Pharmacokinetic and pharmacodynamic studies of mycophenolic acid in renal transplant recipients

PHARMACOKINETIC AND PHARMACODYNAMIC STUDIES
OF MYCOPHENOLIC ACID IN RENAL TRANSPLANT
RECIPIENTS

NWAY NWAY AYE

NATIONAL UNIVERSITY OF SINGAPORE
2008


PHARMACOKINETIC AND PHARMACODYNAMIC STUDIES
OF MYCOPHENOLIC ACID IN RENAL TRANSPLANT
RECIPIENTS

NWAY NWAY AYE
(B. Pharm., Institute of Pharmacy, Yangon, Myanmar)

A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF
SCIENCE

DEPARTMENT OF PHARMACY
NATIONAL UNIVERSITY OF SINGAPORE
2008


ACKNOWLEDGEMENT

I would like to express my deepest gratitude to my supervisor Dr. Eli Chan,
without

whose

stimulating

invaluable

suggestions,

his

generous

and

knowledgeable guidance and his painstaking supervision and constructive
criticism throughout this study, this work would not have been possible.

I owed a special debt of thanks to Dr. Vasthala and Ms. Huixin for allowing me to
carry out this project. I appreciate all the nurses and staffs from renal clinic and
clinical lab (Singapore General Hospital) for excellent technical assistance in
drawing blood sample and enthusiastic help in recruiting patients and colleting
patients’ information.

I owed a special thank to the renal transplant patients for participating in this study
and attending follow-up clinics.

I am deeply indebted to all the academic staffs, non academic staffs and research
staffs in the Department of Pharmacy especially Ms. Ng Swee Eng, Mr. Tang
Chong Wing, Ms. Ng Sek Eng, Ms. Wong Mei Yin for their active suggestions,
help and guidance in my day to day laboratory works.

I would like to express special thanks to my colleagues in my lab, Yau Wai Ping,
Zheng Lin, Chen Xin and Yin Min Maung Maung for sharing this journey, for
their support, kindness and helpful advice they give. And I also would like to

i


thanks to other friends in the department for helping me in one way or another and
encouraging me throughout the year of my days in NUS.

I am grateful to the National University of Singapore for giving me a chance to
learn new things in my life.

Last but not least, I would like to appreciate to my parents and family for their
love and immense support along the way. This thesis dedicates to my beloved
father and mother because their love and care is still the greatest gift they have
given me.

ii


TABLE OF CONTENT
ACKNOWLEDGEMENT…………………………………………………………... i
TALBE OF CONTENTS……………………………………………………………

iii

SUMMARY………………………………………………………………….……….

viii

LIST OF TABLES………………………………………………………….……….

viii

LIST OF FIGURES………………………………………………………………....

xiv

ABBREVIATIONS………………………………………………………………….

xix

Chapter 1. Introduction…………………………………………………………….

1

1.1 Background of organ transplantation…………………………………………

1

1.2 Background of renal transplant………………………………………………

2

1.3 Overview of combination drug therapy in transplantation…………………

4

1.4 Mycophenolate Mofetil…………………………………………………………

1.4.1 Chemistry…………………………………………………………………….
1.4.2 Pharmacology……………………………………………………………......
1.4.2.1 History of MMF………………………………………………………..
1.4.2.2 Indications and clinical uses……………………………………............
1.4.2.3 Pharmacodynamic properties…………………………………………...
1.4.2.4 Pharmacokinetic properties…………………………………………….

7
7
9
10
11
12
17

1.5 Sirolimus………………………………………………………………………….
1.5.1 Pharmacology…………………………………………………………….....
1.5.1.1 History of sirolimus……………………………………………………
1.5.1.2 Pharmacodynamic properties………………………………………….
1.5.1.3 Pharmacokinetic properties…………………………………………….

21
21
22
23
23

1.6 Combination of mycophenolate mofetil with sirolimus and drug-drug
interaction……………………………………………………………………………. 25
Chapter 2. Objectives of the study………………………………………………….

26

Chapter 3. Analytical methods…………………………………….………………..

27

3.1 High-performance liquid chromatographic method for the determination of
total MPA and its metabolite MPAG in biological samples………………………
3.1.1 Materials and methods……………………………………………………….
3.1.1.1 Chemicals and reagents…………………………………………...........
3.1.1.2 Apparatus……………………………………………………………….
3.1.1.3 Chromatographic conditions……………………………………………

27
27
27
28
28

iii


3.2 High-performance liquid chromatographic method for the determination of
free MPA and its metabolite MPAG in ultrafiltrates…………………………….
3.2.1 Materials and methods……………………………………………………….
3.2.1.1 Chemicals and reagents…………………………………………...........
3.2.1.2 Ultrafiltration…………………………………………………………...
3.2.1.3 Apparatus……………………………………………………………….
3.2.1.4 Chromatographic conditions……………………………………...........

29
30
30
30
31
31

3.3 High-performance liquid chromatographic method for the determination of
IMPDH enzyme activity in vitro…………………………………………………….
3.3.1 Materials and methods……………………………………………………….
3.3.1.1 Chemical and reagents………………………………………………….
3.3.1.2 Apparatus………………………………………………………………
3.3.1.3 Chromatographic conditions……………………………………...........
3.3.1.4 Sample preparation……………………………………………………..
3.3.1.4.1 Stock and working standard solution……………………………..
3.3.1.4.2 Preparation of calibration standard…………………….................
3.3.1.4.3 IMPDH enzyme activity assay in vitro…………………………...

31
32
32
33
33
34
34
34
34

3.3.2 Method validation……………………………………………………………

3.3.2.1 Linearity………………………………………………………………...
3.3.2.2 Intra-day and inter-day accuracy and precision………………………...
3.3.2.3 Results………………………………………………………………….

35
35
35
36

3.4 Determination of IMPDH activity in patients’ blood sample (Clinical
application) ………………………………………………………………………….
3.4.1 Materials and methods………………………………………………………
3.4.1.1 Chemicals and reagents………………………………………………..
3.4.1.2 Study subjects……………………………………………………........
3.4.1.3 Sample preparation…… ………………………………………………
3.4.1.3.1 Stock and working standard solution……………………............
3.4.1.3.2 Preparation of calibration standard……………………………...
3.4.1.3.3 Preparation of lymphocyte from blood sample………………….
3.4.1.3.4 Cell counting………………………………………...………......
3.4.1.3.5 Determination of protein concentration in cell lysates……….....
3.4.1.4 Determination of IMPDH enzyme activity in lymphocytes sample….

41
41
41
41
42
42
43
43

44
44
45

3.4.2 Results……………………………………………………………………….

46

3.4.3 Discussion…………………………………………………………………...

54

Chapter 4. Clinical Studies………………………………………………………….

61

4.1 Introduction…………………………………........................................................ 61
4.2 Materials and Methods………………………………………………………….
4.2.1 Pharmacokinetic study of total MPA and MPAG in plasma………………..
4.2.1.1 Chemicals and reagents………………………………………………..
4.2.1.2 Study subjects………………………………………………………….
4.2.1.2.1 Inclusion criteria………………………………………………...

iv

64
64
64
64
65

4.2.1.2.2 Exclusion criteria………………………………………………..
4.2.1.3 Sample collection……………………………………………………...
4.2.1.4 Sample preparation…………………………………………………….
4.2.1.4.1 Stock and working standard solutions…………………………..
4.2.1.4.2 Calibration standards of plasma sample…………….…………..
4.2.1.4.3 Plasma sample preparation……………………………………...
4.2.1.4.4 Calibration standards of urine samples………………………….
4.2.1.4.5 Urine sample preparation………………………………………..
4.2.1.5 Determination of total MPA and MPAG in plasma and urine
samples………………………………………………………………………...

65
68
68
68
69
69
70
70

4.2.2 Protein binding study of free MPA and MPAG in plasma………………….
4.2.2.1 Chemicals and reagents ………………………………………………
4.2.2.2 Study subjects…………………………………………………………
4.2.2.3 Sample preparation……………………………………………………
4.2.2.3.1 Ultrafiltration…………..…………………………………………
4.2.2.3.2 Calibration standard of ultrafiltrate sample and patients’
sample………………………………………………………………………
4.2.2.4 Determination of free MPA and MPAG in ultrafiltrate………………..

71
72
72
73
73

4.2.3 Pharmacodynamic study of MPA……………………………………………
4.2.3.1 Chemicals and reagents………………………………………………..
4.2.3.2 Study subjects………………………………………………………….
4.2.3.3 Determination of IMPDH enzyme activity in patients’
lymphocytes……………………………………………………………………

74
76
77

71

73
74

77

4.3 Data Analysis……………………………………………………………………

77

4.4 Results……………………………………………………………………………
4.4.1 Pharmacokinetic study………………………………………………………

4.4.2 Pharmacodynamic study…………………………………………………….

81
81
93

4.5 Discussion……………………………………………………………………….

94

Chapter 5. Pharmacokinetic and Pharmacodynamic Modeling………………….

102

5.1 Introduction……………………………………………………………………… 102
5.2 Pharmacokinetic modeling………………………………………………………
5.2.1 Patients and methods………………………………………………………...
5.2.1.1 One compartment model……………………………………………….
5.2.1.2 Two compartment model……………………………………………….
5.2.2 Model discrimination………………………………………………………..

103
103
103
104
106

5.3 Pharmacodynamic modeling……………………………………………………
5.3.1 Patients and methods………………………………………………………...
5.3.1.1 Indirect pharmacodynamic response built in model……………………

5.3.2 Model discrimination………………………………………………………...

107
108
108
108

v


5.4 Results and Discussion…………………………………………………………
5.4.1 Pharmacokinetic modeling…………………………………………………..
5.4.2 Pharmacokinetic parameter estimation………………………………………
5.4.3 Pharmacodynamic modeling………………………………………………...
5.4.4 Pharmacodynamic parameter estimation…………………………………….

111
111
121
123
126

Chapter 6. Population Pharamacokinetic and Pharmacodynamic………………. 128
6.1 Introduction……………………………………………………………………… 128
6.2 Objective………………………………………………………………………….

129

6.3 Patients and methods……………………………………………………………. 129
6.4 Data Analysis…………………………………………………………………….. 130

6.5 Population Pharmacokinetic and Pharmacodynamic Modeling……………... 132
6.5.1 Modeling building procedure……………………………………………….. 132
6.5.2 Model validation…………………………………………………………….. 141
6.6 Results…………………………………………………………………………….
6.6.1 Population pharmacokinetic model of total MPA in stable RTxR receiving
chronic oral dosing on MMF for more than 3 months…………………………….
6.6.1.1 Structural model………………………………………………………..
6.6.1.2 Covariate analysis………………………………………………………

142
142
142
143

6.6.2 Population pharmacokinetic model of free MPA in stable RTxR receiving
chronic oral dosing on MMF for more than 3 months…………………………….. 147
6.6.2.1 Structural model………………………………………………………... 147
6.6.2.2 Covariate analysis……………………………………………………… 149
6.6.3 Population PK-PD model of total MPA in stable RTxR receiving chronic
oral dosing on MMF for more than 3 months…………………………………….. 153
6.6.3.1 Structural model……………………………………………………….. 153
6.6.3.2 Covariate analysis……………………………………………………… 153
6.6.4 Population PK-PD model of free MPA in stable RTxR receiving chronic
oral dosing on MMF for more than 3 months……………………………………...
6.6.4.1 Structural model………………………………………………………...
6.6.4.2 Covariate analysis………………………………………………………
6.6.4.3 Model validation………………………………………………………..

152
152

162
167

6.7 Discussion………………………………………………………………………

168

Chapter 7. Conclusion and future perspectives……………………………………

172

7.1 Conclusion………………………………………………………………………..

172

7.2 Future perspectives……………………………………………………………… 176

vi


Bibliography…………………………………………………………………………

vii

177


SUMMARY

This study was done with the objective of identifying the pharmacokinetic profile

of total and free mycophenolic acid (MPA), and mycophenolic acid glucuronide
(MPAG) and pharmacodynamic profile of MPA in mycophenolate mofetil (MMF)
in combination with sirolimus and steroids and also to establish the
pharmacokinetic (PK) and pharmacodynamic (PD) relationship. Population PKPD models for both free and total MPA was also developed to quantify average
population pharmacokinetic and pharmacodynamic parameters value and to
evaluate the influence covariates on the PK-PD variability.

In this study, two groups of patients were included. Altogether 6 stable renal
transplant patients for the basic PK-PD profile study and 46 patients for the PKPD modeling from Singapore General Hospital (SGH) were included in the study
of their follow-ups.

The established reserved-phase high performance liquid chromatography (HPLC)
methods with UV detection were used to quantify MPA and MPAG in patients’
plasma, urine and ultrafiltrates. Determination of the inosine monophosphate
dehydrogenase (IMPDH) activity was performed using the established methods
with some minor modification.

A total of 36 plasma MPA concentration-time data obtained from 6 patients who
had MMF for more than 3 months were analyzed and PK and PD parameters were
shown and discussed.

viii


Pharmacokinetic studies during dosing intervals of free and total MPA and MPAG
from the same patients were also analyzed. It is observed that after oral
administration of MMF, there is a rapid increase in total and free MPA
concentration during absorption phase, followed by a distribution and elimination
phase, reached the peak at about 0.5 h and descended gradually and inverse
relationship was found for the PD. The PK parameters of MPAG were also

shown.

For the pharamacodynamic response of both free and total MPA in population,
WinNonMix software (non linear mixed effects modeling) was used for analysis.
Covariates such as age, sex, ethnic groups may affect PK and PD aspects. To
determine these effects, PK and PD models were developed. Population PD
parameters of structural basic and final model for PK-PD relationship of total and
free MPA concentration and responses were also identified. In this study, PK-PD
model for total drug concentration and response did not identify any significant
covariates relationship. However, only one covariate, white blood cells count
(WBC), had shown significant for the PK-PD model for free drug concentration
and response.

However, further investigations with a large number of patients are needed to
fully explore the impact of covariates on the PK-PD relationship between MPA
and IMPDH activity.

ix


LIST OF TABLE
Table

Description

Page

1.1

Summary of kidney transplantation

3

1.2

Other Non-FDA-approved therapeutic uses of MMF reported
in literatures

12

Pharmacodynamic of MPA in different transplant groups of
multiple doing reported in literatures

16

Pharmacokinetic parameters of mycophenolic acid in different
transplant groups of multiple doing reported in literatures

20

Pharmacokinetic parameters of MPAG in different transplant
groups of multiple doing reported in literatures

21

3.1

Intra-day precision and accuracy of enzymatic assay

40

3.2

Inter-day precision and accuracy of enzymatic assay

40

3.3

Patients’
demographics,
comorbidities,
concomitant
immunosuppressants and biochemical parameters

42

Summary of the IMPDH activity obtained in RTx patients for
conventional
study
and
patients
for
population
pharmacokinetic and pharmacodynamic study following
chronic oral dosing of MMF for more than 3 months

46

Summary of sample preparation and results

pharmacodynamic study of MMF in reported literatures

57

1.3

1.4

1.5

3.4

3.5

4.1

of

RTx Patients’ demographics, comorbidities, concomitant
immunosuppressants and biochemical parameters for the
conventional study

67

4.2

Factor affecting the IMPDH activity in vitro

76

4.3

Pharmacokinetic and Pharmacodynamic parameters at steady
state in RTxRs following chronic oral dosing of MMF for
more than 3 months

87

x


4.4

4.5

5.1

5.2

5.3

5.4

5.5

5.6

5.7

5.8

Normalized PK and PD parameters in patients for the
conventional study following chronic oral dosing of MMF for
more than 3 months

88

Mechanism of renal excretion of MPA and MPAG in RTxR
for conventional study

92

Summary of goodness-of-fit parameters for total MPA in 2
different model for individual patients for conventional study

120

Summary of goodness-of-fit parameters for free MPA in 2
different model for individual patients for conventional study

120

Model discrimination between one compartment and two
compartment model for total MPA concentration using F-test

120

Model discrimination between one compartment and two
compartment model for free MPA concentration using F-test

120

Estimated PK parameters (mean±SD) of total MPA in stable
renal transplant patients for conventional study following
chronic oral dosing of MMF for more than 3 months

122

Estimated PK parameters (mean±SD) of free MPA in stable
renal transplant patients for conventional study following
chronic oral dosing of MMF for more than 3 months

122

Summary of goodness-of-fit parameters for total and free
MPA and IMPDH enzyme activity in Indirect
Pharmacodynamic Response built in model for individual
patients for the conventional study following chronic oral
dosing of MMF for more than 3 months

123

Estimated parameters for IMPDH enzyme activity of total and
free MPA in stable RTx patients for the conventional study
following chronic oral dosing of MMF for more than 3
months

126

xi

6.1

Demographics,
comorbidities,
concomitant
immunosuppressants and biochemical parameters of stable
renal transplant recipients who were on MMF for more than 3
months

131

Illustration of testing of significance of covariates using
ANOVA for PK parameter CL for total MPA

144

Estimates of population PK parameters of total MPA for the
basic structural and final model

144

6.4

Difference in AIC and SC values for PK models (total MPA)

145

6.5

Illustration of testing of significance of covariates using
ANOVA for PK parameter CL for free MPA

149

Estimates of population PK parameters of free MPA for the
basic structural and final model

150

6.7

Difference in AIC and SC values for PK models (free MPA)

150

6.8

Illustration of testing of significance of covariates using
ANOVA for PD parameter IC50

154

6.9

Model development

154

6.10

Estimates of population PD parameters of total MPA for the
basic structural and final PK-PD model

155

Difference in AIC and SC values for PKPD models (response
of total MPA)

155

Predictive performance of population PK-PD model using
total MPA concentration and response in stable RTxR (n=49)

158

Illustration of testing of significance of covariates using
ANOVA for PD parameter IC50

163

6.2

6.3

6.6

6.11

6.12

6.13

xii


6.14

Model development

163

6.15

Estimates of population PD parameters of free MPA for the
basic structural and final PK-PD model

164

Difference in AIC and SC values for PK-PD models (response
of free MPA)

164

Predictive performance of population PK-PD model using
free MPA concentration and response in stable RTxR (n=49)

167

6.16

6.17

xiii


LIST OF FIGURE
Figure

Description

Page

1.1

Chemical structure of mycophenolate mofetil (MMF)

7

1.2

Chemical structure of mycophenolic acid (MPA)

8

1.3

Chemical structure of mycophenolic acid glucuronide (MPAG)

8

1.4

Metabolic pathways of mycophenolic acid in humans

9

1.5

Mechanism of action of MPA on IMPDH enzyme

13

1.6

Chemical structure of sirolimus (SRL)

22

1.7

Mechanism of action of MMF and SRL

25

3.1

Calibration curve for the product XMP

37

3.2

Chromatogram of (A) Blank (phosphate buffer saline spiked with
IMP and NAD); (B) Spiked in pure IMP, NAD and XMP; (C)
sample reacted with 500 nM of pure IMPDH enzyme; (D) A
stable transplant patient sample 2 h after chronic oral dosing of
MMF (500 mg b.d.) for more than 3 months

39

Inter-individual variability of IMPDH activity (nmol/h/mg
protein) in patients for population pharmacokinetic and
pharmacodynamic study (n=46)

46

IMPDH activity in lymphocytes Vs total MPA plasma
concentration (mg/L) in plasma in stable renal transplant patients
for conventional study after chronic oral dosing of MMF for more
than 3 months (n=3, each patient with 6 sampling points)

48

IMPDH activity in lymphocytes Vs free MPA plasma
concentration (mg/L) in plasma in stable renal transplant patients
for conventional study after chronic oral dosing of MMF for more
than 3 months (n=3, each patient with 6 sampling points)

48

IMPDH activity in lymphocytes Vs total MPAG plasma
concentration (mg/L) in plasma in stable renal transplant patients
for conventional study after chronic dosing of MMF for more
than 3 months (n=3, each patient with 6 sampling points)

49

IMPDH activity in lymphocytes Vs free MPAG plasma
concentration (mg/L) in plasma in stable renal transplant patients
for conventional study after chronic oral dosing of MMF for more
than 3 months (n=3, each patient with 6 sampling points)

49

3.3

3.4

3.5

3.6

3.7

xiv


3.8

3.9

3.10

3.11

3.12

3.13

3.14

3.15

IMPDH activity in lymphocytes Vs total MPA plasma
concentration (mg/L) in plasma in stable renal transplant patients
for population PK-PD modeling after chronic oral dosing of MMF
for more than 3 months (n=46, each patient with 1 sampling point
at 0, 2 or 6 h after MMF dosing)

50

IMPDH activity in lymphocytes Vs free MPA plasma
concentration (mg/L) in plasma in stable renal transplant patients
for population PK-PD modeling after chronic oral dosing of MMF
for more than 3 months (n=46, each patient with 1 sampling point
at 0, 2 or 6 h after MMF dosing)

50

IMPDH activity in lymphocytes Vs total MPAG plasma
concentration (mg/L) in plasma in stable renal transplant patients
for population PK-PD modeling after chronic oral dosing of MMF
for more than 3 months (n=46, each patient with 1 sampling point
at 0, 2 or 6 h after MMF dosing)

51

IMPDH activity in lymphocytes Vs free MPAG plasma
concentration (mg/L) in plasma in stable renal transplant patients
for population PK-PD modeling after chronic oral dosing of MMF
for more than 3 months (n=46, each patient with 1 sampling point
at 0, 2 or 6 h after MMF dosing)

51

IMPDH activity in lymphocytes Vs total MPA plasma
concentration (mg/L) in plasma in stable renal transplant patients
for both conventional study and population PK-PD modeling after
chronic oral dosing of MMF for more than 3 months (n=49)

52

IMPDH activity in lymphocytes Vs free MPA plasma
concentration (mg/L) in plasma in stable renal transplant patients
for both conventional study and population PK-PD modeling after
chronic oral dosing of MMF for more than 3 months (n=49)

52

IMPDH activity in lymphocytes Vs total MPAG plasma
concentration (mg/L) in plasma in stable renal transplant patients
for both conventional study and population PK-PD modeling after
chronic oral dosing of MMF for more than 3 months (n=49)

53

IMPDH activity in lymphocytes Vs free MPAG plasma
concentration (mg/L) in plasma in stable renal transplant patients
for both conventional study and population PK-PD modeling after
chronic oral dosing of MMF for more than 3 months (n=49)

53

xv


4.1

(A) Characteristic pharmacokinetic and pharmacodynamic profiles
of MPA and MPAG in patients for conventional study following
chronic oral dosing of MMF for more than 3 months during
interval (0-12, 24 or 48 h) (B) Characteristic total and free
concentration-time profile of MPA and MPAG in patients for
conventional study following chronic oral dosing of MMF for
more than 3 months during interval (0-12, 24 or 48 h) (PD data
not available)

83

(A) Characteristic pharmacokinetic and pharmacodynamic profiles
of MPA and MPAG in patients for conventional study following
chronic oral dosing of MMF for more than 3 months during
interval (0-12, 24 or 48 h) (Semi-log scale) (B) Characteristic total
and free concentration-time profile of MPA and MPAG in patients
for conventional study following chronic oral dosing of MMF for
more than 3 months during interval (0-12, 24 or 48 h) (PD data
not available) (Semi-log scale)

85

4.3

Scatter plot of free fraction of MPA versus MPA concentration

90

4.4

Scatter plot of free fraction of MPAG versus MPA concentration

90

4.5

Scatter plot of free fraction of MPAG versus MPAG concentration

90

4.6

Scatter plot of free fraction of MPA versus MPAG concentration

91

4.7

Scatter plot of free fraction of MPAG versus free fraction of MPA

91

5.1

Schematic presentation of the one-compartment model with first
order elimination

104

Schematic presentation of a
parameterized with micro constants

105

4.2

5.2

5.3

5.4

5.5

5.6

two-compartment

model

Indirect pharmacodynamic response built-in model (Inhibition of
input) for both total an free MPA and it’s response in stable renal
transplant patients for conventional study following chronic oral
dosing of MMF

110

Observed IMPDH activity time course in a stable renal transplant
patient following chronic oral dosing of MMF for more than 3
months

110

Plasma concentration time profile of total MPA in patients for
conventional study following chronic oral dosing of MMF after
fitting in one compartment model

113

Plasma concentration-time profile of free MPA in patients for

conventional study following chronic oral dosing of MMF after
fitting in one compartment model

115

xvi


5.7

5.8

5.9

5.10

6.1

6.2

6.3

6.4

6.5

6.6

6.7

Plasma concentration-time profile of total MPA in patients for
conventional study following chronic oral dosing of MMF after
fitting in two compartment model

117

Plasma concentration-time profile of free MPA in patients for
conventional study following chronic oral dosing of MMF after
fitting in two compartment model

119

Observed and predicted IMPDH enzyme activity-time course at
steady state over the dosing interval (0 to τ) in patients for the
conventional study following chronic oral dosing of MMF for
more than 3 months based on total MPA using indirect
pharmacodynamic response (IPR) built in model

124

Observed and predicted IMPDH enzyme activity-time course at
steady state over the dosing interval (0 to τ) in patients for the
conventional study following chronic oral dosing of MMF for
more than 3 months based on free MPA using indirect
pharmacodynamic response (IPR) built in model

125

Characteristic concentration-time profile of total MPA after
chronic oral administration of MMF for more than 3 months

142

Goodness-of-fit plot for the basic structural model : (A) Predicted
total MPA concentration versus observed total MPA concentration
(population) : (B) Predicted total MPA concentration versus
observed total MPA concentration (individual) : (C) Weighted
residuals (WRES) versus predicted total MPA concentration
(population) : (D) Weighted residuals (WRES) versus predicted
total MPA concentration (individual)

146

Plot of predicted (population and individual) total MPA
concentration against time

147

Characteristic concentration-time profile of free MPA after
chronic oral administration of MMF for more than 3 months

148

Goodness-of-fit plot for the basic structural model: (A) Predicted
free MPA concentration versus observed free MPA concentration
(population): (B) Predicted free MPA concentration versus
observed free MPA concentration (individual): (C) Weighted
residuals (WRES) versus predicted free MPA concentration
(population): (D) Weighted residuals (WRES) versus predicted
free MPA concentration (individual)

152

Plot of predicted (population and individual) free MPA
concentration against time

152

Time course of IMPDH enzyme activity PD profile of MPA after
chronic oral dosing of MMF in stable renal transplant patient

155

xvii


6.8

6.9

6.10

6.11

6.12

6.13

Goodness-of-fit plot for the basic structural model : (A) Predicted
response of total MPA versus observed response of total MPA

(population) : (B) Predicted response of total MPA versus
observed response of total MPA (individual) : (C) Weighted
residuals (WRES) versus predicted response of total MPA
(population) : (D) Weighted residuals (WRES) versus predicted
response of total MPA (individual)

157

A plot of observed vs. final model-predicted responses of total
MPA concentration

158

Goodness-of-fit plot for the basic structural model : (A) Predicted
response of free MPA versus observed response of free MPA
(population) : (B) Predicted response of free MPA versus
observed response of free MPA (individual) : (C) Weighted
residuals (WRES) versus predicted response of free MPA
(population) : (D) Weighted residuals (WRES) versus predicted
response of free MPA (individual)

161

Goodness-of-fit plot for the final model : (A) Predicted response
of free MPA versus observed response of free MPA (population) :
(B) Predicted response of free MPA versus observed response of
free MPA (individual) : (C) Weighted residuals (WRES) versus
predicted response of free MPA (population) : (D) Weighted
residuals (WRES) versus predicted response of free MPA
(individual)

166

Plot of predicted (Population and Individual) PD response of free
MPA against time (final model)

166

A plot of observed vs. final model-predicted responses of free
MPA

168

xviii


ABBREVIATIONS
The following symbols are used in this thesis:
7-O MPAG
Ac-MPAG
AIC
aMDRD
ANOVA
AUC
b.d.
BQR
C
C0
CABG
CL/F

CLCr
CLD2/F
Clformation
Clrenal
Cmax
CsA
DGF
DM
e.o.d.
EC-MPS
F
FDA
FE
GFR
GTP
HL
HPLC
HTN
I
IC50
IMP
IMPDH
IPR
IV
K01
K10
K12
K21
Kin
Kout

Mycophenolate 7-O Glucuronide
Acyl-glucuronide
Akaike Information Criterion
Abbreviated modification of diet in renal disease
Analysis of variance
Area under the concentration-time curve
twice a day
Brequinar
Chinese
Trough concentration
Coronary Artery Bypass Graft
Apparent oral clearance
Creatininie clearance
Distribution clearance of peripheral compartment
Formation clearance
Renal clearance
Maximum plasma concentration
Cyclosporine
Delayed graft failure
Diabetes mellitus
Every other day
Enteric-coated mycophenolate sodium
Female
U.S Food and Drug Administration
Fold error
Glomerular Filtration Rate
Guanosine 5' triphosphate
Hyprelipidemia
High Performance Liquid Chromatography

Hypertension
Indian
Drug concentration which produces 50% of maximum
inhibition
Inosine monophosphate
Inosine monophosphate dehydrogenase activity
Indirect Pharmacodynamic Response
Intravenous
First-order fractional absorption rate constant per unit time
Fractional elimination rate constant from central
compartment per unit time
Fractional rate constant from central compartment to
peripheral compartment per unit time
Fractional rate constant from peripheral compartment to
central compartment per unit time
Zero-order constant for the production of response
First-order constant for loss of response
xix


LEF
LLOQ
LOD
M (in ethnic group)
M (in gender)
MMF
MNC
MPA
MPAC
MPAG

mTOR
mTOR
MWCO
MZ
NAD
O
o.m.
OCM
PBS
PD
PK
RTxRs
SC
SRL
TAC
TBAHS
TCM
Tlag
Tmax
ULOQ
V1
V2
Vd
WRSS
XMP

Leflunomide
Lower limit of quantation
Limit of detection
Malay

Male
Mycophenolate mofetil
Peripheral blood mononuclear cells
Mycophenolic acid
Carboxybutoxy ether of MPA
Mycophenolic acid glucuronide
Mammalian target of rapamycin
Mammalian target of rapamycin
Molecular weight cutoff
Mizoribine
Nicotinamide adenine dinucleotide
Other race
Every morning
One compartment model
Phosphate Buffer Saline
Pharmacodynamic
Pharmacokinetic
Renal transplant recipients
Schwartz Criterion
Sirolimus
Tacrolimus
Tetrabutyl ammonium hydrogen sulphate
Two compartment model
Time lag in absorption
Time to reach Cmax
Upper limit of quantification
Initial dilution volume of distribution
Apparent volume of the peripheral compartment
Volume of distribution
Weighted residual sum of squares

Xanthosine monophosphate

xx


CHAPTER 1
INTRODUCTION

1.1

BACKGROUND OF ORGAN TRANSPLANTATION

Organ transplantation means removing a whole or part of a healthy organ from one
body (the donor) and putting it in another body (the recipient) to replace the
recipient’s damaged or failing organ in order to prolong or save his or her life. In
cases of skin grafts, and recently, face transplant, it is to enhance the quality of life.

Transplantation can be categorized according to donor and recipient as follows:
a) Autograft – Autograft means transplantation of tissue from one part of
own body to another part, e.g. skin grafts, vein extraction in Coronary
Artery Bypass Graft (CABG). Returning back the stem cells to the same
body and string is own blood for later transfusion is also considered as
autograft. There will be no problem with rejection because the body
recognizes its own tissue.

b) Allograft – Allograft means transplantation of an organ or tissue from
genetically non-identical member of the same species. Most of the
transplantations in human fall into this category. Tissue rejection is one
of the major problems in this type of graft as recipient’s body fights
back the transplant organ as a foreign body.

1


c) Isograft – It is transplantation of organ or tissue from the donor who is
genetically identical with the recipient i.e. identical twins. Tissue
responses in these operations are the same as autograft.

d) Xenograft – Xenograft means transplantation of organ or tissue from
donor of different species other than recipient. Replacement of damaged
human heart valves with porcine heart valves is a common procedure of
xenograft. But transplantation of the whole of baboon’s heart to human
failed. Non-human xenografts are done for research [1].

1.2

BACKGROUND OF RENAL TRANSPLANT

The organs that can be transplanted nowadays are heart, lungs, liver, kidney,
pancreas, cornea, and intestines. Although heart transplant made the headlines,
kidney transplantation is the most common transplant procedure. In fact, kidney
is the first organ to be transplanted successfully. As a person can live with only
one kidney, the donor can be either living or deceased.

Renal transplant is considered in those patients with end-stage renal disease who
can tolerate transplant surgery. Table 1.1 shows the criteria of indications and
contraindications essential for transplant patients and donors.

2

Table 1.1 Summary of kidney transplantation
Diseases that can
cause renal failure
which will
eventually lead to
renal dialysis and
transplant
Severe
uncontrollable high
blood pressure

Criteria for donors

Contraindications for
becoming a donor

Age – patients more than
70 years of age

Compatible ABO
typing with potential
recipient

Person with single
kidney or abnormalities
of kidneys.

Infections of
urinary tract

Patients having heart or
circulatory disorders

Age – between 18
and 65 years old

History of kidney stone
or kidney disease

Diabetes

Lung or liver diseases

Medically fit person

Significant urinary tract
infection

Glomerulonephritis

Active infectious disease

Psychosocially
suitable and willing
to undergo
psychological or
psychosocial
assessment if
requested.

Ability to give
informed consent

People from high risk
occupation like military,
special forces,
professional football
player or other contact
sports

Contraindications to
kidney transplantation

Active substance abusers

Those with psychological
or behavioral
abnormalities since they
cannot follow post
operative regime of
immunosuppressive
therapy
Morbidly obese patients

If possible,
biologically related to
the recipient or if not,
have some emotional
connection.
All unrelated donors

must have a
psychiatric evaluation

People having diseases
like HIV AIDS,
Hepatitis, Tuberculosis,
cancer, diabetes etc.
Hypertension

Pregnancy

Active substance abuser
History of psychological
instability
donor with risk to
anesthesia

3