Antimicrobial biguanide metal complexes

Abstract

A compound comprising a metal species and a biologically acceptable ligand, wherein the biologically acceptable ligand comprises a biguanide moiety, and wherein the biologically acceptable ligand forms a complex with the metal species in which the metal species is stabilised in an oxidation state greater than 1+. Compositions and medical devices comprising the compound. A method for the treatment or prophylaxis of microbial, including bacterial, infections, comprising the use of such compounds, compositions or medical devices.

Claims

1. A method for the treatment of microbial infections, comprising administering to an individual a compound comprising a metal species and a biologically acceptable ligand, wherein the metal species is selected from the group consisting of silver (III), copper (III), and gold (III); wherein the biologically acceptable ligand comprises a biguanide moiety; wherein the biologically acceptable ligand forms a complex with the metal species in which the metal species is stabilized in an oxidation state greater than 1+; and wherein the step of administering to an individual comprises contacting the individual with the compound.

2. The method of claim 1, wherein contacting the individual with the compound comprises contacting the individual with a medical device comprising the compound.

3. The method of claim 1, wherein the biologically acceptable ligand has the formula: ##STR00004## wherein R.sup.1, R.sup.2, and R.sup.3 are independently H or a hydrocarbyl group.

4. The method of claim 1, wherein the biologically acceptable ligand has the formula: ##STR00005## wherein R.sup.1, R.sup.2, R.sup.3, and R.sup.4 are independently H or a hydrocarbyl group and R.sup.5 is a hydrocarbadiyl group.

5. The method of claim 1, wherein the biologically acceptable ligand has the formula: ##STR00006## wherein R is a hydrocarbadiyl group and n is 1 or more.

6. The method of claim 1, wherein the biologically acceptable ligand is selected from the group consisting of poly(hexamethylenebiguanide), chlorhexidine (1,1-hexamethylenebis[5-(p-chlorophenyl)biguanide], metformin (N, Ndimethylbiguanide), phenformin (phenethylbiguanide) and buformin (N-butylbiguanide).

7. The method of claim 2, wherein the medical device comprises a wound or burn dressing, an implant, a scaffold for tissue repair, or a stent.

Description

EXAMPLE 1

Preparation of Silver(III) Chlorhexidine (1,1-hexamethylenebis[5-(p-chlorophenyl)biguanide] Complex

(1) Chlorhexidine (1,1-hexamethylenebis[5-(p-chlorophenyl)biguanide] (1.00 g) was dissolved in 100 ml warm methanol. To this stirred solution was added dropwise an aqueous solution of silver nitrate (0.34 g) made up in 5 ml distilled water. This was followed dropwise by an aqueous solution of sodium persulphate (0.94 g) made up in 5 ml distilled water. The reaction mixture was warmed until the orange-brown fully developed. The precipitate was Buchner filtered under vacuum, washed three times with warm methanol and stored at ambient temperature and pressure.

EXAMPLE 2

Preparation of Silver(III) PHMB Complex

(2) PHMB (0.400 g) was dissolved in 50 ml methanol. To this stirred solution was added dropwise an aqueous solution of silver nitrate (0.185 g) made up in 2 ml distilled water. This was followed dropwise by an aqueous solution of sodium persulphate (0.520 g) made up in 2 ml distilled water.

(3) The reaction mixture was stirred until the orange-brown fully developed.

(4) The precipitate was Buchner filtered under vacuum, washed three times with warm methanol and stored at ambient temperature and pressure.

EXAMPLE 3

Preparation of Silver(III) o-tolybiguanide Complex

(5) o-tolylbiguanide (1.00 g) was dissolved in 50 ml methanol. To this stirred solution was added dropwise an aqueous solution of silver nitrate (0.44 g) made up in 5 ml distilled water. This was followed dropwise by an aqueous solution of sodium persulphate (1.25 g) made up in 5 ml distilled water.

(6) The reaction mixture was stirred until the orange-brown fully developed.

(7) The precipitate was Buchner filtered under vacuum, washed three times with warm methanol and stored at ambient temperature and pressure.

EXAMPLE 4

Preparation of a Silver(III) o-tolylbiguanide Complex-coated Material

(8) A 5 cm.sup.2 swatch of Profore WCL (Smith & Nephew Medical Ltd) was immersed in a methanolic solution of o-tolylbiguanide (50 mg/ml) for 5 seconds. The swatch was removed and warm air dried using a hot air gun. The swatch was dipped into an aqueous solution of silver nitrate (10 mg/ml) for 10 seconds, removed and rinsed with excess distilled water. The swatch was then dipped into a warmed aqueous solution of sodium persulphate (10 mg/ml) until the orange colour fully developed (approximately 15 seconds). The swatch was removed, rinsed in excess distilled water and air-dried for storage at ambient temperature and pressure.

EXAMPLE 5

Preparation of Silver(III) Chlorhexidine (1,1-hexamethylenebis[5-(p-chlorophenyl)biguanide] Complex Formulated in IntraSite Gel

(9) 5 mg of silver(III) chlorhexidine complex (Example 1) was dispersed by mechanical mixing into 3 g IntraSite Gel (Smith & Nephew Medical Ltd). After 24 h standing, a stable, uniformly orange-coloured hydrogel was formed.

EXAMPLE 6

Preparation of Silver(III) PHMB Complex Formulated in IntraSite Gel

(10) 5 mg of silver(III) PHMB complex (Example 2) was dispersed by mechanical mixing into 3 g IntraSite Gel (Smith & Nephew Medical Ltd). After 24 h standing, a stable, uniformly orange-coloured hydrogel was formed.

EXAMPLE 7

Evaluation of Stability of IntraSite Gel-based Silver Formulations

(11) The gel formulations prepared in Examples 5 and 6 were compared to alternative silver source formulations, similarly prepared (5 mg silver species per 3 g IntraSite Gel). Alternative silver sources were: silver nitrate, silver carbonate, silver chloride, silver bromide, silver iodide, silver(I) oxide (Ag.sub.2O) and silver(I,III) oxide (AgO). Each formulation was placed into a sterile transparent plastic tube (Sterilin Ltd) for observation over 24 hours.

(12) In every case excepting the silver(III) biguanides prepared in Examples 5 and 6 the formulations had severely discoloured to grey-black, with some multi-coloured discolouration surrounding the oxide particles of the silver oxide formulations.

(13) Although this test was conducted for only 24 hours, the same phenomena can be observed, over a matter of days, weeks or months for other silver presentation system containing oxygen, nitrogen or sulphur ligand species or oxidisable substrates (e.g. sugars or polysaccharides).

EXAMPLE 8

Evaluation of Antimicrobial Activity of Silver(III) Biguanides Prepared in Examples 1-3

(14) Pseudomonas aeruginosa NCIMB 8626 and Staphylococcus aureus NCTC 10788 were harvested. Serial 1:10 dilutions were performed to give a final concentration of 10.sup.8 bacteria/ml. Further dilutions were made for an inoculum count, down to 10.sup.8 bacteria/ml, with the number of bacteria/ml determined using the pour plate method.

(15) Two large assay plates were then set up and 140 ml of Mueller-Hinton agar was added evenly to the large assay plates and allowed to dry (15 minutes). A further 140 ml of agar was seeded with the corresponding test organism and poured over the previous agar layer. Once the agar had set (15 minutes), the plate was dried at 37 C. for 30 minutes with the lid removed. 8 mm plugs were removed from the plate by biopsy punch.

(16) In triplicate, 10 mg of the compounds prepared in Examples 1-3 were placed onto each plug hole followed by 200 ul sterile water. The plates were then sealed and incubated at 37 C. for 24 hours. The size of the microbial, including bacterial, zone cleared was measured using a Vernier calliper gauge, triplicates were averaged:

(17) TABLE-US-00001 Organism Compound Zone of Inhibition/mm Staphylococcus aureus Example 1 6.4 NCTC 10788 Staphlyococcus aureus Example 2 14.3 NCTC 10788 Staphlyococcus aureus Example 3 8.4 NCTC 10788 Pseudomonas aeruginosa Example 1 5.4 NCIMB 8626 Pseudomonas aeruginosa Example 2 9.5 NCIMB 8626 Pseudomonas aeruginosa Example 3 7.4 NCIMB 8626

(18) Thus, Examples 1-3 exhibit significant antimicrobial behaviour.