MDR TB

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MULTI-DRUG RESISITANT TUBERCULOSIS By Dr.Ravi sher sahota

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DEFINITION It is decrease in sensitivity in sufficient degree to be reasonably certain that the strain concerned is different from a sample of wild strains of human type that have never come in contact with the drug. Multiple drug resistant tuberculosis (MDR-TB) - caused by strains resistant to at least isoniazid (INH) and rifampicin (RMP) with or without resistance to other first line of drugs.

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Extensively drug resistant tuberculosis (XDRTB) - Strains that are MDR with additional resistant to any fluroquinolone and anyone of the three second line injectables - Amikacin, Kanamycin or Capreomycin. Pan drug resistant tuberculosis- strains of mycobacterium resistant to all known anti-tubercular drugs. Mono drug resistant tuberculosis- mono resistance to INH and RMP.

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TYPES OF DRUG RESISTANCE 1. Primary - when drug resistance is demonstrated in a patient who has never received anti-TB treatment before. 2 . Acquired – resistance that develops in a patient who has received prior chemotherapy.

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New WHO recommendations – new terms for 1. Primary resistance -“drug resistance in new cases”. 2. Acquired Resistance - “drug resistance in previously treated cases”. Initial drug resistance- When one is not sure whether the resistance is primary or acquired due to concealed history or unawareness of treatment taken before. Combined resistance – Sum of primary and acquired resistance.

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DISEASE BURDEN As per WHO 2008, there are 8.9 to 9.9 million incident cases (1.2 to 1.6 million HIV +ve) and 9.6 to 13.3 million prevalent cases. India and china account for 35% of TB cases worldwide. WHO guidance recommends reporting of all cases of childhood TB (smear positive, negative and extra- pulmonary) in two age bands(0-4 years and 5-14 years)

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In India three percent of the total load of new cases registered, belong to the Pediatric age group. 4, 40, 000 cases MDR-TB India in 2008(3.6% of estimated TB episodes), 3, 60,000 were new and relapse cases and 94,000 were previously treated for TB. As per union global project on anti-tuberculosis drug resistance surveillance report, drug resistance was seen in 70% of new cases, 35% of re-treatment cases and 20% of all TB cases.

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Risk Factors For Drug Resistance The only definite way of diagnosing drug resistance is by isolating M. Tuberculosis from sputum or tissues and assessing its susceptibility pattern. Major historical factors for drug resistance:- 1. Residence and regions with known high MDR/XDR incidence. 2. contact with a case of drug resistant Tb or the contact has been on irregular treatment and continues to be sputum +ve or died after irregular treatment. 3. HIV Aids/ other immunocompromised states.

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4. History of:- Previous Tb Therapy especially within the past year. Relapse/ reoccurrence after previous treatment. Non adherence or defaulters. Malabsorption. Medication known to cause drug interaction with concurrent Tb Therapy. Hospitalisation within past 2 years. 5. The child shows initial improvement on anti-Tb treatment and then deteriorates.

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Mechanism and causes of drug resistance Resistance to anti-Tb drugs arises as a result of spontaneous mutations in the genome of M. Tuberculosis which occur at predictable rates for each anti tubercular drug (e.g.. Isoniazid 10 -6 Rifampicin 10 -8 ) and not as a result of horizontal gene transfer. INH monotherapy selects INH resistant mutants and allows them to multiply. Resistance to additional Tb Drugs can be added in a stepwise manner to create polyresistant strains. Once created, drug resistant Tb strains can be passed on the individuals giving rise to MDR-Tb in individuals never previously exposed to anti – Tb drugs (primary resistance)

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Other contributory factors:- Poor functioning national TB programs. Unnecessary administrative control on purchase and distribution of drugs. Poor quality control. Inappropriate drug combinations. Poor storage conditions. Lack of knowledge of physician regarding dosage, duration, standard regimens and frequent change of brand names. Use of anti-TB antibiotics for indications other than TB Epidemic of HIV infection. Lab delays in identification and susceptibility testing. Improper control measures. Social myths and misconception .

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CLINICAL FEATURES Children and adolescents with drug resistant TB tend to have features of primary TB as hilar and/or mediastinal lypmphadenopathy segmental lesions or pleural involvement. A high index of suspicion is required to diagnose drug resistant tuberculosis early. The presence of risk factors should be sought in every case especially the history of contact with a known case of MDR-TB Drug susceptibility tests should be ordered and the results obtained at the earliest. Isolation of the bacilli should be pursued aggressively using early morning gastric aspirates and/or induced sputum/ bronchoalveolar lavage/ and FNAC or open biopsy or tissue diagnosis.

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As per WHO guidelines, MDRTB can be suspected in any TB patient who is excreting bacilli after 5months of re-treatment regimen, given under direct observation. For the patients who have received two courses of chemotherapy are usually but not always excreters of resistant bacilli and most often, excreters of MDR bacilli. Certain peculiarities of Tb tend to confound the diagnosis of drug resistance, if this is inferred from clinical and/or radiological failure to treatment as persistent symptoms are a poor proxy for activity. Drug resistant TB is ultimately a laboratory diagnosis

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The persistence of clinical symptoms like cough and sputum production can also be due to post tubercular sequel like bronchiectasis and bronchial hyper reactivity. Tuberculomas of brain are known to increase in size and number despite successful therapy in a proportion of cases. Demonstration or isolation of AFB is the only sure way to differentiate such situations from a true failure.

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DIAGNOSIS Microscopy – vital staining for viability of bacilli. Conventional indirect drug susceptibility testing. Automated liquid culture platforms ( radiometric and non-radiometric) Thin layer agar culture MODS assay ( Microscopic observation drug susceptibility) Calorimetric redox indicator assay NRA or Griess assay Genotypic testing Genexpert assay Phage based setting

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Management

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Regimens should be based on history of drugs taken and the prevalence of resistance to 1 st and 2 nd line drugs in the specified area. Regimens should consist of at least 4 drugs. Drugs are administered for at least 6 days a week. ‘Z’, ‘E’ and Fluroquinolones should be given once per day. Once a day dosing is permitted for other 2 nd line drugs depending on patients tolerance. The drug dosage should be determined by body weight.

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An injectable agent is used for a minimum of 6 months and at least 4 months after the patient becomes and remains culture negative. Treatment is for a minimum duration of 18 months beyond conversion. Each dose should be given under observation. DST, when available from a reliable lab should guide the therapy. ‘Z’ can be used for the entire treatment if it is effective. If pulmonary disease is sufficiently localised and the residual lung is functioning adequately, resective surgery should be considered as an adjunct to chemotherapy.

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GROUP DRUGS REMARKS Group 1 (First line Anti-Tb Drugs) H, R, E, Z Most potent and best tolerated. To be used only if there is lab evidence or clinical history of efficacy Group 2 (injectable Anti-Tb Drugs) Streptomycin, Kanamycin, Amikacin, Capreomycin, Viomycin. Given to all with suspected resistance. Kanamycin/ Amikacin are preferred Str. is not used unless supported by sensitivity reports. Capreomycin used if isolate is resistant to both Str. & Kanamycin/ Amikacin. Group 3 Flouroquinolones Ciprofloxacin, Ofloxacin, Levofloxacin, Gatifloxacin, Moxifloxacin Should be used if strain is susceptible. Moxiflox.=Gatiflox.>Levoflox.>Oflox.>Ciproflox

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Group 4 (Oral Bacteriostatic 2 nd line drugs ) Ethionamide, Prothionamide, Cycloserine, Terizidone, PAS, Thioacetazone if 1 agent is needed Ethionamide/ Prothionamide. PAS is used if cost isn’t a concern. if 2 agents are needed Cycloserine is added. Combination of Ethionamide & PAS can result in GI adverse effects. Terizidone has similar efficacy as Cycloserine Thioacetazone can result in Steven Johnsons syndrome Group 5 (Anti-TB Drugs with unclear efficacy) Clofazimine, Co-AmoxiClav, Clarithromycin, Linezolid Not Recommended for routine use used if adequate regimens are impossible to form with drugs from Gp. 1-4

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Monitoring Therapy The child should be examined monthly till bacillary conversion and 2-3 monthly thereafter. A normal growth rate should resume after few months of successful treatment DOT worker should screen the patient regularly for adverse events like rashes, GI symptoms, Psychiatric symptoms (Psychosis, depression, anxiety, suicidal symptoms), Jaundice, Ototoxicity, peripheral neuropathy and symptoms of electrolyte wasting( cramps and palpitations)

Lab Monitoring During Treatment :

Lab Monitoring During Treatment TESTS Follow up 1. Smear And Culture - Monthly Till Smear And Culture Conversion - Thereafter Smear Monthly And Culture Quarterly 2. DST - Repeated If Pt. Remains Smear +Ve 3. Chest Radiograph - Six Monthly 4. Complete Blood Count - 6 – 12 Monthly 5. RFT - Monthly Till Pt. Is On Injectable Drugs 6. Serum Electrolytes - Monthly Till Pt. Is On Injectable Drugs 7. LFT - 3 – 6 Monthly

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Chemoprophylaxis Current WHO guidelines recommend, close follow up of contacts of patients with MDR-TB for a period of 2 years and prompt initiation of treatment with a regimen to treat MDR-TB if active disease develops. In 2005, the CBC published guidelines proposing 2 years of clinical follow up and individual decision making about appropriate LTBI treatment. A Cochraine review in 2006 suggests that a chemoprophylactic regimen customized to the susceptibility pattern of the adult contact’s isolate may be effective in preventing disease.

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