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