Evolving Science in
Bioavailability and
Bioequivalence
Jim Wei, MD, PhD
x.wei@medpace.com
ACPU, Cincinnati, OH, October 18-20, 2010
Agenda



Bioavailability/Bioequivalence
Highly variable drugs (HVD)
Study Design of Bioequivalence
• Average BE
• Replicate BE
- Full replicate
- Partial replicate

Regulatory requirements for BE supplies, sample
storage and data analysis
Bioavailability – defined
“Bioavailability is the fraction (F) of an administered
dose that actually reaches systemic circulation when
compared to a solution (SLN), suspension (SUSP), or
intravenous (IV) dosage form.”
-- 21 CFR 320.25(d)(2)&(3) -absolute: test drug vs. IV reference » BA of an IV drug is assumed to be 100%,
or F = 1.00
» amount reaching circulation = F x Dose
relative: test drug vs. SLN or SUSP reference
Points to Consider – BA
For bioavailability studies, our primary “metric” of
interest is:
• area under the concentration-time curve
(AUC)
• AUC is a derived parameter, it is not observed
Types:
• AUCt = to the last detectable concentration
• AUC = from zero to infinity (single dose)
• AUC = between dosing intervals at steadystate
Approaches to Determining Bioequivalence
(21 CFR 320.24)





In vivo measurement of active
moiety or moieties in biologic
fluid
In vivo pharmacodynamic
comparison
In vivo limited clinical
comparison
In vitro comparison
Any other approach
deemed appropriate by FDA
FeV1 Albuterol
Glucagon
Topicals
Nasal Suspensions
Questran - Binding Studies
Nasal Solutions-Sprayer
Evaluation
Propofol - Droplet Size
BE Study Designs

Single-dose, two-way crossover, fasted

Single-dose, two-way crossover, fed

Alternatives
• Single-dose, parallel, fasted
• Long Half-Life (wash-out): Amiodarone, Etidronate
• Single-dose, replicate design
» Highly Variable Drugs
• Multiple-dose, two-way crossover, fasted
• Less Sensitive: Clozapine (Patient Trials); Chemotherapy Trials
• Clinical endpoint study
• Topicals: Nasal Suspensions
BE Statistical Analysis

Bioequivalence criteria
• Two one-sided tests procedure
» Test (T) is not significantly less than reference
» Reference (R) is not significantly less than test
» Significant difference is 20% ( = 0.05
significance level)
• T/R = 80/100 = 80%
• R/T = 80% (all data expressed as T/R so this
becomes 100/80 = 125%)
Highly Variable Drugs (HVD)


Definition
• Use ANOVA Root Mean Square Error (RMSE) to
estimate within-subject or intra-subject variability:
• Drug is classified as highly variable if RMSE ≥ 0.3 or
30%
 Two main types or sources of variability
• Highly variable PK (inherent drug characteristic)
• Highly variable formulation
• Standard BE study approach may need more
than 100 subjects
Cmax
Ref-1
AUClast
Ref-1
Ref-2
Ref-2
6
16
20
6
7
13
6
13
7
16
13
13
7
16
20
20
27
27
27
27
7
6
20
16
BE Studies in Highly Variable Drugs (HVD)

FDA Study to Characterize Highly Variable Drugs in BE Studies:
• Collected data from 1127 acceptable BE studies,
submitted
» 524 ANDAs from 2003-2005 (3 years)
• Most sponsors used 2-way crossover studies
» Used ANOVA Root Mean Square Error to estimate
within-subject variance
• Drug was classified as highly variable if RMSE ≥ 0.3 or 30%
• BE studies of HVD enrolled more study subjects than studies
of drugs with low variability
» Average N in studies of HVD = 47
» Average N in studies of drugs with lower variability = 33
• Range 18 – 73 subjects
• 10% of studies evaluated were HVD
Reasons for Inconsistent Variability in BE Studies
Differences in formulations
 Improperly handling of Bioanalytical assays
 Subjects with irregular plasma
concentrations
 Number of study subjects
 Uncontrolled food status

90%CIs & BE Limits


Green
• Low WSV (~15%)
• Narrow 90%CI
• Passes
Red
• High WSV (~35%)
• Wide 90%CI
• Lower bound <80%
• Fails
125%
100%
80%
GMR & the # of subjects
are the same in both cases
Replicate BE Study Design

Full replicate crossover design:
Period
Sequence

1
2
3
4
1
T
R
T
R
2
R
T
R
T
Partial replicate crossover design:
Period
Sequence
1
2
3
1
T
R
R
2
R
T
R
3
R
R
T
Scaled Average BE for HVD



Three-period, partial replicate design
• Reference product (R) is administered twice
• Test product (T) is administered once
• Sequences = RTR, TRR, RRT
Sample size: Determined by sponsor (adequate power)
• minimum is 24 subjects
BE criteria scaled to reference variability (Cmax & AUC)
 0.223

BE limits,upper,lower  EXP 
 σ wr 
 σ w0



The point estimate (test/reference geometric mean ratio) must fall
within [0.80-1.25]
Both conditions must be passed by the test product to conclude BE
to the reference product
Average vs. Scaled Average Bioequivalence
CV% = 60, Simulations = 106, N = 36 vs. 24, w0=0.25
Percent of Studies Passing
100
Scaled ABE + Point Estimate (N = 24)
Average BE (N = 24)
Scaled ABE + Point Estimate (N = 36)
Average BE (N = 36)
80
60
40
20
0
1.0
1.1
1.2
1.3
1.4
Geometric Mean Ratio
1.5
1.6
1.7
Advantages of Scaled BE
(Reference Scaled)



Test product will benefit if:
• T variability < R variability
The test product will not benefit if:
• T variability > R variability
What if high variability results from formulations
problems or poor study conduct?
• If T variability > R variability, no benefit in using
scaled approach
• The burden is on the applicant to convince FDA
that product is a HVD
21 CFR 320.36
Requirements for maintenance of records of
bioequivalence testing
•
All records of in vivo or in vitro tests shall be maintained by the
manufacturer for at least 2 years after the expiration date of the batch
and submitted to the Food and Drug Administration on request.
•
Any person who contracts with another party to conduct a
bioequivalence study from which the data are intended to be submitted
to FDA as part of an application submitted under part 314 of this chapter
shall obtain from the person conducting the study sufficient accurate
financial information to allow the submission of complete and accurate
financial certifications or disclosure statements required under part 54 of
this chapter and shall maintain that information and all records relating to
the compensation given for that study and all other financial interest
information required under part 54 of this chapter for 2 years after the
date of approval of the application. The person maintaining these records
shall, upon request for any properly authorized officer or employee of the
Food and Drug Administration, at reasonable time, permit such officer or
employee to have access to and copy and verify these records.
21 CFR -320.38
Retention of bioavailability samples

Each reserve sample shall be stored under conditions
consistent with product labeling and in an area segregated
from the area where testing is conducted and with access
limited to authorized personnel.

Each reserve sample shall be retained for a period of at least 5
years following the date on which the application or
supplemental application is approved, or, if such application
or supplemental application is not approved, at least 5 years
following the date of completion of the bioavailability study in
which the sample from which the reserve sample was
obtained was used.
BE Sample Retention

The guidance highlights
• how the test article and
reference standard for BA
and BE studies should be
distributed to the testing
facilities
• how testing facilities should
randomly select samples for
testing and material to
maintain as reserve samples
• how the reserve samples
should be retained.
FDA/DSI Inspection on BE Studies

A frequent finding from these inspections is the absence of reserve
samples at the testing facilities where the studies are conducted:
• In many cases, DSI finds that testing facilities return reserve
samples to the study sponsors and/or drug manufacturers,
• In other cases, study sponsors and/or drug manufacturers, SMOs,
or contract packaging facilities designate the study test article
and reference standard for each subject, and preclude the
testing facilities from randomly selecting representative reserve
samples from the supplies.

The study sponsor and/or drug manufacturer should send to the
testing facility batches of the test article and reference standard
packaged in such a way that the testing facility can randomly select
samples for bioequivalence testing and samples to maintain as
reserve samples.
FDA/DSI Inspection on BE Studies cont’d



Quantity of Reserve Samples
• Sufficient to perform five times all of the release tests required in
the application or supplemental application
• For solid oral dosage forms (e.g., tablets, capsules), an upper limit
of 300 units each for the test article and reference standard
Each site is asked to retain a reasonable amount of test article and
reference standard
• a minimum limit (e.g., 5 dose units) for each of the test articles
and reference standards
In-House Studies Conducted by a Study Sponsor and/or Drug
Manufacturer
• If a study sponsor and/or drug manufacturer conducts such a
study, manufacturing reserve samples (21 CFR 211.170) and BE
study reserve samples (21 CFR 320.38 and 320.63) should be
separated.
Thank you!
CONTACT INFORMATION
JIM WEI
513-763-9770
E-MAIL: x.wei@medpace.com