Long-lasting aqueous dispersions or suspensions of pressure-resistant gas-filled microvesicles and methods for the preparation thereof

• US 5,413,774 A
• Filed: 12/16/1992
• Issued: 05/09/1995
• Est. Priority Date: 01/24/1992
• Status: Expired

• Current Assignee: Bracco Suisse SA
• Original Assignee: Bracco International B.V. (Bracco SPA)
• Inventors: Yan, Feng, Schneider, Michel, Puginier, Jerome, Barrau, Marie-Bernadette, Grenier, deceased, Pascal
• Primary Examiner(s): Kumar, Shailendra
• Application Number:
  US07/991,237
• Time in Patent Office: 874 Days
• Field of Search: 424/9, 128/662.02, 128/660.01, 128/661.02, 530/427
• US Class Current: 424/9.51
• CPC Class Codes: A61K 49/223 Microbubbles, hollow microspheres, free gas bubbles, gas microspheres

Abstract

One can impart outstanding resistance against collapse under pressure to gas-filled microvesicle used as contrast agents in ultrasonic echography by using as fillers gases whose solubility in water, expressed in liter of gas by liter of water under standard conditions, divided by the square root of the molecular weight does not exceed 0.003.

Claims

1. A method of making a contrast agent having resistance against collapse from pressure increases when used in ultrasonic echography, said contrast agent consisting of gas-filled microvesicles suspended in an aqueous liquid carrier phase, the microvesicles being either microbubbles bounded by an evanescent gas/liquid interfacial closed surface, or microballoons bounded by a material envelope, said method comprising the step of forming the microvesicles in the presence of a physiologically acceptable gas, or gas mixture comprising a physiologically acceptable gas, or filling preformed microvesicles with said gas, or said gas mixture, said physiologically acceptable gas being selected from the group consisting of SF₆, SeF₆, CF₄, CBrF₃, C₄ F₈, CClF₃, CCl₂ F₂, C₂ F₆, C₂ ClF₅, CBrClF₂, C₂ Cl₂ F₄, CBr₂ F₂ and C₄ F₁₀, said microvesicles having resistance against collapse resulting, at least in part, from pressure increases effective when a suspension of said gas-filled microvesicles is in injected into the bloodstream of a patient.

4. The method of claim 1, in which the aqueous phase carrying the microbubbles contains dissolved film-forming surfactants in lamellar or laminar fog said surfactants stabilizing the microbubbles boundary at the gas/liquid innerface.

5. The method of claim 4, in which said surfactants comprise one or more phospholipids.

6. The method of claim 5, in which at least pan of the phospholipids are in the form of liposomes.

7. The method of claim 5, in which m least one of the phospholipids is a diacylphosphatidyl compound wherein the acyl group is a C₁₆ fatty acid residue or a higher homologue thereof.

8. The method of claim 1, in which the microballoon material envelope is made of an organic polymeric membrane.

9. The method of claim 8, in which the polymers of the membrane are selected from the group consisting of polylactic or polyglycolic acid and their copolymers, reticulated serum albumin, reticulated haemoglobin polystyrene, and esters of polyglutamic and polyaspanic acids.

10. The method of claim 1, in which the forming of vesicles with said physiologically acceptable gas is effected by alternately subjecting dry precursors thereof to reduced pressure and restoring the pressure with said gas, and dispersing the precursors in a liquid carrier.

11. The method of claim 1, in which the filling of the microballoons with said physiologically acceptable gas is effected by flushing the suspension with said gas under ambient pressure.

12. The method of claim 1, in which the microvesicles are made under an atmosphere composed at least in part of said gas.

2. A method of making a contrast agent having resistance against collapse from pressure increases when used in ultrasonic echography, said contrast agent consisting of gas-filled microvesicles suspended in an aqueous liquid carder phase, the microvesicles being either microbubbles bounded by an evanescent gas/liquid interfacial closed surface, or microballoons bounded by a material envelope, said method comprising the steps of:

preforming the microvesicles or precursors thereof under an atmosphere of a first gas; and

substantially substituting at least a fraction of said first gas with a second gas which is a physiologically acceptable gas, or gas mixture comprising a physiologically acceptable gas, said physiologically acceptable gas being selected from the group consisting of SF₆, SeF₆, CF₄, CBrF₃, C₄ F₈, CClF₃, CCl₂ F₂, C₂ F₆, C₂ ClF₅, CBrClF₂, C₂ Cl₂ F₄, CBr₂ F₂ and C₄ F₁₀, said microvesicles having resistance against collapse resulting, at least in part, from pressure increases effective when a suspension of said gas-filled microvesicles is injected into the bloodstream of a patient.

3. The method of claim 2, in which the gas used in the first step allows effective control of the average size and concentration of the microvesicles in the carrier liquid, and the physiologically acceptable gas added in the second step ensures prolonged useful echogenic life of the suspension for in-vivo ultrasonic imaging.

13. A method of making a contrast agent for ultrasonic echography which consists of gas-filled microvesicles suspended in an aqueous liquid carrier phase, the microvesicles having resistance against collapse resulting from pressure increases effective when the said suspensions are injected into the bloodstream of a patient, said method comprising the step of forming the microvesicles in the presence of a physiologically acceptable gas or gas mixture comprising a physiologically acceptable gas, or filling preformed microvesicles with said gas or said gas mixture, said physiologically acceptable gas being selected from the group consisting of SF₆, SeF₆, CF₄, CBrF₃, C₄ F₈, CClF₃, CCl₂ F₂, C₂ F₆, C₂ ClF₅, CBrClF₂, C₂ Cl₂ F₄, CBr₂ F₂ and C₄ F₁₀, said gas or at least a gas in said gas mixture being such that, under standard conditions, the pressure difference Δ

P between pressures at which the bubble counts are about 75% and 25% of the original bubble count is at least 25Torr.

14. An aqueous suspension made according to the method of claim 13, wherein the physiologically acceptable gas is such that, under standard conditions, and at a rate of pressure increase to the suspension of about 100 Torr/min, the pressure difference Δ

P between pressures at which the bubble counts are about 75% and 25% of the original bubble count is at least 25Torr.