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Education Materials > Publications > Self-Study Modules on TB > Module 4 > Treatment of TB Infection

Self-Study Modules on Tuberculosis

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Module 4: Treatment of Tuberculosis Infection and Disease

Treatment of TB Infection (Preventive Therapy)

What is preventive therapy?

Preventive therapy is medication that is given to people who have TB infection to prevent them from developing TB disease.

Who should receive preventive therapy?

Some groups of people are at higher risk for TB than others (see Module 2, Epidemiology of TB). These groups are either

  • More likely to be exposed to or infected with M. tuberculosis, or
  • More likely to develop TB disease once infected

People in these groups should receive high priority for preventive therapy if they have a positive tuberculin skin test reaction (Table 4.1).
 

Table 4.1
High-Priority Candidates for Preventive Therapy
People in these groups should be given high priority for preventive therapy if they have a positive skin test reaction1, regardless of their age: People in these groups should be given high priority for preventive therapy if they have a positive skin test reaction1 and they are younger than 35:
People with HIV infection2

Close contacts of people with infectious TB disease2

People whose skin test reaction converted from negative to positive within the past 2 years

People with chest x-ray findings suggestive of previous TB disease

People who inject illicit drugs

People with medical conditions that appear to increase the risk for TB disease (see Module 1, Transmission and Pathogenesis of Tuberculosis)

People born in areas of the world where TB is common (for example, Asia, Africa, or Latin America)

Low-income groups with poor access to health care

People who live in residential facilities (for example, nursing homes or correctional facilities)

Children younger than 4 years old

People in other groups as identified by local public health officials

  1. See Module 3, Diagnosis of Tuberculosis Infection and Disease, for information on classifying the tuberculin skin test reaction.
  2. In certain circumstances, people in these categories may be given preventive therapy even if they do not have a positive tuberculin skin test reaction.

People with no risk factors should be evaluated for preventive therapy if their tuberculin skin test reaction is 15 mm or larger and they are younger than 35 years old.

People who may be exposed to TB on the job (for example, health care workers and staff of nursing homes or correctional facilities) should be evaluated for preventive therapy if they have a positive skin test reaction.

Sometimes preventive therapy is given to people who have a negative tuberculin skin test reaction. For example, some close contacts may start taking preventive therapy if they have a negative skin test reaction but less than 10 weeks have passed since they were last exposed to TB. These contacts include

  • High-risk contacts who have a negative skin test reaction (including contacts who are anergic). High-risk contacts are young children, adolescents, HIV-infected people, and others who may develop TB very quickly after infection.
  • Close contacts who have a negative skin test reaction, if many other close contacts have a positive skin test reaction

Because less than 10 weeks have passed since they were last exposed to TB, these contacts may be infected with M. tuberculosis but have a false-negative skin test reaction (see Module 3, Diagnosis of Tuberculosis Infection and Disease). They should start preventive therapy to prevent them from rapidly developing TB disease. These contacts should be retested 10 weeks after they were last exposed to TB. If they have a negative skin test reaction, they can stop taking preventive therapy. (HIV-infected contacts may be given a full course of preventive therapy, regardless of their skin test results.) If they have a positive skin test reaction, they should continue to take preventive therapy.

Also, children younger than 6 months old who have been exposed to TB should start taking preventive therapy, even if they have a negative skin test reaction. This is because they are at high risk of rapidly developing TB disease and because they may have a false-negative reaction to the tuberculin skin test (see Module 3, Diagnosis of Tuberculosis Infection and Disease). The children should be retested when they are 6 months old. If they have a negative skin test reaction and 10 weeks have passed since they were last exposed to TB, the preventive therapy may be stopped.
 

Study Questions 4.1-4.4

4.1. What is the purpose of preventive therapy?

4.2. Which groups of people should receive high priority for preventive therapy if they have a positive skin test reaction, regardless of their age? Name six.

4.3. Which groups of people should receive high priority for preventive therapy if they have a positive skin test reaction and are younger than 35? Name five.

4.4. In what circumstances may preventive therapy be given to people who have a negative tuberculin skin test reaction?

Answers

Evaluation for Preventive Therapy

All people being considered for preventive therapy should receive a medical evaluation. One reason for this evaluation is to exclude the possibility of TB disease, because treating TB disease with a preventive therapy regimen (usually a single drug) can lead to drug resistance. To rule out the possibility of TB disease, clinicians should determine whether the patient has symptoms of TB disease, and they should evaluate the patient with a chest x-ray (see Module 3, Diagnosis of Tuberculosis Infection and Disease). People with symptoms of TB disease or chest x-ray findings suggestive of TB disease should be given treatment for TB disease, not TB infection.

Another reason for the medical evaluation is to determine whether the patient has ever been treated for TB infection or disease. People who have been adequately treated should not be treated again. The tuberculin skin test cannot be used to determine whether a patient has received treatment for TB infection or disease. This is because most people who have a positive skin test reaction will have a positive reaction if they are skin tested later in their lives, regardless of whether they have received treatment (see Module 3, Diagnosis of Tuberculosis Infection and Disease).

A third reason for the medical evaluation is to find out whether the patient has any medical problems that may complicate therapy or require more careful monitoring (for example, liver disease or alcoholism).
 

Case Study 4.1

You are sent to visit the home of a TB patient who was admitted to the hospital last week and diagnosed with infectious TB disease. Living in the home are his wife and his 1-year-old daughter. Neither one has symptoms of TB disease. You give them both a tuberculin skin test and return 2 days later to read the results. You find that the wife has 14 mm of induration, but the daughter has no induration.

Should either one start preventive therapy?

Why or why not?

Answers

Regimens for Preventive Therapy

The usual regimen for preventive therapy is a drug called isoniazid given daily for 6 months. Six months of isoniazid preventive therapy is very effective in preventing the development of TB disease in people not infected with HIV. Because isoniazid preventive therapy is not always effective when it is given for less than 6 months, every effort must be made to ensure that patients receive preventive therapy for at least 6 months.

Some groups of people should receive isoniazid preventive therapy for longer than 6 months. For example, children should receive at least 9 months of isoniazid preventive therapy. HIV-infected people should receive 12 months of isoniazid preventive therapy. In addition, people with chest x-ray findings suggestive of silicosis or previous TB disease should receive a 12-month regimen of isoniazid preventive therapy or a 4-month regimen of isoniazid and another drug, rifampin.

For most pregnant women with TB infection, preventive therapy should be delayed until after delivery, even though isoniazid has NOT been shown to have harmful effects on the fetus. However, pregnant women who have certain conditions should receive preventive therapy right away if they are found to have TB infection. These conditions include HIV infection, recent TB infection, and other conditions that appear to increase the risk for TB disease (see Module 1, Transmission and Pathogenesis of Tuberculosis). The preventive therapy regimen for pregnant women is the same as the usual preventive therapy regimen -- isoniazid given daily for 6 months.

Alternative Regimens for Preventive Therapy

In some situations, drugs other than isoniazid may be used for preventive therapy. For example, preventive therapy with rifampin is recommended for people with a positive skin test reaction who have been exposed to isoniazid-resistant TB. Preventive therapy with rifampin should be given for 6 months in adults and 9 months in children.

No preventive therapy regimens have been studied for persons exposed to TB resistant to both isoniazid and rifampin. Persons at high risk of developing TB disease (for example, HIV-infected people) who are likely to be infected with multidrug-resistant organisms may be given an alternative preventive therapy regimen. This regimen should consist of two drugs to which the infecting organism is known to be susceptible. Two suggested regimens are ethambutol and pyrazinamide or pyrazinamide and a quinolone. Clinicians who are not experienced in managing patients exposed to drug-resistant TB should seek consultation from medical experts.
 

Study Questions 4.5-4.8

4.5. Name three reasons why patients should receive a medical evaluation before starting preventive therapy.

4.6. Why is it important to exclude the possibility of TB disease before giving a patient preventive therapy?

4.7. What is the usual preventive therapy regimen? How is it different for children and HIV-infected people?

4.8. What preventive therapy regimen is recommended for people with a positive skin test reaction who have been exposed to isoniazid-resistant TB?

Answers

Adverse Reactions to Isoniazid

Sometimes medications cause adverse reactions, or negative side effects. Isoniazid may cause hepatitis, or damage to the liver. Hepatitis prevents the liver from functioning normally, causing symptoms such as:

  • Nausea
  • Vomiting
  • Abdominal pain
  • Fatigue
  • Dark urine

Many things can cause hepatitis, including various viruses and medications.

Isoniazid can cause hepatitis in anyone. In fact, as many as 20% of people treated with isoniazid have some abnormality of liver function tests (tests done to detect damage to the liver) during treatment with isoniazid. In most people, these test results return to normal even when isoniazid treatment is continued.

In some people, however, there is a greater risk that isoniazid will cause serious hepatitis. Age is one factor; older persons are at higher risk for hepatitis. This is why preventive therapy is not recommended for people 35 years and older, unless their risk of developing TB disease is very high. Alcoholism, previous or current liver disease, drug injection, and the use of certain medications are other factors. In addition, some evidence suggests that women, particularly black and Hispanic women, are at increased risk for fatal hepatitis associated with isoniazid. This risk may be even greater for women who have recently given birth. However, fatal hepatitis is very rare.

Isoniazid can also damage the sensory nerves of the hands and feet. This is called peripheral neuropathy. The main symptom of peripheral neuropathy is a tingling sensation or a weakened sense of touch in the hands and feet. Some conditions, such as alcoholism, diabetes, and malnutrition, increase the risk for peripheral neuropathy. People with these conditions should be given vitamin B6 if they are taking isoniazid. Vitamin B6 is also recommended for pregnant women who are taking isoniazid.

Monitoring for Adverse Reactions

First, all patients taking preventive therapy should be educated about the symptoms that are caused by adverse reactions to isoniazid. These patients should be instructed to stop taking the medication and seek medical attention immediately if these symptoms occur. Second, all persons receiving preventive therapy should be evaluated at least monthly during therapy for signs and symptoms of adverse reactions. During each monthly evaluation, clinicians should ask patients whether they have nausea, abdominal pain, or any of the other symptoms that may be caused by adverse reactions. In addition, they should examine patients for signs of these adverse reactions.

People at greatest risk for hepatitis should have liver function tests before starting isoniazid preventive therapy and every month during therapy. This includes:

  • People 35 years of age and older
  • People with a history of liver disease
  • People who abuse alcohol
  • People who inject illicit drugs
  • People who are taking other medications that may increase the risk of hepatitis

In addition, more careful monitoring -- and possibly more liver function tests -- should be considered for black and Hispanic women because they may be at increased risk for isoniazid-associated hepatitis. For all patients, isoniazid should be stopped if the results of liver function tests are much higher than the upper limit of the normal range.
 

Study Questions 4.9-4.10

4.9. What adverse reactions may be caused by isoniazid? Name two, and define each.

4.10. What are the symptoms of hepatitis?

Answers


 

Study Questions 4.11-4.12

4.11. How often should patients be evaluated for signs and symptoms of adverse reactions during preventive therapy?

4.12. Who is at greatest risk for hepatitis? What special precautions should be taken for these patients?

Answers


 

Case Study 4.2

A 65-year-old man is prescribed isoniazid preventive therapy because he is a close contact of a person with infectious TB and he has an induration of 20 mm to the tuberculin skin test. His baseline liver function tests are normal, but he drinks a six-pack of beer every day.

What kind of monitoring is necessary for this patient while he is taking isoniazid?

Answer

 


Released October 2008
Centers for Disease Control and Prevention
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
Division of Tuberculosis Elimination - http://www.cdc.gov/tb

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