1. DRUG BIOAVAILABILITY Prof. Dr. Basavaraj K. Nanjwade M. Pharm., Ph. D
4/23/2017
DRUG BIOAVAILABILITY
Prof. Dr. Basavaraj K. Nanjwade M. Pharm., Ph. D
Department of Pharmaceutics
KLE University’s College of Pharmacy
BELGAUM – , Karnataka, India
Cell No;
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KLECOP, Nipani

2. Contents Introduction Objectives of bioavailability studies
Considerations in bioavailability studies
Bioavailability concept
Importance of bioavailability
Equivalent concept… Chemical, Pharmaceutical, Bioequivalence & Therapeutic equivalence.
Measurement of bioavailability
1. Pharmacokinetic method
2. Pharmacodynamic method
Measurement of Rate of absorption
1. The method of ‘Residuals’
2. Wagner Nelson Method
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3. Contents Bioequivalence studies & Its importance Introduction
FDA Determinations of Bioequivalence Main Terms
FDA Methods to Determine Bioequivalence
Bases for Determining Bioequivalence
Design And Evaluation of Bioequivalence Studies
Evaluation of the Data
Clinical importance of bioequivalence studies
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4. Introduction
The therapeutic effectiveness of a drug depends upon the ability of the dosage form to deliver the medicament to its site of action at a rate & amount sufficient to elicit the desired P’cological response.
This attribute of the dosage form is referred to as physiologic availability or bioavailability.
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5. Introduction
The term bioavailability is defined as the rate and extent of absorption of unchanged drug from its dosage form.
A rapid onset of action is desired as in the treatment of acute conditions like asthma, pain, etc.
A slower absorption is desired when aim is to prolong the duration of action.
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6. Introduction
The influence of route of administration on drug’s bioavailability is generally in the foll. order
parenteral > oral > rectal > topical
Most drugs are administered orally, for reason of stability and convenience.
The dose available to patient – Bioavailable dose.
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7. Introduction
The amount of drug that reaches the systemic circulation – systemic availability.
Bioavailable fraction (F), refers to the fraction of administered dose that enters the systemic circulation.
F = Bioavailable dose
Administered dose
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8. Objectives of bioavailability studies
It is important in
Primary stages of development of a suitable dosage form for new drug entity.
Determination of influence of excipients, patient related factors and interaction with other drugs on the efficiency of absorption.
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9. Objectives of bioavailability studies
4/23/2017
Objectives of bioavailability studies
Development of new formulations of the existing drugs.
Control of quality of a drug product during early stages of marketing (to determine the influence of processing factors, storage & stability of absorption).
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10. Considerations in bioavailability studies
Bioavailability – absolute vs. relative
Single dose vs. multiple dose
Human volunteer – healthy subject vs. patients
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11. Bioavailability – absolute vs. relative
Absolute bioavailability : when the systemic availability of the drug administered orally is determined in comparison to its i.v. administration.
Relative bioavailability : when the systemic availability of the drug administered orally is compared with that of an oral standard of the same drug.
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12. i.v. route Plasma concentration oral route Time (hours)
Plasma concentration vs. time profile of a drug ingested orally & intravenously.
i.v. route
Plasma concentration
oral route
Time (hours)
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13. Single dose vs. multiple dose
Very common & easy
Less exposure to drug & less tedious
Difficult to predict steady state
Multiple dose
Difficult to control
More exposure to drug & tedious
Time consuming
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14. Time to reach steady state
Concentration due to repeated doses
Concentration due to a single dose
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15. Single dose vs. multiple dose
Multiple dose study has several advantages like
More accurately reflects the manner in which the drug should be used.
Drugs levels are higher due to cumulative effect which makes its determination possible even by less sensitive analytical methods.
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16. Single dose vs. multiple dose
Better evaluation of the performance of controlled release formulation is possible.
Small intersubject variability is observed which allows use of fewer subjects.
Nonlinearity in pharmacokinetics, if present, can be easily detected.
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17. Human volunteer – healthy subject vs. patients
Ideally, the bioavailability study should be carried out in patients for whom the drug is intended to be used.
Advantages :
Patient is benefited from the study.
Reflects better therapeutic efficacy of drug.
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18. Human volunteer – healthy subject vs. patients
Drug absorption pattern in disease state can be evaluated.
Avoids the ethical quandary of administering drug to healthy subjects.
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19. Human volunteer – healthy subject vs. patients
There are some drawbacks of using patients as volunteers.
Stringent conditions such as fasting state required is difficult to be followed by the patients.
Studies are therefore performed in young (20-40 yrs.), healthy males adult volunteers.
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20. Human volunteer – healthy subject vs. patients
Female volunteers are used only when drugs such as oral contraceptives are to be tested.
No. of subject- extent of intersubject variability –minimum required to obtain reliable data.
They must be informed about the importance of
Study
conditions to be followed
Possible hazards if any.
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21. Human volunteer – healthy subject vs. patients
Medical examination should be performed.
Drug washout period for min. of ten biological half lives must be allowed for between two studies in same subject.
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22. Bioavailability Concept
Rate and extent at which therapeutically active drug reaches systemic circulation.
The fraction of administered dose that reaches the systemic circulation in contrast to that stated on label.
Rate & extent of absorption of unchanged drug from its dosage form.
A measure relative to some standard of rate & amount of drug ,which reaches the systemic circulation unchanged following the administration of dosage form.
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23. Why bioavailability studies…?
FDA requires that the drug product is safe
and effective.
Measure of bioavailability: AUC/dose
Absolute availability - for drugs with
approved NDA, bioavailability studies are required for new drug formulations -bioequivalence to the reference formulation
Relative availability - for drugs without full NDA, bioequivalence to the reference drug in the standard formulation
For determining safety & efficacy of drug product.
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24. Concept of Equivalents
A comparative term.
One drug product is similar with respect to a specific characters or function to another .
Defined a set of standard.
Four types …
1. Chemical
2. Pharmaceutical
3. Bioequivalence
4 .Therapeutic
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25. Concept of Equivalents
1. Chemical Equivalence
Two or more drug products which contain same amount of same active ingredient.
2. Pharmaceutical Equivalence
Identical in strength,quality,purity, content uniformity & disintegration – dissolution characters … they may differ in containing different excipient.
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26. Concept of Equivalents
3. Bioequivalence
A relative term which denotes ..the drug substance in two or more identical dosage form reaches the systemic circulation at the same relative rate & to same relative extent.
4. Therapeutic Equivalence
Two or more bioequivalent having same therapeutically active ingredient elicit pharmacological effects & can control the disease to same extent.
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27. Measurement of bioavailability
Pharmacokinetic methods ( indirect )
1. Blood analysis
2. Urinary excretion data
Pharmacodynamic methods ( direct )
1. Acute pharmacological response
2. Therapeutic response
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28. Blood analysis
Plasma level time studies or The plasma concentration – time curve or blood level curve.
A direct relationship exists concentration of drug at the site of action & concentration of drug in the plasma.
Serial blood samples are taken after drug administration & analyzed for drug concentration.
A typical blood level curve obtained after oral administration of drug.
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29. 18/11/2010
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30. Parameters determined
Pharmacokinetic parameters
Peak Plasma Concentration (Cmax)
Time of Peak concentration (tmax).
Area Under Curve (AUC)
Minimum Effective Concentration (MEC) / Minimum Inhibitory Concentration (MIC).
Maximum Safe Concentration (MSC) / Maximum Safe Dose (MSD).
Duration of action
Onset of action.
Intensity of action.
Pharmacodynamics parameters
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31. Parameters determined
AUC or Extent of absorption can be measured by 3 methods…
1.Planimeter
Instrument for mechanically measuring the area
2. Cut & weigh method
AUC is cut & weighed on analytical balance. The weight obtained is converted to proper unit by dividing it by the wt of a unit area of same paper.
3. Trapezoidal method
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32. Parameters determined
3. Trapezoidal method
AUC = ½ ( C1 + C2) (t2 – t1) + ½ (C2 + C3) (t3 – t2) +…….
½ (C n-1 + C n ) (tn – tn-1 )
C = Concentration
t = time
subscript= sample number
AUC = Area Under Curve
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33. Parameters determined
Relative bioavailability
F rel = ( AUC) drug . (Dose) standard
(AUC) standard .(Dose) drug
Absolute bioavailability
Fab = (AUC)drug . (Dose) IV
(AUC)IV . (Dose) drug
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34. Parameters determined
From the following blood data obtained after the oral administration of 50mg of drug A. calculate the AUC?
Time in hr
Plasma drug con in mcg/ml 1
5.5 2
9.2 3
14.9 4
10.3 5
7.3 6
2.2
AUC = ½ ( ) (2-1) + ½ ( ) (3-2) + ½ ( ) (4-3) ½ ( )(5-4) + ½ ( ) (6-5)
AUC = mcg/ml hr
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35. Parameters determined
The AUC of a new sustained release diclofenac sodium developed in the lab after giving in a dose of 100mg was found to be mcg/ml hr.The AUC of the standard marketed sustained release tablets of the same at the same dose was found to be mcg/ml hr. what is the the relative bioavailability of he same drug.
F rel = X 100
X 100
= or 95.77%
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36. Parameters determined
The AUC of salbutamol sulphate from a 10 mg IV dose was found to be 94.6mcg/ml hr.when the same dose was given orally, the AUC was found to be 60.5 mcg/ml hr. What is the absolute bioavailability of the drug?
Fabs = X 10
94.6 X 10
Fabs = or 63.95
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37. Urinary excretion data
The method of determination bioavailability provided that the active ingredient is excreted unchanged in the significant quantity of urine.
The cumulative amount of active drug excreted in urine is directly proportional to extent of systemic drug absorption.
The rate of drug excretion is directly proportional to rate of systemic drug absorption.
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38. Advantages
Useful when there is lack of sufficiently sensitive analytical techniques to measure concentration of drug in plasma.
Noninvasive method therefore better subject compliance.
Convenience of collecting urine samples in comparison to drawing of blood periodically.
If any case the urine drug concentration is low, assaying of larger sample volume is relatively more.
Direct measurement of bioavailability, both absolute & relative is possible without the necessity of fitting the data to the mathematical model.
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39. Advantages
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40. Advantages Bioavailability is determined by…. F = ( U ) oral . D IV
(U ) IV . D oral
U = Cumulative amt of unchanged drug excreted in
urine
D IV = IV dose
D oral = oral dose
F = absolute bioavailability
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41. Advantages When equal doses are administered Intravenously & Orally…..
F = ( U ) oral
( U ) IV
F = ( U ) test
( U ) standard
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42. Advantages
When drug A was administered IV to a group of volunteers, 80% of the 500mg dose was recovered unchanged in the urine. When the same drug was administered to the same volunteers orally.280 mg was recovered unchanged in urine. What is the absolute bioavailability of Drug A following oral administration.
Absolute bioavailability = (cumulative amt.of drug excreted)sample
(cumulative amt.of drug excreted)IV =
400
= 0.7 or 70%
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43. Acute pharmacological response
Bioavailability can be determined from the acute pharmacologic effect – time curve as well as from dose response graph.
DISADVANTAGE is that pharmacological response tends to more variable & accurate correlation between the measured response & drug available from the formulation is difficult.
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44. Therapeutic response
This method is based on the observing the clinical response to a drug formulation given to a patients suffering from disease for which it is intended to be used.
Ex …for anti inflammatory drugs, the reduction in the inflammation is determined.
The major DRAWBACK is …quantification of observed response is too improper to allow for reasonable assessment of relative bioavailability between two dosage forms of a same drug.
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45. Rate of Absorption
AUC/dose gives an average extent of bioavailability.
The rate of absorption is usually also important
for the onset of drug action.
The time of peak plasma concentration is used
often as a measure of the rate of drug absorption.
The peak plasma concentration is also an
important parameter - for keeping the drug
concentration within the therapeutic window.
Absorption can be characterized by evaluating the absorption rate constant Ka from the plasma concentration –time data.
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46. The method of ‘Residuals’
Also called as Feathering or peeling or stripping.
ASSUMPTIONS
Absorption & elimination process follows 1st order kinetics.
Absorption from the dosage form is complete.
Ka is at least five times larger than Ke
Kinetic model is
AG AB AE Ka Kc
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47. The method of ‘Residuals’
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48. The method of ‘Residuals’
This technique is used to resolve a multiexponential curve into its individual components.
For a drug that follows one compartment kinetics & administered e.v, the concentration of drug in plasma is expressed by…
C = Ka F X [ e –kEt – e –Kat ]
Vd ( Ka –KE )
If Ka F X0 / Vd ( Ka – kE ) = A, a hybrid constant then,
C = A e –kEt -A e –Kat 1 2
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49. The method of ‘Residuals’
During the elimination phase, when the absorption is almost over, Ka > > KE & the value of second exponential e –Kat approaches zero whereas the 1st exponential e –kEt retains some finite value….at this time the equation is
C = A e –kEt in log form
log C = log A – KEt/ 2.303
Where C is the back extrapolated plasma concentration value.
A plot of log C versus t yields a biexponential curve with a terminal linear phase having slope KE/ 3 4
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50. The method of ‘Residuals’
Back extrapolation of this straight line to zero yields y-intercept equal to log A.
Subtraction of true plasma concentration values that is equation 2 from the extrapolated plasma concentration values that is equation 3 yields a series of residual concentration values Cr
( C - C ) = Cr = A e –Kat ,
in log form the equation is :
log Cr = log A - Kat/ 2.303
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51. The method of ‘Residuals’
A plot of logCr versus t yields a straight line with slope –Ka / & y intercept log A.
Absorption half life can be computed from Ka using the relation 0.693/Ka …thus the method of residual enables resolution of the biexponential plasma level time curve into its exponential components.
The technique works best when the difference between Ka & KE is large ( Ka >= 3)
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52. Wagner Nelson Method ASSUMPTIONS
The body behaves as a single homogenous compartment.
Drug elimination obeys 1st order kinetics.
DISADVANTAGES
The absorption & elimination processes can be quite similar & still accurate determination of Ka can not be made.
The absorption process doesn’t have to be 1st order.
The kinetics of absorption may be zero order, mixed order, mixed zero order & 1st order or even more complex.
This method involves determination of Ka from percent absorbed –time plot & does not require the assumption of zero .
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53. Wagner Nelson Method
The amount of drug in the body X & the amt of drug eliminated in the body XE thus :
XA = X + XE
If the amt of drug in the body is X = V.dC…the amt of drug eliminated at any time t can be calculated as ..
XE = KE Vd ( AUC)to
Substitution of values of X & XE in above equation…
XA = Vd C + KE Vd ( AUC)to
from this equation we can get the value for drug absorbed in to the systemic circulation from time zero to
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54. Wagner Nelson Method
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55. BIOEQUIVALENCE STUDIES & ITS IMPORTANCE
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56. BIOEQUIVALENCE STUDIES
Bioavailability & bioequivalence data is required to be furnished with application of new drugs, as required under schedule Y, depending upon the type of application being submitted.
Both bioavailability & bioequivalence focus on release of drug substance from its dosage form & subsequent absorption into systemic circulation.
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57. Several test methods are available to asses equivalence, including;
Comparative bioequivalence studies, in which the active drug substance or one or more metabolites is measured in accessible biological fluid such as plasma, blood or urine.
Comparatives pharmacodynamic studies in humans
Comparative clinical trials
In-vitro dissolution tests
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58. FDA Determinations of Bioequivalence Main Terms
Pharmaceutical equivalents
Pharmaceutical alternatives
Therapeutic equivalents
Bioequivalence
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59. Pharmaceutical Equivalents
4/23/2017
Pharmaceutical Equivalents
Drug products are considered pharmaceutical equivalents if they contain the same active ingredient (s), have the same dosage form and route of administration, and are identical in strength or concentration
Equivalent products contain the same amount of ingredient in the same dosage form but may differ in characteristics, such as shape, release mechanisms, and packaging
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60. Pharmaceutical Alternatives
Drug products are considered pharmaceutical alternatives if they contain the same therapeutic moiety, are different salts, esters, or complexes of the same moiety, are different dosage forms, or are different strengths
Other pharmaceutical alternatives
Different dosage forms and strengths within a single product line by a single manufacturer
Extended-release formulations when compared with immediate- or standard-release formulations
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61. Therapeutic Equivalents
Drug products are considered therapeutic equivalents if they are all of the following
Pharmaceutical equivalents
Bioequivalent
Approved as safe and effective
Adequately labeled
Manufactured in compliance with current Good Manufacturing Practice regulations
Therapeutic equivalents are expected to have the same clinical effect and safety profile
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62. Bioequivalence
Bioequivalence of a drug product is achieved if its extent & rate of absorption are not statistically significantly different from those of the reference product when administered at the same molar dose.
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63. FDA Methods to Determine Bioequivalence
Generic drug manufacturers must demonstrate that a drug is bioequivalent to a reference drug product
In order of FDA preference, methods used to define bioequivalence
Pharmacokinetic studies
Pharmacodynamic studies
Comparative clinical trials
In vitro studies
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64. Important PK parameters
Cmax:
the observed maximum concentration of a drug
 measure of the rate of absorption
tmax:
time at which Cmax is observed
 measure of the rate of absorption
AUC:
area under the concentration-time curve
 measure of the extent of absorption
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65. Different approach for establishing equivalence
Studies
Different approach for
establishing equivalence
PD studies
clinical
studies
in vitro
methods
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66. Methods for Assessing Bioavailability & Bioequivalence
Plasma Drug Concentration:-
The time for peak plasma (blood) concentration (tmax)
The peak plasma drug concentration (cmax)
The area under the plasma drug concentration versus time curve (AUC)
Contd…
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67. Plasma concentration time profile
Cmax
AUC
Tmax
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68. Urinary Drug Excretion:-
Cumulative amount of drug excreted in the urine (Du)
The rate of drug excretion in the urine (dDu/dt)
The time for maximum urinary excretion (t)
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69. Acute pharmacodynamic effect:- Max. pharmacodynamic effect (Emax)
Time for max. pharmacodynamic effect
3. Area under pharmacodynamic effect versus time curve
4. Onset time for pharmacodynamic effect
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70. Clinical observations Well controlled clinical trials In-Vitro studies
Drug dissolution.
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71. Area Under Curve:-
AUC is the measurement of the extent of the drug bioavailability. It is the area under the drug plasma level-time curve from t =0 & t = ∞, and is equal to the amount of unchanged drug reaching the general circulation divided clearance
[ AUC]0∞ = ∫0∞Cpdt
[ AUC]0∞ = FD = FDO/ kVD
Clearance
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72. Where F = fraction of dose absorbed
Do = dose, k = elimination rate constant,
VD = volume of distribution
AUC is independent of route of administration and process of drug elimination as long as the elimination process don’t change.
The AUC can be determined by numerical integration procedure such as trapezoidal rule method. The units for AUC are concentration time ( μg hr/ml)
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73. For many drugs, AUC is directly proportional to the dose, for eg
For many drugs, AUC is directly proportional to the dose, for eg. If a single dose of drug is increased from mg the AUC will also show a four fold increase fig
Plasma level time curve following administration of single doses of (A)250mg, (B)500mg & (C)1000mg of drug.
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74. Linear relationship between AUC & dose
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75. Relationship between AUC & dose when metabolism is saturable.
In some cases the AUC is not directly proportional to the administered dose for all dosage levels, for eg. As the dosage of the drug is increased, one of the pathway for drug elimination becomes saturated, fig
Relationship between AUC & dose when metabolism is saturable.
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76. Drug elimination includes metabolism and excretion.
for drugs such as salicylates and phenytoin continuous increase of dose causes saturation of one of the enzyme pathway for drug metabolism and consequent prolongation of elimination of half life.
The AUC thus increases disproportionally to the increase in dose because smaller amount of drug is being eliminated.
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77. When AUC is not directly proportional to the dose, bioavailability of the drug is difficult to evaluate because drug kinetics may be dose dependent.
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78. Urinary Drug Excretion Data
It is an indirect method for estimating bioavailability.
The drug must be excreted in significant quantities as unchanged drug in the urine, timely urine samples must be collected and total amount of urinary excretion must be obtained.
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79. Each urine specimen is analyzed for free drug with a specific assay.
Du∞:-
The cumulative amount of drug excreted in the urine, Du∞ is directly related to total amount of drug absorbed. Experimentally, urine samples are collected periodically after administration of the drug product.
Each urine specimen is analyzed for free drug with a specific assay.
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80. Graph is plotted between cumulative drug excreted to the collection time interval.
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81. The relationship between cumulative amount of drug excreted in urine and plasma level time curve is shown in fig.,
( 1)
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82. When the drug is almost completely eliminated (point c), the plasma concentration approaches zero and maximum amount of the drug excreted in the urine, Du∞ is obtained
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83. dDu/dt
Because most drugs are eliminated by first order rate process, the rate of drug excretion is dependent on first order elimination rate constant k and the concentration of drug in the plasma Cp.
In fig, the maximum rate of drug excretion would be at point B, the minimum rate of drug excretion would be at point A and C.
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84. (2)
Graph comparing rate of drug excretion w.r. to time should be similar in shape as the plasma level- time curve for that drug.
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85. t∞ :-
it is the total time for the drug to be excreted. In fig 1 & 2, slope of curve segment A-B is related to the rate of drug absorption, whereas point C is related to the total time required after drug administration for the drug to be absorbed and completely excreted ( t = ∞).
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86. Acute Pharmacodynamic effect
An Acute Pharmacodynamic effect such as an effect on pupil diameter, heart rate, or B.P can be used as an index of drug bioavailability.
In this case, an acute pharmacodynamic effect- time curve is constructed. Measurement of pharmacodynamic effect should be made with sufficient frequency to permit a reasonable estimate of the total AUC for a time period at least three times a half life of the drug.
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87. In this to determine bioavailability requires demonstration of a dose related response.
Bioavailability is determined by characterization of dose-response curve.
PD parameters that are obtained include total area under the acute PD effect- time curve, peak PD effect, & time for peak PD effect.
onset time & duration of PK effect may also be included in the analysis of data.
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88. Clinical Observations
Well-controlled clinical trials in humans that establish the safety & effectiveness of the drug product.
This approach is least accurate, least sensitive & least reproducible of the general approaches for determining in-vivo bioavailability.
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89. The FDA only consider this approach when analytical methods are not available to permit use of one of the approaches described above.
An E.g. of this approach is for the determination of bioequivalence of two topical antifungal products by different mfgs. Containing the same active antifungal agent (ketoconazole)
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90. In-Vitro Studies
Under certain conditions give an indication of drug bioavailability. Ideally, in-vitro dissolution rate should correlate with in-vivo drug bioavailability.
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91. Bases for Determining Bioequivalence
Bioequivalence is established if the in-vivo bioavailability of a test drug product (Generic product) does not differ significantly in the products rate & extent of drug absorption, as determined by comparison of measured parameters (eg, concentration of active drug ingredient in blood, urinary excretion rate, or PD effects), from that of the reference material (Brand name product).
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92. Design And Evaluation of Bioequivalence Studies
Bioequivalence studies are performed to compare bioavailability of generic drug product to the brand name product.
Design and evaluation of bioequivalence studies requires comparative inputs from; PKs, statisticians, clinicians, bioanalytical chemist, & others.
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93. 18/11/2010
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94. Basic design for BE is determined by ;
The scientific questions to be answered,
The nature of reference material & dosage form to be tested,
The availability of analytical methods,
Benefit-risk considerations with regards to testing in humans.
For some generic drugs, FDA offers general guidelines for conducting these studies.
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95. The publication addresses three specific aspects, including;
Eg, “Statistical procedure for bioequivalence studies using a standard two-treatment crossover design”
The publication addresses three specific aspects, including;
Logarithmic transformation of PK data,
Sequence effect
Outlier consideration.
With such guidelines, the principal investigator should prepare a detailed Protocol for the study.
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96. Both single &/or a multiple dose (steady state) study required.
For bioequivalence studies, both test & reference drug formulations contain pharmaceutical equivalent drug in the same dose strength, in similar dosage forms (immediate release or controlled release), & both are given by the same route of administration.
Both single &/or a multiple dose (steady state) study required.
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97. Generally study is performed in normal, healthy male volunteers.
Prior to initiation of the study, the Institutional Review Board (IRB) of the clinical facility in which the study is to be performed must approve the study.
Generally study is performed in normal, healthy male volunteers.
The number of subjects depend upon the expected intersubject variability.
The subject is generally fasted 10 to 12 hrs (overnight) prior to drug administration & may continue to fast for 2 to 4 hr period after dosing.
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98. Reference standard
Before beginning an in-vivo bioequivalence study, the total content of active drug substance in the Test product must be within 5% of reference product.
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99. Study Design
The FDA, Division of Bioequivalence, Office of Generic Drugs provides a guidance for the performance of In-vitro dissolution & in-vivo bioequivalence studies.
Currently, three different studies may be required for solid oral dosage forms, including;
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100. Food intervention study Multiple dose (steady state) Fasting study:-
Bioequivalence studies are evaluated by single dose, two-period, two-treatment, two-sequence, open label, randomized crossover design comparing equal doses of the test and reference products in fasted, adult, healthy subjects.
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101. Both male and female subjects used in the study.
This study required for all immediate release and modified release oral dosage forms.
Both male and female subjects used in the study.
Blood sampling is performed just prior (zero time) to the dose and at appropriate intervals after the dose to obtain an adequate plasma-drug concentration versus time profile.
No other medication is normally given to subject for atleast one week prior to the study.
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102. Food intervention study:-
This study is single dose, randomized, three-treatment, three-period, six-segments, crossover, limited food effect study comparing equal dosage of the test product given under fasting conditions with those of the test and reference products given immediately after a standard high fat content breakfast.
For eg. Ibuprofen
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103. Multiple dose ( steady state study ):-
A multiple dose steady state, randomized, two-treatment, two-way, crossover study comparing equal dosage of the test and reference products in the adult, healthy subject is required for the oral extended release (controlled release) drug products in addition to a single dose fasting study and food intervention study.
Three consecutive trough concentrations (Cmin) on three consecutive days should be determined to ascertain that the subjects are at steady state.
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104. Blood sampling is performed similarly to the single dose study.
The last morning dose is given to the subject after an overnight fast with continuous fasting for atleast two hours following dose administration.
Blood sampling is performed similarly to the single dose study.
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105. Crossover Designs
Subjects who meet the inclusion and exclusion study criteria and have given informed consent are selected at random.
Each subject recieves the test drug product and the reference product.
E.g. of Latin square crossover design for a bioequivalence study In human volunteers, comparing three different drug formulations (A, B, C) are described in tables
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106. Crossover Designs Subject Drug Product Study period 1 Study period 2A B C 2 3 4 5 6
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107. The Latin square design plans the clinical trial so that each subjects receives each drug product only once, with adequate time between medications for the elimination of drug from the body.
In this design, each subject is his own control, and subject-to-subject variation is reduced.
The variation due to sequence, period and treatment (formulation) are reduced, so that all patients don’t receive the same drug product on the same day and in the same order
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108. Possible carry-over effect from any particular drug product are minimized by changing the sequence in which the drug products are given to the subjects as in the table.
This Latin square design for bioequivalence study of 4 drug products in 16 volunteers may also be performed.
After each subject recieves the drug product, blood samples are collected at the appropriate time intervals so that valid blood drug level-time curve is obtained.
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109. In some cases the measurement of drug in urine may be necessary.
The time intervals should be spaced so that peak blood concentration, total AUC, and the absorption and the elimination phases of the curve may be well described.
In some cases the measurement of drug in urine may be necessary.
Period refers to the time period in which study is performed.
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110. A two period study, referred to as two legged study, means that the study is performed on two different days (time periods) seperated by a wash out period during which most of drug has been eliminated from the body- generally 10 elimination half lives.
A sequence refers to the number of different orders in the treatment groups in a study.
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111. E.g. two-sequence, two-period study designed as follows:-
Period Period 2
Sequence T R
Sequence R T
R = reference , T = treatment
As shown in the table
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112. Evaluation of the Data Analytical method:-
The method for measurement of the drug must be validated for accuracy, precision, sensitivity, and specificity.
Data should be presented in tabulated and graphical form for evaluation.
The plasma drug conc. Versus time curve for each drug product and each subject should be available.
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113. Pharmacokinetic evaluation of the data:-
For single dose studies, including fasting study or food intervention study, the PK analyse include calculation for each subject of the AUC to the last quantifiable concentration (AUC0-t) and to infinity (AUC0-∞), Tmax and Cmax.
Elimination rate constant k, elimination half life t ½ may be estimated.
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114. Statistical evaluation of the data:-
To prove bio-equivalence, there must be no statistical difference between the bioavailability of test product and reference product.
Statistical approaches assume that the data are distributed according normal distribution or bell shaped curve.
The log transformation of the bioavailability data (Cmax, AUC) is performed prior to statistical data evaluation for bioequivalence determination.
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115. Analysis of variance (ANOVA):-
It is a statistical procedure used to test the data for difference within and between treatment and controlled groups. The ANOVA may evaluate variability in subjects, treatment groups, study periods, formulation and other variables depending on study design.
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116. One sided tests procedure:-
This is also referred as confidence interval approach.
This method is used to demonstrate if the bioavailability of the drug from the test formulation is too low or high in comparison to the reference drug.
For a single dose, fasting study, analysis of variance (ANOVA) is usually performed on the log-transformed AUC and Cmax. There should be no statistical difference between mean AUC and Cmax parameters for the test (generic) and refernce drug products.
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117. In addition, 90% confidence intervals about the ratio of the mean for AUC and Cmax values of the test drug should not be less than 0.80 (80%) nor greater than 1.25 (125%) of the reference product based on log-transformed data.
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118. Clinical importance of bioequivalence studies
Bioequivalence of different formulations of the same drug substance involves equivalence with respect to the rate and extent of systemic absorption.
Generally two formulations whose rate and extent of absorption differ by 20% or less are considered bioequivalent
When a therapeutic objectives of the drug are considered, an equivalent clinical response should be obtained from the comparison dosage form if the plasma drug concentration remain above MEC for appropriate interval and don’t reach the MTC.
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119. Clinical importance of bioequivalence studies
Bioequivalence studies should be conducted for the comparison of two medicinal products containing the same active substance.
Two products marketed by different licensees, containing same active ingredient(s), must be shown to be therapeutically equivalent to one another in order to be considered interchangeable.
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120. Special concerns in bioavailability & bioequivalence studies.
The bioequivalence determination of the drugs that are not absorbed systemically form the site of application is difficult to assess. For this non-systemic absorbable drugs surrogate marker is needed for the bioequivalence determination
Possible surrogate markers for bioequivalence studies are given in table.
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121. Possible surrogate marker for bioequivalence
Drug product
Drug
Possible surrogate marker for bioequivalence
MDI
Albuterol
FEV1
Topical steroid
Hydrocortisone
Skin blanching
Anion exchange resin
cholestryamine
Binding to bile acids
Antacids
Mg and Al hydroxide gel
Neutraliztion of acid
Topical antifungal
ketoconazole
Drug uptake into stratum corneum
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122. Reference standard
Before beginning an in-vivo bioequivalence study, the total content of active drug substance in the Test product must be within 5% of reference product.
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123. References
Dissolution, bioavailability & bioequivalence – Hamed M. Abdou, Mack publishing company, Pg.no
Biopharmaceutics & pharmacokinetics – D.M.Bramhankar, S.B.Jaiswal, Pg.no
Biopharmaceutics & pharmacokinetics – Robert E. Notari, 2nd edition, Marcel Dekker.
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124. References
“Applied Biopharmaceutics & pharmacokinetics”, Leon Shargel & Andrew B.C.
Leon Shargel, Andrew Yu; “Applied biopharmaceutics & Pharmacokinetics”, 4th edition
Peter G. Welling, Francis L.S. Tse; “Pharmaceutical Bioequivalence”, Vol 48, Dekker Series.
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125. E-mail: bknanjwade@yahoo.co.in
THANK YOU
Cell No:
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KLECOP, Nipani