Controlled-Release Technology - American Chemical Society

it seems that liposomes cannot carry drugs across the skin (2,3) ... through a 0.8 μιη filter (Nucleopore, Pleasanton, CA) to remove very ... The 0...
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Chapter 19

New Liposomal Delivery System for Controlled Drug Release Victoria M. Knepp, Robert S. Hinz, Francis C. Szoka, Jr., and Richard H. Guy

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Departments of Pharmaceutical Chemistry and Pharmacy, University of California—San Francisco, San Francisco, CA 94143

The in vitro release characteristics of a liposomal drug delivery device have been studied. The system consists of a molded agarose matrix in which progesterone is dispersed either free or associated with a liposome formulation. Drug release rates from the devices into aqueous buffer were measured at 37°C. The free progesterone release rate decreased rapidly over 24 hr with > 90% delivered. The liposomal patch, on the other hand, imposed apparent zero-order kinetics, delivering its progesterone payload at about 1%/hr over 24 hr. Further, the liposomal patch significantly slowed transdermal drug delivery across excised hairless mouse skin. The results suggest that the liposomal-based reservoir system can modulate drug input via the skin, and that the zero-order release of progesterone from liposomes is determined by slow transport out of the bilayer. The g o a l o f the r e s e a r c h d e s c r i b e d here was t o c h a r a c t e r i z e a new l i p o s o m a l r e s e r v o i r system f o r c o n t r o l l e d drug r e l e a s e (_1_) and t o determine whether i t c o u l d meter drug d e l i v e r y t o the s k i n . While i t seems t h a t liposomes cannot c a r r y drugs a c r o s s the s k i n ( 2 , 3 ) ( d e s p i t e e a r l i e r c l a i m s (4,5) t o the c o n t r a r y ) , t h e i r a m p h i p a t h i c s t r u c t u r e p r o v i d e s an environment i n which h i g h c o n c e n t r a t i o n s o f d r u g s , of d i v e r s e p h y s i c o c h e m i c a l p r o p e r t i e s , can be s o l u b i l i z e d . A l s o , the b i l a y e r can be used t o modulate drug r e l e a s e through the c h o i c e of l i p i d f o r m u l a t i o n . P r e l i m i n a r y e x p l o r a t i o n o f these p o t e n t i a l a t t r i b u t e s a s s o c i a t e d w i t h drug d e l i v e r y from liposomes i s described. Methods The c o n t r o l l e d r e l e a s e d e v i c e c o n s i s t s of a t h i n drug f o r m u l a t i o n agarose g e l s u p p o r t e d on an impermeable b a c k i n g m a t e r i a l . A number

0097-6156/87/0348-0267$06.00/0 © 1987 American Chemical Society

Lee and Good; Controlled-Release Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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of drug f o r m u l a t i o n s have been c o n s i d e r e d , two of which are d i s c u s s e d here: (a) p r o g e s t e r o n e (PG) a l o n e , (b) PG a s s o c i a t e d w i t h m u l t i l a m e l l a r egg p h o s p h a t i d y l c h o l i n e (EPC) liposomes, PG was purchased from Sigma C h e m i c a l Co. ( S t . L o u i s , MO); f o r a n a l y s i s of drug i n the r e l e a s e e x p e r i m e n t s , a s m a l l amount of Cl a b e l e d PG (R.P.I. Corp., Mount P l e a s a n t o n , IL; 50 yCi/ymole) was i n c o r p o r a t e d i n t o the f o r m u l a t i o n s d u r i n g p r e p a r a t i o n . L i p i d s were o b t a i n e d from Sigma C h e m i c a l Co. ( S t . L o u i s , MO) and were checked f o r p u r i t y by t h i n l a y e r chromatography. Agarose used i n the d e l i v e r y systems was Seaplaque® (FMC Corp., R o c k l a n d , ME) and the d e v i c e s were c a s t on Gelbond (FMC Corp., Marine C o l l o i d s D i v i s i o n , R o c k l a n d , ME). M u l t i l a m e l l a r liposomes were p r e p a r e d by s t a n d a r d methods ( 6 ) , and p r i o r to i n c o r p o r a t i o n i n t o the d e l i v e r y systems, were passed t h r o u g h a 0.8 μιη f i l t e r ( N u c l e o p o r e , P l e a s a n t o n , CA) to remove v e r y l a r g e s t r u c t u r e s and/or a g g r e g a t e s . D e v i c e s were prepared as f o l l o w s : - 0.5 ml of PG f o r m u l a t i o n ( e i t h e r f r e e drug, or drug a s s o c i a t e d w i t h EPC l i p o s o m e s , i n NaCl (0.1 M) - Na c i t r a t e (0.03 mM) pH 4.5 b u f f e r ) and 0.5 ml agarose were warmed to 65-70°C and were then mixed t h o r o u g h l y . The m i x t u r e was poured i n t o a mold (a 2.0 cm d i a m e t e r T e f l o n 0 - r i n g ) s e t up on the Gelbond b a c k i n g . The d e v i c e s produced were a p p r o x i m a t e l y 0.3 cm thick. The 0 - r i n g was removed once the d e v i c e had s o l i d i f i e d on cooling. Systems were s t o r e d f o r no l o n g e r than 24 hr at 4°C p r i o r to t e s t i n g . PG r e l e a s e from the two d e l i v e r y systems was monitored u s i n g an automated, i n v i t r o d i f f u s i o n c e l l system. The d e v i c e s were clamped i n v e r t i c a l g l a s s d i f f u s i o n c e l l s w i t h the r e l e a s i n g s u r f a c e of the system f a c i n g i n t o the r e c e p t o r chamber. The l a t t e r c o n t a i n e d N a C l Na c i t r a t e b u f f e r and was c o n t i n u o u s l y p e r f u s e d at 10 ml/hr. P e r f u s a t e was c o l l e c t e d h o u r l y f o r up to 48 h o u r s . The r e c e p t o r phase of the d i f f u s i o n c e l l was m a g n e t i c a l l y s t i r r e d and was kept at 37°C. Samples were a n a l y z e d by l i q u i d s c i n t i l l a t i o n c o u n t i n g . For each d e l i v e r y system, 6 r e p l i c a t e s were run and the d a t a p r o v i d e d both c u m u l a t i v e PG r e l e a s e d and PG r e l e a s e r a t e per u n i t t i m e . T r a n s d e r m a l t r a n s p o r t of PG was f o l l o w e d ±n_ v i t r o . Fullt h i c k n e s s s k i n , e x c i s e d from h a i r l e s s mice (SKH:HR-1, S k i n Cancer H o s p i t a l , P h i l a d e l p h i a , PA) and used immediately, was i n t e r p o s e d between d e l i v e r y system and r e c e p t o r chamber. S e r i a l samples of r e c e p t o r f l u i d were c o l l e c t e d and a n a l y z e d as b e f o r e . Experiments were performed i n q u a d r u p l i c a t e . Results PG r e l e a s e curves i n t o b u f f e r from f o r m u l a t i o n s (a) and (b) are i n F i g u r e s 1 and 2, r e s p e c t i v e l y . The F i g u r e s show mean (± S.D.) r e l e a s e r a t e of drug as a f u n c t i o n of time and a r e p r e s e n t a t i v e p l o t of the c u m u l a t i v e PG l i b e r a t e d from the d e l i v e r y system d u r i n g the experiment. The ' f r e e ' PG system [ ( a ) ] r e l e a s e d 90.4% (±5.5%) of the dose i n 24 hours compared to the EPC d e v i c e [ ( b ) ] from w h i c h 24.8% (±3.8%) was l i b e r a t e d d u r i n g the same p e r i o d . The v a l u e s are s i g n i f i c a n t l y d i f f e r e n t at ρ < 0.01.

Lee and Good; Controlled-Release Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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19.

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Lee and Good; Controlled-Release Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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PG f l u x e s i n t o the r e c e p t o r chamber f o l l o w i n g d e l i v e r y a c r o s s h a i r l e s s mouse s k i n from f o r m u l a t i o n s (a) and (b) are shown i n F i g u r e s 3 and 4, r e s p e c t i v e l y . PG a s s o c i a t i o n w i t h EPC liposomes [ ( b ) ] lowers by o n e - h a l f the t r a n s d e r m a l d e l i v e r y of the drug when compared to the ' f r e e p a t c h [ ( a ) ] . 1

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Discussion The PG r e l e a s e d a t a i n t o b u f f e r ( F i g u r e s 1 and 2) show that the EPC liposome f o r m u l a t i o n can r e p r o d u c i b l y change the drug d e l i v e r y kinetics. The z e r o - o r d e r b e h a v i o r o b s e r v e d s u g g e s t s t h a t PG i s not r e l e a s e d from system (b) by a s i m p l e d i f f u s i o n mechanism. Such a p r o c e s s would e x h i b i t a c l a s s i c " b u r s t e f f e c t " (7_) and the c u m u l a t i v e PG r e l e a s e d would be l i n e a r w i t h the square r o o t of time; i n s t e a d , c o n s t a n t r e l e a s e r a t e w i t h time i s seen. A p o s s i b l e mechanism i n v o k e s slow t r a n s p o r t of PG out of the l i p o s o m a l b i l a y e r as the r a t e - d e t e r m i n i n g s t e p . The o c t a n o l - w a t e r p a r t i t i o n c o e f f i c i e n t of PG i s almost 1 0 (8) and n e a r l y a l l the PG i n f o r m u l a t i o n (b) i s a s s o c i a t e d w i t h the l i p i d b i l a y e r , t h e r e f o r e . If the i n t e r f a c i a l t r a n s f e r of drug from b i l a y e r to s u r r o u n d i n g aqueous medium i s slow compared to i t s subsequent d i f f u s i o n through the aqueous spaces of the agarose g e l , then the PG e f f l u x r a t e w i l l be p r o p o r t i o n a l to k.c, where k i s the t r a n s f e r r a t e c o n s t a n t and c i s the PG c o n c e n t r a t i o n i n the b i l a y e r . T h i s f o r m a l i s m i s r e a s o n a b l e p r o v i d e d t h a t the b i l a y e r - a s s o c i a t e d PG i s not s i g n i f i c a n t l y depleted. F o r the f i r s t 24 hours of PG r e l e a s e from system ( b ) , a t l e a s t , the r e s u l t s are s u p p o r t i v e of the above h y p o t h e s i s . Further work i s r e q u i r e d to v a l i d a t e f u l l y the mechanism p r o p o s e d . 4

T r a n s d e r m a l PG d e l i v e r y a c r o s s h a i r l e s s mouse s k i n J j i v i t r o demonstrates t h a t the l i p o s o m a l p a t c h can modify percutaneous drug absorption. Comparison of F i g u r e s 1 and 3 shows t h a t PG appearance i n the r e c e p t o r chamber, f o l l o w i n g a d m i n i s t r a t i o n to the s k i n i n the free PG p a t c h [ ( a ) ] , i s s k i n - c o n t r o l l e d . In t h i s c a s e , the s k i n i s a r a t e - l i m i t i n g membrane and the d e l i v e r y system a c t s as a r e s e r v o i r of PG. T r a n s p o r t f o l l o w s F i c k ' s 1st Law of D i f f u s i o n and a s t e a d y - s t a t e f l u x of 0.45% per hour i s o b s e r v e d . PG a s s o c i a t e d w i t h EPC liposomes ( d e v i c e ( b ) , F i g u r e 4 ) , slows t r a n s d e r m a l throughput to one h a l f t h a t o b t a i n e d w i t h d e v i c e ( a ) . A l t h o u g h PG i s r e l e a s e d from system (b) f a s t e r than i t p e n e t r a t e s the s k i n , the d e v i c e does modify the percutaneous k i n e t i c s . I t seems r e a s o n a b l e t o suggest t h a t a p p r o p r i a t e a l t e r a t i o n of the l i p i d c o m p o s i t i o n of the b i l a y e r can slow f u r t h e r the PG r e l e a s e r a t e such t h a t g r e a t e r c o n t r o l of t r a n s d e r m a l d e l i v e r y r e s i d e s w i t h the p a t c h . f

f

Summary A. B. C.

A l i p o s o m a l drug d e l i v e r y system has been p r e p a r e d and characterized. The system has been t e s t e d i n v i t r o and i s c a p a b l e of m o d i f y i n g PG d e l i v e r y a c r o s s h a i r l e s s mouse s k i n . The mechanism of PG r e l e a s e from the l i p o s o m a l system may i n v o l v e slow p a r t i t i o n i n g of drug at the b i l a y e r - a q u e o u s phase interface.

Lee and Good; Controlled-Release Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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Lee and Good; Controlled-Release Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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Acknowledgments P r i n c i p a l f u n d i n g was p r o v i d e d by Liposome Technology I n c . , Menlo Park, CA. A d d i t i o n a l s u p p o r t was r e c e i v e d from the Donors of the P e t r o l e u m R e s e a r c h Fund, a d m i n i s t e r e d by the American C h e m i c a l S o c i e t y (PRF //17438-AC7). We thank Dr. R.A. S i e g e l f o r h e l p f u l i n s i g h t and Andrea Mazel f o r p r e p a r i n g the m a n u s c r i p t .

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. RECEIVED

Wester, R.C.; Szoka, F.C.; Bucks, D.A.W.; Maibach, H.I.; "Abstracts", American Pharmaceutical Association, Academy of Pharmaceutical Sciences, 37th National Meeting, 1984, 14, 229. Ganesan, M.G.; Weiner, N.D.; Flynn, G.L.; Ho, N.F.H. Int. J. Pharm., 1984, 20, 139-154. Ho, N.F.H.; Ganesan, M.G.; Weiner, N.D.; Flynn, G.L. J. Control. Rel., 1985, 2, 61-65. Mezei, M.; Gulasekharam, V. Life Sci., 1980, 26, 1473-1477. Mezei, M.; Gulasekharam, V. J. Pharm. Pharmacol., 1982, 34, 473-477. Szoka, F.C.; Papahadjopoulos, D. Ann. Rev. Biophys. Bioeng., 1980, 9, 467-508. Crank, J. "The Mathematics of Diffusion"; Oxford University Press: New York, 1975, 37. Leo, Α.; Hansch, C.; Elkins, D. Chem. Rev., 1971, 71, 525-616. October 10, 1986

Lee and Good; Controlled-Release Technology ACS Symposium Series; American Chemical Society: Washington, DC, 1987.