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Latent TB infection (LTBI) is diagnosed when a person with a positive TB skin test or IGRA has a negative chest x-ray and is asymptomatic for TB disease.  The Canadian TB Standards recommends treating patients with LTBI, especially those at higher risk for developing active TB. Consider treatment for those who have resided or travelled in a high TB incidence country. Canada defines an endemic country as any country which has a ≥ 30 / 100,000 TB incidence rate per year.  Active disease must be ruled out before treating for LTBI.

The following table identifies patients at risk for developing active TB:

Medical Risk Factors for Developing Active TB

Slightly Increased Risk

Moderate Risk

High Risk

  • Heavy alcohol consumption (≥3 drinks/day)
  • Underweight (<90% ideal body weight)
  • Cigarette smoker (1 pack/day)
  • Abnormal chest x-ray - granuloma
  • Tumour necrosis factor alpha inhibitors
  • Diabetes mellitus (all types)
  • Treatment with glucocorticoids (≥15 mg/d prednisone)
  • Young age when infected (0-4 years)
  • Acquired immunodeficiency syndrome (AIDS)
  • Human immunodeficiency virus infection (HIV)
  • Transplantation (related to immune-suppressant therapy)
  • Silicosis
  • Chronic renal failure requiring hemodialysis
  • Carcinoma of head and neck
  • Recent TB infection (≤ 2 years)
  • Abnormal chest x-ray – fibronodular disease

Recommended Drug Regimen for the Treatment of LTBI

Isoniazid (INH) is the recommended medication to treat LTBI. Nine months of daily self-administered INH is the standard duration choice with a 90% protective efficacy. Six months of daily self-administered INH is an acceptable alternative with a 67%-69% protective efficacy.

INH is available in:

  • 300mg tablets
  • 100mg tablets (scored)
  • 50mg/5ml liquid

Daily Dosage of INH:

Children (12 years old and under): 10-15mg/kg, maximum dose 300mg/day

Adults (over 12 years old): 5 mg/kg, maximum dose 300mg/day

Pyridoxine (Vitamin B6) should be given to minimize the risk of neuropathy in people with risk factors for pyridoxine deficiency (such as malnourished or pregnant individuals) or for neuropathy (patients with diabetes or renal insufficiency). A dose of 25mg daily is usually sufficient. B6 supplements are not routinely needed otherwise.

Patients can obtain TB medication for free from the Windsor-Essex County Health Unit by appointment with a prescription.

Monitoring Liver Function (bilirubin and liver transaminases)

The following table is a suggested follow-up schedule for patients receiving 9 months INH LTBI treatment, as found in the Canadian TB Standards. If an alternate regimen is used, the same schedule is recommended until the end of treatment:

Bilirubin and Transaminases (AST and ALT)

 

Start of treatment

1 month

2 month

3 month

4 month

5 month

6 month

7 month

8 month

9 month

Age <35 years

If clinical suspicion of liver disease

If needed

If needed

If needed

If needed

If needed

If needed

If needed

If needed

If needed

Age 35-50 years

X

X

If needed

 

If needed

 

If needed

 

If needed

X

Age >50 years or other risk factors*

X

X

X

X

X

X

X

X

X

X

* Risk factors requiring monthly monitoring include:

  • Pregnancy or first 3 months postpartum
  • History of previous drug-induced hepatitis
  • Current cirrhosis or chronic active hepatitis of any cause
  • Hepatitis C
  • Hepatitis B with abnormal transaminases
  • Daily alcohol consumption or concomitant treatment with other hepatotoxic drugs (e.g. methotrexate)

Stop INH treatment if the AST or ALT levels increase beyond five times the upper limit of normal, or three times the upper limit of normal in the presence of symptoms of hepatotoxicity.

Windsor-Essex County Health Unit Monitoring and Dispensing

Patients referred to the Windsor-Essex County Health Unit are dispensed one month of medication at their initial appointment and up to two months at subsequent appointments, as the script allows. At each visit, the patient is monitored for adherence and assessed for side effects, weight stability, pregnancy, symptoms of disease, and liver function as per the above schedule.

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Last modified: 
Friday, April 29, 2022 - 10:00am