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TB Flashcards

(18 cards)

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1
Q

pathophysiology of mycobacterium TB

A
  • 98% of cases are airborne transmission
  • M.TB access the lower airways
    ~ no infection if: consumed by macrophages
    ~ with cellular immunity: replication in the lungs can be asymptomatic (latent) OR can become symptomatic (active)

obligate aerobic, slow-growing, acid-fast bacilli

waxy cell membrane - doesn’t produce typical gram-stain response (need Ziehl-Neelsen stain)

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2
Q

epidemiology of mycobacterium TB

A

~2/3 cases in pt > 50yrs

#5 cause of CAP:
- any pt in SG with unexplained cough >= 3 weeks should be evaluated for TB
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3
Q

risk factors of latent M.TB infections

A
  1. Residents of prisons, homeless shelters, nursing homes
  2. Close contact with pulmonary TB patients
  3. Co-infection with HIV
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4
Q

risk factors of active M.TB infections

A
  1. Residents of prisons, homeless shelters, nursing homes
  2. Close contact with pulmonary TB patients
  3. Co-infection with HIV
  4. Children <2 yo
  5. Elderly > 65yo
  6. Malnutrition
  7. Immunosuppression
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5
Q

clinical presentation of pulmonary tuberculosis

A
  • usually as a pulmonary infection
  • extra-pulmonary TB is possible
    ~ e.g. bone and joint, CNS

treatment for extra-pul TB is similar to pul TB
- diff is that additional adjunctive therapy and longer duration treatment

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6
Q

clinical presentation of pulmonary TB (the signs and sx, radiological findings)

A

Signs and symptoms:

  • Productive cough
  • Hemoptysis (coughing out blood)
  • Fever (systemic)
  • Fatigue (systemic)
  • Night sweats
  • Weight loss

Radiological findings:
- infiltrates in the apical region (upper lobe of either lung vs bacterial pneumonia found in the middle/lower lobes)

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7
Q

How to differentiate pneumonia (e.g. CAP) from TB?

A
  • Duration of symptoms
    TB - gradual onset (weeks-months)

Pneumonia - acute onset (hours-days)

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8
Q

2 Procedures for LTBI screening

A
  1. Tuberculin skin test
    - inject 0.1ml of PPD intradermally
    - read after 48-72 hours by a trained reader
    - read the diameter of induration (NOT area of redness)
    - result: most sg’reans are BCG-vaccinated –> >= 10mm of induration

PPD = purified protein derivative

  1. Interferon-gamma release assay
    - blood collection into special tubes
    - measure interferon-gamma released by WBCs in response to incubation with M.tuberculosis - specific antigens in the tube
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9
Q

strengths and weaknesses of the 2 LBTI diagnosis screening

A 
Tuberculin skin test (PPD):
Strengths:
- high sensitivity (95-98%)
- low cost
- no need to collect blood samples

Weakness:

  • false negative = immunocompromised
  • false positive = environmental contact with non-tuberculous mycobacteria, BCG vaccination
  • no universally accepted standard for interpreting results
  • inter-reader variability

Interferon-gamma release assay
Strengths:
- performance good as to PPD
- No false positive in BCG-vaccinated individuals
- Minimal cross-reactivity with non-tuberculous mycobacteria
- results available within few hours

Weaknesses:

  • expensive
  • need for blood samples
  • false negative: immunocompromised
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10
Q

diagnosis of active TB

A

Suspect based on:

  1. History (TB is a gradual onset illness)
  2. Risk factors (immune status - HIV or diabetes, living conditions, nutritional status, age)
  3. Clinical presentation
  4. Physical exam findings
  5. Chest X-ray findings

if sputum obtained for Ziehl-Neelsen stain for acid fast bacilli (AFB) is positive, treatment is initiated

takes 4-8 wks to grow and get confirmation of TB
another 4-6 weeks for drug susceptibility testing results

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11
Q

what are the infection control requirements for TB

A

for LBTI patients:
- no special infection control precautions

for active TB patients:

  1. In hospitals: need airborne precautions
    - negative pressure rooms
    - need to wear PPE (gowns, N95 mask)
  2. treatment decreases infectiousness
    - airborne precautions no longer needed after 2 weeks of effective treatment
  3. In community: no need to avoid household members
    - take TB med, practice cough etiquette, ventilate homes
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12
Q

Patient-specific therapy for latent TB

A

monotherapy is ADEQUATE (progression risk from 10% to 1%)

before initiating therapy NEED to:

  • exclude ACTIVE TB
  • weigh risk vs benefits (if patients have underlying liver disease or risk of hepatotoxicity)
  1. Isoniazid 5mg/kg PO daily (max 300mg PO daily)
    - 6 months or 9 months (HIV)
    - to + 10mg/day pyridoxine
    - can be used for preg, lactation, HIV
  2. Rifampicin 10mg/kg PO daily (max 600mg PO daily)
    - 4 months
    - alt therapy for those who cannot tolerate isoniazid
  3. Isoniazid + Rifapentine 900mg PO weekly
    - not recommended for HIV pt
    - DOT
    - 12 weeks
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13
Q

why treatment of active TB is important?

A

Benefits the patient

  • reduces number of replicating and persisting bacteria
  • achieves durable cure and prevents relapse
  • prevents development of resistance

Benefits public health
- minimised transmission to others

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14
Q

Patient-specific therapy for active TB

A
  • Report to National TB Registry
  • Sg TB Elimination Program (STEP): promotes DOT, National Treatment Surveillance Registry, investigate recent contacts
  1. STANDARD 6-month treatment
    - 2 months Daily administration: RIF + INH + PZA + *EMB/STM

after confirming susceptibility to RIF and INH OR
culture negative pulmonary TB (assuming its susceptible to RIF and INH)

  • 4 months Continuation Phase (daily or 3x/week administration): RIF + INH
    (3x /week more convenient for DOT)
  1. 9-month treatment if unlikely to tolerate PZA (e.g. elderly, liver disease)
    - 2 months intensive phase: daily RIF + INH + EMB

after confirming susceptibility to RIF and INH OR
culture negative pulmonary TB

  • 7 months continuation phase: daily or 3x/week RIF + INH
Drugs involved:
(1) Rifampicin
(a) 10mg/kg daily
(b) 10mg/kg 3x/week
max per dose = 600mg
available preparations: 100mg, 300mg tablets

(2) Isoniazid
(a) 5mg/kg daily
max per dose 300mg
(b) 15mg/kg 3x/week
max per dose = 900mg
available preparations: 150mg, 300mg tablets

RIF and INH no need renal dose adjustment

(3) Pyrazinamide
15-30mg/kg daily
max per dose = 2g
available preparations: 500mg tablets

(4) Ethambutol
15-25mg/kg daily
max per dose 1600mg
available preparations: 100mg, 400mg tablets

(5) Streptomycin IM
10-15mg/kg daily
max per dose 1g
available preparations: 1g vial

PZA, EMB and STM need to be renal dose adjustment

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15
Q

How do we administer the drugs for active TB treatment

A
  • TB med = conc-dependent killing
  • Administered once daily
  • ALL taken at the SAME time

Look out for DDI:
- INH inhibits CYP2C19, 3A4, 2D6, 2E1

  • RIF induces CYP1A2, 2C9. 2C19, 3A4 and PGP
  • evaluate ALL medications closely (other prescription/ non-prescription/ supplements)
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16
Q

Monitoring requirements for active and latent TB treatment

Study These Flashcards
A
  1. hepatotoxicity = RIF, INH, PZA
    - risk factors: >35yo, female, underlying liver disease, concurrent alcohol use, HIV

For ZERO risk factors:

a. Before treatment: no need baseline LFTs
b. During treatment: No need for routine LFTs monitoring

For ONE or MORE risk factors:

a. Before treatment: Check baseline LFTs
b. During treatment: Check LFTs every 2-4 weeks

  1. Educate all patients (latent AND active) on symptoms of hepatotoxicity
    - N/V, unexplained fatigue, abdominal discomfort or pain
    - if present, stop treatment and see a doctor immediately
17
Q

What to do if hepatotoxicity develops for LTBI and Active TB

Study These Flashcards
A

definition: ALT > 3x upper limit of normal [ULN] w symptoms OR
ALT > 5x ULN wo symptoms

for LBTI treatment:
- stop treatment immediately

  • monitor LFTs
  • re-challenge with INH when ALT improves to <2x ULN
  • if patient CANNOT tolerate INH (if hepatotoxicity develops again), switch to RIF x 4 month

for Active TB treatment:
- stop treatment immediately

  • monitor LFTs
  • re-challenge SEQUENTIALLY when LFTs normalized and symptoms resolved
    (e. g. start one TB med at a time; start RIF first, and if can tolerate after a few days, then restart with INH and so on)
  • if re-challenge FAILS, may need non-hepatotoxic regimen (e.g. EMB + FQ + STM)
18
Q

Other monitoring parameters for TB - Ethambutol (EMB)

Study These Flashcards
A

EMB causes visual toxicity

  • reduce visual acuity
  • reduced red-green color discrimination

Monitor for visual acuity and colour discrimination tests:
- at baseline for ALL patients

  • MONTHLY monitoring in patients with ANY of the risk factors:
    (1) taking EMB for more than 2 months (usually only 2 months, based on treatment regimen)
    (2) has renal insufficiency (e.g. CKD)

educate ALL patients to stop TB treatment and see a doc immediately if they experience changes in vision

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