AN IMPROVED TOPICAL PHARMACEUTICAL COMPOSITION COMPRISING NANONIZED SILVER SULFADIAZINE
Field of Invention
The present invention relates to an improved topical pharmaceutical composition comprising nanonized silver sulfadiazine, said composition being useful in burns therapy.
Background of Invention
The invention relates to an improved topical pharmaceutical composition for burn treatment and microbial infections on human beings or animals. The pharmaceutical composition comprises an antimicrobial drug, i.e., silver sulfadiazine and an antiseptic, i.e., chlorhexidine gluconate, wherein silver sulfadiazine is in nanonized form.
Silver sulfadiazine was first described in 1943 by Wruble and was found to be mildly antiseptic. Fox rejuvenated the compound for the topical treatment of burns. The 1% w/w of this active drug, in its cream form, has been in clinical use in the USA since 1973.
Chlorhexidine is a bisbiguanide antiseptic and disinfectant effective against a wide variety of bacteria, some fungi and some viruses. It is used clinically in various preparations for disinfecting purposes.
The antimicrobial effect of silver sulfadiazine and chlorhexidine compounds has been clinically established. It has been well known that silver sulfadiazine is effective against a wide variety of gram-positive and gram-negative organisms, including Pseudomonas and Candida.
The prior art discloses a number of formulations of silver sulfadiazine for treatment of burns. EP326145A1 discloses a composition for the topical treatment of herpes infections, varicella, eczema, and burns (2nd and 3rd degree) comprising 0.01-10% silver sulfadiazine, 0.01-10% polyhydric alcohols, and optionally a local anesthetic.
BE892421A1 relates to stable ointments and lotions for the treatment of mucosal infections without causing irritation containing silver sulfadiazine and a hydrophilic excipient.
JP53044615A relates to a water-soluble ointment consisting of silver salt of sulfadiazine. The patent application identifies antibacterial agents to which bacteria were resistant and treating them with silver salts to prepare useful antibacterial agents.
DE2804931A1 describes lotions, ointments, and powders, containing finely-divided silver sulfadiazine or zinc sulfadiazine. These salts were prepared in situ from sodium sulfadiazine. Thus, a lotion was prepared by dissolving sodium sulfadiazine in water, homogenizing with Tween 80, paraffin, isopropyl palmitate, sorbitan monooleate, Myrj 52, and stearyl alcohol. The mixture was homogenized with silver nitrate in water at 3000 rpm to form finely-divided silver sulfadiazine of particle size <5 urn and with 90% of particle size < 0.7 urn.
IN2005KOL1038 relates to a therapeutic composition for treating burn injury/lesions resulting there from, comprising as active ingredients the following in amounts shown below (a) Sucralfate - 1-8% wt./wt. (b) Silver sulfadiazine - 0.5-2% wt./wt. and (c) Chlorhexidine gluconate - 0.1-0.3% wt./wt., in admixture with pharmaceutically acceptable or compatible herbal plant extracts, additives, excipients, adjuvants, fillers, humectants and/or stabilizers. The subject invention also relates to a process for preparing the above-mentioned therapeutic composition effective for burn wound management.
US6987133 discloses a topical spray preparation for burn treatment comprising silver sulfadiazine dispersed or solubilized in the cream or lotion base matrix, which can be sprayed directly from a common trigger spray device.
Commercial formulations containing chlorhexidine gluconate 0.2 % w/w, and silver sulphadiazine 1 % w/w, e.g., Silvazine®, Nisburn®, or Silverex ® cream, are available in the market; however, the particle size range of the active in these formulations is in the micronised range.
The activity of silver sulfadiazine, in the cream form, may be influenced by the following factors:
(a) the release rate of the active from the cream matrix in the wound environment;
(b) particle size and solubility of the active drug in the fluids of the wound bed; and
(c) stability of the active in the cream matrix.
Amongst these factors, particle size is one critical parameter which affects the solubility and release of the active from the pharmaceutical composition at the wound site. Smaller particle size will lead to increased antimicrobial effectiveness. Therefore, further size reduction of
silver sulfadiazine particles as compared to the marketed micronised product may result in greater antimicrobial effectiveness based on enhanced solubility of silver sulfadiazine.
Particle size reduction to improve the drug performance has long been known and used in the pharmaceutical industry. Nanonization, i.e., particle size reduction to the nano-size range is a known technique for improving the solubility of the active particles, thereby leading to improved absorption and better therapeutic efficacy. However, selection of the optimum particle size range as well as the selection of the method for particle size reduction remains critical for the chosen active drug.
Nesamony et al, in their article entitled "IPM/DOSS/Water Microemulsions as Reactors for Silver Sulfadiazine Nanocrystal Synthesis", have disclosed the preparation method of silver sulfadiazine nanoparticles using microemulsion technique. The silver sulfadiazine nanocrystals so prepared have a particle size of ~670nm. However the article does not disclose any formulation composition details or any studies on efficacy or therapeutic improvement using the Silver Sulfadiazine nanocrystals.
There still remains a need for a topical pharmaceutical composition comprising silver sulfadiazine in nano-size range demonstrating improved efficacy over the already marketed product.
Therefore the object of the present invention is to provide an improved topical pharmaceutical composition comprising an antimicrobial drug, i.e., silver sulfadiazine in a weight ratio of 0.1-1% w/w and an antiseptic, i.e., chlorhexidine gluconate in a weight ratio of 0.2% w/w, wherein silver sulfadiazine is in nanonized form. The pharmaceutical composition of the present invention is advantageous over the currently available micronised products in having improved efficacy thereby leading to dose reduction; faster wound healing as a result of quicker absorption of fine sized particles having increased surface area and no significant increase in toxicity as a result of size reduction.
Summary of the Invention
The present invention relates to an improved topical pharmaceutical composition comprising 0.1-1% w/w silver sulfadiazine and 0.2% w/w chlorhexidine solution characterized in that silver sulfadiazine is present in nanonized form. The composition is useful in burns therapy.
According to one embodiment, the improved topical pharmaceutical composition comprises silver sulfadiazine with a particle size range between 150-500 nm.
According to another embodiment, is provided an improved topical pharmaceutical composition of silver sulfadiazine wherein the microbial log reduction of Pseudomonas aeruginosa count in mouse superficial skin model caused by thermal injury using the composition is found to be equal to or greater than that caused by the marketed product Silverex®1%.
According to yet another embodiment is disclosed a method of preparation of the improved topical pharmaceutical composition of silver sulfadiazine, the process steps comprising of:
a) Dispersing a viscosity enhancer and one or more pharmaceutically acceptable excipients in water to form a slurry;
b) Adding and mixing silver sulfadiazine in the slurry of step (a);
c) Charging the slurry in a Dynomill and collecting after the particle size of silver sulfadiazine in the slurry is in the range of 150-500 nm;
d) Preparation of the oily phase by mixing together one or more hydrophobic bases and heating the mixture to obtain a molten mass;
e) Preparation of the aqueous phase by heating purified water and dissolving a chelating agent in it;
f) Slow addition of the oily phase of step (d) to the aqueous phase of step (e) and homogenization to form an emulsion;
g) Addition of chlorhexidine gluconate solution to the cooled bulk of step (f);
h) Addition and mixing of the silver sulfadiazine slurry of step (c) into the bulk of step
(g);
i) Adjusting the pH using one or more pH modifiers and finally weight adjusting using purified water and mixing.
Detailed Description of the Invention
This is an invention of an improved pharmaceutical composition for topical application to treat the burn wound and infections, wherein the active drug is in the nanonized form.
The pharmaceutical composition for topical application may be in the form of cream, lotion, ointment or gel.
The pharmaceutical composition comprises an antimicrobial drug and an antiseptic, as the active ingredients. The antimicrobial drug as used herein is silver sulfadiazine and the
antiseptic is chlorhexidine gluconate. The active ingredients are dispersed or solubilized in a cream or lotion base, characterized in that silver sulfadiazine is in nanonized form.
The term "nanonized" as used herein refers to a particle size less than or equal to 700 nm, e.g., particle size range between 150-500 nm, determined using known particle size determination methods, e.g., using Nanosizer®.
Nanonization is a size reduction technique that leads to an increased particle surface area and thus increased dissolution velocity. Quicker absorption of fine sized particles having increased surface area leads to faster wound healing and improved efficacy thereby leading to dose reduction. Also, in the present case there is no significant increase in toxicity as a result of size reduction.
The pharmaceutical composition for topical application comprises 0.1-1.0 % w/w of silver sulfadiazine and 0.2% w/w chlorhexidine gluconate solution.
Ointments and creams containing the compositions of the present invention may be formulated using standard techniques known in the industry. For example, such formulations may be produced with an oily (hydrophobic) base with the addition of suitable viscosity enhancer and/or gelling agents.
Such hydrophobic bases may include oils such as liquid paraffin or a vegetable oil such as peanut oil or castor oil.
Viscosity enhancers which may be used according to the characteristics of the base may include, for example, soft paraffin, aluminum stearate, cetostearyl alcohol, propylene glycol, polyethylene glycols, povidone, wool-fat, hydrogenated lanolin, beeswax and the like.
The present compositions may also be formulated into lotions using methods known in the art. For example, such lotions may be formulated with an aqueous or oily base and will include also, in general, one or more of the following: stabilizing agents, emulsifying agents, dispersing agents, suspending agents, thickening agents, coloring agents, perfumes, preservatives, chelating agents, pH modifiers, antioxidants and the like.
Suitable preservative is one or any combination selected from the group consisting of methylparaben, propylparaben, benzyl alcohol, benzoic acid, sodium benzoate, chlorocresol, sorbic acid and its salt or phenylethyl alcohol.
Suitable chelating agents may be selected from one or more of dimercaprol, ethylene diamine tetra acetic acid (EDTA), ethylene glycol tetra acetic acid, deferoxamine, or alfa lipoic acid.
Suitable phi modifiers or buffers may be selected from one or more of citric acid, sodium citrate; acetic acid, sodium acetate; phosphoric acid, disodium orthophosphate; borax, sodium hydroxide and the like.
Silver sulfadiazine is prone to oxidation, thereby causing the nanonized slurry to turn black on exposure to environment during the milling process. This instability problem is more pronounced in case of the nanonized product (due to increased surface area) as compared to the already marketed micronized product. Addition of suitable antioxidants is useful in overcoming this instability problem.
The antioxidant used in the present invention may be selected from one or more of hydrogen peroxide, sodium metabisulfite, butylated hydroxytoluene, butylated hydroxyanisole, propyl gallate, ethyl gallate, methyl gallate, ascorbic acid, or tocopherol.
According to one embodiment of the invention, the improved topical pharmaceutical composition contains a combination of butylated hydroxytoluene, hydrogen peroxide, and sodium metabisulfite, for use as antioxidants.
The present invention also relates to a method of preparation of the nanonized topical pharmaceutical composition of silver sulfadiazine, the process steps comprising of:
a) Dispersing a viscosity enhancer and one or more pharmaceutically acceptable excipients in water to form a slurry;
b) Adding and mixing silver sulfadiazine in the slurry of step (a);
c) Charging the slurry in a Dynomill and collecting after the particle size of silver sulfadiazine in the slurry is in the range of 150-500 nm;
d) Preparation of the oily phase by mixing together one or more hydrophobic bases and heating the mixture to obtain a molten mass;
e) Preparation of the aqueous phase by heating purified water and dissolving a chelating agent in it;
f) Slow addition of the oily phase of step (d) to the aqueous phase of step (e) and homogenization to form an emulsion;
g) Addition of chlorhexidine gluconate solution to the cooled bulk of step (f);
h) Addition and mixing of the silver sulfadiazine slurry of step (c) into the bulk of step
(g);
i) Adjusting the pH using one or more pH modifiers and finally weight adjusting using purified water and mixing.
Animal model studies
The improved efficacy of the nanonized pharmaceutical composition of the present invention has been demonstrated by in vivo efficacy studies in burn wound infection model by comparing the log reduction of Pseudomonas aeruginosa using various concentrations of nanonized silver sulfadiazine to untreated control and commercially available Silverex® (1% micronised silver sulfadiazine). The results of the efficacy of silver sulfadiazine nanonized cream against Pseudomonas aeruginosa in mouse superficial skin model caused by thermal injury have been shown in Figure 1 and Table 1.
Table1. Log reduction as compared to untreated control

Table and Figure Removed

Figure 1
As seen from the results of the in vivo efficacy studies, 1% silver sulfadiazine nanonized (SSN) cream leads to greater log reduction in the Pseudomonas aeruginosa count in mouse superficial skin model caused by thermal injury as compared to the marketed product Silverex® 1%. While the microbial log reduction using 0.5% silver sulfadiazine nanonized cream is found to be similar to the marketed 1% Silverex®.
To further evaluate the efficacy of Silver Sulfadiazine (Nanonized) cream in Thermal Injury Model in Male Sprague Dawley Rats after dermal application once daily for 15 consecutive days, histopathological evaluation of the tissue samples from the site of injury was carried out. The microscopic lesions were evaluated for necrosis, inflammatory cells, immature granulation tissue, mature granulation tissue, fibrosis and reepithelization to interpret the various wound healing events.
Marked to severe necrosis was observed in all the animals belonging to different treatment groups including the control, indicating the accuracy and precision of the thermal injury process. Hence, necrosis, in the present study is not a measure of wound healing process.
Mean score of inflammation (i.e. presence of inflammatory cells) was very less in group II animals (0.5% SSN) compared with group I (control) and other treatment groups III (0.75% SSN), IV (1% SSN) and V (1 % Silverex). Similarly, the mean scores of granulation tissue (immature, mature and fibrosis) was low in group II animals (0.5% SSN) compared with group I (control) and other treatment groups III (0.75% SSN), IV (1% SSN) and V (1 % Silverex).
The reepithelization (expressed as per cent closure of wound by newly forming squamous cells) was high in group II animals (0.5% SSN) followed by group III (0.75% SSN), IV (1% SSN) and V (1 % Silverex).
Tables 2, 3, & 4 present the mean histopathological scores of various wound healing parameters studied in the present study.
Table 2: Mean Histopathology Score of Healing Parameters

Table Removed
Table 3: Summary of Reepithelization (%) Scores

Table Removed
*The numbers of animals showing reepithelization of 100% are more in 0.05% SSN group.
Table 4: Summary of Inflammatory Cells

Table Removed
Overall, all the healing parameters viz. inflammation, granulation tissue and reepithelization evaluated in the present study were well accomplished in 0.5% SSN group animals followed by 0.75% SSN, 1% SSN and 1% Silverex groups.
Pharmacokinetic Studies
The plasma exposures of Silver and Sulfadiazine were determined on day 15 in male Sprague Dawley Rats following once daily dermal application of different strengths of Silver Sulfadiazine (Nanonized) cream as Test Items (SSN 0.5%, 0.75% and 1%) and Silverex cream 1% as (Reference item). Sulfadiazine was quantitated by LC-MS/MS method. Silver concentrations were estimated using ICPMS instrument (Inductively coupled Plasma - Mass Spectrometry).
The pharmacokinetic parameters for test and reference items are given in Table 5.
Table 5: Pharmacokinetic parameter values for Silver and Sulfadiazine

Table Removed
The Cmax of Sulfadiazine for different SSN formulation prototypes increased from 16.71 µg/mL to 34.52 ug/mL with the increase in strengths from 0.5% to 1%. Similarly, the AUC
increased from 254.47 h*µg/mL to 541.95 h*ug/mL with the increase in SSN strengths. The AUC ratio (Test/ Reference) ranged from 0.52 to 1.10 after 15 days of dermal application. The AUC of silver was calculated from silver concentrations of pooled plasma samples. The exposure of silver also increased from 2.44 h*ug/mL to 4.68 h*ug/mL with the increase in strengths of SSN creams from 0.5% to 1%. The AUC ratio (Test/ Reference) ranged from 0.63 to 1.21 after 15 days of dermal application.
Both silver and sulfadiazine were found to be absorbed from the topical application of silver sulfadiazine creams in rat. The systemic exposure of both the components (silver and sulfadiazine) was comparable from 1% test and reference product and dose dependent for SSN after topical application for 15 days.
The silver nanoparticles with their large surface area and reduced particle size provide improved contact and penetration with bacterial cell, which together enhances its antimicrobial activity. The anti-inflammatory effects of silver sulfadiazine depend on concentration of silver at the site, release of silver from the carrier and species of silver used.
The invention is further illustrated by the following non-limiting examples.
Examples
SILVER SULFADIAZINE (NANONIZED CREAM)

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BRIEF MANUFACTURING PROCEDURE PREPARATION OF PART A
1. Hydrogen Peroxide and Sodium Metabisulphite were dissolved in purified water (except in Examples 6 & 7).
2. Polyvinyl pyrrolidone was dispersed into the bulk of step 1.
3. Silver Sulfadiazine was mixed into it.

4. The slurry was passed through Dynomill and collected and the Dynomill was rinsed with purified water.
5. The slurry and rinsing were used in the fabrication of the cream.
6. The particle size of Silver Sulfadiazine in the slurry was between 150-500 nm.
PREPARATION OF CREAM
1. The oil phase was prepared by mixing together cetostearyl alcohol, cetomacrogol 1000, light liquid paraffin, butylated hydroxytoluene and heating to 65-70°C.
2. Water phase was prepared by heating purified water to 65-70°C and dissolving disodium edetate in it.
3. The oil phase was added slowly under homogenization to the water phase to form an emulsion, which was then cooled under stirring.
4. Chlorhexidine gluconate solution was added and mixed into the bulk of step 3.
5. Silver Sulfadiazine slurry and the rinsings were added and mixed into the bulk of step 4.
6. The pH was adjusted using Orthophosphoric Acid and Disodium Orthophosphate.
7. Final weight adjustment was done using purified water followed by mixing.
The formulation of examples 5, 6 & 7 were charged on stability to observe the effect of various antioxidants on product stability. The results of the stability studies are compiled below:

Table Removed
From the above results it is evident that a combination of hydrogen peroxide (50% w/w) and sodium metabisulfite is effective in preventing any color change of silver sulfadiazine in the pharmaceutical composition.

WE CLAIM:
1. An improved topical pharmaceutical composition comprising 0.1-1% w/w silver sulfadiazine, 0.2% w/w chlorhexidine gluconate, and one or more pharmaceutically acceptable excipients; characterized in that silver sulfadiazine is in nanonized form.
2. The pharmaceutical composition according to claim 1, wherein the silver sulfadiazine has a particle size range of 150-500nm.
3. The pharmaceutical composition according to claim 1, wherein the pharmaceutically acceptable excipients are selected from one or more of stabilizing agents, emulsifying agents, dispersing agents, suspending agents, thickening agents, coloring agents, perfumes, preservatives, chelating agents, pH modifiers, and antioxidants.
4. The pharmaceutical composition according to claim 3, wherein the thickening agent is selected from one or more of soft paraffin, aluminum stearate, cetostearyl alcohol, propylene glycol, polyethylene glycols, povidone, wool-fat, hydrogenated lanolin, or beeswax.
5. The pharmaceutical composition according to claim 3, wherein the preservative is selected from one or more of methylparaben, propylparaben, benzyl alcohol, benzoic acid, sodium benzoate, chlorocresol, sorbic acid and its salt or phenylethyl alcohol.
6. The pharmaceutical composition according to claim 3, wherein the chelating agents is selected from one or more of dimercaprol, ethylene diamine tetra acetic acid (EDTA), ethylene glycol tetra acetic acid, deferoxamine, or alfa lipoic acid.
7. The pharmaceutical composition according to claim 3, wherein the pH modifier is
selected from one or more of citric acid, sodium citrate; acetic acid, sodium acetate;
phosphoric acid, disodium orthophosphate; or borax, and sodium hydroxide.
8. The pharmaceutical composition according to claim 3, wherein the antioxidant is selected from one or more of hydrogen peroxide, sodium metabisulfite, butylated hydroxytoluene, butylated hydroxyanisole, propyl gallate, ethyl gallate, methyl gallate, ascorbic acid, or tocopherol.
9. The pharmaceutical composition according to claim 8, wherein the antioxidant is a combination of hydrogen peroxide, sodium metabisulfite, and butylated hydroxytoluene.
10. The pharmaceutical composition according to any of the preceding claims may be in the form of cream, lotion, ointment or gel.
11. A method of preparation of the improved topical pharmaceutical composition of claim 2, wherein the process steps comprise of:
(a) Dispersing a viscosity enhancer and one or more pharmaceutically acceptable excipients in water to form slurry;
(b) adding and mixing silver sulfadiazine in the slurry of step (a);
(c) charging the slurry in a Dynomill and collecting after the particle size of silver sulfadiazine in the slurry is in the range of 150-500 nm;
(d) preparation of the oily phase by mixing together one or more hydrophobic bases and heating the mixture to obtain a molten mass;
(e) preparation of the aqueous phase by heating purified water and dissolving a
chelating agent in it;
(f) slow addition of the oily phase of step (d) to the aqueous phase of step (e) and homogenization to form an emulsion;
(g) addition of chlorhexidine gluconate solution to the cooled bulk of step (f);
(h) addition and mixing of the silver sulfadiazine slurry of step (c) into the bulk of
step (g); (i) adjusting the pH using one or more pH modifiers and finally weight adjusting
using purified water and mixing.
12. The pharmaceutical composition according to claim 2, when applied topically leads to
microbial log reduction of Pseudomonas aeruginosa count in mouse superficial skin
model caused by thermal injury which is equal to or greater than that caused by the
marketed product Silverex®1%.
13. The improved topical pharmaceutical composition comprising nanonized silver sulfadiazine substantially described and exemplified herein.