1. Drug Resistant Tuberculosis
Michael Lauzardo, MD MSc.
Director, Southeastern National Tuberculosis Center
Chief, Division of Infectious Diseases and Global Medicine
University of Florida

3. Epidemiology

4. TB Epidemiology GLOBAL USA Infected cases 1.7 billion (33% population)
10 million (4% population)
New Cases
10 million/year
9557 in 2015
Case Incidence
142 per 100,000
3.0 per 100,000
Deaths
1.4 million/year
493 in 2014
MDR
~500,000/year
<1%

5. Drug Resistant TB Globally
Global Burden of MDR TB
Cases of MDR TB
per year
480,000
Pre-XDR
21% of MDR total
XDR
9.7% of MDR total
Percent of MDR TB diagnosed by lab testing
41%
Number of countries responsible for half of MDR TB 3
(India, China, Russia)

6. Drug Resistant TB in the United States 2010-2013

7. Drug Resistant TB in the United States
Overall the number of cases of drug resistant TB in the United States is decreasing.
The percentage of MDR TB in the US has been stable between ( %).
The percentage of INH and PZA resistance however have increased slightly (INH %; PZA %).
Foreign-born accounted for 90% of all MDR TB in the US between
US-born INH resistance is 5.8%;Foreign-born rate, 11%

10. Transmission and Pathogenesis

11. Transmission of Tuberculosis

12. INH RIF INH PZA Multidrug therapy:
No bacteria resistant to all 3 drugs
Drug-resistant mutants in large bacterial population
INH
RIF
PZA
Monotherapy: INH-resistant bacteria proliferate
If one treats this population with three effective drugs, all bacteria are killed.
However, if one treats with only one drug, say INH, one selects for INH resistant bacteria. --
INH

13. INH RIF INH Spontaneous mutations develop as bacilli
proliferate to >108
INH resistant bacteria multiply
to large numbers
INH
RIF
INH
These bacteria then can multiply to large numbers and once again spontaneous mutations can arise. In this case acquisition of a second drug resistance. Treatment with two drugs then leads to selection of the MDR strain and its proliferation can lead to the acquisition of additional resistance. This sort of amplification of drug resistance can occur one drug at a time to ultimately lead to XDR TB. -
INH mono-resist.
mutants killed,
RIF-resist. mutants proliferate  MDR TB

14. Clinical Significance of Resistance
If pansensitive > 95% chance of cure
If resistant to INH > 90% chance of cure
If resistant to rifampin > 70% chance of cure
If resistant to INH and RIF ~ 50% chance of cure
Before chemotherapy ~ 50% chance of cure

15. Diagnosis

17. Drug Resistance Testing
The interpretation of growth-based susceptibility for tuberculosis is different than that for most other pathogens.
With other pathogens, the clinician compares the minimum inhibitory concentration (MIC) of the pathogen with the achievable serum level.
If a safe dose of the antibiotic will kill the bacteria in the patient, the drug can be successfully used.
The interpretation of susceptibility testing for mycobacteria is not as straightforward; several variables complicate the process:
1)mycobacteria may reside within or outside of human cells;
2) mycobacteria have a long replication time and may exist in a continuum between dormant and active states; and
3) mycobacteria can live in a variety of tissue types for which drugs may have different penetration levels.

18. Drug Resistance Testing
The concentration that constitutes the breakpoint between a resistant and susceptible strain is called the “critical concentration.”
The critical concentration is the level of drug that inhibits a wild-type (a strain that has not been exposed to TB drugs) M. tuberculosis complex strain, but does not appreciably suppress the growth of a resistant strain.
The critical concentration may be different depending on the medium used for the assay.
If, on solid media, more than 1% of the strain’s population grows at the critical concentration of the drug for that particular medium, the isolate is considered to be resistant to that drug and other drugs must be used in the regimen.

19. Agar Proportion Method for Drug Susceptibility Testing (DST)

20. Molecular Testing Drug Gene % mutations RIF rpoB >96%
INH katG %
INH-ETH inhA %
PZA pncA 72-97%
F-quinolones gyrA 75-94%
Capreomycin tlyA unknown
Curry Center: Drug-resistant tuberculosis – A survival guide for clinicians, 2nd Edition. 2008

21. Cepheid GeneXpert MTB/RIF Test
Boehme CC et al. N Engl J Med 2010;363:

22. GenoType MTB-DR (Hain Lifescience)

23. Discordant Results
Discordant test results can occur between different laboratories.
Although new methods are validated against the standard method, perfect agreement cannot always be achieved.
Discrepancies in results due to differences in methodology, medium, and critical concentrations are inevitable.
Some strains of M. tuberculosis complex have MICs that are close to the critical concentration tested.
Experience over time has shown that the reproducibility for testing of these strains can be suboptimal.
Tests at the different laboratories may not have been performed using the same specimen.

24. Possible Errors During Susceptibility Testing
Errors can occur during DST, including:
Failure to use a standardized, well homogenized inoculum
Failure to add a drug to the broth medium
Adding the wrong drug or concentration
Inoculation errors
Failure to recognize a mixed infection (M. tuberculosis complex and an NTM) which is more difficult to detect in broth systems
Failure to recognize contamination with a non-AFB microorganism, which is more difficult to recognize in broth systems
Changes in the performance of DST or support of mycobacterial metabolism can occur when a new lot of culture media is made or received, and when a new lot of drug solutions is prepared or a new drug kit is received.

25. Discordant Results are Found, Now What?
Assess whether results fit the clinical and epidemiological picture.
Talk to the laboratory director and discuss reasons for conflicting results.
Ask how the laboratory ruled out mixed infection with NTM or contamination with non-AFB microorganisms.
If in doubt, your public health laboratory or a reference laboratory should repeat the test using the most recent isolate available.
Discordance between rapid molecular tests and the growth-based (phenotypic) DST results should be investigated further with a sequence- based method.
When the clinical level of suspicion for resistance is strongly at odds with the initial rapid molecular test (Xpert MTB/RIF or line-probe assay) results, confirmation using a sequence-based method is recommended.

26. Treatment of Drug Resistant TB

29. Treatment of Susceptible TB
Four drug regimen pending sensitivity testing: Isoniazid (INH) Rifampin Pyrazinamide Ethambutol Why so many drugs?

31. Treatment of TB
INH-resistance is common in many places around the world.
Multi-drug resistance is most common in parts of Eastern Europe, Africa, and HIV positive patients (MDR TB, XDR TB)
Second line agents

32. Treatment of TB Directly observed therapy (DOT)
The standard of care to treat active TB
Can be done daily or intermittently
DOT has markedly reduced:
The incidence of drug resistance TB
The over all incidence of TB in the US

33. Comparison of US and WHO Classification of TB Drugs

34. Treatment Regimens for Mono-Resistant and Poly-Resistant TB
Pattern of Drug Resistance
Regimen
Duration of Treatment Regimen
Additional Comments
INH
RIF, PZA, EMB
(+/-) fluoroquinolone
6-9 months
Fluoroquinolones may strengthen regimen. High rates of intolerance in some studies
INH and EMB
RIF, PZA, and fluoroquinolone
May need a longer duration of treatment for patients with extensive disease.
INH and PZA
RIF, EMB, and fluoroquinolone
9-12 months
May need a longer duration of treatment for patients with extensive disease.

35. Treatment Regimens for Mono-Resistant and Poly-Resistant TB
Pattern of Drug Resistance
Regimen
Duration of Treatment Regimen
Additional Comments
PZA
INH and RIF
9 months
Most commonly seen with M. bovis infections
RIF
INH, EMB, fluoroquinolone, plus at least 2 months of PZA
12-18 months
An injectable drug may be necessary in patients with extensive disease
RIF and PZA
INH, EMB, fluoroquinolone, plus an injectable for the first 2-3 months
18 months
A longer course of the injectable may be necessary in patients with extensive disease

36. “Short Course” Therapy for MDR TB
Recent studies have reported excellent treatment outcomes using shorter durations of therapy than typically used for the treatment of MDR-TB.
As reported in 2010 by Van Duen, et al., a 9-month regimen consisting of clofazimine (CFZ), high-dose gatifloxacin (GFX), EMB, and PZA throughout the course of treatment, supplemented by prothionamide, KM, and high-dose INH for a minimum of 4 months was associated with a relapse-free cure of 88% among 206 patients with MDR-TB in Bangladesh.
In a 2014 follow-up report including 515 consecutive patients, the 4-month intensive phase was extended until culture conversion. Of the 515 patients enrolled into the observational study, 84.4% had a bacteriologically successful outcome.
Due to extensive disease, only half of the patients completed treatment within 9 months but 95% did so within 12 months.
The strongest predictor for a bacteriologically unfavorable outcome was high- level fluoroquinolone resistance, particularly when compounded by initial PZA resistance.

37. Case 1

40. Isoniazid Mono-Resistance
INH mono-resistance is one of the most common forms of drug resistance.
WHO, American Thoracic Society (ATS), and Infectious Diseases Society of America (IDSA) recommend RIF, EMB, and PZA ± a later generation fluoroquinolone for 6-9 months.
A 2009 systematic review/meta-analysis by Menzies, et al., found that among patients with INH mono-resistant TB, outcomes were improved with longer duration of RIF and PZA, use of daily treatment (not intermittent treatment) and with greater numbers of effective drugs.
Studies in the United States have reported relapse rates of 2 to 5% using 3- to 4- drug regimens administered for 6 or more months.
However, a large proportion (26-59%) of patients had treatment discontinued or the duration of treatment extended because of drug-related adverse reactions, usually associated with PZA.

41. Isoniazid Mono-Resistance
However, a large proportion (26-59%) of patients had treatment discontinued or the duration of treatment extended because of drug-related adverse reactions, usually associated with PZA.
Treatment outcomes do not differ based on whether the isolate has low- or high- level INH resistance in vitro.
Addition of a fluoroquinolone was associated with improved outcomes in studies from Taiwan and the Republic of Korea.
In the RIFAQUIN trial, a 6-month regimen that included daily RIF, EMB, PZA and moxifloxacin (MFX) (400 mg) for 2 months followed by once-weekly doses of both MFX and high-dose rifapentine (RPT) (1200 mg) for 4 months, was reported to be as effective as a standard 6-month regimen in drug-susceptible TB.
Therefore, the 6-month regimen should be effective for INH mono-resistant TB as long as the isolate is susceptible to the fluoroquinolones.

42. Treatment Options for Patients with Isoniazid Mono-Resistance
OPTION 1: Daily RIF, EMB, and PZA (± fluoroquinolone), all given for 6 to 9 months depending on the microbiologic, clinical, and radiographic response to treatment.
If a patient was on a standard 4-drug regimen, INH can be stopped when resistance is documented, and RIF, EMB, and PZA continued. Continuation of INH in the setting of documented isolated resistance to INH is not necessary, given the high cure rate with this regimen. A fluoroquinolone may be added to the regimen, especially in patients with extensive and/or cavitary disease.
OPTION 2: If the patient does not tolerate PZA, a regimen consisting of RIF, EMB and a later-generation fluoroquinolone for 9-12 months could be used.
OPTION 3: Daily RIF, EMB, PZA and MFX (400 mg) for 2 months followed by once- weekly doses of both MFX and high-dose RPT (1200 mg) for 4 months.

43. Case 2

46. Rifampin Mono-Resistance
Uncommon but increasing in some areas of the world.
The loss of RIF requires a longer duration of therapy.
Resistance to RPT is universal in RIF resistance.
In approximately 80% of strains where RIF resistance is documented, the strain is also resistant to RFB.
Using molecular testing to identify the particular mutation associated with RIF resistance may help to rapidly identify isolates that retain susceptibility to RFB.
This is also important as various labs use different cut points to test RFB susceptibility, and the molecular test is likely to be a better indicator.

47. Treatment Options for RIF Mono-Resistant TB
OPTION 1 (preferred): INH, EMB, and a fluoroquinolone daily for 12 to 18 months, supplemented with PZA for at least 2 months during the intensive phase
OPTION 2: INH, EMB, PZA daily for 18 months
For both options 1 and 2:
In patients with extensive cavitary disease, or to shorten the duration of therapy (e.g., 12 months), addition of an injectable agent for at least the first 2 months is recommended.
OPTION 3: INH, PZA, SM daily for 9 months

48. Case 3

49. Initial CXR

50. After two months of treatment

52. Building a Treatment Regimen for MDR TB

53. Treatment Regimens for MDR TB
Pattern of Drug Resistance
Regimen
Duration of Treatment Regimen
Additional Comments
INH and RIF
PZA, EMB, fluoroquinolone (MFX or high-dose LFX), and injectable during the intensive phase (for at least 6 months beyond culture conversion), and 1 additional oral agent (LZD, ETA, CS or PAS).
18 months beyond culture conversion
In patients with extensive
or cavitary disease, a longer duration for the injectable agent may be considered, as well as an
additional oral drug. Consider using more than 1 additional oral drug if there has been prior use of PZA or EMB.
INH, RIF, and EMB or PZA
EMB or PZA, fluoroquinolone (MFX or high-dose LFX), injectable agent during the intensive phase (for at least
6 months beyond culture conversion), and 2 additional agents (LZD,ETA, CS, or PAS).
In patients with extensive or cavitary disease, a longer duration for the injectable agent may be considered, as well as an
additional oral drug.
INH, RIF, EMB, and PZA
Injectable agent during the intensive phase (for at least 6 months beyond culture conversion), and a newer generation fluoroquinolone (MFX or
high-dose LFX), and 3-4 oral agents
(LZD, ETA, CS, PAS or additional
second- or third- line agents if
needed).

54. Treatment Regimens for Pre-XDR/XDRMDR TB
Pattern of Drug Resistance
Regimen
Duration of Treatment Regimen
Additional Comments
INH, RIF, EMB, PZA, fluoroquinolone (pre-XDR)
4-5 second- or third-line drugs
(include LZD, BDQ, or DLM) and an
injectable agent.
24 months beyond culture conversion
Duration of injectables should be at least 12 months if tolerated.
Consider high-dose MFX.
Consider surgery.
TDM may be useful.
INH, RIF, EMB, PZA, injectables
(pre-XDR)
MFX (or high-dose LFX) plus at least
4-5 second- or third-line oral drugs.
Include LZD, BDQ, or DLM, if
available. Include an injectable drug if there is 1 available to which the
isolate is susceptible.
INH, RIF, fluroquinolone, injectable
(XDR)
5-6 second- and third-line agents.
LZD, BDQ, or DLM should be used;
high-dose MFX can be added (unless documented resistance). Use PZA and/or EMB if remains susceptible. Include an injectable drug if there is one available to which the isolate is susceptible.
Consider high-dose INH treatment if low-level resistance is documented.
Consider surgery. TDM may be useful.
CALL FOR CONSULT

55. Summary
Consultation with an expert should be obtained in all cases of MDR/XDR- TB.
Design of individualized MDR-TB regimens should be based on DST results, prior history of TB treatment, potential for cross-resistance, potential for overlapping drug toxicities, and other key clinical and epidemiologic factors.
MDR-TB regimens should contain at least 4-6 likely effective drugs(optimally 5), and XDR-TB regimens should contain at least 6 likely effective drugs.
For MDR-TB:
The intensive phase of treatment should continue at least 6 months beyond culture conversion.
The continuation phase should continue at least 18 months beyond culture conversion.

56. Summary
For XDR-TB:
The total duration of treatment should be at least 24 months beyond culture conversion.
Case management is critical to successful treatment in drug-resistant TB.
DOT should be used for all patients with MDR/XDR-TB.
New drugs may eventually lead to better outcomes and shorter durations