Formulation and Evaluation of Spray-dried Combination Respirable Powder Based on Selection of Excipients for Pulmonary Delivery: Comparison between Lactose and Mannitol

 

R.  R. Shah, M. S. Kondawar, S. S. Shinde and N. D. Shah*

Appasaheb Birnale College of Pharmacy, Sangli-416416, Maharashtra, India.

*Corresponding Author E-mail: nutanu56@gmail.com

 

ABSTRACT:

The aim of this study was to examine the influence of excipients on physical characteristics of combination dry powder inhaler formulation which contains salmeterol xinafoate (SX) and fluticasone propionate (FP).  The formulation was prepared by Spray drying of micropariculate suspensions. The excipients used were α-lactose monohydrate and D-mannitol. Poloxamer 188 was used as a stabilizer. The powders generated were of a suitable size for inhalation with satisfactory yield. It was found that in optimum concentration with poloxamer 188; lactose and mannitol gave increased spray drying thermal efficiency. FTIR study showed the close agreement among the spectra of all spray dried formulations and APIs. Effect of excipients was further investigated by different physical characters of spray-dried formulations. The formulation was evaluated for in vitro drug release study by the modified USP II dissolution apparatus. Dissolution study gave immediate drug release profiles. The stability study indicated that all the formulations were quite stable at accelerated storage conditions. The results obtained from all observations indicate that in presence of poloxamer 188; mannitol was found to be superior over the lactose as an excipient; for the combination dry powder inhaler formulation containing salmeterol xinafoate and fluticasone propionate.

 

KEYWORDS: Combination dry powder, Long-acting β-2 agonist, Long acting corticosteroid, Pulmonary delivery, Spray drying.

 

 


INTRODUCTION:

The respiratory tract is established as an attractive route for drug delivery. For drugs that exert their biological effect in the lung, these include rapid onset of action, reduced dose and minimized side effects compared to the same drug delivered by mouth1. Pulmonary drug delivery has attracted tremendous scientific and biomedical interest in recent years and has progressed considerably within the context of local treatment for lung diseases, by virtue of enhanced local targeting and reduced systemic side effects with the administration of minute drug dosages. Pulmonary tract tends to be considered as very promising and attractive route for the administration of active substances intended to treat local pulmonary (e.g., asthma, chronic obstructive pulmonary disease (COPD), microbial infections) as well as systemic diseases (e.g., diabetes)2.

 

A wide variety of agents has been administered to the lung via oral inhalation, for the treatment of diverse disease states. The most frequent use of inhalation therapy is for the treatment of obstructive airway diseases using drugs such as short and long-acting β sympathomimetics, corticosteroids, and anticholinergic agents. However, the respiratory route has been receiving increased attention since the early 1990s as an alternative to parenteral drug delivery, most notably for the delivery of inhaled insulin3.

 

Small molecules such as β2 agonists e.g. Salbutamol (Ventolin®), Terbutaline (Bricanyl®), Salmeterol (Serverent®), Formeterol  Oxis®), and glucocorticoids e.g. Budesonide (Pulmicort®) and Fluticasone (Flutide®), for local administration in the lungs, are all part of successful treatment of respiratory disease such as asthma, rhinitis and chronic obstructive pulmonary disease (COPD). Drug delivery to the lung can be improved not only by using better devices but also through more rationalized formulation. DPI consists of drug and carrier particles either mixed or co-precipitated together into dry powder form. Size of drug/dry powder is important and should be near spherical in shape and monodispersed with aerodynamic diameter range of 0.5 to 5 μm4.

A particle size of 2–5 μm yields optimal benefit, whereas for systemic effects particle size of less than 2 μm is needed for drug deposition in the small peripheral airways. Spray drying offers an alternative approach to the generation of dry, potentially respirable powders for local pulmonary drug delivery. Spray drying is a one-step constructive process that provides greater control over particle size, particle morphology and powder density5.

 

The other techniques for formulation of stable micron sized DPI products includes milling, simple mixing of carrier with the drug, co-precipitation of drug and carrier by lyophilization and milling, specialized spray-drying, spray freeze drying, ultrasound assisted crystallization, flash crystallization, controlled precipitation, and supercritical fluid technologies. These methods have the advantages of higher product yield, lower operating temperature, and higher powder crystallinity. However, all the techniques suffer from the disadvantage of high operating cost and impurity4.

 

Currently, lactose is the most commonly used excipient in marketed DPIs (Beclophar®, Flixotide®, Relenza®, Seretide®, Spiriva®, Symbicort®). It has an established safety and stability profile, different manufacturing processes with tight controls over purity and physical properties, is easily available at different grades and is inexpensive. Published inhalation studies in humans have shown no local effects of lactose by inhalation.

 

Furthermore, in contrast to oral administration, lactose swallowed at the levels present in inhaled preparations (up to 25 mg) is unlikely to present problems even in patients with lactose intolerance. Nearly all DPI products already on the market rely on lactose as a carrier material. Manufacturers utilize different physical forms of lactose for inhalation such as α-lactose monohydrate or anhydrous β-lactose, obtained by various techniques such as milling or spray drying and presenting a wide range of particle-size distribution. It has been shown that the crystallinity of lactose plays an important role; having high-energy surfaces, amorphous lactose exhibits strong adhesive interactions with drug particles, leading to low inhalation efficiency. Therefore, α-lactose monohydrate, the crystalline form is most commonly employed as a drug carrier in DPIs. But lactose may not be the carrier of choice due to its sugar-associated reducing function that may interact with functional groups of drugs such as formoterol or peptides and proteins.

 

Mannitol, which is a sugar alcohol previously inhaled for diagnosis of bronchial hyper responsiveness, has emerged as a promising carrier. In addition, mannitol was shown to stimulate the reserve capacity of the mucociliary system and to enhance clearance of mucus6.

 

It has been demonstrated that the presence of Poloxamer 188 in the feed emulsion results in particles with improved dispersibility and a higher fine particle fraction7. It is interesting to note that 2% of Poloxamer 188 significantly improved powder flowability6.

 

Co-precipitation or co-spray drying a solution containing two APIs is a potential alternative to produce particles of uniform drug composition. However, this process usually results in amorphous powders which are cohesive and physically unstable. The low FPF was attributed to low flow ability and high adhesiveness of the amorphous powder.  Furthermore, due to the low-dose of both a long-acting β-2 agonist and a long-acting corticosteroid (50–100µg) the co-spray dried or co-precipitated powders cannot be administered without a diluent or bulking agent. Thus, blending with carriers will introduce additional process variables. These shortfalls can potentially be avoided by incorporating a crystalline excipient into the co-spray drying solution. Suspensions were prepared by liquid anti-solvent precipitation technique i.e. Solvent   displacement method6, 8.

 

MATERIALS AND METHODS:

Materials:

Micronised Salmeterol xinafoate and Fluticasone propionate were donated by Vamsi Labs Ltd., Solapur and Sun pharm. Ind. Ltd., Mumbai respectively. α-lactose monohydrate and Poloxamer 188 were obtained from  Research Lab., Mumbai, D-mannitol was procured from S. D. fine chemicals, Mumbai, Potassium dihydrogen phosphate (KH2PO4) and Sodium hydroxide (NaOH) were purchased from Finar chemicals Ltd., Ahmadabad, KBr was obtained from Loba chemicals, Mumbai. Ethanol was supplied by Fisher Scientific LTD. (Loughborough, UK). Water was purified by reverse osmosis (MilliQ, Molsheim, France). All other materials used were of analytical grade.

 

From this point forward, α-lactose monohydrate and D-mannitol will be referred to as lactose and mannitol. L-series batches are containing lactose and poloxamer 188 as excipients whereas M-series batches contained mannitol and poloxamer 188 as excipients

.

Formulation of microsuspension:

Microsuspensions were prepared by liquid anti-solvent precipitation technique (solvent displacement method) according to the formulae given in Table-1 and Table 2. Ethanol (95%) was used as a Solvent while Distilled Water as Antisolvent.  Solvent: Anti-solvent ratio: 30:70. For L series batches, lactose (500 mg) was used as diluent for each batch.

 

 

Table 1: Formulation component for Batch L series

Formulation code

SX:FP

SX:FP: Poloxamer 188

L1

1:2

1:0.5

L2

1:2

1:1

L3

1:2

1:1.5

Lactose (500 mg) was used as diluent for each batch.

 

 

Table 2: Formulation component for Batch M series

Formulation code

SX:FP

Mannitol

Poloxamer 188

(% w/v)

M1

1:2

0.5 gm

-

M2

1:2

1 gm

0.1

M3

1:2

1 gm

0.05

 

Briefly, the fine drugs were dissolved in ethanol (solvent) and sonicated to get the diffusing phase. Excipients were dissolved in distilled water (non-solvent) to obtain dispersing phase. For every batch, different concentrations of excipients were added as shown in formulation Table 1 and Table 2. Diffusing phase was then added to the dispersing phase i.e. to non-solvent by means of a 18 G 11/2 TW syringe positioned with the needle directly in the medium under continuous stirring for 1 hr at 1200-1500 rpm by using Lab stirrer (Remi-Motors).

 

Conversion of dispersion (microsuspension by solvent displacement method) into Dry powder for inhalation by spray drying9

Table 3: Spray drying parameters

Parameter

Optimized conditions

Inlet Temperature

1200C

Outlet Temperature

600C

Aspirator Speed

80 %

Feed Pump Speed

10 ml

Atomization pressure

20-30 psi

Vacuum (mmWc)

-80 mmWc

 

Spray drying using a ,Lab Spray Dryer(LU-222 LABULTIMA, Mumbai) with a co-current 0.7 mm, two fluid nozzle equipped with autojet  deblocking system, was applied in order to retrieve respirable powders in dried state from suspension described above. Suspensions were spray dried with constant stirring with the help of magnetic stirring (Whirlmatic Mega, SPECTRALAB). The conditions used during spray drying were as mentioned in the Table 3. The resultant dry powder was blown through cyclone separator and collected in container. Powders were kept in glass vials and stored in glass vials and stored in desiccator at ambient temperature before use.

 

CHARACTERIZATION OF DRY POWDER FOR INHALATION (DPI):

Particle size analysis, Percentage yield and drug content:

The particle size was measured by laser diffraction (HELOS, Sympatec, Germany). The Sample was suspended in double distilled water saturated with both drugs under ultrasonication in an appropriate dilutions and immediately afterwards transferred to a 6 ml cuvette for measurement. For each batch, the measurement was carried out in triplicate using three individual samples. The polydispersity index (PI) is also an important parameter as it gives an indication about the width of particle size distribution as well as the long-term stability of dispersion. A PI value of 0.1–0.25 indicates a narrow size distribution whereas a PI value greater than 0.5 indicates a very broad distribution10. The yields of preparation were determined by the weight of the products, spray dried powders, with respect to the weight of the initial drugs and excipients used.

 

The drug content of spray dried powders was determined using UV spectrophotometry. Samples from each batch of spray dried formulation were dissolved in phosphate buffer (pH-7.4); ethanol (95%) in 90:10 proportions and the actual drug content was determined by first-derivative UV spectrophotometer (JASCO model V-550, JAPAN UV-visible double beam spectrophotometer). Drug loading was calculated from the ratio of actual drug content to total weight of spray dried powders taken for analysis and expressed as a percentage11.

 

Fourier transform infrared spectrometry (FTIR):

While developing a new formulation, it is necessary to check the drug compatibility with the carrier or excipient used and that the drug has not undergone any degradation when it passes through the various processes. Infrared spectroscopy is one of most powerful analytical technique when it comes to the determination of presence of various functional groups involved in making up the molecule. It provides very well accountable spectral data regarding any change in the functional group characteristics of a drug molecule occurring while in the processing of a formulation.

 

Fourier transform infrared spectrometry (FTIR) spectra of pure drugs; salmeterol and fluticasone, physical mixture, and all formulations were recorded with a JASCO FTIR-410, JAPAN FTIR Spectrophotomer in order to rule out drug-carrier interaction occurring during the formulation process. The spectra were scanned over wavelength region of 400 to 4000 cm-1, resolution of 4 cm-1 and accumulation of 20 scans were used in order to obtain good quality spectra by making a pellet of the sample with KBr. The procedure consisted of grinding the sample with KBr in an agate mortar and pestle and compressing the sample in an evacuable KBr die by applying a pressure of 5 tons for 5 min in a hydraulic press, Techno search instrument M-15 KBr press (KBr pellet method). The pellet was placed in the light path and the spectrum was obtained12.

 

Scanning electron microscopy (SEM):

The Surface appearance and shape of the spray dried powders were investigated by scanning electron microscopy. Drugs and all spray dried formulations were mounted onto separate, adhesive coated aluminium pin stubs. Excess powder was removed by tapping the stubs sharply and then gently blowing a jet of particle-free compressed gas across each. The specimen stubs were sputter coated with a thin layer of gold in a JEC-550 Twin coating unit at 10 mA for 4 min using an argon gas purge. The specimens were examined using a scanning electron microscope (SEM, JEOL-JSM-5400).The SEM was operated at high vacuum with an accelerating voltage 0f 5-10 kV. Secondary electron images were recorded digitally at higher magnification. Particles surface was determined by examining the microphotographs13.

Differential scanning calorimetry (DSC):

The phase transition of the pure drug, excipients, and all spray dried formulation batches  were studied by thermogram obtained by using Differential scanning calorimeter (Dupont 2000, model SDT- 2960, USA).  An empty aluminum pan was used as reference.  DSC measurements were performed at the heating rate of 10 oC/ min from 25 to 350oC using aluminum sealed pan. Sample weight was kept between 5- 10 mg. During the measurement, the sample cell was purged with nitrogen gas8.

 

X-Ray powder diffraction study (XRD):

The crystalline nature of pure drug and all spray dried formulation batches were examined by studying its X-Ray diffraction patterns by using powder X-Ray diffractometer (PW- 3710 BASED). It was determined whether the obtained formulation after precipitation is a coprecipitate of individual substances or whether it becomes cocrystal. The operating parameters for instrument were Cu filtered K (α) radiations, a voltage of 40 kV, current of 25 mA and receiving slit of 0.2 In. The instrument was operated over 2θ scale. The angular range was 5 to 50o (2θ) and counts were accumulated for 0.8 second at each step14.

 

Powder density:

The poured density of all spray dried formulations was determined by pouring a known mass of powder under gravity into a calibrated measuring cylinder and recording the volume occupied by the powder. The tapped density of the spray dried powders was determined by tapped density measurements on the same samples until no further change in the powder volume was observed. Measurements were performed in triplicate13.

 

Carr’s Index values for each spray-dried powder were derived from poured density and tapped density data, according to given formula. The Carr’s Index value gives an indication of powder flow; a value less than 25 % indicates a fluid powder15.

 

In vitro drug release:

The in-vitro drug release of all the spray dried formulations was investigated by dissolution study.  An accurately weighed amount of DPI equivalent to 50 µg of SX and 100 µg was added to 700 ml of dissolution medium; Phosphate buffer pH 7.4: Ethanol (95%), in 90:10 proportion and drug release was investigated using the USP rotating paddle dissolution apparatus (Lab India 2000) at 100 rpm and 37 oC.  A percent release study was continued from 5 min. to 3 hrs. The final volume in all cases was 700 ml. The samples were withdrawn from the dissolution medium at various time intervals. 5 ml of sample was diluted to 10 ml with dissolution medium and subjected to UV Spectrophotometric analysis at 214 nm and 246 nm for SX and FP respectively. All the samples were analyzed in triplicate13.

 

 

Stability study:

After the characterizations of physical properties of spray dried powders and drug content, all the formulations batches were kept for 1 month at accelerated stability conditions of temperature and relative humidity 400C and 75% RH. The choice of appropriate storage condition during accelerated stability study is necessary to predict the long term stability of SX and FP respirable particles. The humidity during storage is also extremely important considering the stability of formulation. Therefore, for the present study, accelerated temperature and relative humidity 400 C and 75% RH were selected during stability; All study was conducted inside an environmental test chamber (Stability chamber: CHM- 10 S. Remi, Mumbai), capable of maintaining an environment of 10-95% RH (-0.2%RH) at 250C. Samples were withdrawn after one month and characterized for drug content and stability was predicted16.

 

RESULT AND DISCUSSION:

Particle size, Percentage yield and Drug loading:

The particle size of all spray dried formulations was found in the range of 1.53 to 3.62 µm (Table 4). The PI value obtained for all batches of DPI was found to have very broad distribution for L and M series.

 

 

Table 4: Particle size of DPI

Batch code

Mean Diameter

± S.D. (µm)

PI ± S.D.

L1

3.622 ± 0.5006

0.906 ± 0.0552

L2

2.435 ± 0.4156

0.767 ± 0.0412

L3

3.603 ± 0.4648

0.826 ± 0.0435

M1

2.227 ± 0.3538

0.672 ± 0.0372

M2

1.534 ± 0.2964

0.549 ± 0.0249

M3

1.660 ± 0.3134

0.648 ± 0.0324

S.D. - Standard deviation (n=3),

PI-  Mean polydispersity index (n=3)

 

 

From the observations it was observed that the formulations prepared by using lactose as an excipient gives larger particle size than that of mannitol. The observed reasons for the particle size and its distribution pattern are crystalline nature of lactose over the mannitol because of which degree of conversion of crystalline form of Lactose into amorphous was less as compared to that of mannitol. Also, based upon the observations from table 4; poloxamer 188 concentration affects the particle size; as in Mannitol series, it was more than that of Lactose series which indicates that Poloxamer 188 acts as a stabilizer in certain amount which will give small particle size. In case of Lactose series, Poloxamer concentration was found to be optimum up to 1:1(Drug: Poloxamer) proportion, below and beyond this proportion; little increase was found in particle size observations. Also, particle size of M series formulation suggests that incorporation of stabilizer such as poloxamer 188 but in optimum concentration improves the particle size reduction.3, 7

 

 


Table 5: Percentage yield (%) and drug content of spray powder powders

Batch Code

% Yield

 

Theoretical drug Content  % (w/w)

Actual drug content % (w/w)

SX

FP

SX

± SD

FP

± SD

L1

38.13

1.98

4.31

1.8962

0.0012

3.6955

0.0009

L2

47.98

2.10

4.20

1.9847

0.0011

3.8055

0.0018

L3

60.79

2.15

4.31

2.0061

0.0010

4.3358

0.0022

M1

44.42

2.31

4.63

2.1588

0.0009

4.4648

0.0013

M2

40.97

2.11

4.22

1.9925

0.0013

4.1148

0.0007

M3

49.46

2.20

4.41

2.0074

0.0010

4.3332

0.0009

SX: Salmeterol xinafoate, FP: Fluticasone propionate S.D. - Standard deviation (n=3)

 


Percentage yield and actual drug content are mentioned in the table 6, which showed as the Poloxamer concentration was increased, the yield of the product increased. Presence of Poloxamer 188 was found to increase the flow properties of L and M series which is beneficial during the collection of spray dried particle from cyclone and collector, to increase the percent yield of respirable DPI.

 

All the formulations showed satisfactory drug loading from 18.5 mg to 31.5 mg so as to get the appropriate dose containing 50µg of SX and 100µg of FP from the individual respirable DPI.

 

FTIR spectrometry:

Fourier transform infrared spectrometry (FTIR) spectra were recorded with a JASCO FTIR-410, JAPAN FTIR Spectrophotomer to evaluate the molecular states of pure drugs: SX and FP; physical mixture and all spray dried formulations and are shown in Figure 1. Close agreement between the spectra of all spray dried formulations with FTIR of pure SX and FP suggested that there were no changes in the structure of SX and FP induced by solvent displacement technique as well as spray drying.

 

(a)

 

(b)

Figure 1: a) FTIR spectra of SX, FP, physical mixture and L series formulations; b) FTIR spectra of SX, FP, physical mixture and M series formulations

 

Particle surface morphology by scanning electron microscopy (SEM):

Scanning electron microscopy was used to visualize the particle diameter, structural and surface morphology of the spray dried powders. The scanning electron micrograph of pure SX (Figure 2) showed the powder to be of a crystalline flat material, needle like in structure. Many irregular particles with much fragmentation were observed.  The scanning electron micrograph of pure FP showed the powder to be typical aggregate of amorphous material. Many irregular particles with cluster were observed.

 

Figure 2: SEM micrograph of : a) SX b) FP c) L1 d) L2 e) L3 f) M1 g) M2 h) M3

 

Figure 2 presents SEM micrographs of the DPI containing SX, FP, lactose and Poloxamer 188. It shows partial crystalline, prism shaped structure. Batch L2 and L3 were quite amorphous with pitted surface and shrunken surface than batch L1. The difference in morphological behavior was found because of incorporation of Poloxamer 188 which acts as crystal growth inhibitor.14

 

The SEM images shown in Fig. 2 indicated that the powders formed after spray drying were amorphous in nature; but shows broad distribution in clusters. SEM micrograph showed aggregation which indicates about the cohesive nature powder. The possible reason is due to different precipitation behavior of drug in presence of Poloxamer 188 during the course of solvent removal and resulting in the deformation of microparticles.16

 

DSC analysis:

DSC analysis of the SX, FP and spray dried formulations were performed in order to characterize the physical state of the drug and excipient before and after spray drying are shown in Figure 3. It was also used to determine the existence of possible interaction between the excipient and drug.8

 

Figure 3 (c-e)represents thermogram of L series formulations. All are indicating broad peak of Poloxamer 188 but melting endotherm of SX was found to be shifted towards right side. Also, absence of sharp peak indicates the amorphous nature of drug after spray drying. Figure 3 (f-h)shows thermogram of M series formulations, presenting indicative but no sharp peaks of SX and Mannitol. As it contains little amount of Poloxamer 188, peak could not be detected.

a)

 

b)

 

(c)

 

(d)

 

(e)

 

(f)

 

(g)

 

(h)

Figure 3: DSC thermogram of: a) SX b)FP c) L1 d) L2 e) L3 f) M1 g) M2 h) M3

 

From the observations of all thermograms, DSC measurements revealed a small melting peak of SX in the precipitate, whereas a FP melting peak could not be detected because it melts under decomposition and therefore, creates no interpretable signal. Also, the lack of endotherm can be concluded that drugs were dispersed inside the matrix of excipients as a solid solution. Since no single DSC curve showed sharp endotherms indicative of melting of crystalline material, the SX, FP and excipients coprecipitate exist as glass solution. Furthermore, flattened, a broad curve indicates amorphous nature of drug after spray drying. Hence, DSC data lead to assumption that coprecipitate is formed.14

 

XRD measurements:

Figure 4 shows XRD patterns of L series formulations. It is clear that degree of crystallinity of pure drugs; SX and FP is reduced and it is shifted towards amorphous nature. So, the L1 formulation tends to be partial crystalline. The probable reason is the effect of stabilizer in reducing surface tension of droplet may have role in conversion of crystalline nature of pure drugs into amorphous one during spray drying process. Peak intensity in L2 is less than that of L1. This data helps in prediction about optimum concentration of stabilizer in the formulation, as concentration of Poloxamer is more in L2 than in L1 batch. XRD pattern of L3 formulation indicates slight crystalline nature as compared to batch L1 and L2.

 

Figure 4 shows XRD patterns of M series formulations. The degree of crystallinity of pure drugs; SX and FP is further reduced than L series formulations and it is shifted towards amorphous nature. It indicates the difference in excipient behavior as M series contains mannitol as an excipient. M2 formulation suggests further increase in amorphous nature of pure drugs, as peak intensity in M2 is less than that of M1. This indicates the effect of stabilizer in the formulation, as batch M1 is with only mannitol as an excipient. M3 formulation was found to be partial crystalline with peak intensity of M3 is less than M1 and more than M2. From this observation it gives an idea regarding the optimum concentration of stabilizer in the formulation.

 

Figure 4: XRD pattern of SX, FP, L and M series formulations

 

All spray dried formulations showed less intensive peaks as compared to pure drugs confirming that drugs are converted in amorphous nature. Results showed that as the drug to excipient ratio increases upto certain level, crystallinity decreases. Also, it reveals that presence of Mannitol gives more amorphous formulation than with lactose.6

 

Above discussed XRD pattern is due to proper dispersion of drug particle into the excipient matrix. This is in good agreement with previous DSC results. It has been known that transforming the crystalline state to the amorphous state leads to a high energy state and high disorder, resulting in enhancing solubility and dissolution rate. Analysis of relative degree of crystallinity (RDC) helps to study the change of the crystalline to amorphous nature.

RDC= Highest peak intensity of formulation/ Highest peak intensity of drug

 

Table 6: Relative degree of crystallinity (RDC)

Sample

Angle 2θ

Peak intensity

RDC

SX

FP

SX

24.6

1803

-

-

FP

10.0

1313

L1

19.1

1366

0.75

1.04

L2

17.2

1208

0.66

0.92

L3

18.4

1387

0.76

1.05

M1

17.3

939

0.52

0.71

M2

17.4

877

0.48

0.66

M3

17.2

909

0.50

0.69

 

It was determined whether the obtained formulation after precipitation is a coprecipitate of individual substances or whether it becomes cocrystal. In the case of cocrystal formation, one would expect different physic-chemical properties of the formulation such as different thermal behavior and different XRD patterns. From all XRD patterns of pure drugs and spray dried formulations, it seems that XRD measurements of all formulation showed a partly crystalline pattern masking the crystalline peaks of pure drugs. Therefore it is assumed that the formulation resulted from coprecipitation.14

 

Powder density:

Table 7 shows the values for Carr’s Index which is used as an indication of powder flow properties; a value less than 25% indicates a fluid flowing powder, whereas a value greater than 25% indicates cohesive powder characteristics.15

 

Powder flow is important in dry powder aerosol formulation for both the filling of gelatin capsules or devices and for subsequent release of drug from the dry powder inhaler. Tapped density of a formulation is associated with good aerosolization; as more porous particles hold better aerodynamic property over solid particles of the same dimensions.

 

Table 7: Tapped density, Carr’s index and Flowability of spray dried powders

Batch code

Poured density

(g/cm-3)

Tapped density

(g/cm-3)

Carr’s Index (%)

Flowability

L1

0.2094

0.2417 ± 0.03

13.36

Good

L2

0.4078

0.4392 ±  0.04

7.14

Excellent

L3

0.3088

0.3706 ± 0.03

16.67

Good

M1

0.0915

0.1282 ± 0.02

28.01

Poor, cohesive

M2

0.0886

0.1108 ± 0.00

22.75

Poor, fluid

M3

0.1320

0.3300 ± 0.01

27.28

Poor, cohesive

 

It was found that tapped densities for M1-M2 among M series were consistent. Though L series formulations seem to have good and excellent powder flow, tapped density distribution is uneven. The difference in powder flow characteristics was because of excipient nature in the formulation. This suggests that the lactose gives better flow to spray dried formulation than that of mannitol.

 

It would, however, be expected that the spray dried material would have better flow properties than that of the micronized material because of its spherical nature, there being fewer points for physical contact. Poor flowability may have been due to differences in the surface energies of the individual components in the formulation17.

 

In vitro drug release:

Although, several in vitro models for the prediction of respirable fraction and site of deposition in the lung following pulmonary administration (e.g. Twin stage impinge, MSLI, Anderson cascade impactor, Next generation impactor, etc.), there is no readily available in vitro model to predict the rate and extent of drug dissolution in the lung following inhalation.

 

Currently, no pharmacopoeia methodology exists for the evaluation of the in vitro release rates from respirable dry powders. To study the dissolution pattern of all spray dried formulation, In vitro dissolution study was carried out using USP rotating paddle dissolution apparatus (Lab India 2000). The dissolution medium used was Phosphate buffer (pH 7.4): Ethanol (95%). The dissolution method used in this study has previously been used in this research area.2, 18.

 

Figure 5: Release profile of all formulations

 

As shown in Figure 5, L series formulation drug release in the first 45 min was in the range of 97.51% to 99.08 % while that of M series formulations was in the range of 92.91% to 95.47 % (Table 58-60). An initial burst effect was observed due to the drug located on or near the surface of the microspheres. The pores formed during rapid evaporation of the solvent may also lead to the rapid release of the drug.

 

The rate of drug release from the formulation depended on the drug to excipient binding while processing, as adhesive force between drug-excipient becomes more than cohesive force between drug molecules themselves. Furthermore, smaller microspheres have a larger surface area exposed to dissolution medium, giving rise to faster drug release. The initial rapid drug release can be attributed to the formation of solid dispersion of the drug where the drug would have higher solubility and hence dissolution rates.

 

STABILITY STUDY:

The result of accelerated stability studies as shown in table 9 indicated that the selected formulations did not show any physical changes during the study period and the drug content was found to have close agreement with the drug content of formulation before stability study. This indicates that all formulations were quite stable at accelerated storage conditions

 

Table 8: drug content (%w/w) after one month short term stability study

Batch code

Drug content % (w/w)

Before stability study

After stability study

SX

FP

SX

FP

L1

0.3596

0.4055

0.3548

0.4035

L2

0.3847

0.4260

0.3806

0.4224

L3

0.4761

0.4648

0.4728

0.4616

M1

0.1588

0.3358

0.1540

0.3338

M2

0.2125

0.4348

0.2136

0.4308

M3

0.1601

0.3332

0.1618

0.3313

 

CONCLUSION:

Ethanol was found to have good behavior for both API’s among different solvents; as it was expected that the particle size of spray dried particles should be in micrometer range (2-5 µm). From the evaluation of different physical characteristics of DPI, it demonstrates that mannitol has given combination particle with expected respirable size in comparison with lactose. Also, the use of excipients is suggested to optimize the flow property and morphological characters of formulations. Formulations containing Lactose and Mannitol were found to have immediate release in dissolution media. Also, all the formulations were quite stable at accelerated storage conditions.\

 

Thus, it concludes co-spray drying of salmeterol xinafoate and fluticasone along with mannitol-poloxamer 188 provided a simple alternative to lactose for effective implementation of combination formulations for inhalation. It gives an effective alternative over the lactose with respect to chemical stability of lactose with APIs as it is reducing sugar,  physical characterization and drug release.

 

ACKNOWLEDGEMENT:

Authors are thankful to Prof. D. D. Chougale, Principal, A.B. College of Pharmacy, Sangli for providing necessary facilities. The authors are also thankful to Vamsi Labs Ltd., Solapur and Sun Pharmaceutical Industries Ltd., Mumbai for providing the gift samples of pure drug of Salmeterol xinafoate and Fluticasone propionate respectively.

 

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Received on 07.07.2011          Modified on 13.08.2011

Accepted on 05.09.2011         © RJPT All right reserved

Research J. Pharm. and Tech. 4(10): Oct. 2011; Page 1604-1614