1. Evolving Science in Bioavailability and Bioequivalence
Jim Wei, MD, PhD
ACPU, Cincinnati, OH, October 18-20, 2010

2. 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

3. 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 (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

4. 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 steady-state

5. 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

6. 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

7. 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%)

8. 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

9. Cmax
AUClast
Ref-1
Ref-2 6 13 27 7 16 20
This plot is the actual data from the study
High lighted are some subjects with the greatest variability between doses. The same subjects contribute to the high WSV of Cmax and AUC
The next slide shows these 6 subjects only

10. 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 (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

11. 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

12. 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

13. Replicate BE Study Design
Full replicate crossover design:
Partial replicate crossover design:
Period 1 2 3 4
Sequence T R
Period 1 2 3
Sequence T R

14. 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)
The point estimate (test/reference geometric mean ratio) must fall within [ ]
Both conditions must be passed by the test product to conclude BE to the reference product

16. 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

17. 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.

18. 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.

19. 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.

20. 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.

21. 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 ) and BE study reserve samples (21 CFR and ) should be separated.

22. Thank you!
CONTACT INFORMATION JIM WEI