September 1989
`
`Notes
`
`Chem. Pharm. Bull. 37(9) 2539—2541 (1989)
`
`2539
`
`Gastric pH Profile and Its Control in Fasting Beagle Dogs
`
`Ichimaro YAMADA,‘ Hiroaki MlZUTA. Tomoko GODA, Keiichiro HAGA and Kenji OGAWA
`Research Laboratories, Yoshitami Pharmaceutical Induslries Ltd., 955 Kniwai, Yoshitomi-cha, Chikujo—gun, Fukuoka 87], Japan.
`Received January 13, 1989
`
`The gastric pH of fasting beagle dogs was measured by using an ion-selective field effect transistor pH sensor. In
`addition, a novel procedure to control the gastric pH in fasting beagle dogs was investigated. Inter- and intra-day
`variations in the gastric pH of the dogs were observed. The gastric pH of the dogs could be controlled by a single
`intravenous administration of omeprazole, an H+, K +-adenosine triphosphatase (ATPase) inhibitor (1 mg/0.25 ml/kg).
`The pH in the stomach was 6.6 i 0.2 (mean -1_- S.D., n =6) at lh after the omeprazole treatment, and this level of pH was
`maintained for a period of at least 3h. Beagle dogs in which the gastric pH has been controlled by omeprazole are
`considered to be useful as an animal model to be used for the pharmaceutical evaluation of drugs in subjects with a low
`acidity level.
`
`Keywords
`
`beagle dog; ion-selective field effect transistor pH sensor; gastric pH; omeprazole; gastric pH control
`
`,
`
`It is known that the bioavailability of a drug which is
`administered in the form of a pH-dependent release prep-
`arations affected by the gastrointestinal pH, especially the
`gastric pH. In fact, several early studies demonstrated that
`the bioavailability of diazepam," indomethacin,” metroni-
`dazole” and cinnarizine‘” from preparations exhibiting pH—
`dependent dissolution was significantly affected by the
`gastric pH of the human individuals. Clinically, such
`variation in the drug bioavailability often causes individual
`differences in drug efficacy and safety. Accordingly, it is
`necessary to develop pharmaceutical preparations the drug
`bioavailability from which is not affected by the gastric pH.
`Beagle dogs are commonly used as a model species for
`the evaluation of the drug bioavailability because of the
`easiness of their handling. But, the bioavailability in beagle
`dogs differs considerably from that in humans because of
`species differences in gastrointestinal physiology, e.g., gas—
`tric pH and gastric emptying rate. The gastric pH in fasting
`beagle dogs has so far been measured by a radiotelemet-
`ric5 '7’ or an intubation method.” However, there is a slight
`discrepancy between the results obtained by these two
`methods. Nakata et al.” and Ninai et al.‘°’ announced that
`they had controlled the gastric pH of beagle dogs at a high
`acidity level (less than pH 2.0) by intramuscular adminis-
`tration of pentagastrin. However, a procedure for control-
`ling and maintaining the gastric pH at a low acidity level
`(higher than pH 6.0) has been established for rabbits,“’ but
`not for beagle dogs.
`In the present study, an ion—selective field effect transistor
`pH sensor which was developed for the accurate and
`continuous measurement of a small pH change in the blood
`pH in arteries and veins”) was applied to measurements of
`gastric pH in fasting beagle dogs. In addition, this paper
`describes a method for controlling and maintaining the
`gastric pH of beagle dogs at a low acidity level by in—
`travenous administration of omeprazole, an H+,K+-
`adenosine triphosphatase (ATPase) inhibitor.
`
`Experimental
`Materials Omeprazole ((J_r)-S-methoxy-2-[[(4-methoxy-3,5-dimethyl—
`2-pyridyl)methyl]sulfinyl]benzimidazole) was used as received from AB
`Hassle. Sweden. All other chemicals were standard commercial products
`of analytical grade.
`Animals Six healthy 2-year-old male beagle dogs weighing 9.5 to
`l 1.0 kg were used after being fasted overnight. All dogs were allowed free
`
`access to water, but no food was given until the experiment was finished,
`Measurement of the Gastric pH in Fasting Beagle Dogs A KR-SOO pH/
`pCO2 Monitor (Kuraray Co.. Ltd., Japan) connected with an ion-selective
`field effect transistor pH sensor (pH sensor) was used in these experiments.
`The pH sensor was placed in Teflon tubing (6 mm in outside diameter,
`4mm in inside diameter. 70 cm long) in order to protect it from possible
`damage during the experimental period. The gastric pH was measured via
`the pH sensor inserted perorally into the stomach of conscious beagle
`dogs. Dissection of an anesthetized beagle dog revealed that the end ofthe
`Teflon tubing had reached in the stomach following insertion of a length of
`about 60 ~70 cm. For each experiment, the pH sensor was calibrated using
`pH 1.68 and 6.86 standard buffer solutions. A detailed description of the
`geometry and fabrication of the pH sensor has been given by Bergveld.”’
`Procedure for the Gastric pH Control The beagle dogs having a weakly
`acidic to neutral gastric pH (higher than pH 6.0) were prepared by a single
`intravenous administration of omeprazole (1 mg/kg). Omeprazole was
`dissolved in the mixture of polyethylene glycol 400 and 1‘34, sodium
`hydrogencarbonate (1:1, v/v) within an hour before injection, and the
`concentration of omeprazole was adjusted to 4mg/m1.
`
`Results and Discussion
`
`A typical gastric pH—time profile obtained in a fasting
`beagle dog by measuring the pH with the pH sensor is
`shown in Fig.
`1. The gastric pH of beagle dog varied
`irregularly during a short period. This pH sensor thus
`enables us to make successive measurement of the gastric
`pH of beagle dogs by persistently placing it in the stomach.
`In the present study, however, the sensor was inserted into
`the stomach at each time of measurement.
`Figure 2 shows intraday variations in the gastric pH in
`fasting beagle dogs (n = 6). Measurement was carried out at
`9:00, 11:00, 13:00, 15:00 and 17:00. Wide intra- and
`inter-individual variations ranging from pH 0.9 to 7.0 were
`observed. Figure 3 shows the result of the day-to-day
`measurement of gastric pH. The experiments were repeated
`
`8
`5:
`ca
`0 6
`-.-i
`b 4
`3U 2
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`10
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`20
`
`30
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`[to
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`50
`
`60
`
`70
`
`80
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`90
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`100
`
`Time (min)
`
`1. Typical Gastric pH~Time Profile in Fasting Beagle Dog as
`Fig.
`Measured by the Ion»Selective Field Effect Transistor pH Sensor
`
`© 1989 Pharmaceutical Society of Japan
`
`NII-Electronic Library Service
`
`Griin. Exhibit 1077
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`Griinenthal v. Antecip
`PGR2017-00022
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`NII-Electronic Library Service
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`Grün. Exhibit 1077
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`

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`2540
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`on
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`GastricpH ;>as
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`N
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`Fig. 2.
`("=6)
`
`Fig. 4. Gastric pHATime Profile after Intravenous Administration of
`Omeprazole in Fasting Beagle Dogs (n=6)
`A: omeprazole lmg/kg. i.v.
`
`6.6i0.2 (meaniS.D., n=6). This level of pH was main-
`tained consistently until 4 h after the intravenous adminis-
`tration of omeprazole.
`It has been suggested that expulsion of large indigestible
`objects from the stomach is dependent on the interdiges-
`tive migrating myoelectric complex (IMMC) termed the
`“housekeeper wave”.7) This wave occurs at about 1.5—
`2 h intervals in fasting dogs“) Accordingly, the effect of the
`gastric pH on drug absorption must be largest during the
`first 2h after oral administration of the drug. The present
`study revealed that
`the gastric pH of beagle dogs was
`controlled at a level of pH 6 or higher for a period of at
`least 3 h by intravenous administration of omeprazole. This
`method makes it possible to evaluate exactly the effect of
`the gastric pH on drug absorption. Earlier studies have
`demonstrated that
`the gastric pH of beagle dogs was
`controlled at pH 2 or lower by intramuscular adminis-
`tration of pentagastrin.9"°’ However, pentagastrin delays
`gastric emptying and increases the frequency of antral and
`duodenal slow waves in dogs”) On the other hand, ome-
`prazole had no significant effect on the gastric emptying of
`solids or liquids or on several phases of myoelectric activity
`in the stomach in the fasting state.”"
`The beagle dog has not been considered to be a suitable
`animal species for the pharmaceutical evaluation of weakly
`basic and weakly acidic drugs. However, gastric pH-
`controlled beagle dogs are considered to be useful as an
`animal model to estimate the bioavailability of drugs and
`formulations with pH-dependent dissolution profiles at a
`low acidity level.
`
`References
`
`Int. J. Clin.
`
`1) H. Ogata, N. Aoyagi, N. Kaniwa, T. Shibazaki and A. Ejima, Int. J.
`Clin. Phdrmacol. Ther. Toxicol., 20, 166 (1982).
`2) N. Aoyagi, H. Ogata. N. Kaniwa and A. Ejima,
`Pharmacol. Ther. Toxicol.. 23, 469 (1985).
`3) H. Ogata, N. Aoyagi, N. Kaniwa, T. Shibazaki, A. Ejima, Y.
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`NIT—Electronic Library Service
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`lst
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`2nd
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`3rd
`Trials
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`4th
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`8
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`6
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`ll
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`2
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`a:
`n.
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`.3
`H
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`U 3u
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`Fig. 3.
`
`Inter-day Variation of Gastric pH in Fasting Beagle Dogs (n=6)
`
`4 times during two weeks. The mesurement was carried out
`at 9: 00 for each trial. The gastric pH of beagle dogs was
`most variable in the fasting state. There was no consistent
`pattern in inter-day variations.
`We have established a rapid and accurate method for
`measurement of the gastric pH using the ion-selective field
`effect transistor pH sensor. The results obtained by this
`method were in agreement with those obtained by the
`intubation method“ rather than by the radiotelemetric
`method?“
`
`It was found in the present study using the ion-selective
`field effect
`transistor pH sensor that the gastric pH of
`beagle dogs was variable. Accordingly, the beagle dog is not
`a suitable animal
`species
`for
`the evaluation of
`the
`bioavailability of drugs and dosage forms whose disso-
`lution may be influenced by the gastric pH. To evaluate the
`relationship between the bioavailability and physicochemi-
`cal properties of drugs or formulation characteristics, it is
`necessary to establish an accurate method for controlling
`the gastric pH. Omeprazole, a substituted benzimidazole,
`has a potent and long-lasting inhibitory effect on basal and
`stimulated gastric secretion”) It rapidly raises the gastric
`pH of patients with in duodenal ulcers and maintains the
`gastric pH at higher than 4.0 for a long time after in-
`travenous administration at a dose of 1mg/kg.15’ On the
`basis of this finding, we chose 1mg/kg as the dose to be
`used in the present experiment. Figure 4 shows the gastric
`pH versus time curve before and after intravenous adminis-
`tration of omeprazole at a dose of 1mg/kg in the fasting
`state. The measurement were carried out immediately be-
`fore and at 0.5, 1, 2, 4, 6 and 8h after administration. A
`wide variation in the gastric pH was not found at I h after
`the omeprazole administration, and the gastric pH was
`
`Vol. 37, No. 9
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`GastricpH
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`Time of the day (h)
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`Intra-day Variation of Gastric pH in Fasting Beagle Dogs
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`September 1989
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`2541
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