Bioavailability & Bioequivalence Studies

Bioavailability and  Bioequivalence Studies

Introduction

• It is essential to ensure uniformity in standards of quality, efficacy & safety of Pharmaceutical products
• Reasonable assurance is to be provided that various products containing the same active ingredient, marketed by different licensees are clinically equivalent & interchangeable
• Release of an active substance should be known & reproducible
• Both Bioavailability & Bioequivalence focus on the release of the drug substance from its dosage form & subsequent absorption in circulation
• Similar approaches to measure Bioavailability should be followed in demonstrating Bioequivalence 

Bioavailability

• Measurement of the relative amount & rate at which, the drug from the administered dosage form, reaches the systemic circulation & becomes available at the site of action
• Bioavailable fraction (F), refers to the fraction of administered dose that enters the systemic circulation

F   =  Bioavailable dose/Administered dose

OBJECTIVES OF BIOAVAILABILITY STUDIES

• Primary stages of development of a suitable dosage for a new drug entity.
• Development of a new formulation of the existing drugs.
• Control of quality of a drug product during the early stages of marketing in order to determine the influence of processing factors, storage and stability on drug absorption.
• Useful in determining the safety and efficacy of the drug product.

 Concept of Equivalents

• Bioequivalence
• Pharmaceutical equivalent/alternative of the test product,
• when administered at the same molar dose,
• has the rate and extent of absorption
• not statistically significantly  different from that of the reference product

• Pharmaceutical equivalents

• Pharmaceutical alternatives

• Therapeutic equivalence – FDA classifies those products as therapeutically equivalent which
• Same active substance or therapeutic moiety
• Clinically show the same efficacy & safety profile

Reference Product

• Identified by the Regulatory Authorities as “Designated Reference Product”
• Usually the Global Innovator’s Product
• Protected by a patent
• Marketed under manufacturers brand name
• Clinical efficacy & safety profile is well documented in extensive trials
• All generics must be Bioequivalent to it
• In India, CDSCO may approve another product as a Reference product

Generic Drug

• Drug product which is identical or bioequivalent to Brand/ Reference drug in: Active ingredient (s), Route of administration, Dosage form, Strength, Indications, Safety

• May have different:
• Inactive ingredients,  Colour, Shape
• Almost half of the drugs in the market have Generics
• An Abbreviated New Drug Application (ANDA) is an application for a U.S. generic drug approval for an existing licensed medication or approved drug

Fundamental Bioequivalence Assumption

When a generic drug is claimed bioequivalent to a Reference drug, it is assumed that they are therapeutically equivalent

Bioequivalence Background

•  Using bioequivalence as the basis for approving generic copies in the US

“Drug Price Competition and Patent Term Restoration Act of 1984,” also known as the Waxman-Hatch Act

•  Created Generic Industry & ↑ their availability
•  Most successful legislation
•  Benefited Brand & Generic firms
•  Generic firms→ Rely  on findings of safety & efficacy of Innovator drug after Patent expiration
•  Innovator firms→ Patent extensions of 5yrs to make up for time lost while their products were going through FDA’s approval process

Indian Legislation

•  In India, CDSCO provides “Guidelines for Bioavailability & 

    Bioequivalence Studies”  mentioned in Schedule Y

•  As per the Drugs & Cosmetics Rules (II^nd Amendment) 2005, all bioavailability and bioequivalence studies should be conducted in accordance with these Guidelines

The requirement of BA & BE Studies

•  For IND/NDAs:

    To establish equivalence between:

• Early & late clinical trial formulations
• Formulations used in clinical trial & stability studies
• Clinical trial formulations & to-be-marketed drug product
• Any other comparisons, if appropriate
• ANDA for a generic drug product
• Change in components, composition, &/or  manufacturing process
• Change in dosage form (capsules to tablet)

Objectives of BA & BE Studies

•  Development of suitable dosage form for a New Drug Entity
•  Determination of the influence of excipients, patient-related factors & possible interactions with other drugs
•  Development of new drug formulations of existing drugs
•  Control of quality of drug products, the influence of → processing factors, storage & stability
•  Comparison of availability of a drug substance from a different form or same dosage form produced by different manufacturers

When is Bioequivalence not necessary (Biowaivers)?

1. Aqueous parental Solution; a same active substance with the same concentration, same excipient
2. Oral Solution; a same active substance with the same concentration, excipient not affecting GI transit or absorption
3. Gas
4. Powder for reconstitution as a solution; meets criterion (a) or (b)
5. Otic/Ophthalmic/Topical Solution; a same active substance with the same concentration, same excipient
6. Inhalational Product/ Nasal Spray; administered with or w/o same device as reference product; prepared as an aqueous solution; a same active substance with the same concentration, same excipient

Orange Book

•  All FDA approved drugs listed (NDA’s, ANDA’s & OTC’s)
•  Expiration of patent dates
•  Drug, Price and Competition Act (1984) – FDA required to publish Approved Drug Products with Therapeutic Equivalence & Evaluations

Methods used to assess Equivalence

1. Pharmacokinetic Studies
2. Pharmacodynamic Studies
3. Comparative Clinical Studies
4. Dissolution Studies

Pharmacokinetic Studies

Subject selection

• Healthy adult volunteers
• Age: 18-45 yrs
• Age/Sex representation corresponding to a therapeutic & safety profile
• Weight within normal limits→ BMI
• Women: Pregnancy test prior to 1^st & last dose of study; OC pills C/I
• Drug use intended in Elders  (Age >60yrs)
• Teratogenic Drugs→ Male volunteers
• Highly toxic drugs: Patients with the concerned disease (stable) eg. Cancer

Exclusion Criteria

• H/o allergy to test drug
• H/o liver or kidney dysfunction
• H/o jaundice in the past 6 months
• Chronic diseases eg. Asthma, arthritis
• Psychiatric illness
• Chronic smoker, alcohol addiction, drug abuse
• Intake of enzyme modifying drug in the past 3 months
• Intake of OTC/Prescription drugs past 2 weeks
• HIV positive
• BA & BE studies in the past 3 months
• H/o bleeding disorder

Selection of Number of Subjects

•  The sample size is estimated by:
•  Pilot experiment
•  Previous studies
•  Published data
•  Significance level desired, usually  0.05
•  Power of the study, normally 80% or more
•  Expected deviation (Δ) from the reference product, as compatible with BE
•  If no data available, reference ratio of 0.95 (Δ = 5%) used

Study Design

• Good experimental design enhances the power of the study
• Depends on: question to be answered, nature of reference drug/ dosage form, the benefit-risk ratio
• As far as possible, the study should be of crossover design & suitably randomized
• Ideal design: Randomized two-period, two-sequence, Crossover design with an adequate washout period
• If the half-life is long: Parallel design
• For highly variable drugs: Replicate design

1. Two-Period Crossover Design
2. 2 formulations, even number of subjects, randomly divided into 2 equal groups
3. First period, each member of one group receive a single dose of the test formulation; each member of the other group receive the standard formulation
4. After a wash period (5 half-lives), in the second period, each member of the respective groups will receive an alternative formulation & the experiment will be repeated.

Parallel-Group Design

• Even the number of subjects in two groups
• Each receives a different formulation
• No washout necessary
• For drugs with a long half-life

Genetic Phenotyping

• The drug is known to be subject to genetic polymorphism
• Cross-over design→ Safety & Pharmacokinetic reasons
• All Parallel group design
• Indian population:
• Captures genetic diversity of the world
• Forms continuum of the genetic spectrum
• >1000 medically relevant genes
• Diverse patient/ volunteer pool for conducting BA & BE studies

Characteristics to be measured

• Accessible biological fluids like blood, plasma &/or serum to indicate the release of the drug substance from the drug product into the systemic circulation
• Mostly: Active drug substance
• Active / Inactive metabolite may be measured in cases of:
• The concentration of drug too low, Limitation of the analytical method, Unstable drug, Drug with a very short half-life, Pro-drugs
• Excretion of drug & its metabolites in urine→ Non-linear  kinetics

• Drugs that are not absorbed systemically from the site of application surrogate marker needed for BA & BE determination

Blood Sampling points/ Schedule

A single-dose study of an immediate release product:

•  For at least three elimination half-lives (cover >80% of AUC)
  •  Absorption phase: 3-4 points
  •  Around T_max: 3-4points
  •  During elimination: 4 points
•  Intervals not longer than the half-life of the drug
•  If urine tested, collect it for at least 7 half-lives

Parameters to be measured

• Pharmacokinetic Parameters  measured are:
•  C_max
•  T_max
•  AUC_0-t
•  AUC_0-∞

Fasting & Fed State Conditions

Fasting Conditions:

• Single-dose study:
• Overnight fast (10 hrs) and subsequent fast of 4 hrs
• Multiple-dose study:
•  Two hours fasting before and after the dose

Fed State Studies

• Required when:
•  The drug recommended with food
•  Modified release product
•  Assessment of C_max and T_max difficult with fasting state study
•  Requires consumption of high-fat food, 15 minutes before dosing
•  Provide 950-1000 kcals
•  Fat- 50%, Proteins 15-20%, Carbohydrate- 30-35%
•  Ethnic & cultural variation considered
•  Specified in protocol

  Statistical Evaluation

• C_max & AUC analyzed using ANOVA
•  T_max analyzed by non-parametric methods

To establish BE:

•  The calculated 90% CI for C_max & AUC, should fall within  range: 80-125%  (Range of Bioequivalence)
•  Non-parametric data 90% CI for T_max should lie within a clinically acceptable range

Documentation

•  Signed detailed protocol
•  Approval by Ethics Committee
•  Participant Information sheet
•  Informed Consent Form (ICF)
•  Case Record Form (CRF)
•  Undertaking by investigator
•  CV of investigator
•  Randomization chart
•  Laboratory certification
•  Analytical method validation details
•  Chromatograms of all volunteers including any aberrant ones
•  Tabulated Raw Data of volunteers

Maintenance of Records & Retention of Study Samples

•  All Records of in vivo tests on any marketed batch of a drug product should be maintained by the Sponsor

    for at least 2 years after the expiry date of the batch

• All Drug samples to be retained for a period of at least 3 years after the conduct of the study

                                         OR

    1year after the expiry of the batch [Stored in conditions consistent with the product labeling]