4
8/18/2019 [email protected]@Generic 50BD1D2D9633 http://slidepdf.com/reader/full/100000wwwncbinlmnihgovgeneric-50bd1d2d9633 1/4 Br. J. clin. Pharmac. 1991), 31, 275-278 Influence of acid secretorystatus on absorption of omeprazole fromenteric coatedgranules TOMMY ANDERSSON, ROBERT BERGSTRAND & CHRISTER CEDERBERG Research Laboratories, AB Hassle,Molndal, Sweden 1 In order to study the absorption of omeprazole undernormal acidic conditions in the stomach as well as when the granules are exposed to minimal gastric acid, eight healthy males were given 20 mg omeprazole as enteric coated(EC) granules either alone or 2 h after a ranitidine dose of 300 mg, respectively. 2 Blood samples were collected at intervals for 12 h following both omeprazole admini- strations. The pH was recordedduring the first 4 h in half the subjects in each experiment to document the difference in pH during the absorptionphase of omeprazole. 3 The area under the plasmaconcentration-time curve, AUC, of omeprazole was virtually the same irrespective of whether or not the granules were exposed to gastric acid. However, the maximumplasma concentration (Cmax) was higher and the time to reach Cmax was shorter when omeprazole was administered after a ranitidine dose. 4 It is concluded t h a tg a s t r ic acidity has negligible influence on the AUC of omeprazole, which is directly correlated to the antisecretory effect, when administered as EC granules. Keywords absorption omeprazole substituted benzimidazole acid influence EC granules Introduction Omeprazole, a substituted benzimidazole, has been shown effectively to suppress gastric acidsecretion by inhibiting the H+,K+-ATPase in the parietal cell Fellenius et al., 1981, Wallmark et al., 1985). The degree of suppression of gastric acidsecretion is cor- related to the area under the plasma concentration-time curve (AUC) of omeprazole and is not directly related to plasma concentration of the drug at any given time(Lind et al., 1983). Despite the fact that omeprazole is rapidly eliminated fromplasma with a half-life usually less than 1 h, some effect is still present 24 to 72 h after dose (Lind et al., 1983). The long-lasting binding of the active form of omeprazole to the H+,K+-ATPase in the parietal cells accounts for the lack of correlation between plasma concentration and degree of acid inhibition (Wallmark et al., 1984). The effective control of acid secretion by omeprazole resultsin a rapid healing of peptic ulcers and erosive reflux oesophagitis and in this respect omeprazole is more effective thanH2-receptor antagonists (Bardhan et al., 1986; Hetzel et al., 1988; Klinkenberg-Knol et al., 1987; Walan et al., 1989). Omeprazole is acidlabile and consequently acid resistant enteric coated (EC) granules, dispensed in hard gelatin capsules, haveb e e nd e v e l o p e d to minimise acid degradation in the stomach.Previous studies with repeatedonce daily oral administration of omeprazole as EC granules in different doseshave shown that the AUC increases during the first 4 days of treatment with no further risethereafter duringcontinued treatment (Andersson et al., 1990; Muller et al., 1983; Prichard et al., 1985). The increase in AUC has also beenshown to be dose-dependent between 10 and 40 mg witha more pronounced increase with higher doses (Andersson et al., 1989). Proposed explanations for the higher AUC values obtained duringrepeateddosing are a decreased hepatic metabolism, primarily first-pass, and/or increased absorption due to an increased stability of the granules as a result of the decreased intragastric acidity during omeprazole treatment.Thus, we were not 100 confi- dentthat the enteric coating protected all of the omepra- zole dose on the first day of administration. This study was performed to investigate whether a decrease in gastric acidity wouldlead to higher AUC of orally administered omeprazole, which in turn could answer the question if decreased acidity during repeated dosing could be an explanation of the increased AUCs pre- Correspondence: Tommy Andersson, Gastrointestinal Research, Department of Clinical Pharmacology and Medicine, AB Hassle, S-431 83 M6lndal, Sweden 275 A D 0 N I S 030652519100055F

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B r .J . c l i n .P h a r m a c . 1 9 9 1 ) ,3 1 ,2 7 5 - 2 7 8

I n f l u e n c eo f a c i d s e c r e t o r ys t a t u s on a b s o r p t i o no f o m e p r a z o l ef r o me n t e r i cc o a t e dg r a n u l e s

TOMMY ANDERSSON, ROBERT BERGSTRAND & CHRISTER CEDERBERGR e s e a r c hL a b o r a t o r i e s ,AB H a s s l e ,M o l n d a l ,Sweden

1 I n o r d e r t o s t u d yt h e a b s o r p t i o no f o m e p r a z o l eu n d e r n o r m a la c i d i c c o n d i t i o n si n t h es t o m a c ha s w e l la s w h e n t h e g r a n u l e sa re e x p o s e dt o m i n i m a lg a s t r i ca c i d ,e i g h th e a l t h ym a l e sw e r e g i v e n2 0 mg o m e p r a z o l ea s e n t e r i cc o a t e d( E C )g r a n u l e se i t h e r a l o n eor 2 ha f t e ra r a n i t i d i n ed o s e o f 3 0 0 mg, r e s p e c t i v e l y .

2 B l o o ds a m p l e sw e r e c o l l e c t e da t i n t e r v a l sf o r 1 2 h f o l l o w i n gb o t ho m e p r a z o l ea d m i n i -s t r a t i o n s .T h e pH was r e c o r d e dd u r i n g t h e f i r s t4 h i n h a l f t h e s u b j e c t si n e a c he x p e r i m e n tt o d o c u m e n tt h e d i f f e r e n c e i n pH d u r i n g t h e a b s o r p t i o np h a s e o fo m e p r a z o l e .

3 T h e a r e a u n d e r t h e p l a s m ac o n c e n t r a t i o n - t i m ec u r v e , AUC, o f o m e p r a z o l ew a s

v i r t u a l l yt h e same i r r e s p e c t i v eo f w h e t h e ror n o t t h e g r a n u l e sw e r e e x p o s e dt o g a s t r i ca c i d .H o w e v e r ,t h e maximum p l a s m ac o n c e n t r a t i o n( C m a x )was h i g h e ra n d t h e t i m e t or e a c h C m a xwas s h o r t e rwhen o m e p r a z o l ew a s a d m i n i s t e r e da f t e ra r a n i t i d i n ed o s e .

4 I t i sc o n c l u d e dt h a tg a s t r i ca c i d i t yh a s n e g l i g i b l ei n f l u e n c eon t h e AUC o f o m e p r a z o l e ,w h i c hi s d i r e c t l yc o r r e l a t e d t o t h e a n t i s e c r e t o r ye f f e c t ,w h e n a d m i n i s t e r e da s ECg r a n u l e s .

K e y w o r d sa b s o r p t i o n

o m e p r a z o l e s u b s t i t u t e db e n z i m i d a z o l e a c i di n f l u e n c eEC g r a n u l e s

I n t r o d u c t i o n

O m e p r a z o l e ,a s u b s t i t u t e db e n z i m i d a z o l e ,h a s b e e ns h o w ne f f e c t i v e l yt o s u p p r e s sg a s t r i ca c i ds e c r e t i o nb yi n h i b i t i n gt h e H + , K + - AT P a s ei n t h e p a r i e t a lc e l l F e l l e n i u se t a l . , 1 9 8 1 ,W a l l m a r ke t a l . , 1 9 8 5 ) .T h ed e g r e eo f s u p p r e s s i o no f g a s t r i ca c i ds e c r e t i o ni s c o r -r e l a t e dt o t h ea r e a u n d e rt h ep l a s m ac o n c e n t r a t i o n - t i m ec u r v e( A U C )o f o m e p r a z o l ea n di sn o t d i r e c t l yr e l a t e dt op l a s m ac o n c e n t r a t i o no f t h ed r u ga ta n yg i v e nt i m e( L i n de ta l . ,1 9 8 3 ) .D e s p i t et h ef a c tt h a to m e p r a z o l ei s r a p i d l ye l i m i n a t e df r o mp l a s m aw i t ha h a l f - l i f eu s u a l l yl e s st h a n1 h , s o m ee f f e c ti ss t i l lp r e s e n t2 4 t o7 2 h a f t e rd o s e ( L i n de ta l . ,1 9 8 3 ) .T h e l o n g - l a s t i n gb i n d i n go f t h ea c t i v ef o r mo f o m e p r a z o l et o t h eH + , K + - AT P a s ei n t h ep a r i e t a lc e l l sa c c o u n t sf o rt h el a c ko f c o r r e l a t i o nb e t w e e np l a s m ac o n c e n t r a t i o na n d d e g r e eo fa c i di n h i b i t i o n( Wa l l m a r ke t a l . ,1 9 8 4 ) .T h e e f f e c t i v ec o n t r o lo f a c i ds e c r e t i o nb yo m e p r a z o l er e s u l t s i na r a p i dh e a l i n go f p e p t i cu l c e r sa n de r o s i v er e f l u xo e s o p h a g i t i sa n d i nt h i sr e s p e c to m e p r a z o l ei sm o r ee f f e c t i v et h a n H 2 - r e c e p t o ra n t a g o n i s t s( B a r d h a ne ta l . ,1 9 8 6 ;H e t z e le ta l . ,1 9 8 8 ;K l i n k e n b e r g - K n o le ta l . ,1 9 8 7 ;W a l a ne t a l . , 1 9 8 9 ) .

O m e p r a z o l ei s a c i dl a b i l ea n d c o n s e q u e n t l ya c i dr e s i s t a n te n t e r i cc o a t e d ( E C ) g r a n u l e s ,d i s p e n s e di n

h a r dg e l a t i nc a p s u l e s ,h a v eb e e nd e v e l o p e dt o m i n i m i s ea c i dd e g r a d a t i o ni n t h es t o m a c h .P r e v i o u ss t u d i e sw i t hr e p e a t e do n c ed a i l y o r a la d m i n i s t r a t i o no fo m e p r a z o l ea s EC g r a n u l e si n d i f f e r e n td o s e sh a v es h o w nt h a tt h eAUC i n c r e a s e sd u r i n gt h ef i r s t4 d a y so f t r e a t m e n tw i t hn o f u r t h e rr i s et h e r e a f t e rd u r i n gc o n t i n u e dt r e a t m e n t( A n d e r s s o ne t a l . , 1 9 9 0 ;M u l l e re t a l . , 1 9 8 3 ;P r i c h a r de ta l . ,1 9 8 5 ) .T h e i n c r e a s ei nAUC h a s a l s ob e e ns h o w nt o b e d o s e - d e p e n d e n tb e t w e e n1 0 a n d4 0 mg w i t ha m o r ep r o n o u n c e di n c r e a s ew i t h h i g h e rd o s e s ( A n d e r s s o ne ta l . ,1 9 8 9 ) .P r o p o s e de x p l a n a t i o n sf o rt h eh i g h e rAUCv a l u e so b t a i n e dd u r i n gr e p e a t e dd o s i n ga r e a d e c r e a s e dh e p a t i cm e t a b o l i s m ,p r i m a r i l yf i r s t - p a s s ,a n d / o ri n c r e a s e da b s o r p t i o nd u e t o a n i n c r e a s e ds t a b i l i t yo f t h e g r a n u l e sa s a r e s u l to f t h ed e c r e a s e di n t r a g a s t r i ca c i d i t yd u r i n go m e p r a z o l et r e a t m e n t .T h u s , w e w e r en o t 1 0 0 c o n f i -d e n tt h a tt h ee n t e r i cc o a t i n gp r o t e c t e da l lo ft h eo m e p r a -z o l ed o s eo n t h e f i r s td a y o f a d m i n i s t r a t i o n .T h i s s t u d yw a s p e r f o r m e dt o i n v e s t i g a t ew h e t h e ra d e c r e a s ei ng a s t r i ca c i d i t yw o u l dl e a d t o h i g h e r AUC o f o r a l l ya d m i n i s t e r e do m e p r a z o l e ,w h i c hi n t u r n c o u l da n s w e rt h e q u e s t i o ni fd e c r e a s e da c i d i t yd u r i n gr e p e a t e dd o s i n gc o u l db e a n e x p l a n a t i o no f t h e i n c r e a s e dA U C s p r e -

C o r r e s p o n d e n c e :Tommy A n d e r s s o n ,G a s t r o i n t e s t i n a lR e s e a r c h ,D e p a r t m e n to f C l i n i c a lP h a r m a c o l o g ya n dM e d i c i n e ,AB H a s s l e ,S - 4 3 18 3 M 6 l n d a l ,S w e d e n

2 7 5

A D 0 N I S 0 3 0 6 5 2 5 1 9 1 0 0 0 5 5 F

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2 7 6 Tommy A n d e r s s o n , R o b e r tB e r g s t r a n d& C h r i s t e rC e d e r b e r g

v i o u s l yr e p o r t e d . R e d u c t i o no f t h e g a s t r i ca c i ds e c r e -t i o nw a s o b t a i n e d b y p r e t r e a t m e n tw i t h r a n i t i d i n e3 0 0mg o n t h e p r e c e d i n ge v e n i n ga n d a g a i n2 h p r i o rt ot h e o m e p r a z o l ed o s e .

M e t h o d s

E i g h t h e a l t h ym a l e so f m e d i a na g e 2 8 y e a r s r a n g e :2 4 -4 8 )a n d m e d i a nw e i g h t8 1 k g r a n g e :7 0 - 8 6 )c o m p l e t e dt h es t u d yw h i c h w a sc o n d u c t e di n a c c o r d a n c ew i t h t h eD e c l a r a t i o no f H e l s i n k i .T h es t u d yw a sa p p r o v e db y t h eE t h i c sC o m m i t t e eo ft h eM e d i c a lF a c u l t yo f t h eU n i v e r -s i t yo fG o t e b o r ga n db y t h eS w e d i s hN a t i o n a lB o a r do fH e a l t h a n d We l f a r e . W r i t t e n i n f o r m e dc o n s e n tw a so b t a i n e df r o me a c hs u b j e c t p r i o rt o p a r t i c i p a t i o n .

T h i s s t u d yw a sc o n d u c t e da sa r a n d o m i s e dc r o s s - o v e rt r i a lw i t ht w oe x p e r i m e n t ss e p a r a t e db y a t l e a s t1 w e e k sw a s h o u t .I n e a c h e x p e r i m e n to m e p r a z o l ew a sa d m i n i s -t e r e de i t h e ra l o n e o r 2 h a f t e ra r a n i t i d i n ed o s e a n df o l l o w e db y b l o o ds a m p l i n g .

O m e p r a z o l e2 0 mg w a s g i v e na s EC g r a n u l e sd i s -p e n s e di n a h a r d g e l a t i nc a p s u l e .T h ec a p s u l ew a ss w a l -l o w e dw i t h - 2 5 0 m l o f w a t e r . R an i t i d i n e 2x 1 5 0 mg Z a n t a c ®t a b l e t s )w a s g i v e ni n t h ea p p r o p r i a t ee x p e r i -m e n ta t b e d t i m eo n t h ee v e n i n gb e f o r et h ei n v e s t i g a t i o na n d a f u r t h e r2 x 1 5 0mg w e r eg i v e ni n t h em o r n i n g2 hb e f o r et h eo m e p r a z o l ed o s e .

E a c h e x p e r i m e n ts t a r t e da t a b o u t 0 8 .0 0h w i t h t h es u b j e c t sh a v i n ga b s t a i n e df r o ma l lf o o da n dl i q u i d ss i n c e2 2 . 0 0h t h ep r e v i o u sd a y .B l o o ds a m p l e s 5m l )f o ra s s a yo fo m e p r a z o l ew e r ec o l l e c t e df r o ma n a n t e c u b i t a lv e i nv i aa n i n d w e l l i n gc a n n u l ap r i o rt oa n de v e r y0 . 5h f o r4 ht h e n e v e r yh o u r f o r1 2 h a f t e ro m e p r a z o l ea d m i n i s t r a -t i o n .T h e b l o o ds a m p l e sw e r ec o l l e c t e di n h e p a r i n i s e dt u b e s ,k e p t a t room t e m p e r a t u r ef o ra t l e a s t5 m i na n dt h e nc e n t r i f u g e df o r1 0 m i n .T h ep l a s m aw a st r a n s f e r r e dt o p l a s t i ct u b e s a n d s t o r e d a t - 2 0 ° C u n t i la n a l y s i s .I ns u b j e c t s5 t o 8 i n c l u s i v et h epH i n t h es t o m a c hw a sr e c o r d e d v i a a n a n t i m o n ye l e c t r o d e S y n e c t i c s ® )d u r i n gt h ef i r s t4 h a f t e ro m e p r a z o l ed o s i n gi n b o t h e x -

p e r i m e n t s .S t a n d a r d i s e dm e a l sw e r e s e r v e d2 . 5 ,6 a n d1 0h a f t e rt h eo m e p r a z o l ea d m i n i s t r a t i o n .A l c o h o la n da l lm e d i c a t i o n , i n c l u d i n g o v e r t h ec o u n t e rd r u g s ,w e r en o t a l l o w e df o r2 d a y sp r i o rt o e a c he x p e r i m e n t .

T h e c o n c e n t r a t i o n so f o m e p r a z o l ei n p l a s m aw e r ed e t e r m i n e da t t h e D e p a r t m e n to fB i o a n a l y t i c a lC h e m i s -t r y , AB H a s s l e ,b y l i q u i dc h r o m a t o g r a p h ya n du . v . - d e t e c t i o n L a g e r s t r o m& P e r s s o n ,1 9 8 4 ) .

T h e a r e a u n d e rt h ep l a s m ao m e p r a z o l ec o n c e n t r a t i o n -t i m e c u r v e ( A U C )w a s c a l c u l a t e du s i n gt h e l i n e a rt r a p e z o i d a lr u l ea n d e x t r a p o l a t e dt o i n f i n i t yb y a d d i n gt h e r e s i d u a la r e a o b t a i n e db y d i v i d i n gt h el a s tm e a s u r e dp l a s m ac o n c e n t r a t i o nw i t ht h e r a t e c o n s t a n td e t e r m i n e df r o mt h e t e r m i n a ls l o p eo f t h el o gp l a s m ac o n c e n t r a t i o n -t i m e c u r v e ( 0 . 6 9 3 / t l / ½ ) .P l a s m ae l i m i n a t i o nh a l f - l i f e t ½ l , )w a sc a l c u l a t e df r o mt h e r e g r e s s i o nl i n eo f t he t e rm i na ll o g p l a s m a c o n c e n t r a t i o n sv s t i m e .T h e maximump l a s m ac o n c e n t r a t i o n C m a x )a n d t h et i m e t o r e a c hC m a x t m a x )w e r er e c o r d e d .M e a n v a l u e sw i t h9 5 c o n f i d e n c e

i n t e r v a l sa r e p r e s e n t e df o r t h e d i f f e r e n tp h a r m a c o -k i n e t i cp a r a m e t e r s .D i f f e r e n c e si n k i n e t i cp a r a m e t e r sb e t w e e nt h ee x p e r i m e n t sw i t ha n dw i t h o u tr a n i t i d i n ea r e

e x p r e s s e da s means w i t h 9 5 c o n f i d e n c ei n t e r v a l s .A

d i f f e r e n c ei s r e g a r d e da s s t a t i s t i c a l l ys i g n i f i c a n t( P <0 . 0 5 )w h e nt h ec o n f i d e n c ei n t e r v a ld o e sn o t s p a n0 . 0 0 .

R e s u l t s

M e d i a npH v a l u e s ,w i t h r a n g e s ,d u r i n gt h e f i r s t4 ho f t h et w o e x p e r i m e n t sa r e s h o w ni n F i g u r e 1 . T h em e d i a npH i n t h es t o m a c h w a s b e t w e e n6 a n d 8 d u r i n gt h ef i r s th o u r so f t h e r a n i t i d i n ee x p e r i m e n tw h i l ei t w a sa s l o wa s 1 - 2 w h e no m e p r a z o l ew a sg i v e na l o n e .

T h e mean p l a s m a c o n c e n t r a t i o n - t i m ep r o f i l e so fo m e p r a z o l ef o l l o w i n ga d m i n i s t r a t i o no f t h eEC g r a n u l e si n t h et w od i f f e r e n te x p e r i m e n t sa r es h o w ni n F i g u r e2 ,

i .

; i,

0 . 0 1 . 0 2 . 0 3 . 0 4 . 0

F i g u r e1 M e d i a npH v a l u e s ,w i t h r a n g e s , d u r i n gt h e4 hf o l l o w i n go m e p r a z o l ea d m i n i s t r a t i o ni n t h et w o e x p e r i m e n t s n = 4 ) .( O o m e p r a z o l e. . . . . . r a n g e ;* o m e p r a z o l e+r a n i t i d i n e ,- - - - r a n g e ) .

4 0 0 L 4 . .. . ; :. .t

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- I 4t - e . MX* : . 1>- i : . 3 ' . ~' ^ : ,i d WjI i

0 | § ) > t .e.; . , ;s = - . - . . . . 1; .. , D i. ; , *

., g g - - . ;. - i : l . t;..Pt;;~J.

0 1 2 ' i E

F i g u r e2 M e a n ± s . e . m e a n )p l a s m ac o n c e n t r a t i o n - t i m ep r o f i l e so f o m e p r a z o l ef o l l o w i n ga d m i n i s t r a t i o no f 2 0 mg a sECg r a n u l e sa l o n e( - - - - ) o r a f t e rr a n i t i d i n e3 0 0mg ( - 4 * - ) i ne i g h th e a l t h ys u b j e c t s .

M r . , I .i : . . . ; . . : A i i . . 0 0 0 . 9 1 .-, --.1--i0 - -i l i o

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a n dmean p h a r m a c o k i n e t i cp a r a m e t e r sa r e p r e s e n t e di nTa b l e 1 . T h e maximum p l a s m a c o n c e n t r a t i o n so fo m e p r a z o l ew e r eh i g h e ra n dw e r e r e ac h e de a r l i e rwhent h eo m e p r a z o l ed o s e w a sg i v e na f t e rr a n i t i d i n e .How-e v e r ,t h e AUC v a l u e sw e r e v i r t u a l l yt h es a m e , b e i n g0 . 5 4p u m o l1 - 1h w h e no m e p r a z o l ew a s a d m i n i s t e r e da l o n e a n d 0 . 6 5, u m o l1 - 1h when g i v e na f t e rr a n i t i d i n e( Ta b l e 1 ) .T h e e l i m i n a t i o nh a l f - l i f eo f o m e p r a z o l ed i d

n o t d i f f e rb e t w e e nt h e t w oe x p e r i m e n t s 0 . 5 8v s0 . 5 9h ) .

D i s c u s s i o n

R a n i t i d i n ea d m i n i s t r a t i o nd e c r e a s e dt h ea c i d i t yi n t h es t o m a c hb y a p p r o x i m a t e l y5 l o gu n i t s .T h e g o a lo fo b t a i n i n ge x p e r i m e n t a lc o n d i t i o n sw i t h a s u b s t a n t i a l l yd e c r e a s e dg a s t r i ca c i d i t yw a st h u s f u l f i l l e db y t h i sr a n i t i -d i n e d o s i n g .T h e s i m i l a rAUC v a l u e so f o m e p r a z o l ew h e ng i v e na l o n ea n da f t e rp r e t r e a t m e n tw i t ht w od o s e so f3 0 0 mg r a n i t i d i n ec o n s e q u e n t l yi n d i c a t e t h a tg a s t r i ca c i d i t yh a s n e g l i g i b l ee f f e c to n t h e b i o a v a i l a b i l i t yo fo m e p r a z o l e .B y c o m p a r i s o n ,p r i o ri n v e s t i g a t i o n sw i t hr e p e a t e d o m e p r a z o l ed o s i n gi n t h e same s u b j e c t sr e s u l t e di n a n i n c r e a s e dAUC f r o m0 . 5 7t o 1 . 0 2, u m o l- 1h f r o mt h e f i r s tt o t h el a s td a yo f 1 w e e k st r e a t m e n t ,

i . e .a n i n c r e a s eo f7 8 ( P < 0 . 0 0 3 ) .A p r e v i o u ss t u d yw i t hr e p e a t e dd o s i n go f o m e p r a z o l e

i nt h ed o s er a n g e1 0 t o 4 0mg a sEC g r a n u l e s )r e s u l t e di na d o s e - d e p e n d e n ti n c r e a s ei n t h e AUC ( A n d e r s s o ne t a l . ,1 9 8 9 )a n d t h ei n h i b i t i o no f g a s t r i ca c i ds e c r e t i o nw a s f o u n dt o b e d o s e - d e p e n d e n t L i n de t a l . , 1 9 8 3 ) .S i n c eo m e p r a z o l ei sa n a c i dl a b i l ec o m p o u n d ,t h e s etwoo b s e r v a t i o n smade u s s u g g e s tt h a ta p o s s i b l ee x p l a n a t i o no f t h e i n c r e a s e d AUCs p r e v i o u s l yo b t a i n e d w a sa ni n c r e a s e da b s o r p t i o na s a c o n s e q u e n c eo f i n c r e a s e ds t a b i l i t yo f t h e g r a n u l e sa n d ,h e n c e d e c r e a s e da c i dd e g r a d a t i o no f o m e p r a z o l ei n t h e s t o m a c hr e s u l t i n gf r o m d e c r e a s e dg a s t r i ca c i ds e c r e t i o nd u r i n gr e p e a t e dd o s i n go f t h e d r u g( A n d e r s s o ne t a l . ,1 9 8 9 ,1 9 9 0 ) .T h er e s u l t sf r o m t h e p r e s e n ts t u d yc l e a r l ys h o w ,h o w e v e r ,t h a tt h i se x p l a n a t i o nc a n b e r u l e do u t a sa m a j o rc o n t r i -b u t i n gf a c t o rt o t h e i n c r e a s e dAUC d u ri n g r e p e at e dd o s i n g .F u r t h e r m o r e ,c o n c o m i t a n ta d m i n i s t r a t i o no fa n t a c i d sa n d o m e p r a z o l ed i dn o t r e s u l ti n a n i n c r e a s e dAUC o fo m e p r a z o l ew h i c hp r o v i d e sf u r t h e rs u p p o r tt oo u r c o n c l u s i o n( T u y n m a ne t a l . ,1 9 8 7 ) .T h u s ,t h ea l t e r -n a t i v ee x p l a n a t i o n ,t h a ta d e c r e a s e dh e p a t i cm e t a b o l i s mo f o m e p r a z o l em i g h t b e r e s p o n s i b l ef o r t h ei n i t i a li n c r e a s ei n AUC d u r i n g r e p e a t e dd o s i n g( A n d e r s s o ne ta l . ,1 9 8 9 ,1 9 9 0 )m i g h ti n s t e a db e c o n s i d e r e dt o b e t h emore l i k e l ye x p l a n a t i o n .S i n c e t h ee l i m i n a t i o nh a l f - l i f eo fo m e p r a z o l ew a s s i m i l a ri n t h et w o e x p e r i m e n t si t i sp r o b a b l ya d e c r e a s e df i r s t - p a s se l i m i n a t i o nt h a tc a u s e st h e i n c r e a s e dAUC. S i m i l a rf i n d i n g sh a v eb e e nr e p o r t e df o r o t h e r d r u g s ,f o r i n s t a n c em e t o p r o l o l ,w h i c h a l s od i s p l a y sa n i n c r e a s ei n AUC d u r i n g r e p e a t e d d o s i n g J o r d oe t a l . ,1 9 8 0 ) .

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d i s s o l v e di n t h e s t o m a c h a n d h e n c ec a n b e a b s o r b e dm o r er a p i d l y .

I t c a n b e c o n cl u d e dt h a tg a s t r i c a c i d i t yh a s n e g l i g i b l ei n f l u e n c eo n t h e b i o a v a i l a b i l i t y( i . e .AUC) o f o m e p r a -z o l ea d m i n i s t e r e da sEC g r a n u l e s .

We t h a n k S t i n aG a b r i e l s s o na n d An n L a r k o f o re x c e l l e n tt e c h n i c a lp e r f o r m a n c e ,a n d B r i t t - M a r i eG i a i n af o rt y p i n gt h em a n u s c r i p t .

R e f e r e n c e s

A n d e r s s o n ,T . , A n d r e n ,K . , C e d e r b e r g ,C . , L a g e r s t r o m ,P . O . , L u n d b o r g ,P . & S k a n b e r g ,I .- 1 9 9 0 ) .P h a r m a c o -k i n e t i c sa n d b i o a v a i l a b i l i t yo fo m e p r a z o l ea f t e rs i n g l ea n dr e p e a t e d a d m i n i s t r a t i o ni n h e a l t h y s u b j e c t s .B r .J . c l i n .P h a r m a c . ,2 9 ,5 5 7 - 5 6 3 .

A n d e r s s o n ,T . ,C e d e r b e r g ,C . ,H e g g e l u n d ,A . & L u n d b o r g ,P . 1 9 8 9 ) .O m e p r a z o l ep h a r m a c o k i n e t i c so f s i n g l ea n dr e p e a t e do n c ed a i l ya d m i n i s t r a t i o no f1 0 ,2 0 a n d 4 0 mg a se n t e r i cc o a t e d g r a n u l e s .E u r . J . c l i n . P h a r m ac . , 3 6 S u p p l . ) ,A 1 4 2

B a r d h a n ,K . D . , B i a n c h iP o r r o , G . , B o se ,K . , D a l y , M . ,H i n c h l i f f e ,R . F . C . ,J o n s s o n ,E . ,L a z z a r o n i ,M . , N a e s d a l ,J . , R i k n e r , L . & W a l a n ,A . 1 9 8 6 ) .A c o m p a r i s o no f t w od i f f e r e n td o s e so fo m e p r a z o l ev e r s u sr a n i t i d i n ei nt r e a t m e n to f d u o d e n a lu l c e r .J . c l i n .G a s t r o e n t e r o l . ,8 , 4 0 8 - 4 1 3 .

F e l l e n i u s ,E . ,B e r g l i n d h ,T . & S a c h s ,G . 1 9 8 1 ) .S u b s t i t u t e db e n z i m i d a z o l e si n h i b i tg a s t r i ca c i ds e c r e t i o nb y b l o c k i n g( H + , K + ) - AT P a s e .N a t u r e ,2 9 0 ,1 5 9 - 1 6 1 .

H e t z e l ,D . J . , D e n t , J . , R e e d , W. D . , N a r i e l v a l a ,F . M . ,M a c k i n n o n ,M . , M c C a r t h y ,J . H . , M i t c h e l l ,B . ,B e v e r i d g e ,B . R . , L a u r e n c e ,B . H . , G i b s o n ,C . G . , G r a n t , A . K . ,S h e a r m a n ,D . J . C . ,W h i t e h e a d ,R . & B u c k l e ,P . J . 1 9 8 8 ) .H e a l i n ga n dr e l a p s eo fs e v e r ep e p t i c e s o p h a g i t i sa f t e rt r e a t -m e n tw i t ho m e p r a z o l e .G a s t r o e n t e r o l o g y ,9 5 ,9 0 3 - 9 1 2 .

H u n t , J . N . K n o x ,M. T 1 9 7 2 ) .T h e s l o w i n go f g a s t r i ce m p t y i n gb y n i n e a c i d s .J . P h y s i o l . L o n d . ) ,2 0 1 ,1 6 1 - 1 7 9 .

J o r d o ,L . , A t t m a n , P . O . , A u r e l l ,M . J o h a n s s o n , L . ,J o h n s s o n ,G . & R e g a r d h ,C . G . 1 9 8 0 ) .P h a r m a c o k i n e t i ca n dp h a r m a c o d y n a m i cp r o p e r t i e so fm e t o p r o l o li np a t i e n t sw i t h i m p a i r e dr e n a lf u n c t i o n .C l i n .P h a r m a c o k i n . ,5 , 1 6 9 -1 8 0 .

K l i n k e n b e r g - K n o l ,E . C . , J a n s e n ,J . M. B . J . , F e s t e n ,H . P . M . , M e u w i s s e n ,S . G . M . & L a m e r s ,C . B . H . W. 1 9 8 7 ) .D o u b l e - b l i n dm u l t i c e n t r ec o m p a r i s o no fo m e p r a -z o l ea n d r a n i t i d i n ei n t h et r e a t m e n to fr e f l u xo e s o p h a g i t i s .L a n c e t ,i , 3 4 9 - 3 5 1 .

L a g e r s t r o m ,P . 0 . P e r s s o n ,B . A . 1 9 8 4 ) .D e t e r m i n a t i o no f

o m e p r a z o l ea n d m e t a b o l i t e si n p l a s m aa n d u r i n eb y l i q u i dc h r o m a t o g r a p h y .J . C h r o m a t o g r . ,3 0 9 ,3 4 7 - 3 5 6 .

L i n d , T . , C e d e r b e r g ,C . , E k e n v e d ,G . , H a g l u n d ,U . &O l b e , L . 1 9 8 3 ) .E f f e c t o fo m e p r a z o l e - ag a s t r i cp r o t o npump i n h i b i t o r - o np e n t a g a s t r i n s t i m u l a t e da c i d s e c r e t i o ni n m a n .G u t , 2 4 ,2 7 0 - 2 7 6 .

M u l l e r ,P . , S e i t z ,H . K . , S i m o n ,B . & Dammann, H . G . 1 9 8 3 ) .S a u r e s e k r e t i o n s v e r h a l t e nu n dP l a s m a s p i e g e lu n t e re i n e rm e h r t a g i g e nO m e p r a z o l e - G a b e / R e p e a t e do n c ed a i l ya d m i n i s t r a t i o no fo m e p r a z o l e :e f f e c to n g a s t r i ca c i ds e c r e -t i o na n d p l a s mal e v e l si n m a n . A r z n e i m i t t e l f o r s c h . ,3 3 ,1 6 8 5 - 1 6 8 6 .

P r i c h a r d ,P .J . , Y e o m a n s ,N . D . , M i h a l y ,G . W . ,J o n e s ,D . B . ,B u c k l e ,P . J . , S m a l l w o o d ,R . A . & L o u i s ,W. J . 1 9 8 5 ) .O m e p r a z o l e :a s t u d yo fi t si n h i b i t i o no f g a s t r i cpH a n do r a lp h a r m a c o k i n e t i c sa f t e rm o r n i n go r e v e n i n gd o s a g e .G a s t r o -e n t e r o l o g y ,8 8 ,6 4 - 6 9 .

T u y n m a n ,H . A . R . E . , F e s t e n , H . P . M . , R o h s s , K . M e u w i s s e n ,S . G . M. 1 9 8 7 ) .L a c ko fe f f e c to f a n t a c i d so np l a s m a c o n c e n t r a t i o n so f o m e p r a z o l eg i v e na s e n t e r i cc o a t e dg r a n u l e s .B r .J . c l i n .P h a r m a c . ,2 4 ,8 3 3 - 8 3 5 .

W a l a n ,A. , B a d e r , J . P . ,C l a s s e n ,M . , L a m e r s ,C .B . H . W . ,P i p e r ,D . W . , R u t g e r s s o n ,K . & E r i k s s o n ,S . 1 9 8 9 ) .E f f e c to fo m e p r a z o l ea n d r a n i t i d i n eo n u l c e rh e a l i n ga n d r e l a p s er a t e si n p a t i e n t sw i t h b e n i g ng a s t r i cu l c e r .Ne w E n g l .J .M e d . ,3 2 0 ,6 9 - 7 5 .

Wa l l m a r k ,B . ,B r a n d s t r o m ,A . & L a r s s o n ,H . 1 9 8 4 ) .E v i -d e n c ef o ra c i d - i n d u c e dt r a n s f o r m a t i o no f o m e p r a z o l ei n t oa n a c t i v ei n h i b i t o ro f( H + , K + ) - AT P a s ew i t h i nt h ep a r i e t a lc e l l .B i o c h i m .B i o p h y sA c t a , 7 7 8 ,5 4 9 - 5 5 8 .

W a l l m a r k ,B . , L o r e n t z o n ,P . & L a r s s o n , H . 1 9 8 5 ) .T h em e c h a n i s mo fa c t i o no f o m e p r a z o l e - as u r v e yo fi t si n h i b i -t o r ya c t i o n si n v i t r o .S c a n d . J . G a s t r o e n t e r o l . ,2 0 ,S u p p l .1 0 8 ,3 7 - 5 1 .

( R e c e i v e d1 M a y 1 9 9 0 ,a c c e p t e d2 2 O c t o b e r1 9 9 0 )