MICRONISED PHARMACEUTICAL COMPOSITIONS
The present application relates to improvements in or relating
to pharmaceutical compositions comprising micronised colistin
sulphomethate sodium.
Background and Prior Art
Colistin is an anti-bacterial cationic cyclic polypeptide
belonging to the polymixin group. It is produced as a
secondary metabolite of Bacillus polymyxa var. colistinus.
Treatment of colistin base with formaldehyde and sodium
bisulphite results in the production of colistin sulphomethate
sodium. This is described in Japanese patent 4898/1957. The
product is a crystalline powder which is soluble in water.
Colistin sulphomethate sodium is a combination of the
negatively charged molecular ion colistin sulphomethate with
positive sodium ions. It should be carefully distinguished
from colistin sulphate. Both are described in the European
Pharmacopoeia.
Colistin is of particular benefit in the treatment of serious
infections caused by bacterial pathogens such as Pseudomonas
aeruginosa, Escherichia coli and Klebsiella sp. An important
property of colistin is that bacteria which are sensitive to
the drug do not readily acquire resistance. Colistin as a
pharmaceutical may be prepared into numerous different
preparations, e.g. topical, bladder irrigation, oral such as
tablets, or as intravenous or intra-muscular injections.
Colistin sulphate can be prepared from colistin. It is
currently used to treat gram negative infections of the body
such as intestinal infections due to various micro-organisms
and, usually in association with other antibiotics, for the
suppression of bowel flora. As noted above, colistin sulphate
should be distinguished from colistin sulphomethate sodium.
Colistin sulphomethate sodium can also be prepared. It exists
as a white to slightly yellow hygroscopic powder. It is
commercially supplied at a particle size of 100-200 µm mass
median diameter. The powder is highly soluble in water and as
such is used for parenteral administration. As a powder,
colistin sulphomethate sodium must be stored in air-tight
containers, preferably protected from the light. Colistin
sulphomethate sodium is used in the treatment of infections in
patients suffering from cystic fibrosis, a genetic disease
which affects many body systems, and which develops at a young
age. Various glands of the body do not function properly. The
disease is marked by a malfunction of the glands in the lining
of the bronchial tubes. Instead of producing their normal thin
mucus, the bronchial glands produce a thick, sticky mucus that
stagnates in the tubes. Microbes are able to multiply readily,
causing serious respiratory infections ultimately leading to
respiratory failure. It is known that colistin sulphomethate
sodium is effective in treatment of infections caused by these
microbes e.g. Pseudomonas aeruginosa. The usual form of
administration is as a solution for inhalation after
nebulisation. The nebulised solution is prepared by taking a
vial in which there is a known dosage of colistin sulphomethate
sodium powder, injecting water into the vial and then inhaling
the solution into the lungs through a nebuliser. Colistin
sulphomethate sodium is poorly absorbed into the bloodstream.
This is preferred as the bacteria can be attacked in the mucus
which lines the lungs during illness.
Whilst jet nebulisation therapy has been shown to be
successful, the nebulisation technique has several drawbacks.
Jet nebulisers utilise compressed gases (usually air) to
convert a drug solution into a spray. The compressed air
passes through a narrow venturi orifice and negative pressure
is created. Liquid is drawn from a fluid reservoir through a
feed tube, fragments into droplets, and is accelerated to a
velocity sufficient for more than 99% of the droplet mass to
impact on baffles or on the nebuliser where droplets coalesce
and drain back into the fluid reservoir. Only 1% of the
aerosol mass leaves the nebuliser directly. The outgoing air
becomes saturated with water derived from liquid retained in
the nebuliser, and this has two important consequences:
Firstly, the nebuliser is cooled and reaches an equilibrium
temperature approximately 10 °C below ambient, so that the
patient inhales a relatively cold spray. Secondly, the
evaporation of water causes the concentration of solutes to
increase with time.
There are many different designs of nebuliser available which
use different flow rates of compressed gas. The output from
these nebulisers will all be different and accordingly it is
difficult for a patient to ensure that a constant dose is
administered. The nebulisers themselves are bulky due to the
compressors which are required. Although described as being
transportable, the nebuliser/compressor system is not truly
portable. When they are undergoing treatment, patients need to
remain connected to the mouthpiece of the nebuliser for
approximately 20 minutes in order to complete the therapy and
in order to ensure that the correct dose is administered. An
electrical supply is needed to run the nebuliser.
It will be seen from the above that, although colistin
sulphomethate sodium is a valuable pharmaceutical in the
treatment of infections occurring during cystic fibrosis and
other bacterial infections, there are a number of disadvantages
which mean that it is not widely accepted as a treatment
regime, particularly for infants. It has been determined that
many of the problems arise from the preferred delivery method
described above, i.e. as a nebulised liquid.
WO 95/00128 (Astra) describes the delivery to the lungs of dry-
powder polypeptides. An enhancer compound is used to promote
absorption into the systemic circulation. In contrast,
colistin sulphomethate sodium is used very locally in the lungs
- absorption into the bloodstream is not an objective.
US-A-5,767,068 (Pathogenesis) describes the separation and use
of individual components of colistin sulphate. Colistin
sulphate is separated into individual components in free base
form. Such components are described by Ebverdam, Larsen and
Lund (Journal of Chromatography, 218 (1981) 653-661).

WO-A-98/20836 is to be noted as the international publication
which is equivalent to US-A-5,767, 068.
J. of Clinical Pharmacology and the J. of New drugs,
1970(10), 274-281, describes sodium colistimethate aerosols for
use in the treatment of gram-negative infections of the
respiratory tract. The aerosol is prepared by dissolving sodium
colistimethate sterile powder in sterile water. When
administered through a suitable nebuliser the aerosol has a
particle size of 1-7 microns._
Archives of Diseases in Childhood, 68,1993, 788-792, describes
the treatment of cystic fibrosis using aerosols. The paper
refers to the delivery of micronised gentamicin powder using a
Rotahaler (registered trade mark). It was found that the powder
caused coughing. The paper concludes that aerosol forms of drugs
delivered through a nebuliser are more suitable for treatment of
cystic fibrosis.
Summary of Invention
It has now been discovered that micronised colistin sulphomethate
sodium can be administered to the airways of a patient using a
powder dose inhalation device. The micronised
cplistin may be used alone or with a carrier, such as lactose.
According to the present invention, there is firstly provided
the use of micronised colistin sulphomethate sodium in a method
of treatment of the human body, particularly in the treatment
of bacterial infections of the pulmonary system, most
particularly in the treatment of secondary infections in
patients suffering from cystic fibrosis, by powder inhalation.
According to a further aspect of the present application, there
is provided a pharmaceutical composition comprising micronised
colistin sulphomethate sodium and a carrier, in the absence of
free liquid.
According to a yet further aspect of the present invention,
there is provided a pharmaceutical dosage form suitable for use
with a dry powder inhaler comprising micronised colistin
sulphomethate sodium, optionally together with a carrier, and
a container. The container is preferably a capsule.
Detailed Description
Micronised colistin sulphomethate sodium may be defined as
being a powder wherein at least: 90% by volume of the powder
comprises particles have a diameter of less than 10
micrometers. Most preferably, at least 50% of the particles
have a diameter of less than 8 micrometers. More preferably,
at least 25% of the particles have a diameters of less than 6
micrometers.
Figure 1 shows a particle size analysis of micronised colistin
sulphomethate sodium.
Medicaments for administration by inhalation should be of a
controlled particle size in order to achieve maximum
penetration into the lungs, a suitable particle size range
being 0.01-10, usually 1-8 micrometers. Particle sizes may be
measured by a number of methods, e.g. by laser diffraction or
microscope analysis.
Micronised colistin sulphomethate sodium may be prepared by
fluid energy milling, ball milling, spray drying or
precipitation. The colistin sulphomethate sodium may be
administered in conjunction with a carrier. The carrier may be
any non-toxic material which is chemically inert to the
colistin sulphomethate sodium and will be acceptable for
inhalation or for administration. Examples of carriers which
may be used include inorganic salts, e.g. sodium chloride or
calcium carbonate; organic salts, e.g. sodium tartrate or
calcium lactate; organic compounds, e.g. urea; monosaccharides,
e.g. lactose, arabinose or dextrose; disaccharides, e.g.
maltose or sucrose; polysaccharides, e.g. starches and
dextrans. A particularly preferred carrier is a lactose, e.g.
crystalline lactose.
The present invention also provides a method for preparing a
composition of the invention which comprises mixing together
micronised colistin sulphomethate sodium and a carrier. The
colistin sulphomethate sodium and the carrier may be blended in
a drum, hoop or Y-cone blender as known in the art.
The carrier does not have to have the same particle size
specification as the colistin sulphomethate sodium. The
carrier may in fact generally be of a larger particle size than
that of the colistin sulphomethate sodium in order to
facilitate delivery from the inhalation device and yet not be
deposited in the finer airways of the lungs. The inclusion of
a carrier may ease dosage of pharmaceutical and carrier into
capsules. Preferably at least 50%, and more desirably at least
70% by volume of the carrier particles have an effective
particle size in the range of 30 to 150, especially 30 to 80,
micrometers. The admixture of pharmaceutical and carrier may
contain up to 75% by weight, more preferably up to 50% by
weight of carrier. Generally the ratio of colistin
sulphomethate sodium will be xn the range of 5:1 to 1:2
preferably 4:1 to 1:1 by weight.
Colistin sulphomethate sodium is a negatively charged molecular
ion with positively charged sodium counter ions. Figure 2
shows the structure. There are five sulphomethate groups (CH2-
OSO2-) - In contrast, Pathogenesis are producing a neutral base
shown in Figure 3. US-A-5,767,068 refers to variable groups R,
and R2; R1 is identified as 6-methyloctanoyl or
6-methylheptanoyl, and R2 as sec-butyl, isobutyl or isopropyl.
It has now been surprisingly found that the negatively charged
colistin sulphomethate ion (preferably in its sodium form) can
be delivered to the lungs. As absorption into the blood stream
is not wanted, the negatively charged ion is preferred to the
base colistin.
It has been found that colistin sulphomethate sodium is a
mixture of at least ten components. Tests carried out on
mixtures of antibacterial preservatives show that the mixture
of components found in colistin sulphomethate sodium show
synergy of activity against gram negative microbial organisms.
It has been surprisingly found that water absorption of a
micronised powder is comparatively low, e.g. approximately 5-7%
by weight under normal atmospheric conditions. It has also
been found that the micronised powder does not stick together.
In powders having a larger particle size, the particles can
stick together because of static forces. This sticking occurs
will colistin and colistin sulphate. However, this is not
found in the colistin sulphomethate sodium of the present
invention. This is a further surprising advantage of the
present application.
In addition to the micronised colistin sulphomethate sodium
and, optionally, the carrier, the composition may contain other
ingredients, such as colouring matter or flavouring agents such
as saccharine, which may be present in inhalant compositions.
Antistatic agents may also be added, e.g. as described in GB-A-
2269992 (Rhone-Poulenc Rorer Ltd) . It is preferred to use the
minimum of such other ingredients.
The powder formulation may contain other pharmaceutical
ingredients such as bronchodilators e.g. salbutamol Such other
pharmaceutical ingredients preferably have an effective
particle size similar to that of the colistin. The
bronchodilatory drug will be delivered in very smali
(microgram) quantities. For example a capsule may contain from
50 to 150, e.g. 125, milligrams of colistin sulphomethate
sodium and from 1 to 250, e.g. 200, micrograms of salbutamol.
The micronised powder may be delivered to the lungs through a
specialised powder inhalation device. Most preferred is
location of the powdered pharmaceutical within a hard capsule
or a blister package. The capsule or blister is ruptured or
broached within the inhaler device, thereby enabling the powder
to be inhaled through the mouthpiece as air is sucked in.
There is also provided, therefore, as a further feature of the
invention, a dosage unit comprising a capsule containing
colistin sulphomethate sodium, preferably in the form of a
pharmaceutical composition of the present invention. The
capsule may be formed of gelatin or a plastics material.
By carefully controlling the conditions under which capsules
and blisters and filled, the final moisture level in the
product can be kept to below 15 wt %, preferably below 5 wt %.
The humidity level is preferably below 25% RH, most preferably
below 15% RH. The low moisture level is important for product
stability, and enables the product to be filled with minimal
static effects. Flow out of the' capsule or blister is also
improved.
By careful selection of capsule and packaging components,
stability and dosing can be controlled. The level of lubricant:
is kept low (preferably below 0.2% wt %) . Capsules for oral
use usually contain 2-3 wt % lubricant. Mould lubricant could
interact with the dry powder. Capsule integrity is important,
and accordingly a peelable lid to the blister package is
preferred to a conventional "push out" seal. The blister may
be, e.g. aluminium (40-50 µm thick) laminated with PVC (50-70
µm thick) and PA (20-30 µm thick) . The peelable seal may be
formed of soft aluminium (18-22 µm thick) laminated with PE7
(20-25 µm thick) .
The amount of composition contained in the capsule will, of
course, depend upon the desired dosage. However, the capsule
suitably contains from 10 to 200 milligrams, most preferably 30
to 150 milligrams of the colistin sulphomethate sodium.. The
colistin sulphomethate sodium may be delivered with or without
a carrier. If a carrier is used then clearly a larger amount
of the mix of carrier and pharmaceutical is required. It has
been found that the capsule should contain a larger dose of
drug than the amount which will actually be delivered to the
lungs. Dosages are usually expressed in "units". 80 mg of
colistin sulphomethate is equivalent to approximately 1 million
units of colistin sulphomethate. One unit of colistin
sulphomethate is contained in 0.00007874 mg of the first
International Reference Preparation (1966) of colistin
sulphomethate. Children with cystic fibrosis may be treated
with nebulised colistin sulphomethate sodium at a level of
500,000 units, twice daily. The respirable fraction from a
conventional nebuliser (CR 50 System 22) is approximately 9 mg
of colistin sulphomethate sodium from a 500,000 unit dose.
This can be tested using a multistage impinger and measuring
mass collected at stages 3 and 4.
A preferred device for delivering the pharmaceutical
composition according to the present invention is the Turbospm
(Registered Trade Mark) originating from PH & T. This device-
uses a gelatin capsule which is pierced in the bottom by a
single metal needle. When the patient inhales through the
mouthpiece, air is drawn in through the tangencially ranged
slits around the chamber. This spins the capsule and throws
out the contents into the airstream. A flip top on the device
allows up to three spare capsules to be stored. Another
preferred device for delivering the pharmaceutical composition
is the Aerohaler (Registered Trade Mark) from Boehringer
Ingelheim. This device uses a hard gelatin capsule which is
pierced by two metal needles in the side of a capsule. When
the patient inhales through the mouthpiece, air enters the
bottom of the chamber causing the capsule to spin and throw out
its contents into the airstream. The unit holds six capsules
in a carousel cartridge. When all six capsules have been used,
the unit locks and it must be re-loaded. Other devices known
in the art for delivery of encapsulated powders by inhalation
can be used.
The capsule keeps the powder dry and thus in flowable form.
The capsules should preferably be designed to protect their
contents from light, e.g. they should be opaque or the capsules
may be packed and/or stored in opaque containers, e.g. coloured
or covered containers,.or metal foil.
The invention is further described by reference to the
following Examples, illustrated by the following figures.
Figure 1 shows a particle size analysis of micronised colistin
sulphomethate sodium.
Figure 2 shows the structure of colistin sulphomethate with
accompanying sodium ions.
Figure 3 shows a neutralised colistin base, as described in
US-A-5,767,068.
Examples
Example 1
Micronised colistin sulphomethate sodium was produced by
fluidised energy milling using a Hosokawa Alpine mill of
powdered colistin sulphomethate sodium having an average
particle size of approximately 100 µm supplied by Dumex
Pharmaceuticals. A sample of the micronised colistin
sulphomethate sodium was suspended in chloroform and the
particle size analysed by a laser counter. Figure 1 shows the
range of particle sizes of the micronised colistin.
Example 2
Gelatin pharmaceutical capsules (standard size 2) were obtained
from Shionogi Qualicaps. The capsules were filled using a
standard dosator (Zanassi LZ64) under controlled temperature
and humidity conditions (17°C/lO%-15% RH). Colistin
sulphomethate sodium was filled into the capsules either as
pure micronised powder or together with a lactose carrier
(lactose monohydrate lactochem pharmaceutical grade from
Borculo Whey Products) . The fills are as shown on Table 1.
When colistin sulphomethate sodium is used alone, it flows
well. Filling weights are standard. If a mixture of colistin.
to lactose as in Run 2 is used then the mixed powder flows well
through the machine but there is sticking of the components of
the dosator. Sticking reduces in Runs 3 and 4. Tests found
respirable fractions in the region of 16 to 20 mg. This is the
mass of colistin sulphomethate sodium collected on stages 3 and
4 of the multistage liquid impinger and equates to particles
having a size less than about 3 to 4 micrometers.
Example 3
Filled capsules produced from Runs 1 to 4 above were stored for
nine months under various humidity conditions. There was no
degradation or clumping of the colistin sulphomethate sodium.
There was no noticeable clumping of colistin sulphomethate
sodium on the capsule walls.
Tests
Clinical trials were carried out. In one trial, the absorption
of the powdered colistin sulphomethate sodium into the airways
of the lungs was measured (specific airway conductance) . It
was found that 80% of patients, inhaling the micronised dry
powder colistin sulphomethate sodium, were able to mobilise 80
mg of the drug, i.e. 1 mega unit. This is a very high uptake,
and more than would be expected from a powdered drug. The
powder does not cause irritation, and thus construction, of the
lungs.
In a second trial, patients were given a premedication dose of
200 micrograms of salbutamol. This appeared to improve airway
conductance.
In an alternative medication regime, the salbutamol can be
mixed into the same capsule as the colistin sulphomethate
sodium.
A further trial compared specific airway conductance, as
measured by whole body plethysmography, of traditional
nebulised colistin sulphomethate sodium and dry powder. There
did not seem to be any noticeable difference.
We claim:
1. Micronised particles of colistin sulphomethats sodium wherein at
least 90 % by volume of the mlcronised particles have a diameter
of less than 10 micrometers for use in the treatment of a
pulmonary infection by powder inhalation, wherein the colistion
sulphomethate sodium is not separated into component form.
2. Collstln sulphomethate sodium for the use as claimed In claim 1
wherein the mlcronised powder is mixed with a carrier wherein
the ratio of colistin sulphomethate sodium to carrier is from 5:1 to
1:2 by weight.
3. Colistin sulphomethate sodium for the use as claimed in claim 2
wherein the carrier is lactose.
4. A composition comprising micronised colistin sulphomethate
sodium as defined in claim 1 and a carrier, in the absence of free
liquid.
3. A composition as claimed in claim 4 wherein the carrier is lactose.
6. A composition as claimed in claim 4 or claim 5 wherein the ratio
of colistin sulphomethate sodium to carrier is from 4:1 to 1:1 by
weight
7. The composition as claimed in any one of claims 4 to 6 wherein at
least 50 % by volume of the carrier particles have an effective
particle size in the range of 30-150 micrometers.
8. A composition as claimed in any one of claims 4 to 7 wherein at
least 50 % by volume of the micronised colistin sulphomethate
sodium has a particle diameter of less than 8 micrometers.
9. A composition as claimed In any one of claims 4 to 8 wherein at
least 25 % of the particles of micron ised colistin sulphomethate
sodium have a diameter of less than 6 micrometers.
10. A composition as claimed in any one of claims 4 to 9 wherein
the micronised colistin sulphomethate sodium is prepared in the
desired particle size range using a fluid energy mill.
11. A process for the preparation of a composition as claimed in
any one of claims 4 to 10 which comprises mixing micronised
coiistin sulphomethate sodium and a carrier,
12. A pharmaceutical dosage form suitable for use with a dry
powder inhaler comprising micronised colistin sulphomethate
sodium wherein at least 90 % by volume of the particles have a
diameter less than 10 micrometers or e composition according to
any one of claims 4 to 10 and a hard gelatin capsule, said dosage
having a content of below 10.
13. A capsule containing micronised colistin sulphomethate sodium
wherein at least 90 % by volume of the micronised particles have
a diameter of less than 10 micrometers.
14. A capsule as claimed in claim 14 containing from 10 to 200
micrograms of micronised colistin sulphomethate sodium.
15. A capsule as claimed in claim 14 containing from 30 to 150
milligrams of micronised colistin sulphomethate sodium.
16. A capsule as claimed in any one of claims 14 to 16 further
comprising a carrier.
17. A capsule as claimed in claim 17 when the carrier is lactose.
18. A capsule as claimed in any one of claims 14 to 18 which is
opaque.
19. A capsule as claimed in any one of claims 14 to 18 or a
composition as claimed in any one of claims 4 to 11 packed in an
opaque container.
20. A capsule containing micronised colistin suiphomethate sodium
when the micronised particles have a diameter of less than 10
micrometers, in unit dosage form,
21. A capsule as claimed in any one of Claims 14 to 2.1 which
additionally comprises a micronised oronchodiiatory drug.
22. A capsule as claimed in claim 22, wherein the bronchodilatory
drug is salbutamol.
23. A capsule as claimed in claim 22 or 23 which comprises from 50
to 150 milligrams of colistin suiphomethate sodium and from 1 to
250 micrograms of bronchodilatory drug.

Micronised particles of colistin sulphomethate sodium wherein at least
90% by volume of the micronised particles have a diameter of less
than 10 micrometers for use in the treatment of a pulmonary
infection by powder inhalation, wherein the colistin sulphomethate
sodium is not separated into component form.