Method of steam sterilization using a steam sterilization indicator

• US 6,149,863 A
• Filed: 09/10/1999
• Issued: 11/21/2000
• Est. Priority Date: 02/19/1997
• Status: Expired due to Term

• Current Assignee: Albert Browne Limited (Steris Corporation)
• Original Assignee: Albert Browne Limited (Steris Corporation)
• Inventors: James, Phillip Richard
• Primary Examiner(s): MCKANE, ELIZABETH L
• Application Number:
  US09/394,384
• Time in Patent Office: 438 Days
• Field of Search: 422/26, 422/55, 422/56, 422/119, 436/1, 116/206, 116/207
• US Class Current: 422/26
• CPC Class Codes: A61L 2/28 Devices for testing the effectiveness or completeness of sterilisation, e.g. indicators which change colour apparatus involving enzymes or microorganisms C12M1/34; methods involving enzymes or microorganisms C12Q1/00
• CPC Class Codes: C09D 11/50 Sympathetic, colour changing or similar inks
• CPC Class Codes: C12Q 2326/92 Nitro blue tetrazolium chloride, i.e. NBT
• CPC Class Codes: G01N 31/226 for investigating the degree of sterilisation

Abstract

A steam-sensitive ink comprises, as active ingredient, a tetrazolium salt. The ink may be coated on, or impregnated into, a substrate to form a steam sterilization indicator.

Claims

1. A method of steam sterilization of an article comprising:

exposing to steam both said article and a steam sterilization indicator, said indicator comprising a tetrazolium salt that is reduced to a formazan compound or salt thereof and thereby undergoes a color change as a direct result of exposure to steam sterilization conditions.

2. A method as claimed in claim 1, wherein the tetrazolium salt is a member of the class of compounds including the general structure I:

##STR3## wherein X^- represents an anion, and at least one of R², R³ and R⁵, which may be same or different, represents an aromatic group.

3. A method as claimed in claim 2, wherein at least one of R² and R³ represents an aromatic group.

4. A method as claimed in claim 2, wherein each of R², R³ and R⁵ represents an aromatic group.

5. A method as claimed in claim 2, wherein the aromatic groups which R², R³ and/or R⁵ represent are selected from the group of 5- and 6-membered monocyclic ring systems, both carbocyclic and heterocyclic, and fused ring systems.

6. A method as claimed in claim 2, wherein the aromatic groups which R², R³ and/or R⁵ represent are selected from the group of phenyl, naphthyl, quinolinyl, pyridyl and azolyl.

7. A method as claimed in claim 2, wherein the aromatic groups which R², R³ and/or R⁵ represent are unsubstituted, or are substituted by one or more substituents selected from the group of lower alkyl, lower alkoxy, aryl groups, aryloxy, halogen, nitro, amino, cyanide, and azide.

8. A method as claimed in claim 2, wherein R², R³ and/or R⁵ represent phenyl or oxazolyl groups.

9. A method as claimed in claim 2, wherein R² and R³ both represent phenyl.

10. A method as claimed in claim 2, wherein X^- represents a counterion selected from the group of chloride, bromide, iodide, tetrafluoroborate, hexafluorophosphate, perchlorate and sulphate.

11. A method as claimed in claim 1, wherein the active ingredient is of the general formula II:

##STR4##

12. A method as claimed in claim 11, wherein R² is a biphenyl group.

13. A method as claimed in claim 1, wherein the tetrazolium salt is selected from the group of 2,3,5-triphenyl-2H-tetrazolium chloride;

2-(p-iodophenyl)-3-(nitrophenyl)-5-phenyl-2H-tetrazolium chloride;

3-(1-naphthyl)-2,5-diphenyl-2H-tetrazolium chloride;

3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide;

2-(2-benzothiazolyl)-3-(4-phthalhydrazidyl)-5-styryl-2H-tetrazolium chloride;

3,3'"'"'-(3,3'"'"'-dimethoxy-4,4'"'"'-biphenylene)-bis-(2-(p-nitrophenyl)-5-(p-thiocarbamylphenyl)-2H-tetrazolium chloride);

3,3'"'"'-(4,4'"'"'-biphenylene)-bis-(2,5-diphenyl-2H-tetrazolium chloride);

3,3 '"'"'-(3,3'"'"'-dimethoxy-4,4'"'"'-biphenylene)-bis-(2,5-diphenyl-2H-tetrazolium chloride);

3,3'"'"'-(3,3'"'"'-dimethoxy-4,4'"'"'-biphenylene)-bis-(2-(p-nitrophenyl)-5-phenyl-2H-tetrazolium chloride); and

3,3'"'"'-(3,3'"'"'-dimethoxy-4,4'"'"'-biphenylene)-bis-(2,5-(p-nitrophenyl)-2H-tetrazolium chloride).

14. A method as claimed in claim 1, wherein said indicator further comprises a binder.

15. A method as claimed in claim 14, wherein the binder is selected from the group of ethyl and nitro cellulose, cellulose acetate and its derivatives, hydroxypropyl cellulose, polystyrene, polymethacrylates, polyvinyl chloride, polyvinyl acetate;

emulsion latexes cross-linking resins;

uv curing systems; and

drying oils.

16. A method as claimed in claim 14, wherein the binder is a cellulose derivative.

17. A method as claimed in claim 1, wherein said indicator further comprises a solvent.

18. A method as claimed in claim 17, wherein the solvent is selected from the group of aliphatic alcohols, industrial methylated spirit, ethylene glycol alkyl ethers, white spirit, aliphatic esters, aliphatic hydrocarbon solvents, water, and mixtures of two or more thereof.

19. A method as claimed in claim 17, wherein the solvent is 2-ethoxyethanol.

20. A method as claimed in claim 1, wherein said tetrazolium salt is coated on or impregnated in a substrate.

21. A method as claimed in claim 20, wherein the substrate is a paper material which is permeable to steam but which maintains its integrity under steam sterilization conditions.