Bioavailability and Bioequivalence Studies

BA and BE studies.
Seminar presented in All India Institute of Medical Sciences (AIIMS - New Delhi).
Focus in Pharmacokinetic parameters (Cmax, AUC)
Single dose PK study, Steady state PK study, Modified drug release PK study, In vivo mechanisms, invitro mechanisms, Pharmacodynamic Study, Comparatice Clinical Trials. Biowavers and Biosimilimars.
Reference: CDSCO guideline, USFDA guideline, ICH guidelines

1. Bioavailability and Bioequivalence studies Dr Pranav Sopory Junior Resident (Academic) Department of Pharmacology AIIMS- New Delhi Mob: [phone] Email: [email protected] BA/BE 1

2. Contents 1 Introduction on BA/BE 2 Discussion of a “single dose” PK study 3 CDSCO guidelines 4 Cases requiring a “steady state” PK study 5 Special considerations for modified-release drug products 6 Methods apart from PK studies 7 Approval without BE study 8 Biowaivers 9 Biosimilars 10 Conclusion BA: Bioavailability BE: Bioequivalence CDSCO: Central Drugs Standard Control Organization PK: Pharmacokinetic 2

3. BA and BE BA of a drug is defined as the extent and rate to which the active ingredient or active moiety from the drug product is absorbed and becomes available at the site of drug action. BE is achieved when the extent and rate of absorption are not statistically significantly different from those of the reference product when administered at the same molar dose (under similar conditions in an appropriately designed study). 3

4. CDSCO (2005) approved methods to establish BE: In vivo study PK study Highest order of preference among BA/BE study: USFDA PD study Active drug/ its metabolite cannot be detected in biological matrix Can be detected but not with sufficient accuracy or sensitivity Can be detected but has no correlation to its action (topical) Comparative clinical study Absence of PK parameters along with lack of meaningful PD parameters PK and PD studies are not feasible In vitro study 4

5. BE: in brief BA is measured via AUC and C max Measure AUC and C max for the test drug Measure AUC and C max for the reference drug If the ratio (test/reference) falls between 80-125% range: BE established 5

6. PK study: For a single dose Time after drug administration (hours) Drug concentration in plasma (ng/ml) 0.017 (1 min) 0.49 0.08 (5 min) 0.99 0.17 (10 min) 10.12 0.5 (30 min) 50.01 1 90.10 2 87.10 4 65.71 8 41.11 12 20.22 24 6.00 36 1.31 PK parameters Cmax AUC (0-t) AUC (0-∞) K el t 1/2 6

7. Calculating the AUC (exposure to the drug) 7

8. Calculating the AUC (exposure to the drug) BE study requires TOTAL EXPOSURE: AUC (0-∞) This is AUC (0-t) 8

9. Calculating: Elimination rate constant ( K el ) 9

10. Calculating AUC (0-∞) from AUC (0-t) and K el Involves extrapolation of 2% Upto 20% allowed 10

11. Why not just measure the exposure to the drug (AUC)? 11

12. Statistical analysis & criteria to establish BE To assume normality of data, logarithmic transformation of PK parameters: C max and AUC The 90% confidence interval for the ratio of the population means (test/reference) OR Two one sided t-tests with the H for non-BE at the 5% significance level To establish BE: 90% C.I. for C max and AUC should fall within the BE range ( 80-125% ) This is equivalent to the REJECTION of two one sided-t tests with the H for non-BE at the 5% significance level Assess T max if clinically relevant 12

13. PK parameters are lognormally distributed A normal distribution reaches from (– ∞) to (+ ∞) A lognormal distribution reaches from 0 to (+ ∞) There are physiologic limits to PK parameters. They cannot be negative. Also the data is highly skewed. To perform statistical tests: LOGARITHMIC TRANSFORMATION The values are normally distributed The values are less skewed 13

14. Why the 80-125% range to establish BE? USFDA: differences in systemic drug exposure up to 20% are not clinically significant. Shouldn’t the appropriate range be 80-120% (100% ± 20%)? PK parameters are log-normally distributed. Thus, the symmetrical ± 20% has to be in the log-transformed space so that the statistical test of bioequivalence will be valid. Maximum BE 14

15. Exceptions to the criteria USFDA: Distinct limits for permissible differences in BA required for drugs that have: A narrow therapeutic window (90% to 111.11%, ln ratio: -0.105 to + 0.105) A wide therapeutic window (75% to 133%, ln ratio: -0.286 to +0.286) A non-linear PK within the therapeutic dose range (tighter limits due to fluctuations in conc.) Suprabioavailability Reformulation followed by a fresh BE study Otherwise perform a clinical trial 15

16. Study design: CROSSOVER DESIGN Standard: 2 sequence 2 period (2X2) crossover design Test drug: T Reference drug: R Study design (TR, RT) Randomisation Washout period Test drug Reference drug Test drug Reference drug Advantages: Each subject serves as his/her control (decreased confounding variation) Statistically efficient; require lesser subjects (≥16 subjects: CDSCO) Disadvantages: Order effect Carry-out effect Intra-subject variability 16

17. PK study: Study design: Other designs REPLICATE CROSSOVER STUDY DESIGN For highly variable drugs Study design (TRTR, RTRT) Minimum no. of subjects: 24 (USFDA) Allows comparisons within subject variances PARALLEL STUDY DESIGN For drugs with long half-lives Administer each treatment to a separate group of subjects with similar demographics USFDA: Measure truncated AUC [ eg. AUC (0-24) ]: PK simulations show it to be an equally effective parameter. Period 1 2 3 4 Group 1 T R T R Group 2 R T R T 17

18. Requirement of BA/BE studies Establish BE in case of: NDA : Early and late clinical trial formulations Post-marketing changes : Clinical trial formulations and to be marketed formulations ANDA: for generics NDA: New Drug Application ANDA: Abbreviated New Drug Application 18

19. Regulations for generic drugs 1984: USFDA authorized “Drug Price Competition and Patent Term Restoration Act”. USFDA approved generic drugs under this act based on BA/BE studies. MCI: Indian Medical Council (Professional Conduct, Etiquette and Ethics) (Amendment) Regulations, 2016 – Part – I.  “Every physician should prescribe drugs with generic names legibly and preferably in capital letters and he/she shall ensure that there is a rational prescription and use of drugs.” 19

20. CDSCO guidelines : Introduction Reasonable assurance that the test product when compared to the reference product is therapeutically and clinically equivalent and interchangeable. Assessing this via clinical trial is cumbersome. Systemic exposure profile during clinical trials in early drug development serves as a benchmark for subsequent BE studies. 20

21. Definitions in the guideline Reference product: Identified by licensing authority as “Designated Reference Product”/ “Global Innovator Product”. Contains the same active ingredient(s) as the new drug. Applicants seeking approval to market a generic equivalent must refer to the DRP to which all generic versions must be shown to be bioequivalent. For subsequent new drug application, the Licensing Authority, may however, approve another Indian product as DRP. Active Moiety Salt/ester Dosage form Excipient Equivalence Pharmaceutical equivalents + + + - BA/BE outcome Pharmaceutical alternatives + +/- +/- N/A BA/BE outcome Therapeutic equivalents + +/- +/- N/A + (Clinical efficacy) 21 + : Similar - : Not similar

22. In vivo BE studies are necessary A. Oral immediate-release with systemic action when one or more of the following criteria applies: Indicated for serious conditions requiring assured therapeutic response; Narrow therapeutic window Complicated PK (Non-linear) B. Non-oral and non-parenteral formulations designed to act by systemic absorption (e.g. transdermal patches, suppositories) C. Modified-release drug formulations D. FDC products with systemic action E. Non-solution pharmaceutical products for non-systemic use (nasal, ocular, dermal, rectal, etc.): Act without systemic absorption. In these cases, the PK parameter concept is not suitable. Perform comparative clinical study or pharmacodynamic study 22

23. Study conditions: Characteristics to be investigated Measurement of active drug substance(s) in the biological matrix Measurement of drug metabolites Limitations in the analytical method Drug concentration is too low to be recorded Prodrugs Drugs with a very short half-life Racemates (90% of drugs in the market) should be measured using an achiral assay method Measure individual enantiomer in case of Different PD parameters ( eg : S-enantiomer of citalopram more potent) Different PK parameters ( eg : l-enantiomer of MTX: 40 times higher AUC than d-enantiomer) 23

24. CDSCO - Bioanalytical methodology: Pre-study phase Sensitivity: Reliable lowest limit quantification of plasma concentration Limit of detection should be lower than limit of quantification Precision and Accuracy Document on 3 concentrations (lowest measurable, medium and C max ) 24 Intra-assay COV ≤ 20% Range of accuracy: ± 15% Accuracy: ( Accepted value – Observed value* ) X 100 Accepted value

25. Cases requiring an additional “Steady state study” Toxic drugs requiring multiple dose therapy e.g. many cytotoxics . Drugs with long terminal half life and blood concentrations after a single dose cannot be followed for a sufficient time. For modified-release products where it is necessary to assess the fluctuation in plasma conc. over a dosage interval at steady state. 25

26. PK parameters assessed in steady state study Statistical analysis of AUC (0-𝛕 )SS: AUC over one dosing interval. C max C min Degree of fluctuation Criteria to establish BE Same as single dose study 26

27. AUC (0-tau) , C (max) , C (min) and Degree of fluctuation Dose No C max ( ug /mL) C min ( ug /mL) C avg ( ug /mL) 1 3.2 1.6 2.4 2 4.8 2.4 3.6 3 5.6 2.8 4.2 4 6 3 4.5 5 6.2 3.1 4.65 6 6.3 3.15 4.725 Calc. C max SS C min SS C avg SS C avg SS ( ug /mL): C max SS + C min SS 2 Degree of Fluctuation: C max SS - C min SS C avg SS Why measure AUC (0-tau) 27

28. Special considerations for Modified-release drug products Consideration 1: RP: FOOD AFFECTS ABSORTION? ?/YES : Two 2X2 crossover NO : 3X3 crossover Consideration 2: ACCUMULATION ? AUC (0-tau) / AUC (0-∞) ? ≥0.8: Unlikely: SINGLE DOSE Study ≤0.8: Likely: Additional SS Study 3. If test product first market entry: RP: IR 4. Additional parameter: C pd : pre-dose conc. just before steady state is achieved 28

29. Requirements of a PD study Response measured should be a pharmacological effect. ( substitute for plasma conc.) Response should be measured in a double blinded fashion . Pilot study can be conducted to check non-responders If placebo effect can occur, include a third period/phase in the study design Crossover or parallel study design can be used Conventional acceptance rate applicable for PK study is not appropriate (too large). The range should be defined in the protocol on a case-to-case basis 29

30. PK evaluation of acarbose is difficult because <2% is absorbed systemically. Glucobay ®  100 mg tablet (Bayer Healthcare) Vs. Generic acarbose 100‐mg tablet PD parameter: G max (Serial blood samples over 24 hours) 30

31. Cases requiring Comparative clinical trials Absence of PK parameters along lack of meaningful PD parameters PK and PD studies are not feasible Parameter: Clinical endpoint 31

32. PK: Analytical studies for dihydroartemesnin : Not feasible 45 patients followed up for 28 days Mean time to fever subsidence (clinical parameter) Cure rate by Day 28 (clinical parameter) Time to parasite clearance 32

33. Biowaiver: in vivo BA/BE studies are waived Applicant has to provide data to substantiate in vitro studies Different strengths of drug manufactured by the same manufacturer where all of the following criteria are fulfilled: 1. The ratio of active ingredients and excipients between the strengths is essentially the same, or, in the case of small strengths, the ratio between the excipients is the same; 2. The method of manufacture is essentially the same 3. An appropriate equivalence study has been performed on the highest strength, unless a lower strength is chosen for reasons of safety 4. In case of systemic availability- pharmacokinetics have shown to be linear over the therapeutic dose range 33

34. CDSCO Guideline: BE study not necessary for approval New drug Active substance(s) Excipient A. Parenteral ( IV, IM, SC, IT) adm. as aqueous solution Same concentration Comparable concentrations B. Solution for oral use Same concentration Not suspected to affect GI transit or absorption of active substance C. Gas - - D. Powder for reconstitution as a solution Meets criterion A. or B. Meets criterion A. or B. E. Otic or ophthalmic or topical product prepared as an aqueous solution Same concentration Comparable concentration F. Inhalational product or a nasal spray: adm. with/without the same device as the reference product (in vitro testing to document device performance between reference and test product) Same concentration Same concentration For E. and F. the applicant is expected to demonstrate that the excipients in the new drug are comparable concentrations as those in the reference product 34

35. What about Biopharmaceuticals Vaccines, , blood components, gene therapies, tissues, monoclonal antibodies TERM: Biosimilar Establishing biosimilarity Animal study A clinical study or studies [including the assessment of immunogenicity and pharmacokinetics (PK) or pharmacodynamics (PD)] that are sufficient to demonstrate safety, purity, and potency in 1 or more appropriate conditions of use for which the reference product is licensed and for which licensure is sought for the biosimilar product. CDSCO guidelines available: http:// www.cdsco.nic.in / writereaddata /Proposed%20Guidelines%20for%20Similar%20Biologic%202016.pdf 35

36. Retrospective analysis comparing BE parameters between innovator drugs and USFDA approved generic drugs b/w 1996-2007 (12 y) Result: 1. The average difference in C max : 4.35% and in AUC: 3.56% between generic and innovator products 2. 98% of BE studies: the generic product AUC differed from that of the innovator product by less than 10%. 36

37. FDA Orange book: Mobile app PK/PD software www.certara.com cdsco.nic.in ONLINE 37

38. Conclusion Concept of BE has been adopted by the pharmaceutical industry & national regulatory authorities throughout the world. Generics help patients by making drugs available at affordable price while retaining their quality. Translates into increased opportunities for Indian pharmaceutical companies (Current value: US $ 55 billion) Thank you 38

39. PK terms Cmax : maximum drug concentration achieved in systemic circulation following drug administration Cmin : minimum drug concentration achieved in systemic circulation following multiple dosing at steady state Cpd : the pre-dose concentrations determined immediately before a dose in given at a steady state AUC 0-t: from 0 h to the last quantifiable concentration, to be calculated using the trapezoid rule AUC 0-∞: from 0h to infinity to be calculated as the sum of AUC0-t plus the ratio of last measureable concentration to the elimination rate constant AUC 0-𝛕: AUC over one dosing interval following single dose or modified release products AUC 0-𝛕 (SS): AUC over one dosing interval in multiple dose study at steady state Kel : Terminal elimination rate constant calculated from a semi-log plot of plasma concentration versus time curve t1/2: time necessary to reduce the drug concentration in the blood, plasma, serum to one-half after equilibrium in reached 39