RECOMPRESSION OF TABLETS FORMED FROM

DIRECT COMPRESSION B A S E S

D . N . T r a v e r s , M . A 1 Shammat and K. Shah, School of Pharmacy, L e i c e s t e r P o l y t e c h n i c , L e i c e s t e r , L E 1 9BH, U . K .

When t a b l e t s a r e formed and recompressed r e p e a t e d l y b e f o r e e j e c t i o n t h e h y s t e r e s i s l o o p s o b t a i n e d by p l o t t i n g compression f o r c e a g a i n s t punch d i s p l a c e m e n t d e c r e a s e i n a r e a w i t h t h e number of r e c o m p r e s s i o n s (White,1977; T r a v e r s and Cox,1977). This c o u l d be due t o f u r t h e r v i s c o e l a s t i c / p l a s t i c d e f o r m a t i o n and should r e s u l t i n demonstrable changes i n t h e p h y s i c a l p r o p e r t i e s of t h e t a b l e t s . W e p r e p a r e d t a b l e t s (12 mm d i a . ) and compacts (39 mm d i a . ) of common d i r e c t compression b a s e s by slow compression i n a D a r t e c t e s t i n g machine. The f o r c e vs punch displacement p l o t s on r e c o m p r e s s i o n were o b t a i n e d d i r e c t l y v i a a n XY p l o t t e r and b o t h d i e s gave h y s t e r e s i s l o o p s which were s i m i l a r i n form. The e j e c t i o n f o r c e vs a x i a l d i s p l a c e m e n t p l o t s w e r e o b t a i n e d f o r e j e c t i o n a t c o n s t a n t s t r a i n r a t e . No l u b r i c a n t s were used. Some r e s u l t s f o r t a b l e t s a r e g i v e n below.

No. of Recompressions t o 20 kN

3

4

5

Max. E j e c t i o n Force? (N)

Sta-Rx 1500

1.15* 0.80

0.72

0.60

0.52

10

A v i c e l pH 101

0.74

0.54

0.52

0.48

157

Base

1

2

0.58

Paracetamol DC

0.61

0.54

0.51

0.49

0.49

800

Emdex

0.53

0.48

0.46

0.46

0.49

1200

Encompres s

0.32

0.24

0.23

0.23

0.22

1400

*

Area w i t h i n h y s t e r e s i s l o o p s (cm2).

1 cm2 E 0.1.J

t Mean of f i v e r e s u l t s . The r e s u l t s s u g g e s t t h a t t h e r e l a t i v e e a s e of e j e c t i o n i s r e l a t e d t o t h e r e d u c t i o n i n loop a r e a . Both Sta-Rx and A v i c e l a r e good t r a n s m i t t e r s of r a d i a l s t r e s s when under a x i a l l o a d ( S i x s m i t h , l 9 7 5 ; T r a v e r s and Cox,1977), and t h e i r e a s e o f e j e c t i o n p r o b a b l y r e s u l t s from s t r e s s r e l i e f by e l a s t i c o r v i s c o e l a s t i c r e l a x a t i o n w i t h i n t h e d i e ( c f . Rees and Rue, 1977; H i e s t a n d and o t h e r s , 1977). Moreover, a l t h o u g h t h e shape and v a l u e s f o r t h e e j e c t i o n f o r c e vs displacement p l o t s d i f f e r e d f o r compacts and t a b l e t s made from t h e same b a s e , they were r e p r o d u c i b l e f o r a l l e x c e p t Sta-Rx and A v i c e l . This would be e x p e c t e d i f t h e s e m a t e r i a l s e x h i b i t time-dependent s t r e s s r e l i e f w i t h i n t h e d i e . F u r t h e r e v i d e n c e f o r t h i s view h a s been o b t a i n e d from a s t u d y of s h o r t - t e r m ( t h i r t y minutes) r e l a x a t i o n o f t h e e j e c t e d compacts. Force vs d i s p l a c e m e n t p l o t s on d i a m e t r a l compression t o f r a c t u r e i n d i c a t e d t h a t A v i c e l and Sta-Rx b o t h showed s t r e s s r e l i e f by time-dependent y i e l d i n g ( c f . Rees and Rue,1977). H i e s t a n d , E . N . , Wells, J . E . & o t h e r s (1977). J . P h a r m . S c i . , 4 , 510-519. Rees, J . E . and Rue, P . J . (1977). J.Pharm.Pharmac., (Suppl),37P. S i x s m i t h D.G. (1975). Ph.D. T h e s i s , L ' n i v e r s i t y of Bradford. T r a v e r s , D.N. and Cox, M. (1977). 1 s t I n t e r n a t i o n a l Conference on P h a r m a c e u t i c a l Technology, Chatenay Malabry P a r i s 4, 121-134. White, P.J.P. (1977). Ph.D. Thesis (CNAA), L e i c e s t e r P o l y t e c h n i c .