Therapeutic Drug Monitoring of Anti-Retroviral Drugs
Dr. Bhaswat S. ChakrabortySenior VP, Cadila Pharmaceuticals Ltd.
02.11.2010
Track 3-1 Lecture at International Conference and Exhibition on Analytical and Bioanalytical Techniques, Hyderabad, India
November 1-3, 2010
Contents• Current highly active antiretroviral therapy (HAART)• Guidelines for administering HAART • Correlation between plasma concentrations and
therapeutic effects • Drug –toxicity relationships• Drug-drug interactions within different HAART regimes• Therapeutic drug monitoring (TDM)
▫ Purpose▫ Challenges▫ Approaches
• Bioanalytical challenges• Conclusions
MaravirocRaltegravirEtravirine
Darunavir
Tipranavir
EnfuvirtideAtazanavir
EmtricitabineFosamprenavir
Tenofovir
Lopinavir/r
Amprenavir
EfavirenzAbacavir
NelfinavirDelavirdine
RitonavirIndinavir
Nevirapine
3TCSaquinavir
d4TddCddl
AZT
• NRTI, Nucleoside reverse transcriptase inhibitor;• NNRTI, Non-nucleoside reverse transcriptase inhibitor;• PI, protease inhibitor• Integrase Inhibitor• CCR5 Antagonist/Entry Inhibitor
ARV Drugs
Source : Dr. David Back, Univ. of Liverpool
Main classes of ARV drugs• Nucleoside and nucleotide reverse transcriptase
inhibitors (NRTI) inhibit reverse transcription by being incorporated into the newly synthesized viral DNA and preventing its further elongation.
• Non-nucleoside reverse transcriptase inhibitors (NNRTI) inhibit reverse transcriptase directly by binding to the enzyme and interfering with its function.
• Protease inhibitors (PIs) target viral assembly by inhibiting the activity of protease, an enzyme used by HIV to cleave nascent proteins for final assembly of new virons.
• Integrase inhibitors (II) inhibit the enzyme integrase, which is responsible for integration of viral DNA into the DNA of the infected cell.
Highly active antiretroviral therapy (HAART) regimens for HIV-positive patients
• Most current HAART regimens consist of three (3) drugs: 2 NRTIs + a PI or NNRTI or II
▫ Initial regimens use "first-line" drugs with a high efficacy and low side-effect profile.
• Current preferred initial regimens
• Emtricitabine, tenofovir (both NRTI) and efavirenz (a NNRTI).
• Efavirenz should not be given to pregnant women.
• Emtricitabine, tenofovir and raltegravir (an II)
• Emtricitabine, tenofovir, ritonavir and darunavir (both latter are PI)
• Emtricitabine, tenofovir, ritonavir and atazanavir (both latter are PI)
Meaningful inhibitory concentration• A parameter to estimate in vivo potency of antiretroviral drugs• Cmin/IC50 is suitable for across-study, across-patient and across-drug
comparison• ICmin is generated from in vivo pharmacokinetic data• IC50 or IC95 are generated in vitro, increasing drug concentration
until 50% or 95% of the virus is inhibited How close the IC50 and IC95 values are to each other depends on how
steep the curve is (see lower graph) How reliable the values are depends on the system used to measure
them• IQ (inhibitory quotient):
IQ = trough concentration in plasma/concentration required for inhibition in vitro
Gives an index of how far the concentration of a drug in vivo is in excess of the viral IC50
Guideline websites
Country Website
France www.sante.gouv.fr
Germany and Austria www.rki.de/infekt/aids_std/az_eng/az_e.htm
Italy www.ministerodellasalute/aids/aids.jsp
UK www.bhiva.org
USA www.cdc.org
Netherlands www.NVAB.org
Hammer, S. M. et al. JAMA 2008;300:555-570.
Therapeutic Drug Monitoring (DHHS Guidelines 2009)
1. When food-drug and drug-drug interactions lead to decreased efficacy
2. Pathophysiological conditions that impair GI, hepatic function, and renal function, thereby affecting ADME
3. Treatment-experienced pts with virus with reduced susceptibility to ARVs (higher concentrations may be required).
4. Treatment-naive pts with suboptimal virologic response
5. In pregnant women due to metabolic and physiological changes that can affect PK
6. For prevention of ARV-induced concentration-dependent toxicity
7. When using unconventional ARV regimens or dosing not studied in clinical trials
8. Consider in pediatric pts when there are limited dosing data
Recommended trough concentrations
DHHS Guidelines
Simulated probabilities of target trough concentrations of Efavirenz in children
Antivir Ther. 2008;13:77987.
Plasma concentrations and viral clearancein 4 drug therapy
Hoetelmans et al. (1998), AIDS. 12:F111-F115
Plasma concentrations and viral clearancein mono & multi therapy
Lotsh et al. (2007), Antimicrob Agents Chemotherap, 51:3264–3272
Steady-state saquinavir plasma concentration-versus-time profiles; n = 56
Lotsh et al. (2007), Antimicrob Agents Chemotherap, 51:3264–3272
Very similar
Inter-individual variation in saquinavir plasma concentrations; n = 56
Lotsh et al. (2007), Antimicrob Agents Chemotherap, 51:3264–3272
ADRs vs. Saquinavir plasma concentrations; n = 56
Lotsh et al. (2007), Antimicrob Agents Chemotherap, 51:3264–3272
Log Cmax,saquinavir was predictive (P 0.001 [chi-square after logistic regression]) of constitutional side effects such as asthenia and sleepiness (n 7), lymphadenopathy (n 2), orthostatic dizziness (n 2), fever without infection (n 1), weight gain (n 1), peripheral edema (n 1), and spontaneous pneumothorax (n 1) and GI side effects.0
Drug-drug interactions
New York State Department of Health AIDS Guidelines
Enzyme induction or inhibition
Drug Enzyme Inhibition Enzyme Induction
Atazanavir ++ —
Delavirdine ++ —
Efavirenz + +++
Fosamprenavir + ++
Indinavir ++ —
Lopinavir/ritonavir ++++ ++
Tipranavir/ritonavir ++++ +++
Nelfinavir ++ +
Nevirapine — ++
Ritonavir ++++ ++
Saquinavir — —
Source: Flexner CW. http://clinicaloptions.com/2004PK
TDM of antiretroviral drugs – rationale and purpose
1. Compliance2. ARV plasma or cell drug concentrations correlate
with antiviral effects3. Drug concentrations also correlate with excessive
toxicity4. High variations are present in plasma or cell drug
concentrations5. Hepatic dysfunction changes clearance of the drug
TDM of antiretroviral drugs – approaches
1. Exactly knowing the target concentrations especially multi-therapy targets
2. Four drug therapy failures do not tell you exactly what concentrations of which drug should be changed
3. Resistant isolates may require higher drug concentrations4. Inter- and intra-individual variability5. Drug-drug and drug food interaction6. Bioavalilability enhancement
1. e.g., of indinavir by ritonavir7. Which PK parameter (AUC, Cmin Cmin/IC50)?
Bioanalytical Development of antiretroviral drugs – approaches
1. Many PIs show low nanograms of levels (also do hair and blood spots)
2. Sensitive and accurate HPLC or LC-MS-MS methods are most suitable
3. Plasma, dried blood spots, hair, saliva or lysates of peripheral blood mononeuclear cells (PBMCs) are the drug containing matrices
4. Simultaneous analysis many drugs and internal standards
1. Selecting MRMs for all is challenging
5. PBMC or dried blood spot concentration for PIs or NNRTIs would be more relevant as these drugs act intracellularly
6. Sample pre treatments (e.g., PBMC) may be required for CCs and QCs
Acyclovir
Case study – LC-MS-MS of multi ARVs in PBMC samples
Selection of IS, RT and MRMs (PBMC samples)
Heine et al, (2009) J Chromatogr B Analyt Technol Biomed Life Sci. 877: 57580
LLOQ
Heine et al, (2009) J Chromatogr B Analyt Technol Biomed Life Sci. 877: 57580
Validation of assay
Heine et al, (2009) J Chromatogr B Analyt Technol Biomed Life Sci. 877: 57580
Incu
rred
(cl
inic
al)
sam
ple
anal
ysis
Heine et al, (2009) J Chromatogr B Analyt Technol Biomed Life Sci. 877: 57580
Lopinavir
Ritonavir
Atazanavir
PBMC matrix effect• The number of PBMC cells vary significantly from
sample to sample due to
▫ Natural variation in systemic circulation
▫ Variation in cell recovery
• Therfore, investigation of PBMC ME is required
Heine et al, (2009) J Chromatogr B Analyt Technol Biomed Life Sci. 877: 57580
Conclusions
Thank You Very Much