The subject matter relates to an overcap (10) containing a desiccant
(30) for use with a metered dose inhaler (12) to adsorb moisture.
The overcap advantageously reduces the amount and rate of moisture
ingress into the metered dose inhaler. The operation of metered
dose inhalers containing agroscopic drug particles is improved by
reducing moisture ingress.
What is claimed:
1. An apparatus comprising: a first housing fitted with a moisture
absorber comprising a second housing containing a desiccant.
2. The apparatus of claim 1 wherein the second housing is constructed
from a radially oriented material connected to a moisture permeable
3. The apparatus of claim 2 wherein the radially oriented material
is an injection moldable plastic.
4. The apparatus of claim 2 wherein the moisture permeable material
5. The apparatus of claim 2 wherein the moisture permeable material
6. The apparatus of claim 2 wherein the moisture permeable material
is connected to the radially oriented material by crimping over
a portion of the radially oriented material.
7. The apparatus of claim 3 wherein the injection moldable plastic
is a polypropylene.
8. The apparatus of claim 1 wherein the desiccant comprises granular
9. The apparatus of claim 2 wherein the second housing includes
at least one radially oriented fin.
10. The apparatus of claim 9 wherein the radially oriented fin
is a circumferential fin.
11. The apparatus of claim 10 comprising a plurality of circumferential
12. The apparatus of claim 1 wherein the first housing is constructed
from an injection moldable plastic.
13. The apparatus of claim 12 wherein the injection moldable plastic
is a polypropylene.
14. The apparatus of claim 1 further comprising a metered dose
inhaler connected to the first housing by a sealant.
15. The apparatus of claim 14 wherein the sealant is constructed
from an epoxy material.
16. The apparatus of claim 14 wherein a valve stem, ferrule, valve
housing and neck are contained and sealed withing the first housing.
17. The apparatus of claim 14 wherein the sealant is a foil label.
18. The apparatus of claim 17 wherein the foil label is a structural
laminate comprising an oriented ployamide layer, an aluminum foil
layer and a pressure sensitive adhesive.
19. The apparatus of claim 18 wherein the foil label has a thickness
in the range of 9-20 .mu.m.
20. The apparatus of claim 14 wherein the sealant provides a hermetic
seal between the metered dose inhaler and the first housing.
21. The apparatus of claim 8 comprising 2-10 g granular silica
22. The apparatus of claim 14 wherein the metered dose inhaler
contains albuterol sulfate.
23. An overcap for an aerosol container comprising: a first housing
fitted with a means for absorbing moisture.
CROSS REFERENCE TO RELATED APPLICATIONS
 U.S. Application having serial No. 60/204252 filed on May
15 2000 entitled "Method and Package for Storing A Pressurized
Container Containing A Drug" is hereby incorporated herein
by reference in its entirety.
BACKGROUND OF THE INVENTION
 As discussed in the above-referenced application, moisture
ingress into HFC MDI's is problematic, particularly for MDI's containing
agroscopic drug particles which readily adsorb and/or absord water
and form aggregates. One solution to the problem has been to incorporate
a dessicant to absorb moisture that in its absence would ingress
into the MDI. The manner in which the desiccant is employed can,
however, impact to varying degrees several factors.
 For example, the structures employed for the desiccant can
affect the cost of manufacturing. Complex and difficult mechanisms
may reduce throughput, decrease efficiencies, and increase material
costs. The form of desiccant packaging can also affect the visual
and commercial appeal of the MDI. For example, to some vendors and
customers, an internal, unseen desiccant may be more appealing than
the overrap and loose desiccant pouch disclosed in the above-referenced
 Moreover, there is a strong need for effective prevention
of moisture ingress in HFC propellant MDI's. It is well established
that non-CFC propellants, especially HFC 134a, have much greater
water solubility that the CFC propellants traditionally used in
MDI's. The maximum water solubility in HFC 134a is about 2200 ppm
(and about 1000 ppm in pressurized/stored MDI's) compared to about
130 ppm (and 50-100 ppm in pressurized/stored MDI's) for CFC 11
12 and 114. The maximum solubility may be further increased where
co-solvents such as ethanol are employed in the aerosol formulation.
The mechanism of moisture ingress into HFC MDI's may be found in
Williams, G. and Tcherevatchenkoff, A. (1999), "Moisture Transport
Into CFC-Free MDI's," Respiratory Drug Deleivery VI, Hilton
Head, S.C., USA.
 They concluded that moisture ingress is influenced by the
elastomeric nature of the valve gaskets as well as the type of HFA
formulation and storage conditions employed. It may be appropriate
under some circumstances to control moisture ingress into HFC-based
MDI's. One example is where hygroscopic drug substance are used,
such as albuterol sulfate. The present invention advantageously
reduces moisture ingress into MDI's to suitable levels. The present
invention employs a desiccant in a manner that is visually appealing
and commercially advantageous. The design and structure of the present
invention is also advantageously simple, efficient to manufacture,
cost effective, smaller and less bulky that other secondary packaging
SUMMARY OF THE INVENTION
 One aspect of the invention is an overcap including an outer
housing fitted with a moisture absorber structure having a housing
containing a desiccant. The housing of the absorber is preferably
constructed from a radially oriented material connected to a moisture
permeable material. The radially oriented material is preferably
an injection moldable plastic. The moisture permeable material is
preferably fiberboard or TYVEK.TM. available from DuPont.
 Preferably, the moisture permeable material is connected
to the radially oriented material by crimping over a portion of
the radially oriented material. The injection moldable plastic is
preferably a polypropylene. The desiccant preferably includes a
granular silica gel, preferably 2-10 grams.
 In another aspect of the invention, the housing of the absorber
includes at least one radially oriented fin. The radially oriented
fin may be a circumferential fin. The absorber may also include
a plurality of circumferential fins or a combination of radial and
circumferential fins. The outer housing is preferably constructed
from an injection moldable plastic, and more preferably a polypropylene.
 In another aspect of the invention, the overcap is connected
to a metered dose inhaler by a sealant. The sealant is preferably
constructed from an epoxy material, such as DEVCON 2-TON EPOXY.TM..
Preferably, the overcap and sealant seals off a valve stem, ferrule,
valve housing and neck of the metered dose inhaler. The sealant
is preferably a foil label. The foil label may be a structural laminate
including an oriented ployamide layer, an aluminum foil layer and
a pressure sensitive adhesive. The foil label preferably has a thickness
in the range of 9-20 .mu.m. The sealant may provide a hermetic seal
between the metered dose inhaler and the outer housing. The metered
dose inhaler may contain a drug such as albuterol sulfate.
BRIEF DESCRIPTION OF THE DRAWING
 The present invention will become more fully understood
from the detailed description herein and the accompanying drawing
which are provided by way of illustration only and are not to be
construed as limiting the full scope of the invention.
 FIG. 1 is a cross-sectional, cut-away view of the overcap
of the present invention in combination with a portion of the metered
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
 Shown in FIG. 1 is a cross-sectional, cut-away view of an
overcap 10 connected to a portion of an MDI 12. The overcap 10 is
connected to the MDI 12 by a sealant 14. The portion of the MDI
12 shown in FIG. 1 includes a stem 16 a ferrule 18 a valve housing
20 a neck assembly 22 and a cannister 24.
 The overcap 10 includes an outer housing 26 fitted with
a desiccant container 28 containing a desiccant 30. The desiccant
container 28 includes a fitment housing 31 connected to a moisture-permeable
overlay 32 to contain the desiccant 30. The fitment 31 is connected
to the overlay 32 by a crimp 34 in the fitment 31. The fitment 31
also includes a radial fin 36 for friction fitting the desiccant
container 28 within the outer housing 26.
 An MDI containing albuterol sulfate and HFC 134a propellant
was evaluated for moisture ingress using the overcap of the present
invention. The sealant was DEVCON 2-TON EPOXY.TM.; the injection
moldable plastic was polypropylene, the desiccant was 10 g silica
gel, and the overlay material was fiberboard. The results are shown
in Table 1. The numerical values are the mean moisture content (ppm)
of the MDI contents after storage at 40.degree. C. and 85% RH. The
overcap was compared to a conventional shrink wrap seal and adhesive
1 TABLE 1 System Initial 6 weeks 3 months Epoxy Seal 204 280 232
Shrink Wrap 204 266 371 Adhesive Band 204 383 281 As the data demonstrates,
the overcap was exceptionally effective at reducing the rate of
moisure ingress into the MDI.