Systemic delivery of insulin to a mammalian host is accomplished by inhalation of a dry powder of insulin. It has been found that dry insulin powders are rapidly absorbed through the alveolar regions of the lungs.

Description of the Invention

SUMMARY OF THE INVENTION

According to the present invention, methods and compositions for the aerosolization and systemic delivery of insulin to a mammalian host, particularly a human patient suffering from diabetes, provide for rapid absorption into blood circulation while avoiding subcutaneous injection. In particular, the methods of the present invention rely on pulmonary delivery of insulin in the form of a dry powder. Surprisingly, it has been found that inhaled dry insulin powders are deposited in the alveolar regions of the lung and rapidly absorbed through the epithelial cells of the alveolar region into blood circulation. Thus, pulmonary delivery of insulin powders can be an effective alternative to administration by subcutaneous injection.

In a first aspect of the present invention, insulin is provided as a dry powder, usually but not necessarily in a substantially amorphous state, and dispersed in an air or other physiologically acceptable gas stream to form an aerosol. The aerosol is captured in a chamber having a mouthpiece, where it is available for a subsequent inhalation by a patient. Optionally, the dry powder insulin is combined with a pharmaceutically acceptable dry powder carrier, as described in more detail below. The insulin powder preferably comprises particles having a diameter less then 10 .mu.m, more preferably less than 7.5 .mu.m, and most preferably below 5 .mu.m, usually being in the range from 0.1 .mu.m to 5 .mu.m. Surprisingly, it has been found that the dry powder insulin compositions of the present invention are absorbed in the lung without the use of penetration enhancers such as those required for absorption through the nasal mucosa and upper respiratory tract.

In a second aspect, the present invention provides insulin compositions consisting essentially of dry powder insulin having an average particle size below 10 .mu.m which may be combined with dry powder pharmaceutical carriers. The insulin composition is preferably free from penetration enhancers and comprises particles having a diameter less than 10 .mu.m, preferably less than 7.5 .mu.m, and most preferably below 5 .mu.m, usually being in the range from 0.1 .mu.m to 5 .mu.m. Usually, the insulin dry powder will have from 5% to 99% by weight insulin in the composition, more usually from 15% to 80%, in a suitable pharmaceutical carrier, usually a carbohydrate, an organic salt, an amino acid, peptide, or protein, as described in more detail hereinafter.

In a third aspect of the present invention, insulin dry powders are prepared by dissolving insulin in an aqueous buffer to form a solution and spray drying the solution to produce substantially amorphous particles having a particle size less than 10 .mu.m, preferably less than 7.5 .mu.m, and most preferably below 5 .mu.m, usually being in the range from 0.1 .mu.m to 5 .mu.m. Optionally, the pharmaceutical carrier is also dissolved in the buffer, to form a homogeneous solution, wherein spray drying of the solution produces individual particles comprising insulin, carrier buffer, and any other components which were present in the solution. Preferably the carrier is a carbohydrate, organic salt, amino acid, peptide, or protein which produces a substantially amorphous structure upon spray drying. The amorphous carrier may be either glassy or rubbery and enhances stability of the insulin during storage. Advantageously, such stabilized formulations are also able to effectively deliver insulin to the blood stream upon inhalation to the alveolar regions of the lungs.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

According to the present invention, insulin is provided as a dry power. By "dry powder" it is meant that the moisture content of the powder is below about 10% by weight, usually below about 5% by weight, and preferably being below about 3% by weight. By "powder," it is meant that the insulin comprises free flowing particulates having a size selected to permit penetration into the alveoli of the lungs, preferably being less than 10 .mu.m in diameter, preferably less than 7.5 .mu.m, and most preferably less than 5 .mu.m, and usually being in the range from 0.1 .mu.m to 5 .mu.m in diameter.

The present invention is based at least in part on the unexpected observation that dry powder insulins are readily and rapidly absorbed through the lungs of a host. It was surprising that dry powder insulins could reach the alveolar region of the lungs, as water-soluble drugs such as insulin particles are known to be hygroscopic. See, e.g. Byron, ed., Respiratory Drug Delivery, CRC Press, Boca Raton (1990), p. 150. Thus, it would have been expected that as the particles passed through the airways of the lung (which has a relative humidity in excess of 99% at 37.degree. C.), the individual particles would have a tendency to absorb water and grow to an effective particle size larger than the 10 .mu.m upper limit of the present invention. If a substantial fraction of the insulin particles were larger than the target size range, it would be expected that the particles would deposit within the central airways of the lungs rather than the alveolar region, thus limiting delivery and subsequent systemic absorption. Moreover, the fluid layer over the epithelial cells of the lungs is very thin, usually a fraction of the diameter of the insulin powders being delivered. Thus, it was unpredictable prior to the present invention whether the dry insulin particles would dissolve upon deposition within the alveolar regions of the lungs. Surprisingly, the dry insulin powders are apparently able to both penetrate into the alveolar regions of the lungs and dissolve once they have deposited within the alveolar region of the lung. The dissolved insulin is then able to cross the epithelial cells into circulation.

It is presently believed that the effective absorption of insulin results from a rapid dissolution in the ultrathin (<0.1 .mu.m) fluid layer of the alveolar lining. The particles of the present invention thus have a mean size which is from 10 to 50 times larger than the lung fluid layer, making it unexpected that the particles are dissolved and the insulin systemically absorbed in a rapid manner. Indeed, as shown in the Experimental section hereinafter, the dry insulin formulations of the present invention can provide even more rapid serum insulin peaks and glucose troughs than afforded by subcutaneous injection, which is presently the most common form of administration. An understanding of the precise mechanism, however, is not necessary for practicing the present invention as described herein.

Preferred compositions according to the present invention will be substantially free from penetration enhancers. "Penetration enhancers" are surface active compounds which promote penetration of insulin (or other drugs) through a mucosal membrane or lining and are proposed for use in intranasal, intrarectal, and intravaginal drug formulations. Exemplary penetration enhancers include bile salts, e.g., taurocholate, glycocholate, and deoxycholate; fusidates, e.g., taurodehydrofusidate; and biocompatible detergents, e.g., Tweens, Laureth-9, and the like. The use of penetration enhancers in formulations for the lungs, however, is generally undesirable because the epithelial blood barrier in the lung can be adversely affected by such surface active compounds. Surprisingly, it has been found that the dry powder insulin compositions of the present invention are readily absorbed in the lungs without the need to employ penetration enhancers.

Insulin dry powders suitable for use in the present invention include amorphous insulins, crystalline insulins, and mixtures of both amorphous and crystalline insulins. Dry powder insulins are preferably prepared by spray drying under conditions which result in a substantially amorphous powder having a particle size within the above-stated range. Alternatively, amorphous insulins could be prepared by lyophilization (freeze-drying), vacuum drying, or evaporative drying of a suitable insulin solution under conditions to produce the amorphous structure. The amorphous insulin so produced can then be ground or milled to produce particles within the desired size range. Crystalline dry powder insulins may be formed by grinding or jet milling of bulk crystalline insulin. The preferred method for forming insulin powders comprising particulates in the desired size range is spray drying, where pure, bulk insulin (usually in a crystalline form) is first dissolved in a physiologically acceptable aqueous buffer, typically a citrate buffer having a pH in the range from about 2 to 9. The insulin is dissolved at a concentration from 0.01% by weight to 1% by weight, usually from 0.1% to 0.2%. The solutions may then be spray dried in conventional spray drying equipment from commercial suppliers, such as Buchi, Niro, and the like, resulting in a substantially amorphous particulate product.

The dry insulin powders may consist essentially of insulin particles within the requisite size range and be substantially free from any other biologically active components, pharmaceutical carriers, and the like. Such "neat" formulations may include minor components, such as preservatives, present in low amounts, typically below 10% by weight and usually below 5% by weight. Using such neat formulations, the number of inhalations required for even high dosages can be substantially reduced, often to only a single breath.

The insulin powders of the present invention may optionally be combined with pharmaceutical carriers or excipients which are suitable for respiratory and pulmonary administration. Such carriers may serve simply as bulking agents when it is desired to reduce the insulin concentration in the powder which is being delivered to a patient, but may also serve to enhance the stability of the insulin compositions and to improve the dispersability of the powder within a powder dispersion device in order to provide more efficient and reproducible delivery of the insulin and to improve handling characteristics of the insulin such as flowability and consistency to facilitate manufacturing and powder filling.

Suitable carrier materials may be in the form of an amorphous powder, a crystalline powder, or a combination of amorphous and crystalline powders. Suitable materials include carbohydrates, e.g., monosaccharides such as fructose, galactose, glucose, D-mannose, sorbose, and the like; disaccharides, such as lactose, trehalose, cellobiose, and the like; cyclodextrins, such as 2-hydroxypropyl-.beta.-cyclodextrin; and polysaccharides, such as raffinose, maltodextrins, dextrans, and the like; (b) amino acids, such as glycine, arginine, aspartic acid, glutamic acid, cysteine, lysine, and the like; (c) organic salts prepared from organic acids and bases, such as sodium citrate, sodium ascorbate, magnesium gluconate, sodium gluconate, tromethamine hydrochloride, and the like; (d) peptides and proteins, such as aspartame, human serum albumin, gelatin, and the like; (e) alditols, such as mannitol, xylitol, and the like. A preferred group of carriers includes lactose, trehalose, raffinose, maltodextrins, glycine, sodium citrate, tromethamine hydrochloride, human serum albumin, and mannitol.

Such carrier materials may be combined with the insulin prior to spray drying, i.e., by adding the carrier material to the buffer solution which is prepared for spray drying. In that way, the carrier material will be formed simultaneously with and as part of the insulin particles. Typically, when the carrier is formed by spray drying together with the insulin, the insulin will be present in each individual particle at a weight percent in the range from 5% to 95%, preferably from 20% to 80%. The remainder of the particle will primarily be carrier material (typically being from 5% to 95%, usually being from 20% to 80% by weight), but will also include buffer(s) and may include other components as described above. The presence of carrier material in the particles which are delivered to the alveolar region of the lung (i.e., those in the requisite size range below 10 .mu.m) has been found not to significantly interfere with systemic absorption of insulin.

Alternatively, the carriers may be separately prepared in a dry powder form and combined with the dry powder insulin by blending. The separately prepared powder carriers will usually be crystalline (to avoid water absorption), but might in some cases be amorphous or mixtures of crystalline and amorphous. The size of the carrier particles may be selected to improve the flowability of the insulin powder, typically being in the range from 25 .mu.m to 100 .mu.m. Carrier particles in this size range will generally not penetrate into the alveolar region of the lung and will often separate from the insulin in the delivery device prior to inhalation. Thus, the particles which penetrate into the alveolar region of the lung will consist essentially of insulin and buffer. A preferred carrier material is crystalline mannitol having a size in the above-stated range.

The dry insulin powders of the present inventions may also be combined with other active components. For example, it may be desirable to combine small amounts of amylin or active amylin analogues in the insulin powders to improve the treatment of diabetes. Amylin is a hormone which is secreted with insulin from the pancreatic cells in normal (non-diabetic) individuals. It is believed that amylin modulates insulin activity in vivo, and it has been proposed that simultaneous administration of amylin with insulin could improve blood glucose control. Combining dry powder amylin with insulin in the compositions of the present invention will provide a particularly convenient product for achieving such simultaneous administration. Amylin may be combined with insulin at from 0.1% by weight to 10% by weight (based on the total weight of insulin in a dose), preferably from 0.5% by weight to 2.5% by weight. Amylin is available from commercial suppliers, such as Amylin Corporation, San Diego, Calif., and can be readily formulated in the compositions of the present invention. For example, amylin may be dissolved in aqueous or other suitable solutions together with the insulin, and optionally carriers, and the solution spray dried to produce the powder product.

The dry powder insulin compositions of the present invention are preferably aerosolized by dispersion in a flowing air or other physiologically acceptable gas stream in a conventional manner. One system suitable for such dispersion is described in copending application Ser. No. 07/910,048, which has been published as WO 93/00951, the full disclosures of which are incorporated herein by reference. Referring to FIG. 1 (see Original Patent) herein, dry, free-flowing insulin powder is introduced into a high velocity air or gas stream, and the resulting dispersion introduced into a holding chamber 10. The holding chamber 10 includes a mouthpiece 12 at an end opposite to the entry point of the air powder dispersion. The volume of the chamber 10 is sufficiently large to capture a desired dose and may optionally have baffles and/or one-way valves for promoting containment. After a dose of the insulin powder has been captured in chamber 10, a patient P (FIG. 2 (see Original Patent)) inhales on the mouthpiece 12 to draw the aerosolized dispersion into his lungs. As the patient P inhales, make-up air is introduced through a tangentially oriented air inlet port 14, whereby the air flows in a generally vortical pattern to sweep the aerosolized insulin from the chamber into the patient's lungs. The volume of the chamber and the aerosolized dose are such that a patient is able to completely inhale the entire aerosolized insulin dose followed by sufficient air to ensure that the insulin reaches the lower alveolar regions of the lung.

Such aerosolized insulin powders are particularly useful in place of subcutaneous injections of rapid acting insulin in the treatment of diabetes and related insulin-deficiencies. Surprisingly, it has been found that the aerosol administration of dry powder insulin results in significantly more rapid insulin absorption and glucose response than is achieved by subcutaneous injection. Thus, the methods and compositions of the present invention will be particularly valuable in treatment protocols where a patient monitors blood glucose levels frequently and administers insulin as needed to maintain a target serum concentration, but will also be useful whenever systemic insulin administration is required. The patient can achieve a desired dosage by inhaling an appropriate amount of insulin, as just described. The efficiency of systemic insulin delivery via the method as just described will typically be in the range from about 15% to 30%, with individual dosages (on a per inhalation basis), typically being in the range from about 0.5 mg to 10 mg. Usually, the total dosage of insulin desired during a single respiratory administration will be in the range from about 0.5 mg to 15 mg. Thus, the desired dosage may be effective by the patient taking from 1 breath to 4 breaths.
 

Claim 1 of 34 Claims

1. A method for preparing a dry powder insulin composition, said method comprising: dissolving insulin in an aqueous buffer at a concentration in the range from 0.01% to 1% to form a solution; and spray drying the solution to produce particles having an average size below 10 .mu.m.

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