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Tubersol

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Tubersol

CLINICAL PHARMACOLOGY

The number of tuberculosis (TB) cases reported in the United States declined from more than 84,000 cases in 1953 to 22,255 cases in 1984. However, since 1984 dramatic changes in TB morbidity trends have occurred, and these changes jeopardize the control of TB. From 1985 through 1991, reported TB cases increased 18% - representing approximately 39,000 more cases than expected had the previous downward trend continued.7 The excess number of cases is due to many factors, including the human immunodeficiency virus (HIV) epidemic, a deterioration in the health-care infrastructure, and increases in the number of cases among foreign-born persons.7

Case rates of tuberculosis for all ages are highest in urban, low-income areas,and in non-white racial and ethnic groups, among whom more than two-thirds of reported cases in the United States now occur. Some rural areas also have high rates. Foreign-born children in recent years accounted for nearly one-quarter of newly diagnosed pediatric cases. More than 35% of those cases 5 to 14 years are foreign-born in comparison to approximately 15% of those younger than 5 years. Specific groups with the highest rates of infection and disease include first-generation immigrants from high-risk countries (e.g.,in Asia); Native Americans, including Alaskan natives; the homeless; and residents of correctional facilities.8

Tuberculosis has become a relatively uncommon disease in Canada.From 1988 to 1992 over 2,000 active cases were diagnosed annually, and fewer than 200 deaths annually were attributed to tuberculosis. However, declines in tuberculosis notification rates, which characterized the 1960s through the early 1980s, ceased in the late 1980s. In Canada, groups at high risk for tuberculosis include Aboriginal Canadians, foreign-born residents from countries with a high prevalence of the disease and certain disadvantaged inner-city groups, including the poor the unemployed and the homeless, particularly single men. The proportion of active cases of tuberculosis due to reactivated disease has been quite constant, at about 10% during the 1980s. Tuberculosis rates are similar for males and females until middle age.After 55, the rates rise progressively, with particularly steep increases among men.9

Tuberculin Purified Protein Derivative (Mantoux) - TUBERSOL (tuberculin purified protein) ® is indicated for the detection of a delayed hypersensitivity reaction to tuberculin as an aid in the detection of infection with Mycobacterium tuberculosis.

Independent studies conducted by the U.S. Public Health Service in humans have determined the amount of CT68 in stabilized solution necessary to produce bio-equivalency with Tuberculin PPD-S (in phosphate buffer without Tween 80) using 5 U.S. units (TU) Tuberculin PPD-S as the standard.10

The reaction to intradermally injected tuberculin is a delayed (cellular) hypersensitivity reaction. The reaction which characteristically shows a delayed course, reaching its peak more than 48-72 hours after administration, consists of induration caused by cellular infiltration of lyphocytes.Clinically, a delayed hypersensitivity reaction to tuberculin is a manifestation of previous infection with M. tuberculosis or a variety of non-tuberculosis bacteria. Sensitization may be induced by natural mycobacterial infection or by vaccination with BCG Vaccine.

The sensitization following infection with mycobacteria occurs primarily in the regional lymph nodes. Small lymphocytes (T lymphocytes) proliferate in response to the antigenic stimulus to give rise to specifically sensitized lymphocytes. After about 6 weeks, these lymphocytes enter the blood stream and circulate for years. Subsequent restimulation of these sensitized lymphocytes with the same or a similar antigen, such as the intradermal injection of tuberculin, evokes a local reaction caused by infiltration of these cells.

The tuberculin reaction is characterized by the early predominance of mononuclear cells (small and medium sized lymphocytes and monocytes). Only a small proportion of these cells appear to be lymphocytes sensitized to tuberculin. Most cells are brought into the reaction through the release of biologically active substances by sensitized lymphocytes. An increase in vascular permeability leading to erythema and edema also occurs in tuberculin reactions.

Characteristically, delayed hypersensitivity reactions to tuberculin begin at 5 to 6 hours, are maximal at 48 to 72 hours and subside over a period of days. Immediate hypersensitivity (allergic) reactions to tuberculin or to constituents of the diluent may also occur, but these allergic reactions have no diagnostic importance.

Not all infected persons will have a delayed hypersensitivity reaction to a tuberculin test. A large number of factors has been reported to cause a decreased ability to respond to the tuberculin test in the presence of tuberculous infection including viral infections (measles, mumps, chickenpox and HIV), live virus vaccinations (measles, mumps, rubella, oral polio and yellow fever), overwhelming tuberculosis, other bacterial infections, drugs (corticosteroids and many other immunosuppressive agents), and malignancy.11,12

Because in HIV-infected individuals, tuberculin skin-test results are less reliable as CD4 counts decline, screening should be completed as early as possible after HIV-infection occurs. Those HIV-infected patients at high risk for continuing exposure to patients who have TB should be screened periodically for TB infection. If they have TB symptoms or if they are exposed to a patient who has pulmonary TB, HIV-infected persons should be evaluated promptly for TB. Because active disease can develop rapidly in HIV-infected persons, the highest priority for contact investigation should be given to persons potentially coinfected with HIV and TB.13

Two-step testing should be performed on the initial testing if tuberculin testing will subsequently be conducted at regular intervals, for instance among health-care workers.9 If the first test showed either or no reaction or a small reaction, the second test should be performed one to four weeks later. Both tests should be read and recorded at 48 to 72 hours.9 Patients with a second tuberculin test (booster) response of 10 mm or more should be considered to have experienced past or old infection.14

Persons who do not boost when given repeat tests at one week, but whose tuberculin reactions change to positive after one year, should be considered to have newly acquired tuberculosis infection and managed accordingly.15

The repeated testing of uninfected persons does not sensitize them to tuberculin.13,14,16,17

REFERENCES

7. Recommendations and Reports. Initial therapy for tuberculosis in the era of multidrug resistance - Recommendations of the Advisory Council for the Elimination of Tuberculosis.MMWR 1993;42,RR-7.

8. American Academy of Pediatrics. Peter G, ed. 2000 Red Book: Report of the Committee on Infectious Diseases. 25th ed. Elk Grove Village, IL: American Academy of Pediatrics.2000.

9. Canadian Lung Association. Canadian Tuberculosis Standards. 5th edition. 2000.

10. Data on file; Aventis Pasteur Limited.

11. Mori and Shiozawa. Suppression of tuberculin hypersensitivity caused by rubella infection. Am Rev Respir Dis 1985;886-890.

12. Brickman HF, et al.The timing of tuberculin tests in relation to immunization with live viral vaccines. Pediatrics:1975;55:392-396.

13. Screening for tuberculosis and tuberculosis infection in high-risk populations. Recommendations of the Advisory Council for the Elimination of Tuberculosis. MMWR 1995;44,RR-11.

14. American Thoracic Society: Diagnostic standards and classification of tuberculosis in adults and children. Am J Respir Crit Care Med 2000;161:1376-1395.

15. Thompson N, et al.The booster phenomenon in serial tuberculin testing. Am Rev Respir Dis 1979;119:587-597.

16. The tuberculin skin test. Clin Infect Dis 1993;17:968-975.

17. Menzies D. Interpretation of repeated tuberculin tests. Am J Respir Cit Care Med 1999;59:15-21.

Last reviewed on RxList: 1/30/2009
This monograph has been modified to include the generic and brand name in many instances.

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