Introduction to pharmacokinetics and pharmacodynamics of TB drugs XIth International Child TB Training Course Goudini Spa, South Africa, September 12, 2017 Presented by: Kelly Dooley MD, PhD Johns Hopkins University School of Medicine D I V I S I O N O F CLINICAL PHARMACOLOGY
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Introduction to pharmacokinetics and pharmacodynamics of TB … · 2018-09-04 · •Phase II dose-finding •Understand dose-concentration-effect (PK/PD) relationships to pick dose
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Introduction to pharmacokinetics and pharmacodynamics of TB drugs
XIth International Child TB Training CourseGoudini Spa, South Africa, September 12, 2017
Presented by: Kelly Dooley MD, PhD
Johns Hopkins University School of Medicine
D I V I S I O N O F
CLINICAL
PHARMACOLOGY
Part IClinical Pharmacology
An Overview of Vocabulary and Tools
The Context: What’s wrong with TB therapy?
• 6 months is not “short-course”
• Only a minority of pts completes TB therapy in 6 mos• < 90% complete in 12 months
• We extrapolate drugs/dosing from adult pulmonary TB to other populations and other forms of TB
• Adverse drug reactions cause morbidity & mortality
• Drug-drug interactions create challenges
• Resistance happens
Better understanding and application of PK/PD science can help
Slide, adapted, from E Nuermberger
PK or PK/PD Studies: Role in Optimizing Treatment
• Phase I studies• Determine PK characteristics of a drug, maximal tolerated dose, food effect
• Drug-interaction studies• Evaluate pharmacokinetic drug interactions, assess overlapping toxicities
• Phase II dose-finding• Understand dose-concentration-effect (PK/PD) relationships to pick dose to take forward
• Pharmacogenomics• Helps explain variability in pharmacokinetics and treatment response
• Establishing dosing for special populations• children, pregnant women, patients with disease in a pharmacologically less-accessible site
• Phase III trials• Determine the reasons that treatment was not effective in some subpopulations
Bioavailability (F)Fraction of a dose of drug that reaches the systemic circulation after an extravascular dose (oral, intramuscular, etc.)(unitless, %)
Clearance (Cl)Rate at which a volume of fluid is completely cleared of drug (mL/min)
Volume of Distribution, VdVolume into which a dose “appears” to have been uniformly distributed
Some terms…
Dose (mg)
Vd (mL) Conc’n
(mg/mL)
Dose (mg)
Vd (mL)= Concentration (mg/mL)
Audience participation: What is the volume of distribution of…
Drug Volume of distribution
Warfarin 8L (high protein binding)
Ethanol 30L (distribution in total body water)
Chloroquine 15,000L (highly lipophilic, sequesters into fat)
Rifampin
Rifabutin
Clofazimine
60 L
540 L
1470 L
Determinants
• Genetic differences in drug transporter enzymes1
• Patient-specific characteristics
Large body mass3,4
Diabetes mellitus3,4
HIV infection2,3
Childhood5
• Food effect and other causes of dose-to-dose variability2
Diffusion of drugs into necrotic lesions with poor blood supply
Drug CSF:serum ratio*
Isoniazid 0.8-1.0
Rifampicin 0.04-0.11
Pyrazinamide 0.79-1.05
Ethambutol Negligible (<MIC even with meningitis)
Ethionamide Good
Fluoroquinolones 0.7-0.8
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Do TB Drugs get to the site of infection: TB meningitis?
*Depends on lipid solubility, ionization, molecular weight, protein binding, meningeal inflammation, etc.
Part IINew and Old TB drugs
Using clinical pharmacology to inform treatment optimization
Which PK/PD parameter correlates best with INH activity?
AUC/MIC has best correlation with bactericidal effect
Jayaram et al, AAC 2004; 48:2951
Audience response #2The first time the term ‘Pharmacogenetics’ was used in a PubMed- cited article was by geneticists at JHU in reference to genetically-determined differences in the metabolism of which anti-TB drug?
A. Isoniazid
B. Rifampicin
C. Pyrazinamide
D. Ethambutol
E. Amikacin
Pharmacokinetics of Isoniazid
• Metabolized by n-acetyltransferase 2 (NAT2)
• Half-life depends on acetylator status, or NAT2 genotype
Pharmacokinetics of Isoniazid: the birth of Pharmacogenetics
• In 1960, McCusick and colleagues report genetically determined difference in the metabolism of isoniazid – slow metabolism is an autosomal homozygous recessive trait
• Evans, a co-investigator on this publishes article:
Pharmacogenetics (1961).Br Med Bull 17: 234-40
Isoniazid Pharmacogenetics
Slow acetylators Fast acetylators
Maximal EBA activity of isoniazid, for DS-TB Donald (1997) AJRCCM 156: 895.
Maximum EBA achieved with dose of 300 mg (~5 mg/kg) for drug-sensitive TBn.b. There is measurable activity against DS isolates even with doses as small as 18.75 mg (0.38 mg/kg).
Isoniazid: What’s the right dose for patients with MDR-TB?Design of A5312
INH-resistant TB
M. tuberculosis with inhA mutation
M. tuberculosis with katG mutation
Gather MIC data
MIC data (bug)
Apply treatmentINH 5, 10, or 15 mg/kg (drug)
Measure 7-day Early Bactericidal Activity
(EBA)
Individual INH PK
NAT2 metabolizer genotype (host)
Treatment response
• Define Target AUC/MIC (based on positive control arm, max effect in experimental arms)
• Monte Carlo simulation using MIC, NAT2, AUC to determine dose required to achieve targets.
Drug-sensitive TB
Apply treatmentINH 5mg/kg (drug)
Measure 7-day Early Bactericidal Activity
(EBA)
Positive Control ArmStandard INH dosing
Group 1: Dose-ranging Group 3: MIC only
Group 2:
Why it’s important to get it (dosing, esp. rifampin) right
What happens when drug concentrations are too low?
JID, 2013
Why is rifampin special? What is “sterilizing activity”?
Dickinson & Mitchison 1981
‘Everyone does fine’– or do they?
Among successfully treated patients with TB, incidence risk of relapse is 2,836/100,000 in first year following treatment
Marx et al CID (2014) 58:1676
Effects of HIV infection on:TB drug concentrations and treatment outcomes
for treatment success
PLoS One 2013 8: e56248
Rockwood et al AAC 2016
McIlleron et al AAC 2006:
•HIV infection associated with 39% reduction in rifampin exposures
•Formulation was determinant of rifampin bioavailability
Higher-dose rifamycins in patients with advanced HIV
RAFA trial
•Immediate ART (2 wks) vs.•Delayed ART (8 wks) vs.•Delayed ART but RIF 15 mg/kg(intensive phase)
Audience responseMatch each drug to its important PK or PK/PD characteristic
– Rifapentine
– Bedaquiline
– Delamanid
– Amikacin
– Linezolid
A. Mitochondrial toxicity related to cumulative exposure
B. Potent inducer of metabolizing enzymes
C. Cytochrome P450 substrate, therefore victim of many DDI
D. Extremely slow half-life of disappearance from inner ear tissues
E. Low bioavailability, must be dosed separately from other drugs
Part IIIPharmacology of TB Drugs in Children
When are efficacy trials required for children (vs. PK/safety alone)?
ER=exposure-response
Modified, from FDA Guidance
Minimal disease?Severe disease?LTBI-> active disease?
Developmental pharmacology:
A Moving Target,role of ontogeny
38Kearns et al NEJM 2003 349: 1157.
Pediatric TB ≠ Adult TB: What does pediatric TB look like?
Age (yrs) No disease Pulmonary dz TBM/miliary dz
<1 50 30-40 10-20
1-2 70-80 10-15 2-5
2-5 95 5 0.5
5-10 98 2 <0.5
>10 80-90 10-20 <0.5
Table 4. Average age-specific risk for disease development following primary infection (immune-competent children)**Adapted from Marais et al 2004 IJTLD. The natural history of childhood intra-thoracic tuberculosis: a critical review of literature from the pre-chemotherapy era
It depends (on how old you are)!
Pulmonary disease
Disease risk and presentation
Age (yrs) Ghon/LN Bronchial Effusion “Adult-type”
<1 X X
1-2 X X
2-5 X X
5-10 X X X X
>10 X X
Site of action PK: Pediatric TB
Disease type Where the bacilli live
Disseminated Intracellular Note the role of cell-mediated immunity
TB meningitis Brain, meninges, cerebrospinal fluidDrugs must cross BBB, BCSF barriers; not be PGP substrateCNS Multiparameter Optimization desirability score
Minimal disease Lymph nodes, intrathoracic lymph nodes or bronchi
Adult-type cavitary lung disease Necrotic, caseous content of cavityDrugs must diffuse through caseum
“Drug must be present at the site of disease at sufficient concentrations for sufficient duration to effect functional cure”
Tucker et al (2017) IJTLD, in press
Revised WHO dosing for children-Are we achieving target concentrations?
Drug Revised dose 2-hour target Mean concentration
% achieving target
Isoniazid 10-15 mg/kg 3 mcg/mL 4.5 mcg/mL 65%
Rifampicin 10-15 mg/kg 8 mcg/mL 2.9 mcg/mL 6%
Pyrazinamide 30-40 mg/kg 20 mcg/mL 23 mcg/mL 55%
Ethambutol 15-25 mg/kg 2 mcg/mL 1.1 mcg/mL 15%
PHATISA Study (n=23, Durban, SA): Hiruy et al JAC doi:10.1093/jac/dku478
Mean plasma rifampin (RMP) concentrations (μg/ml) after the intake of a mean dose of 12.9 mg/kg for RMP formulation 1 (n = 14) and of a mean dose of 16.7 mg/kg for RMP formulation 2 (n = 25).
A. Bekker et al. Antimicrob. Agents Chemother. 2016;60:2171-2179
Young childrenCape Town, RSA
Yes, but do TB drug concentrations in children matter? “they all do well…”
Figure 3. The logistic regression model
predictions of the probability of unfavorable
treatment outcome (Punfavorable) as a function of
the rifampin exposure at steady state over a 48-h
period (AUCRIF,0–48h,ss).
Ramachandran et al PIDJ 2016 35:530Modeling of NIRT data: Benjamin Guiastrennec Uppsala/UCSF
The Indian experience
Predicted probability of unfavorable treatment outcome (Punfavorable) under the current (left panel) and future (right panel) revised national
tuberculosis control program (RNTCP) dosing recommendations..
Based on NIRT data from children with TB mono-infection and TB/HIV co-infection
What about second-line drugs for children?Example of Levofloxacin: What is the right dose? Is it safe?How about LFX 15 mg/kg daily (NICHD R01 PI=Hesseling)?
Thee, Antimicrob Agents Chemother, 2013
Parameter Target valueMean (sd) PK value/MIC
if MIC is 0.5Mean (sd) PK value/MIC
if MIC is 1.0
Cmax /MIC 8-10 13.1 (4.0) 6.5 (2.0)
AUC/MIC 100 65.3 (18.4) 32.6 (9.2)
Slide modified from A. Hesseling
QTc interval in children on levofloxacin (n=22)
Levofloxacin 15mg/kg
Mean QTc in ms (SD) 369.1 (21.9)
QTc ≥450 ms (%) 0 (0)
15 mg/kg likely not quite enough for children > 2 years of age
TB/HIV Co-Treatment: Limited Options for Children
Rifabutin dosing for children with TB/HIV co-infection taking PI-based ART
RBT 5 mg/kg three times a week in children < 5 years of age taking LPV/rStudy stopped after 6 participants by IRB because of severe, transient neutropenia
Then, from adult and pediatric data, predict (then confirm) doses children need to achieve targets…
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Figure 3. Range of recommended rifampicin doses for children with TB meningitis, by weight and age, to achieve AUC target of 92 mg*h/L. Black bars represent the range for intravenous dosing and grey bars represent the range for oral dosing.
Collaborative effort: Rada Savic; Rovina Ruslami; Jenn Hibma; Anneke Hesseling; Geetha Ramachandran; A RizlamGaniem; Soumya Swaminathan; Helen McIlleron; Amita Gupta; Reinout van Crevel; Robert Aarnoutse; Kelly E. Dooley
0.5−1 1−2 2−3 3−5 5−8 8−12
6−9 9−12 12−14 14−18 18−30 30−40
Age (years)
Weight (kg)
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At least 30 mg/kg orally(or 15 mg/kg IV)
New drugs for TB: dosing for kids(1) Start with knowledge of age-to-weight distribution of children w TB, clearance/metabolic pathway, all available PK info(2) Build model, decide weight bands, simulate likely PK(3) Test the doses to make sure they achieve targets and are safe
Work of Maria Kjellsson, Elin Svensson, Mats Karlsson
Summary
• Doses of most first-line drugs are suboptimal, and are particularly low in certain populations, including young or HIV-infected children
• Clinical pharmacology and its tools can help us explain variability in drug exposures, PK-efficacy, and PK-toxicity relationships (which may differ in adults and children)– this can help us choose right drugs and doses
• One size does NOT fit all
• Mathematical modeling (pharmacometrics) in design and analysis phases of studies can increase yield and efficiency of trials, especially in children
• Lots of work to do to improve treatment for drug-sensitive TB, drug-resistant TB, TB meningitis, TB/HIV co-infection, LTBI in children
Acknowledgements• Johns Hopkins University
• Center for TB Research• Richard Chaisson, Eric Nuermberger, (Susan
Dorman), Jonathan Golub, Amita Gupta
• Division of Clinical Pharmacology• Lisa Wolf, Grace Barnes, Craig Hendrix,