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`The effect of food ahd
`
`gastrointestinal residehoe
`oh drug absorptioh:
`case studies which merit
`
`the /h vivo study of dosage form
`behavior ahd its reiatiohship
`to oral drug absorptioh
`
`George A. DIGENIS and Erik P. SAND: _
`
`Capsugel
`
`i
`
`Dr. Falk Ex. 2033
`GeneriCo v. Dr. Falk IPR2016-00297
`Page 1
`
`

`
`The effect of food and gastrointestinal
`residence on drug absorption:
`case studies which merit the in vivo study
`of dosage form behavior and its relationship
`to oral drug absorption
`
`George A. DIGENIS and Erik P. SANDEFER
`
`Division of Medicinal Chemistry and Pharmaceutics,
`College of Pharmacy University of Kentucky, Lexington, KY 40536~0082
`(606)257-1970; FAX (606)257-7585
`
`Contents
`
`introduction ........................................... ..2
`
`.Case Study 1: The effect of variable gastric emp-
`tying on the oral bioavailabllity of an acid-labile
`compound ............. ..' ............................... ..8
`
`. Case Study 2: An enteric coated mu/tr’/oarticulate
`of erythromycin and diminished absorption with
`food intake after close administration .......... ..4
`
`'
`
`. Case Study 3: An enteric coated erythromycin
`tablet and the effect of food intake after dose
`administration ........................................ ,.7
`
`. Case Study 4: The effect of pre—dose food
`consumption on the onset of acetaminophen ab-
`sorption from an enterlc coated tablet.
`
`. Case Study 5: The effect of an efiervescing exci-
`pient (sodium acid pyrophosphate) on intestinal
`transit and ranitidine absorption ................ ..iO
`
`. Case Study 6: The influence of gastric emptying
`time and the gastrointestinal site of absorption
`on the bioavaiiabiiity of a poorly soluble drug...t1
`
`. Case Study 7: intestinal transit changes obser-
`ved from an enteric formulation containing
`absorption enhancers and an acid—labilo. low-
`permeability cephaiosporin ...................... ..l 4 .
`
`8. Summary .............................................. ..1?
`
`9. References ........................................... ..18
`
`Introduction
`
`Over the last twenty years, we have observed
`instances where food and/or specific dosage for
`mutations have profoundly affected gastrointestinal
`transit and oral drug absorption. in some instances
`we have shown that variations in gastrointestinal
`transit have proportionally altered oral bioavaiiability
`of compounds known to exhibit large inter— and in-
`_tra—subject variability. Thus, the ability to evaluate
`the in vivo gastrointestinal behavior of pharmaceuti-
`cal dosage forms and correlate this character to re-
`sulting drug levels ultimately provides a valuable ba-
`sis for the rational design of drug delivery systems
`as well as a means to explain apparent drug ab-
`sorption anomalies. To study this relationship, the
`techniques of external gamma scintigraphy have
`provided a noninvasive method to quantitate gas-
`trointestinal transit and also to assess the in vlvo
`condition of the drug delivery system.
`
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`
`The effects of food on drug absorption have
`been well documented in the literature (1 .2). howe-
`ver, few studies have attempted to systematically
`identity the causal agents to explain altered oral bio-
`availability. Indeed, many factors may influence oral
`drug absorption. A partial listing of these factors in-
`clude the intimate interaction of the following; at
`gastrointestinal physiology and residence of the
`drug at its site of absorption. b) chemical nature of
`food nutrients (e.g. caloric value, amount of fats,
`carbohydrates, protein and fiber) and the timing of
`the meat‘ relative to dose administration, c) chemical
`and physical properties of the drug and d) formula-
`tion factors which affect the in vivo rate and gas-
`trointestinal site ot drug release from its delivery sys-
`term.
`
`The following communication will describe some
`of our findings in the format of case studies. Our in-
`tent is to demonstrate the need to methodically
`study the factors which etiect oral drug absorption
`by combining the techniques of external gamma
`scintigraphy with conventional pharmacoklnetics.
`By making these in vivo / in viva correlations, this
`knowledge will contribute towards the design of
`drug delivery systems which perform consistently
`and predictably and will ultimately advance drug
`therapies.
`
`1. Case study 1: the effect of
`variable gastric emptying on the
`oral bioavailability of an acid-labile
`compound
`
`This first case study demonstrates the influence
`of gastric residence on the oral bioavailability ofan
`acid sensitive compound. It also shows that intra-
`subject changes in drug absorption can be explai-
`ned by the day-to-day variations in gastric emp-
`tying.
`
`Solutions of the acid—|abile monomer of polyvinyl-
`pyrrolidone, N-vinyl pyrrolidinone (NVP), were orally
`administered to fasted beagles at doses of 5, 10
`and 20 mg/kg. Plasma levels of NVP were extre-
`mely erratic as indicated by the Cmax of the 5
`mg/kg dose being greater in some instances than
`the Cmax of the 20 mg/kg close. Because of the
`acid sensitivity of NVP,
`it was shown that slow gas-
`tric emptying maniiested in poor NVP absorption,
`and when gastric emptying was rapid, NVP absorp-
`tion was maximized (E). This is demonstrated gra-
`phically in Figure 1
`for beagle 3487 given a
`
`20 mg/Kg dose on three separate occasions. The
`top graph in Figure 1 shows that when gastric emp-
`tying was slow, NVP levels were low, and when
`gastric emptying was rapid as shown in the bottom
`graph of Figure 1, N\/P levels were greatest.
`The results from this study demonstrated the
`need to monitor gastrointestinal transit when mea-
`suring the bioavailbility of an acid labile compound.
`
`A'f.'i:%3J."§'.-v‘m‘:«7!gi:aseat
`
`Figure 7. intrasubject correlations {Beagle #3487).
`Three modes of gastric emptying and the corres-
`ponding NVP plasma levels (20 mg/irg).
`
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`2. Case study 2: an enteric coated
`multiparticulate of erythromycin
`and diminished absorption with
`food intake after dose
`administration
`
`Though we have frequently used this study as an
`example in several symposia and publications,
`it still
`provides a powerful illustration regarding the effect
`of food on gastrointestinal transit and absorption of
`erythromycin from an enteric coated multiparticulate.
`Briefly, this study investigated a marketed erythro-
`mycin product (Eryc|@ 250 mg, Parl<e—Davis) adminis-
`tered under tasted and non—fasted conditions. An ex-
`tremely important distinction in dosing regimen
`between this study and others which have previously
`evaluated gastrointestinal transit (4) was that the fed
`condition was achieved 30 min after drug dose,
`thus. the dosage was actually swallowed while the
`subjects were still under a fasted condition. The ma-
`jority of studies which have examined the effect of
`food on gastrointestinal transit have given the do-
`sage form on a full stomach with food typically inges-
`ted 30 min before drug dose. Additionally, the stan-
`dard breakfast meal used in this study was high in
`carbohydrate and relatively low in fat (765 cal, 183 g
`carbohydrate, 21 g protein and 18 g fat).
`The manufacture of similar enteric beads and in
`vitro testing after neutron activation has previously
`been reported (5). The in vivo study has also been
`described in the literature in the form of an abstract
`(6), a research article (7), and in a review article
`which described the uses of neutron activation and
`gamma scintigraphy (8). This particular dosage form
`was radiolabeled with samariurn-153 (y : 103 keV,
`tr/2 = 46.7 hr) and only five radiolabeled beads were
`in each unit dose; the remainder was unadulterated
`ERYCE’, thus, by radiolabeling only a few of the
`beads we were able to determine the gastrointesti-
`nal site of bead disintegration and drug release.
`
`The results of this study showed striking diffe-
`rences in the plasma concentration curves of ery-
`thromycin between the fasted and fed condition. All
`subjects showed earlier Tm and lower Cm when
`the enteric formulation was administered under this
`fed dosing regimen where food intake was 30 min
`post drug close. To summarize these differences,
`the area under the concentration curves are expres-
`sed as a bar graph shown in Figure 2. Without ex-
`ception, all subjects showed a decrease in AUG in
`the fed condition, and the mean for the fed condi-
`V tion was approximately 50% of the fasted study.
`
`
`
`Hmtart;i‘€*§.i‘!.2:§
`
`Figure 2. AUC‘s following oral administration of 250
`mg E—mycin from enteric coated muitiparticulate
`(Eryc, Parke—Davis).
`
`We were initially inclined to explain reduced bio-
`availability in the fed condition due to an initial tran-
`sient rise in gastric pH which occurs with food in-
`take. This in turn may compromise the integrity of
`the enteric coating. We conjectured that as the sto-
`mach became more acidic again, a percentage of
`the erythromycin was hydrolyzed, thus, the bioavai-
`lability in the fed condition should inherently be less
`than the fasted condition. However, the results from
`analyzing the scintigraphic images showed a far dif-
`ferent outcome. lt was evident that some subjects
`emptied the enteric multiparticulates even before
`the meal was ingested at 30 min post close (e.g.
`subjects 2, 3, 5, 6. Figure SA), thus, the enteric coa-
`ting was not exposed to the transient pH rise for
`these subjects, yet these individuals still showed re-
`duced AUC's, in the fed condition. Most dramatic
`from the scintigraphic analysis was the rapid transit
`of intact beads through the proximal small intestine
`in the fed condition as compared to the fasted
`condition. Because of this rapid transit, enteric coa-
`ting dissolution and drug release occurred more dis-
`tal in the small intestine for the fed study as compa-
`red to the site of release for the fasted condition.
`The gastric emptying (GE) and small intestine transit
`time (SITU results are depicted graphically for indivi-
`dual subjects in Figure 3. The figure to the left
`shows that gastric emptying was not effected by a
`meal at 30 min post dose, however, small intestine
`transit was alwaysfaster in the fed study.
`
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`Figure 3. Individual gastric emptying (A) and small intestine transit (B) of '“Srn-/abe/ed ERYC“ beads
`administered under fasted and fed condition.
`
`The physiologic cause for this change in small in-
`testine transit warrants further investigation since
`these results and conclusions are contradictory to
`that which is published in the pharmaceutical litera-
`ture, l.e., food does not change the small intestinal
`transit time of pharmaceutical dosage forms (4) at
`least when food is ingested 30 min before drug
`dose. it is our opinion that food may not affect the
`absolute transit time from pylorus to cecum, but the
`manner in which it transits the small intestine can be
`very different.
`
`The most straight forward explanation based on
`these data is that the intake of food at 30 min post
`close resulted in a teedforwarcl mechanism inducing
`increased small intestine motility. Because of this in-
`creased motility, conlents already present in the
`small intestine were pushed rapidly towards the co—
`ion where absorption of erythromycin is less effi-
`cient. lncreased motility is certainly a well documen-
`ted phenomenon with regard to the gastrocolonic
`response following food intake where there is tre-
`quenfly an urge to defecate following a meal. l-lowe-
`
`ver, the regulatory mechanisms which control gut
`function are numerous and other explanations are
`possible (9).
`it is also conceivable that the induced
`intestinal transit and apparent rapid gastric emp-
`tying was due to an anticipatory response to lee-
`ding (10).
`
`it is reasonable that other delayed or sustained
`release formulations may be susceptible to altered
`oral absorption when administered under this parti-
`cular dosing regimen for drugs not absorbed throu-
`ghout the gastrointestinal tract or if the drug. like
`erythromycin. is poorly absorbed by the oral route
`(50% or less oral bioavailability). Regardless of the
`physiologic reasons for this phenomenon, there are
`instances where therapeutic drug levels are not
`achieved when particular delivery systems are used
`as the following example will describe.
`
`As a point of completeness, the individual ery-
`thromycin concentration curves are included in
`Figure 4.
`
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`
`v w:v:<:\\'1'!« 4.. L.{..A ..
` m'
`
`A ..._...as.
`i“«—v-.
`‘er
`
`:w*.'s.%;°»“;‘YE~.‘l"1~
`fiéxfsr
`
`in --»—~ .94
`‘r-—- "W 5%
`
`Figure 4.’ Individual and mean E-rnycin concentrafion/time curves following 250 mg dose from an enteric—
`coated mu/tiparticulate (ERYCTM): fasted vs fed.
`.
`
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`Q
`
`Figure 5. E~mycin enteric coated tablet (250 mg free base: fasted vs fed) individual and mean E-mycin
`concentrat/on/time curves.
`-
`
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`
`3. Case study 3: an enteric coated
`erythromycin tablet and the effect
`of food intake after close
`administration
`
`The preceding study encouraged us to examine
`if enteric coated tablets are susceptible to similar
`food effects when a standard breakfast meal is in-
`gested 30 min after drug administration. To test
`this, a mared erythromycin (250 mg) tablet was
`chosen, and administered to four subjects in a two-
`wav complete cross-over study under the fasted
`and fed condition. The exact dosing regimen was
`used with an identical standard breakfast meal
`consumed at 80 min post close. Three of the four
`subjects were also in the preceding ERYC” study.
`The results of this study are shown in Figure 5.
`The mean data shows the typical "|eft shift" of the
`curve for this particular fed condition as indicated
`by an earlier Tmax. This observation was consistent
`with the results from the multiparticulate study des-
`cribed in case study 2. Though the mean data indi-
`cated that the dosage form was efficacious and
`adequate blood levels were achieved (MlC =
`0.10 jig/mL), the individual plasma concentration
`profiles indicated a far different result. The enteric
`tablet was not able to provide therapeutic blood le-
`vels when administered under the fed condition to
`subjects 007-RJM and OO8—STE.
`The reason for this failure was obvious upon ana-
`lysis of the scintigraphic images. Subject O07-RJl\/I
`showed gastric emptying of the tablet at 16 min
`post dose. and when this subject ate at 30 min post
`dose, scintigraphic imaging revealed that the intact
`enteric tablet rapidly moved through the small bo-
`wel and reached the cecum at 40 min post close.
`The tablet was later observed to transit to the trans-
`verse colon by 2 hr post close and tablet disintegra-
`tion was noted at 5 hr. This rapid transit was confir-
`med by defecation of the radioactivity at 5.5 hr post
`dose. Subject O08-STE showed similar results with
`gastric emptying of the tablet actually occurring
`while the subject was still eating the breakfast meal
`at 44 min post dose. This was followed by rapid
`transit of the intact tablet to the ascending colon at
`T60 min where the enteric coated tablet was obser-
`ved to have disintegrated. However. it should also
`be noted that subject O01-WRB showed improved
`erythromycin plasma levels under the fed condition.
`This was apparently due to very rapid enteric poly-
`mer dissolution and tablet disintegration in the early
`small intestine as indicated by tho scintigraphic
`images.
`
`Nonetheless, as with the example given in Case
`Study 2, peristalsis of the small intestine is apica-
`reinduced when food is consumed at 30 rndose.
`This increased motility in turn affects the transit time
`of the dosage form through the optimal absorptive
`regions which results in lower erythromycin plasma
`levels. The observation of dosage form failure occu-
`ring in two of the four subjects suggests that the
`single unit enteric tablet may perform less consis-
`tently than its multiparticulate counterpart.
`
`We have not yet mentioned that radlolabeled pla-
`cebo pellets in a capsule (3 mm, density 2.0 g/mL)
`were coadministered with the erythromycin tablet so
`that a direct comparison between the gastrointesti-
`nal transit of a single unit dose versus a multiparti-
`culate dosage form could be made. Consistent with
`results in Case Study 2, the placebo pellets reached
`the cecum earlier in the fed study as compared to
`the fasted study. however, it was apparent that
`some of the pellets were still in the distal small in-
`testine of subjects O07-RJM and O08-STE whilst
`the tablet hadalready entered the colon. The pre-
`mature arrival the erythromycin tablet before the
`placebo pellets may or may not be formulation de-
`pendent; more studies are needed to reach a defini-
`tive conclusion regarding this. However, the present
`observation tends to support the idea that consis-
`tent and predictable drug delivery is more easily
`achieved with a multiparticulate enteric formulation
`when the intended site of drug release is the small
`intestine.
`
`4. Case study 4: the effect of
`pre-dose food consumption
`on the onset-of acetaminophen
`absorption from an enteric
`coated tablet
`
`This fourth case study represents a more com-
`mon dosing schedule where food was consumed
`30 min before dose administration. The original ob-
`jective of this investigation was to determine the site
`of drug delivery of an enteric coated tablet designed
`to release in the proximal small intestine. Each ta-
`blet contained two drug markers and was radiois-
`beled with neutron activated samarium—i 53 oxide.
`Acetaminophen (325 mg) was used as marker of
`drugs absorbed throughout the small intestine (and
`probably the colon, too), and riboflavin (30 mg) was
`used to indicate the efficacy of drug release in the
`proximal small intestine. A complete cross-over
`study was conducted in six subjects under fed and
`
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`

`
`a’:’EtFx:r_§:j:w<
`
`.. vN':¢1~t:'*\:g‘_4=;»m:....",.......“».-.~.sa»—~
`
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`Wfihiztt xkxwsatsrispéme
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`
`
`E-smi.-m‘..=s;:.t«*t-‘schas*='
`
`Figure 6. Individual APAP levels from an enteric coated tablet (325 mg APAP) in fasted and fed (30 min
`before dose) volunteers. GE = Gastric Emptying,‘ Dis/nt : Tablet Disintegration,
`
`fasted conditions and two additional subjects were
`administered an uncoated tablet to serve as
`controls_(11). The standard meal was consumed
`80 min before drug dose and was high in fat (1080
`calories, i1B'g carbohydrate, 88 g protein, 134 g
`tat); no other food was ingested until it was confir-
`med that the tablet was out of the stomach.
`
`The purpose of providing this case study is to
`demonstrate the well known incidence of prolonged
`gastric residence of large single unit doses in the
`prodose fed stomach, and also to make compari-
`sons between the results seen in case studies
`2 and 3 where food was consumed 30 min atter
`drug dose. For the purpose of this communication,
`only acetaminophen serum levels will be described
`tor the enterio coated tablet. These are shown in
`Figure 6.
`
`During the actual data acquisition of this study, it
`was obvious that gastric residence was extremely
`long in some subjects. The original study protocol
`designated blood sampling times at O, 1, 1.5, 2, 3,
`4, 6, 8 and 20 hr which were certainty adequate for
`the tasted condition. However, it became quite ap—
`parent with subjects dosed in the fed condition that
`it the sampling times were not modiiied during the
`acquisition period, then some subjects probably
`would show zero absorption through 8 hr with a
`jump in APAP concentration at the 20 hr sample.
`Fortunately, we realized this early during the acquisi»
`tion period and modified the sampling times depen~
`ding upon when gastric emptying of the enteric ta-
`blet was observed. As figure 6 indicates, gastric
`emptying of the tablet in the fed condition was ex-
`tremely variable with a range of 207 to 645 min
`
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`
`bioequivalent to the control tablct. Since the formu-
`lation also contained several other excipients which
`were unique to it, a separate study was necessary
`to isolate the causal agent which was ultimately de-
`termined to be SAPP (12).
`
`it was hypothesized that faster gastrointestinal
`transit was the cause for this reduced ranitidine ab-
`sorption. A stuclywas completed to test the in-
`fluence of SAPP (1.132 g) on gastrointestinal transit
`by gamma scintigraphy, thus, twelve fasted subjects
`each received 200 mt of water with or without SAPP
`
`and were imaged continuously until all radioactivity
`lnC|s) had entered the cecum or colon.
`
`twétaritl
`
`gzfit.‘-W '
`
`..§’{§:'ii’!§hri.%1i3fi%
`
`(mean i o = 374 1 171 min). intuitively, the onset of
`AP/-\P absorption showed a concomitant delay in
`the fed condition dependent upon the gastric emp-
`tying time. As stated previously, the gastric retention
`of similar dosage forms is well known, arid in fact,
`we have since observed gastric retention as long as
`24 hr when a standard breakfast is consumed at
`30 min before dose followed by a standard lunch at
`5 hr and dinner at 10 hr. Such extreme gastric resi-
`dence of single unit enteric tablets can have pro-
`found implications on drug concentrations whether
`the therapy is chronic or acute.
`
`The gastric emptying times of enteric tablels in
`this Case Study with a high fat meal (1080 cal, 134
`g fat) ingested at 30 min before dose was drastically
`different than that observed in Case Study 3 when
`a low fat meal (765 cal, 18 g fat) was consumed
`30 min after dose. The gastric emptying time of the
`enteric erythromycin tablets in the fed condition for
`Case Study 3 ranged from 16 to 68 min (mean i
`o = 41 : ‘21 min). There is considerable information
`which is needed to fully elucidate these differences
`of meal timing and drug absorption, however, it
`should be apparent that depending on the type of
`drug therapy required and the absorption characte-
`ristics of a drug, the dosing regimen of enteric coa-
`ted products can have a significant effect in the
`successful treatment of a disease.
`
`5. Case study 5: the effect
`of an effervescing excipient
`(sodium acid pyrophosphate)
`on intestinal transit and ranitidine
`absorption
`The next three case studies do not describe direct
`food effects on drug absorption, but instead, will re-
`count intra- and inter-subject differences in gastroin-
`testinal transit which resulted in proportional changes
`in drug absorption. These examples will still have im-
`plications of possible food effects due to the charac-
`ter of absorption changes which will be described.
`
`Case Study 5 was indeed an interesting one
`since it showed the anomalous result of an efferves-
`cent ranitidine solution being less bioavailable than
`a Zantacm tablet (150 mg ranitidine, Glaxo, |nc.). Of
`several effervescent formulations tested, all were
`bioequivalent to the immediate release Zantac‘ with
`the exception of one which contained sodium acid
`pyrephosphate (SAPP, 1. 132 g) as the acid exci-
`pient (12); this formulation was approximately 50%
`
`Figure 7. Small intestine transit time (Sl7T‘) in fasted
`subjects administered.
`
`The results to this study are shown in Figure 7.
`As indicated by Figure 7,
`it is readily apparent that
`all subjects showed fast-er small intestine transit
`when administered the SAPP solution. The mean
`SITT values were reported as 325 : 66 min and 185
`:1: 52 min for the control and SAPP solutions. res-
`pectively (p = 0.0002). The effect of SAPP on intes-
`tinal transit is consistent with the pharmacologic ac-
`tion of sodium phosphate salts. thus. SAPP may be
`considered in this case a saline cathartic where wa-
`ter is osmotically maintained in the gut lumen to in-
`directly stimulate peristalsis.
`
`This study contradicts the conventional wisdom
`that bioequivalence to standard solid oral formula-
`tions will be either met or exceeded by oral solution
`formulations. This result may also have implications
`towards food effects on drug absorption in ins-
`tances where a drug therapy has been ingested
`with substantial amounts of liquids that are high in
`phosphates or a similar pharmacologic agent.
`
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`
`6. Case study 6: the influence
`of gastric emptying time
`and the gastrointestinal site
`of absorption on the bioavailability
`of a poorly soluble drug
`
`It is frequently the case with the gamma scinti-
`graphy experiment that much more is learned about
`the drug and potential delivery systems than what is
`hoped for while setting the initial objectives. This fol-
`lowing example supports such a concept.
`
`The drug under consideration was a potent hy-
`polipidemic agent in phase i studies. it had poor
`solubility (< 1 pg/mL), and for this reason oral bio-
`availability was low, however, the absolute extent of
`oral absorption was unknown since a sensitive se-
`rum assay was unavailable. We were contacted to
`conduct an « input / output » study where nonab-
`sorbable radioactive samarium-153 oxide was co-
`administered with the drug, and feces samples
`were collected for a one week period. Thus. the
`percent dose orally absorbed would be equal to the
`percent of samarium—153 oxide recovered in the
`feces minus the percent of drug close in the feces.
`Blood and urine were also collected with the gua-
`rantee that a sensitive drug assay was forthcoming
`for these matrices.
`
`A hygienic and convenient method was imple-
`mented to collect feces samples on an outpatient
`basis. The amount of radioactive ‘5“Sm (t,,, = 46.7 hr,
`y : 103 keV) was determined in whole homogeni-
`zed feces samples using a conventional gamma
`camera as a quantitative detector. These samples
`were eventually freeze dried and the drug content
`in the powdered feces was determined by extrac-
`tion and HPLC / MS. The results from two of the six
`subjects are shown in Figure 8. As Figure 8 indi-
`cates, the transit or non—absorbable samarium
`oxide correlated very well with the non—absorbed
`drug dose, even to the point of inflection between
`the first and third samples of subject DUR—OO6 (lo-
`wer graph in Figure 8). This confirmation that the
`radioactive marker and the non-absorbed dose
`moved through the gastrointestinal tract at similar
`rates was important to demonstrate since one of
`the criticisms which the technique of gamma scinti-
`graphy often suffers is that the transit of the actual
`drug is not evaluated. To our knowledge, this was
`the first time that this has been unequivocally de-
`monstrated.
`
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`I...”
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`an?‘axe.>§'§§5{{3
`
`Figure 8. Sm—753 oxide and hypo/ipidemic drug de-
`termination in feces: confirmation of similar rates of
`gastrointestinal transit.
`
`To our good fortune. a sensitive plasma assay
`was validated by study's end which allowed us to
`examine for in vivo /in vivo correlations between
`gastrointestinal transit and systemic drug absorp-
`tion. Shown are the individual plasma concentration
`curves in Figure 9. The plasma profiles demons-
`
`;n ‘ares: ~ afiatiet-l"~.'&!i:i‘5
`
`Km-3t§
`
`/ntersubject variation on the absorption of
`Figure
`a hypolipidemic crime (800 mg).
`
`Dr. Falk Ex. 2033
`GeneriCo v. Dr. Falk IPR2016-00297
`Page 11
`
`

`
`trated a remarkable consistency with the absorptive
`phase starting in all subjects at 4 hr and a Tmnx
`achieved at 6 hr. However, the extent of absorption
`appeared to be highly variable with an inter—subject
`AUC ranging from 554 to 7519 ng - hr mL" (3363
`: 2470 rig - hr mL", rsd% = 73%]. This was nearly
`a 14-fold variation in drug plasma AUG.
`
`if at B
`
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`set-"Jr?-ttitwist*its
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`at at «mm: M: :2 it
`
`Figure 70. GI transit of “Sm oxide and correlation
`with drug plasma levels. Evidence of delayed drug
`absorption in the distal small intestine.
`
`The typical strategy we use to explain such
`absorption anomalies is to examine if correlations
`exist between gastrointestinal transit and drug ab-
`sorption. This is most easily accomplished by over-
`laying the drug plasma profile over the gastrointesti-
`nal transit profile. An example of such a plot is
`shown in Figure 10, and may require a brief expla-
`nation. The lett y—axis in Figure 10 indicates the rela-
`tive percent of “Sm in the stomach, jejunum or
`ileum, while the right y-axis is drug concentration.
`Sinceit was shown in Figure 8 that both the drug
`and radioactive marker transit through the GI tract
`at the same rate, it is possible to elucidate the re-
`gion of drug absorption by correlating the position
`of the radioactive marker at the start of the drug ab-
`sorption phase. Figure 1O indicates that for subject
`DUR—OO6, the absorption phase coincided with the
`arrival otthe radioactive marker at the terminal jeju-
`num, and maximum drug concentration was achie-
`ved as the radioactive marker moved across the
`ileal-cecal junction into the ascending colon. This in
`fact was consistent with the other five subjects.
`thus. the delay in absorption was apparently depen-
`dent upon the arrival of the drug at its region of
`
`absorption in the ileum. There are of course other
`possibilities to explain this delay such as sequestra-
`tion ot the drug in the liver followed by gall bladder
`emptying with meal intake. This is a distinct possibi-
`lity since a standard breakfast meal was provided at
`2 hr post dose, however, to definitively evaluate this
`would require additional studies with variable dosing
`and meal timing.
`
`Regarding the large inter-subject variability and
`the extent of absorption shown in the plasma
`concentration profiles of Figure 9, possible explana-
`tions are again sought by evaluating individual Gl
`transit / drug concentration overlay plots like that
`shown above in Figure i0. It was apparent after
`completing this analysis for all six subjects that Cmax
`was the greatest when subjects exhibited slow
`gastric emptying, i.e., subject DUR—OO6 shown in
`Figure to had the slowest gastric emptying and
`also had the greatest Cmax while subject DAR-O02
`had the smallest Gnax (Figure 9) and the fastest gas-
`tric emptying.
`
`Once a qualtative trend like this is observed, a
`quantitative analysis can be completed by genera-
`ting plots of gastrointestinal residence values versus
`pharmacokinetic values. Accordingly, a plot of the
`area under the gastric emptying curve (x—axis) ver-
`sus the area underthe plasma concentration curve
`(y-axis) was generated and is shown in Figure 11.
`This relationship predicted that drug absorption will
`be improved under the fed condition since gastric
`emptying is slower in the presence of food. Another
`phase I study was completed to and evaluate the
`effect of food given 30 min before dose. Food in-
`creased average AUC values 15-told (verbal com-
`munication) and the inter-subject variability was
`
`
`
`tgiiifittixfiarms;
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`#3‘as
`
`ta3§
`
`Figure 77. influence of gastric emptying upon drug
`absorption. Slow gastric emptying improved ab-
`sorption of hypolipidemic drug inter subject compa-
`risons (n = 6, fasted study).
`
`Dr. Falk Ex. 2033
`GeneriCo v. Dr. Falk IPR2016-00297
`Page 12
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`

`
`much less as compared to the fasted condition,
`thus, the prediction made from the data in Figure it
`proved correct. Furthermore, the follow-up fed
`study also showed a delay in the onset of drug ab
`sorption and a late Tm (verbal communication)
`which supported the ‘nypothesis of regional absorp-
`tion of this drug in the terminal ileum.
`
`In summary, the added benefits of conducting a
`gastrointestinal transit study concomitant with initial
`phase 1 clinical studies are that it ultimately aids in
`the formulation development of the delivery system,
`and it also helps to interpret errant results which
`tirequently are discarded as outlyers or trivial obser-
`vations. lt is in fact these « outlyers » which fre-
`quently contribute the greatest when we staid to
`sort through the data and make the in vivo / in vivo
`correlations, From the results discussed with this
`case study, it is apparent that the oral absorption of
`this drug will be the greatest if dosed after a meal.
`Formulation factors which may also improve its ab-
`sorption would of course be a gastric retentive sys
`tem, and it may also benefit from enhancer systems
`which target the terminal ileum and bile salt trans-
`port system, e.g., triglycerides, fatty acids as well as
`bile salts may prove to be useful absorption enhan-
`cers for this insoluble drug.
`
`7. Case study 7: intestinal transit
`changes observed from an enteric
`formulation containing absorption
`enhancers and an acid-labile,
`
`low-permeability cephalosporin
`
`We recently examined the use of enhancers to
`improve the bioavailability of the acid-labile, highly
`polar cephalosporin, ceftriaxone sodium (Roce~
`plain”, l-lottmann—La Roche). Enteric coated formula-
`tions of cettriaxone, without absorp