MULTIDRUG RESISTANT TB AND NEWER ANTI TB DRUGSPRESENTER – DR.MANJUSH HALBHAVIMODERATOR – DR.H.B.GADIYAR

TUBERCULOSIS – AN OVERVIEW

TB: Oldest recognized disease of mankind

India – Rigveda and Atharvaveda (3500-1800 BC) and Samhita’s of Charaka and Shushruta (1000 and 600 BC) : “YAKSHMA”

TB also recognized in Egyptian mummies – confirmd by PCR

TUBERCULOSIS – AN OVERVIEW

Robert Koch : Discovered Mycobacterium tuberculosis in 1882

DRUG RESISTANCEWHO DEFINITION: Drug resistance is when a micro organism changes in ways that render medications that used to cure the infections they cause ineffective.The presence of drug resistant strains result from simple Darwinian pressures brought out by the presence of antibiotics.Multiple drug resistance results from stepwise accumulation of individual elements.Hence MDR – TB is a man made catastrophe.

DRUG RESISTANCE – TYPES

When drug resistance is demonstrated in a patient who has never received anti-TB treatment previously, it is termed primary (Initial) resistance, i.e. TB patient’s initial M.TB population resistant to drugs

Secondary (Acquired) resistance is that which occurs as a result of specific previous treatment, i.e. Drug-resistant M. TB in initial population, selected by inappropriate drug use (inadequate treatment or non-adherence)

DRUG RESISTANCE – TYPES

• Drug resistant TB Mono resistance Poly resistance Multi Drug Resistant TB(MDR - TB) Extensive Drug Resistant TB (XDR - TB) Total Drug Resistance (TDR – TB)

DRUG RESISTANCEMono Drug Resistance

(Resistance to single first line ATT)

Poly Drug Resistance(Resistance to two or more first line ATT except MDR-TB)

MDR – TB – strains with resistance to both first line drugs i.e, Rifampicin and Isoniazid. (a laboratory diagnosis)

XDR – TB – strains with MDR + resistance to any fluoroquinolone + resistance to at least one 2nd-line injectable drug (amikacin, kanamycin, or capreomycin)

TDR – TB – Resistance to all first-line anti-TB drugs (FLD) and second-line anti-TB drugs (SLD) that were tested.

EPIDEMIOLOGY Globally in 2014, there were an estimated 3.3% of new cases and 20% of previously treated cases with MDR-TB.Extensively drug-resistant TB (XDR-TB) has been reported by 105 countries in 2014. On average, an estimated 9.7% of people with MDR-TB have XDR

EPIDEMIOLOGY

BURDEN OF MDR – TB IN INDIA

Each year about 2.2 million people develop TB in India and an estimated 220,000 die from the disease In 2015 the RNTCP covered a population of 1.28 billion. A total of 9,132,306 cases of suspected TB were examined by sputum smear microscopy and 1,423,181 people were diagnosed and registered for TB treatment

BURDEN OF MDR – TB IN INDIA

The notification of TB cases is estimated to be only 58%. Over one third of cases are not diagnosed, or they are diagnosed but not treated, or they are diagnosed and treated but not notified to the RNTCP.The emergence of MDR – TB in India is mainly due to non compliance of patients in taking the drugs completing the regimen, hence giving rise to the need for DOTS, which includes supervising people taking their drugs to prevent the emergence of resistance.

EMERGENCE OF MDR TB

Resistance is a man-made amplification of a natural phenomenon. i.e. Selection & proliferation of pre existing mutants due to man made factors leads to drug resistance.Inadequate drug delivery is main cause of secondary drug resistance.Secondary drug resistance is the main cause of primary drug resistance due to transmission of resistant strains.MDR due to spontaneous mutations is not possible as the genes encoding resistance for anti TB are unlinked.

MECHANISM OF DRUG RESISTANCE

FACTORS RESPONSIBLE FOR DEVELOPMENT OF DRUG

RESISTANCECLINICAL / OPERATIONAL FACTORS

Unreliable treatment regimen by doctorsLesser number of drugsInadequate dosage / duration

Addition of a single drug in failing regimen

Easy availability of drugs in private sector

Poor drug supply

Poor quality of drugs : poor bioavailability

FACTORS RESPONSIBLE FOR DEVELOPMENT OF DRUG

RESISTANCEBIOLOGICAL FACTORS :

Initial bacillary populationLocal factors in host favorable for multiplication of bacilliPresence of drug in insufficient concentration

FACTORS RESPONSIBLE FOR DEVELOPMENT OF DRUG

RESISTANCESOCIOLOGICAL FACTORS :

Irregular intake inadequate durationNeglect of diseaseIgnorance

DRUG RESISTANCE : MOLECULAR BASIS

DRUG RESISTANT ISOLATES SHOW MUTATION IN GENES

INH : kat g, inhARIFAMPICIN : rpoBSTREPTOMYCIN : rpsLETHIONAMIDE : inhAFLUOROQUINOLONES : gyrA, gyrB

DNA probes using genetic information have been devised

MANAGEMENT PRINCIPLES

SUSPICIONDIAGNOSISTREATMENT

SUSPICIONA close contact of Drug Resistant TB case.Treatment failures.All retreatment cases.No sputum conversion after initial 2 months of ATT.Extensive disease at start of treatment.All HIV patients with TB.Extrapulmonary TB not responding to standard ATT regime

RNTCP CRITERIA – MDR TB

Following are the criteria to label a patient as MDR-TB suspect –

A new smear (+) pt. remaining smear (+) at end of 5th month

A new smear (-) pt. becoming smear (+) at the end of 5th month

A pt. treated with regimen for previously treated remaining (+) at fourth month

Smear-positive contacts of an established / confirmed MDR-TB case

LABORATORY DIAGNOSIS

Mantoux testErythema of more than 20 mm at 72 hours – Positive Negative test, in general, rules out the disease

Guinea pig InoculationPus/ aspirate is inoculated intraperitoneally .Positive cases reveal tubercle after 5-8 weeksOne of the most reliable proof of Tuberculous pathology

LABORATORY DIAGNOSIS

Sputum smears stained by Z – N staining

• Three morning successive mucopurulent sputum samples are needed

to diagnose pulmonary TB.

Advantage: - cheap – rapid

- Easy to perform

- High predictive value > 90%

- Specificity of 98%

Disadvantages:

- sputum ( need to contain 5000-10000 AFB/ ml.)

- Young children, elderly & HIV infected persons may not produce cavities &

sputum containing AFB.

LABORATORY DIAGNOSIS

Detecting AFB by fluorochrome stain using fluorescence microscopy

The smear may be stained by aura mine-O dye. In this method the TB bacilli are stained yellow against dark background & easily visualized using florescent microscope.

Advantages:

- More sensitive

- Rapid

Disadvantages:

- Hazards of dye toxicity

- more expensive

- must be confirmed by Z-N stain

LABORATORY DIAGNOSIS

Tuberculin TestInterpretation: * A positive test indicates previous exposure and carriage of T.B.* A negative tuberculin test excludes infection in suspected persons * Tuberculin positive persons may develop reactivation type of T.B.* Tuberculin negative persons are at risk of gaining new infection * False positive reactions are mainly due to: - Infection with nontuberculous mycobacteria* False negative reactions may be due to: - Sever tuberculosis infection (Miliary T.B.) - Hodgkin’s

disease - Corticosteroid therapy - Malnutrition - AIDS* Children below 5 years of age with no exposure history: - Positive test must be regarded suspicious

LABORATORY DIAGNOSIS

BACTEC 460

specimens are cultured in a liquid medium (Middle brook7H9 broth base )containing C14 – labeled palmitic acid & PANTA antibiotic mixture.

Growing mycobacteria utilize the acid, releasing radioactive CO2 which is measured as growth index (GI) in the BACTEC instrument. The daily increase in GI output is directly proportional to the rate & amount of growth in the medium.

LABORATORY DIAGNOSIS

Polymerase Chain Reaction (PCR) & Gene probeNucleic acid probes & nucleic acid amplification tests in which polymerase enzymes are used to amplify ( make many copies of specific DNA or RNA sequences extracted from mycobacterial cells.)

DRUG SUSCEPTIBILITY TESTING

DEFINITION : Drug-susceptibility testing (DST) refers to in vitro testing using either phenotypic methods to determine susceptibility or molecular techniques to detect resistance-conferring mutations to a particular medicine. Types:

Culture – LJ medium/ Middle Brook medium/ Sula mediumMolecular DST – Beacon assays/ Line probe assays

CULTURESLOWENSTEIN – JENSEN MEDIUM – SOLID MEDIUM

Lowenstein –Jensen medium is an egg based media with addition of salts, 5 % glycerol, Malachite green & penicillin.

M.tuberculosis appear dry, rough raised irregular coloniesAppear wrinkled and creamy white which become yellowish later.

LOWENSTEIN – JENSEN MEDIUM

CULTURESMGIT - MYCOBACTERIUM GROWTH INDICATOR TUBE – LIQUID MEDIUMThe MGIT Mycobacteria Growth Indicator Tube contains 7 mL of modified Middlebrook 7H9 Broth base. The complete medium, with OADC enrichment and PANTA antibiotic mixture, is one of the most commonly used liquid media for the cultivation of mycobacteria.

 

BACTEC MGIT 960

COMPARISON – MGIT VS LJ MEDIUM

National Health Laboratory Services tuberculosis (TB) laboratory, South Africa did a study to To compare Mycobacterium Growth Indicator Tube (MGIT) with Löwenstein-Jensen (LJ) medium with regard to Mycobacterium tuberculosis yield, time to positive culture and contamination, and to assess MGIT cost-effectiveness. The study concluded that MGIT gives higher yield and faster results at relatively high cost.

MOLECULAR DST – BEACON ASSAYS

Beacon assays detect M. tuberculosis complex and associated rifampicin resistance directly from sputum samples using ultra sensitive PCR. The GeneXpert TB assay is an automated real time based system that has a number of advantages including the fact that it is a closed tube system. The WHO is encouraging the use of the GeneXpert TB test, but it has a number of disadvantages including cost.

GeneXpert

MOLECULAR DST – LINE PROBE ASSAYS

The WHO Expert Group concluded that there was sufficient generalisable evidence to justify a recommendation on the use of line probe assays for rapid detection of MDR-TB, at country level, and with further operational research to address country-specific implementation needs.Line probe assays are tests that use PCR and reverse hybridization methods for the rapid detection of mutations associated with drug resistance.One of the disadvantages with these assays is that they have an open-tube format, which can lead to cross contamination and an increased risk of false positive results

LINE PROBE ASSAYS

LABORATORY DIAGNOSIS

TREATMENT – PRINCIPLES

1. Use at least 4 reliable drugs .2. Do not use drugs with cross resistance .3. Eliminate drugs that are not safe for the

patient.4. Include drugs from Groups A-D in a

hierarchical order.5. Monitor and manage adverse effects of

drugs. 6. Never add a single drug to failing regime.

ANTI TB DRUGS

REGIMEN UNDER DOTS PLUS PROGRAMME IN INDIA (PMDT)

INITIAL INTENSIVE PHASE : 6- 9 monthsInj. Kanamycin Tab Ethionamide Tab Ofloxacin Tab. Pyrazinamide Tab. EthambutolCap Cycloserine

CONTINUATION PHASE : 18 months

Tab Ethionamide Tab Ofloxacin Tab EthambutolCap Cycloserine

REGIMEN UNDER DOTS PLUS PROGRAMME IN INDIA (PMDT)

A second-line TB medicine (drug or agent) is used to treat drug-resistant TB. For the treatment of RR-TB and MDR-TB, streptomycin is included as a substitute for second-line injectable agents when aminoglycosides or capreomycin cannot be used and susceptibility is highly likely. core second-line TB medicines (or agents) refer to those in Groups A, B or C.

WHO GUIDELINES FOR DR – TB (2016 UPDATE) – SECOND LINE ANTI TB

DRUGS

WHO GUIDELINES FOR DR – TB (2016 UPDATE)

WHO GUIDELINES FOR DR – TB (2016 UPDATE)

CHANGES IN 2016 The main changes in the 2016 recommendations are as follows:

A shorter MDR-TB treatment regimen is recommended under specific conditionsMedicines used in the design of longer MDR-TB treatment regimens are now regrouped differently based upon current evidence on their effectiveness and safetyClofazimine and linezolid are now recommended as core second-line medicines in the MDR-TB regimen while p-aminosalicylic acid is an add-on agent. MDR-TB treatment is recommended for all patients with RR-TB, regardless of confirmation of isoniazid resistance. Specific recommendations are made on the treatment of children with RR-TB or MDR-TB. Clarithromycin and other macrolides are no longer included among the medicines to be used for the treatment of MDR/RR-TB. Evidence-informed recommendations on the role of surgery are now included.

 

WHO – CURRENT RECOMMENDATIONS 2016

SHORTER MDR TB REGIMEN: In patients with RR-TB or MDR-TB who were not previously treated with second-line drugs and in whom resistance to fluoroquinolones and second-line injectable agents was excluded or is considered highly unlikely, a shorter MDR-TB regimen of 9–12 months may be used instead of the longer regimens (conditional recommendation, very low certainty in the evidence). Intensive phase of four months (extended up to a maximum of six months in case of lack of sputum smear conversion) with gatifloxacin (or moxifloxacin), kanamycin, prothionamide, clofazimine, high-dose isoniazid, pyrazinamide and ethambutolContinuation phase for 5 months with gatifloxacin (or moxifloxacin), clofazimine, pyrazinamide and ethambutol.

WHO – CURRENT RECOMMENDATIONS 2016

LONGER MDR TB REGIMEN: are treatments for RR-TB or MDR-TB which last 18 months or more and which may be standardized or individualized.In patients with RR-TB or MDR-TB, a regimen with at least five effective TB medicines during the intensive phase is recommended, including pyrazinamide and four core second-line TB medicines – one chosen from Group A, one from Group B, and at least two from Group C.If the minimum number of effective TB medicines cannot be composed as given above, an agent from Group D2 and other agents from Group D3 may be added to bring the total to five.In patients with RR-TB or MDR-TB, it is recommended that the regimen be further strengthened with high-dose isoniazid and/or ethambutol.

WHO – CURRENT RECOMMENDATIONS 2016

SURGICAL INTERVENTION IN MDR TB:

In patients with RR-TB or MDR-TB patients, elective partial lung resection (lobectomy or wedge resection) may be used alongside a recommended MDR-TB regimen

 

END TB STRATEGYThe END TB Strategy, approved by the 67th World Health Assembly in 2014, is designed to achieve a health-related target under the United Nations SDG 3 that calls for ending the TB epidemic by 2035PRINCIPLES:

Government stewardship and accountability, with monitoring and evaluation Strong coalition with civil society organizations and communities Protection and promotion of human rights, ethics and equity Adaptation of the strategy and targets at country level, with global collaboration

END TB STRATEGY

NEWER ANTI TB DRUGS GROUP A – FLUOROQUINOLONES

ciprofloxacin, levofloxacin, gatifloxacin, and moxifloxacin inhibit strains of M tuberculosisMoxifloxacin is the most active against M tuberculosis by weightthe drug must be used in combination with two or more other active agents-to prevent resistance standard dosage of ciprofloxacin is 750 mg orally twice a day, levofloxacin is 500–750 mg once a day, moxifloxacin is 400 mg once a day.

NEWER ANTI TB DRUGS MECHANISM OF ACTION:Quinolones and fluoroquinolones inhibit bacterial replication by blocking their DNA replication pathway.In gram-positive bacteria, the main target for fluoroquinolones is DNA gyrase (topoisomerase II), an enzyme responsible for supercoiling of bacterial DNA during DNA replication; in gram-negative bacteria, the primary target is topoisomerase IV, an enzyme responsible for relaxation of supercoiled circular DNA and separation of the inter-linked daughter chromosomes

NEWER ANTI TB DRUGS GROUP B – SECOND LINE INJECTABLE DRUGS – AMINOGLYCOSIDES

Amikacin, Kanamycin.

aminoglycosides primarily act by binding to the aminoacyl site of 16S ribosomal RNA within the 30S ribosomal subunit, leading to misreading of the genetic code and inhibition of translocation.Most MDR strains are amikacin sensitive

Amikacin is also active against atypical mycobacteria

NEWER ANTI TB DRUGS GROUP C : OTHER CORE SECOND LINE AGENTS

Ethionamide/ProthionamideCycloserine/ TerizidoneLinezolidClofazimine

NEWER ANTI TB DRUGS Ethionamide/Prothionamide:

nicotinic acid derivative related to isoniazid. It is thought that they undergo intracellular modification and act in a similar fashion to isoniazid i.e competitive inhibition of Inh A resulting in inhibition of synthesis of mycolic acids.Dose:

500mg – 1g/day per oral – adult dose10 to 20 mg/kg orally in 2 or 3 divided doses per day or 15 mg/kg orally once per day after meals – Paediatric dose

Adverse effects:Intense gastric irritation , neurologic symptoms Hepatotoxic. Neurologic symptoms may be alleviated by pyridoxine.

NEWER ANTI TB DRUGS Cycloserine/ Terizidone:

Terizidone is a derivative of Cycloserine.Cycloserine is an inhibitor of cell wall synthesis.

ADVERSE EFFECTS:peripheral neuropathy and central nervous system dysfunction depression and psychotic reactions

Pyridoxine 150 mg/d should be given with cycloserine to ameliorates neurologic toxicity CONTRAINDICATIONS: Epilepsy; depression; severe anxiety or psychosis; severe renal insufficiency; excessive concurrent use of alcohol

NEWER ANTI TB DRUGS Linezolid:

Prevents the formation of a functional 70S initiation complex, which is essential to the bacterial translation process.It achieves good intracellular concentrations. Linezolid has been used in combination with other second- and third-line drugs to treat patients with tuberculosis caused by multidrug-resistant strainsADVERSE EFFECTS:

bone marrow suppression irreversible peripheral and optic neuropathy

600-mg (adult) dose administered once a dayit should be considered a drug of last resort for infection caused by multidrug-resistant strains

NEWER ANTI TB DRUGS Clofazimine:

Clofazimine exerts a slow bactericidal effectClofazimine inhibits mycobacterial growth and binds preferentially to mycobacterial DNAAppears to preferentially bind to mycobacterial DNA leading to disruption of the cell cycle and eventually kills the bacterium. It may also bind to bacterial potassium transporters, thereby inhibiting their function. Lysophospholipids have been found to mediate the activity of this drug. ADVERSE EFFECTS:

Splenic infarction, bowel obstruction, and gastrointestinal bleeding

NEWER ANTI TB DRUGS Bedaquiline:

Bedaquiline works by blocking an enzyme inside the Mycobacterium tuberculosis bacteria called ATP synthase. The recommended dose is 400 mg a day for two weeks and then 200 mg taken three times a week (with at least 48 hours between doses).ADVERSE EFFECTS:

The most common side effects are headache, dizziness, malaise, joint pain, QT prolongation and increases in liver enzymes

NEWER ANTI TB DRUGS Delamanid:

Delamanid is a dihydro-nitroimidazooxazole derivative. It acts by inhibiting the synthesis of mycobacterial cell wall components, methoxy mycolic acid and ketomycolic acid. Dose: 100 mg/dayADVERSE EFFECTS:

The most common side effects are nausea, vomiting and dizziness. Anxiety, pins & needles, and shaking are other important side effects QT prolongation

Ann Thorac Med. 2016 Oct-Dec; 11(4): 233–236.Multi-drug resistant tuberculous spondylitis: A review of the literatureQuratulain Fatima Kizilbash1,2,3 and Barbara Joyce Seaworth1,2,3

While tuberculous vertebral osteomyelitis is an ancient scourge, multi-drug resistant-tuberculosis (MDR-TB) is a modern major public health concern. The objective of this study was to review and summarize the data available on MDR-TB spondylitis. An extensive search of the PubMed database was conducted for articles in English relevant to MDR-TB spondylitis by December 2015. Tuberculous spondylitis accounts for 0.5–1% of all TB cases, and it is estimated that there are probably 5000 MDR-TB spondylitis cases each year worldwide. The diagnosis of MDR-TB spondylitis requires a high index of suspicion based on epidemiologic, clinical, and radiologic features. Cultures and susceptibility testing remain the gold standard for the diagnosis of MDR-TB, but this can take several weeks to obtain. Medical treatment is the mainstay of therapy, and ideally, it should be based on drug susceptibility testing. If empiric treatment is necessary, it should be based on drug exposure history, contact history, epidemiology, and local drug resistance data, if available. The total duration of treatment should not be <18–24 months. Clinical, radiographic, and if possible, bacteriologic improvement should be used to assess the treatment success. Surgery should be reserved for neurologic deterioration, significant kyphosis, spinal instability, severe pain, and failure of medical management.

REFERENCESTUBERCULOSIS OF SKELETAL SYSTEM – SM TULI, 5TH EDITIONRNTCP GUIDELINES 2016IMPLEMENTING THE END TB STRATEGY: THE ESSENTIALS – WHO WHO TREATMENT GUIDELINES FOR DRUG RESISTANT TUBERCULOSIS – 2016 UPDATEKD TRIPATHI TEXT BOOK OF PHARMACOLOGY, 7TH EDITIONPARKS TEXTBOOK OF P AND SM , 23RD EDITIONANNALS OF THORACIC MEDICINE, 2016 Oct-Dec; 11(4): 233–236.

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