclovir?

A
  • Increases exposure to aminophylline and theophylline so adjust dose

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