The in vitro dissolution was undertaken according to the USPXXI dissolution, apparatus II or paddle method (Pharmatest dissolution tester type PTWS, Hainburg, Germany) with a stirring speed of 100 rpm, in 900 ml of a dissolution medium, the temperature of which was kept a t3 7 °C ± 0 .5 °C . For each formulation, 6 replicates of
the dissolution test were carried out with a weighed amount of pellets (Oertling balance Model 1702, W&T Avery Ltd., Warley, UK) from sieve fractions 1000-1400 pm and/or 1400-1700 pm, depending on the study, indicated in the result section.
To ensure sink conditions and the ability to analyse the drug released into the solution, the drug content in each formulation was adjusted. For pellets of paracetamol, sufficient pellets to give 1 0 mg of paracetamol were used and the dissolution study was
carried out in SGF. For diclofenac sodium, ibuprofen, and indomethacin, pellets containing 20 mg, 14 mg, and 12 mg of the drug, respectively, were used and the dissolution studies were undertaken in SIF.
Approximately 3 ml of filtered samples were automatically taken (Pharmatest PTFCII Sample collector, Hainburg, Germany) when the dissolution proceeded up to the predetermined time, t, 5, 10, 15, 30, 45, 60, 90, 120, 150, 180 min, and thereafter at 60 min intervals until 360 min ( 6 h) of total dissolution testing time for relatively water
soluble drugs (paracetamol and diclofenac sodium), and 15,30,60,90,120,150,180 min and thereafter at 60 min intervals until 720 min (12 h) of total dissolution testing time for water insoluble drugs (ibuprofen and indomethacin).
The sample collected was then analysed for the dissolved drug content by a UV- Vis spectrophotometry (UV-Vis spectrophotometer model 554, Bodenseewerk Perkin- Elmer & Co. GmbH, Uberlingen, Germany) at the maximum wavelength of 243 nm (paracetamol), 276 nm (diclofenac sodium), 222 nm (ibuprofen), and 266 nm (indomethacin). The cumulative percentage of drug released from pellets into the
dissolution medium up to time, t h, was then determined, based on the drug content in the formulation o f pellets. The corresponding data were further analysed according to the statistical moment theory proposed by Voegele et al. (1988), provided that a minimum cumulative percentage of drug released o f up to 95% at time, t, otherwise a cumulative percentage of drug released up to the total dissolution testing time, which exceeded 50%, was the final measuring value for the integration procedure. The arithmetic mean and standard deviation of the area under the dissolution curve (AUC), the mean dissolution time (MDT), the variance associated with the MDT (VR), and the relative dispersion of the dissolution time (RD), represent the dissolution characteristics of the drug. The RD value is used to be indicative of the specific model of drug release, as proposed by Voegele et al. (1988).
CHAPTERS:
THE INFLUENCE OF CHITOSAN, SODIUM ALGINATE
AND FORMULATION VARIABLES
ON THE FORMATION AND DRUG RELEASE
3.1 INTRODUCTION
Chitosan and sodium alginate in an aqueous solution of desired pH level show, respectively, the polycationic and polyanionic properties, described in section 2.1.1.1.
With consideration of the possibility of interaction between the oppositely charged polymers in aqueous media, i.e. binder liquid and/or dissolution medium, the addition of these polymers into the formulation of pellets was of interest. A set of experiments was designed to determine the influence of these polymers and the effect of potentially influencing factors such as the level of a model drug, the pH level of binder liquid, and the level of microcrystalline cellulose in the formulation of pellets assessed by the ability to form spherical pellets by the process of extrusion/spheronization and the in vitro drug release from resultant pellets.
3.2 MATERIALS
3.2.1 Excipients
Microcrystalline cellulose (Avicel PH-101 (MCC)), chitosan, sodium alginate, lactose. The details of these materials are given in section 2.1.1.1.
3.2.2 Drug
Paracetamol. The detail of this drug is described in section 2.1.2.
3.2.3 Binder liquids
Freshly prepared McILVAINE buffers of pH 2.2, 3, 3.8, 4.6 and 5.4, prepared as described in section 2.1.3; distilled water of a measured pH of 5.2.
3.2.4 Dissolution medium
Simulated gastric fluid, without pepsin. The composition of this dissolution medium is given in section 2.1.4.
3.3 METHODS
3.3.1 Formulation
The dry mixtures of 250 g total weight were studied. The compositions of the formulations o f pellets are presented in Table 3.1. Twenty-nine formulations were chosen to perform a statistically experimental plan based on the centre of gravity design as presented by Podczeck (1995).
On the basis of the design, a scale of five values for each variable with a constant level of other variables at the centre value of the experimental design were chosen. Five formulation variables were investigated. These were: level of paracetamol (LP) ranging from 2.5% to 40%, formulations no. 1- 4 and no. 11; level of MCC or Avicel PH-101 (LA) ranging from 30% to 70%, formulations no. 5-8 and no. 11; levels of chitosan (LC) and sodium alginate (LSA), each of which varied from 0% to 4% while a total amount of LC and LSA remained constant at a 4% level, formulations no. 9-13; pH level of binder liquids (PH) ranging from 2.2 to 5.4, formulations no. 14-17 and no. 11.
In addition to the basic design, the plan was expanded to evaluate the effect of the pH level of distilled water used as a binder liquid instead o f the buffer, formulation no. 18; the formulation with no added polymer, formulation no. 19; the interaction between the minimum pH level studied (pH 2.2) and the 4 % level of each added polymer, formulations no. 20-21; the interaction between the maximum pH level studied (pH 5.4) and the 4 % level o f each added polymer, formulations no. 22-23; and the equilibrium time o f 0, 18 and 36 h, formulations no. 24, no. 11 and no. 25, respectively. Two relatively high levels (8 % and 16%) of chitosan, formulations no. 26-27 and of sodium
alginate, formulations no. 28-29 were also taken into the plan to obtain more information. The formulation variables were thus investigated, their influence, if any, and to which extent they produced an effect on the required binder liquid level, the steady state extrusion force, the characteristics of pellets (size, shape, perimeter, density, porosity), and in vitro drug release from pellets. Despite the fact that the level of lactose (LL) varied (Table 3.1), it was not considered as a variable because it represented the missing amount of additives to make the formulation up to the 1 00 % level.
Table 3.1 The experimental plan used to investigate the influence of chitosan, sodium Formulation LP(%) LA (%) LC (%) LSA (%) LL(%) PH 1 2.5 50 2 2 43.5 3.8 2 5 50 2 2 41 3.8 3 20 50 2 2 26 3.8 4 40 50 2 2 6 3.8 5 1 0 30 2 2 56 3.8 6 1 0 40 2 2 46 3.8 7 1 0 60 2 2 26 3.8 8 1 0 70 2 2 16 3.8 9 1 0 50 4 0 36 3.8 1 0 1 0 50 3 1 36 3.8 IH 1 0 50 2 2 36 3.8 1 2 1 0 50 1 3 36 3.8 13 1 0 50 0 4 36 3.8 14 1 0 50 2 2 36 2 . 2 15 1 0 50 2 2 36 3.0 16 1 0 50 2 2 36 4.6 17 1 0 50 2 2 36 5.4 18 1 0 50 2 2 36 5.2 19 1 0 50 0 0 40 3.8 2 0 1 0 50 4 0 36 2 . 2 2 1 1 0 50 0 4 36 2 . 2 2 2 1 0 50 4 0 36 5.4 23 1 0 50 0 4 36 5.4 24^ 1 0 50 2 2 36 3.8 25' 1 0 50 2 2 36 3.8 26 1 0 50 8 0 32 3.8 27 1 0 50 16 0 24 3.8 28 1 0 50 0 8 32 3.8 29 1 0 50 0 16 24 3.8
LP, level of paracetamol; LA, level of microcrystalline cellulose (Avicel PH-101); LC, level of chitosan; LSA, level of sodium alginate; LL, level of lactose; PH, pH level of binder liquid.
^ Centre of gravity experiment with the equilibrium time of 18 h. ^ Equilibrium time o f 0 h.
3.3.2 Preparation of the wet powder mass
For most formulations (Table 3.1), the standard process of preparing the wet powder mass, as described in section 2.2.2.1, was carried out using McILVAINE buffers as binder liquids, except formulation no. 18 in which distilled water was used. After mixing, the wet powder mass was placed in a polythene bag, sealed and equilibrated for 18 h for formulations no. 1-23 and no. 26-29, and 36 h for formulation no. 25 before being extruded, to allow the water to distribute throughout the mass. For one of the formulations studied, formulation no. 24, the wet powder mass was extruded immediately after the preparation of wet powder mass, i.e. equilibrium time was 0 h.