Foam Drug Delivery in Dermatology

Abstract

Consumers of topical formulations apply a wide spectrum of preparations, both cosmetic and dermatological, to their healthy or diseased skin. These formulations range in physicochemical nature from solid through semisolid to liquid.
Pharmaceutical foams are pressurized dosage forms containing one or more active ingredients that, upon valve actuation, emit a fine dispersion of liquid and/or solid materials in a gaseous medium. Foam formulations are generally easier to apply, are less dense, and spread more easily than other topical dosage forms. Foams may be formulated in various ways to provide emollient or drying functions to the skin, depending on the formulation constituents. Therefore, this delivery technology should be a useful addition to the spectrum of formulations available for topical use; however, as yet, only a few are commercially available. Probably the most convincing argument for the use of foams is ease of use by the patient, and consumer acceptance. Most foam dosage forms used in dermatology to date have incorporated corticosteroids, although some products have also been used to deliver antiseptics, antifungal agents, anti-inflammatory agents, local anesthetic agents, skin emollients, and protectants.
Although there is no clinical evidence that foam formulations are currently superior to other conventional delivery vehicles, these formulations have a clear application advantage and with continued developments in the science of supersaturation technology, it seems certain that foam delivery systems will retain their place in the dermatological and cosmetic armamentarium.

Full text

Foam Drug Delivery in Dermatology
Beyond the Scalp
Carryn H. Purdon,1 John M. Haigh,2 Christian Surber3 and Eric W. Smith1
1 College of Pharmacy, University of South Carolina, Columbia, South Carolina, USA
2 Faculty of Pharmacy, Rhodes University, Grahamstown, South Africa
3 Department of Dermatology and Department of Pharmacy, Institute of Hospital-Pharmacy, University Hospital of Basel,
University of Basel, Basel, Switzerland
Contents
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
1. Foam Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
2. Review of Data on Foam Formulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
3. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Abstract Consumers of topical formulations apply a wide spectrum of preparations, both cosmetic and dermatological,
to their healthy or diseased skin. These formulations range in physicochemical nature from solid through
semisolid to liquid.
Pharmaceutical foams are pressurized dosage forms containing one or more active ingredients that, upon
valve actuation, emit a fine dispersion of liquid and/or solid materials in a gaseous medium. Foam formulations
are generally easier to apply, are less dense, and spread more easily than other topical dosage forms. Foams may
be formulated in various ways to provide emollient or drying functions to the skin, depending on the formulation
constituents. Therefore, this delivery technology should be a useful addition to the spectrum of formulations
available for topical use; however, as yet, only a few are commercially available. Probably the most convincing
argument for the use of foams is ease of use by the patient, and consumer acceptance. Most foam dosage forms
used in dermatology to date have incorporated corticosteroids, although some products have also been used to
deliver antiseptics, antifungal agents, anti-inflammatory agents, local anesthetic agents, skin emollients, and
protectants.
Although there is no clinical evidence that foam formulations are currently superior to other conventional
delivery vehicles, these formulations have a clear application advantage and with continued developments in
the science of supersaturation technology, it seems certain that foam delivery systems will retain their place in
the dermatological and cosmetic armamentarium.
TECHNOLOGY iN PRACTICE Am J Drug Deliv 2003; 1 (1): 71-75
1175-9038/03/0001-0071/$30.00/0
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Consumers of topical formulations apply a wide spectrum of
preparations, both cosmetic and dermatological, to their healthy
or diseased skin. These formulations range in physicochemical
nature from solid through semisolid to liquid. Drug substances
are seldom administered alone, but rather as part of a formulation,
in combination with one or more nonmedical agents that serve
varied and specialized pharmaceutical functions.[1] Drugs are ad-
ministered topically for their action at the site of application, or
for systemic effects. Drug absorption through the skin is en-
hanced if the drug substance is in solution, if it has a favorable
lipid/water partition coefficient, and if it is a nonelectrolyte. For
the most part, pharmaceutical preparations applied to the skin are
intended to serve some local action and, as such, are formulated
to provide prolonged local contact, with minimal systemic drug
absorption. Drugs applied to the skin for their local action include
antiseptics, antifungal agents, anti-inflammatory drugs, local an-
esthetics, skin emollients, and protectants.[1,2]
1. Foam Properties
Pharmaceutical foams are pressurized dosage forms, con-
taining one or more active ingredients that, upon valve actuation,
emit a fine dispersion of liquid and/or solid materials in a gaseous
medium. They differ from most other dosage forms in their de-

pendence on the function of the container, its valve assembly and
the pressurized propellant, for the physical delivery of the drug
in proper vehicle form.[1,2] This is perceived to be the major dis-
advantage of foam formulations in that the propellant technology
is relatively complex and expensive to manufacture, thereby in-
creasing the overall cost of the product. The production expense
of this type of formulation is probably the major factor that has
limited the number of dermatological foam formulations avail-
able to the clinician to date, in spite of several advantages that
this dosage form offers in terms of drug delivery and patient
acceptance.
Foam formulations are generally easier to apply, are less
dense, and spread more easily compared with other topical dos-
age forms. When assessed, particularly in terms of ointments, or
even creams and lotions, foams require negligible mechanical
shearing force in order to spread the formulation on the skin. This
is a major advantage when applying a medicament to highly in-
flamed skin; for example, in cases of sunburn where rubbing the
formulation on to the skin to effect spreading may be painful or
cause further inflammation. Hydrocortisone-containing formula-
tions have been used in Europe for some time to successfully treat
moderate to severe sunburn, the rationale for product selection
based on this ‘minimal-touch’ delivery convenience. Further-
more, even when applied to hirsute areas such as the scalp, these
formulations break down relatively rapidly, and easily reach the
stratum corneum through the hair shafts. In this respect, they
behave much like lotions and scalp application solutions, there-
fore resulting in enhanced patient compliance.
There are several other properties that distinguish foams
from other, more conventional, topical dosage forms. In clinical
and experimental situations, foam vehicles (structural matrix and
ingredients) undergo considerable changes after removal from
the primary container and application to the skin. The initial
structural matrix of the foam vehicle will undoubtedly change
during and after the mechanical agitation and physico-chemical
changes (e.g. evaporation of volatiles) associated with applica-
tion of the foam product. This inunction and/or evaporation of
ingredients (often causing phase inversion) will influence the rate
of drug transfer from the foam vehicle into the skin in a time-
dependent manner. The maximum drug transfer into the skin
takes place when the drug is in saturated solution at the vehicle-
skin interface.[3,4] If this is not the case, the rate of drug transfer
across the interface is proportional to its degree of saturation
(concentration/solubility).[3,4] Rapid evaporation of the volatile
components of foam vehicles results in an appreciable increase
in drug concentration in the vehicle. Evaporative concentration
first leads to saturation and then to supersaturation, which, although
generally a transient condition, results in a drug delivery rate
exceeding that achievable with a saturated solution.[3,4]
The thermodynamic activity or leaving potential of a perme-
ant molecule in a foam delivery vehicle formulation has an im-
portant influence on the rate of drug transfer from the vehicle into
the skin. As a drug molecule dissolves and enters into the matrix
of solvent molecules in the foam delivery vehicle, there are a
number of weak bonding interactions that take place between
substituent groups on the solute and solvent species. This attrac-
tive interaction stabilizes the dissolved molecule in solution and
prevents its precipitation. As the concentration of the solution
increases, so the total number of solvent molecules that are the-
oretically available to interact with each solute species decreases.
Therefore, there is a proportionally greater tendency for the so-
lute molecules to be lost by partitioning to a membrane in contact
with the formulation; the solute molecules have a greater thermo-
dynamic activity or leaving potential. Thermodynamic activity is
maximal in saturated solutions since there is minimal potential
for the partitioning to be retarded by bonding between the solute
and solvent molecules. A saturated solution is, therefore, prefer-
able as a topical drug delivery system as the maximum concen-
tration gradient and maximum thermodynamic activity are
achieved with such a system.[3]
2. Review of Data on Foam Formulations
Foam formulations, although not commonly available com-
mercially, have been in use for several years.[5] A comprehensive
search of the published literature was performed (including
Medline, International Pharmaceutical Abstracts, and Embase),
which yielded a surprisingly small number of references for the
use of foam dosage forms in dermatology. Table I lists repre-
sentative products that are currently available on the market. The
active ingredients that have been incorporated into these formu-
lations have mainly been topical corticosteroids (e.g. betametha-
sone valerate) that have been used effectively in the treatment of
corticosteroid-responsive dermatoses of the skin and scalp, such
as eczema, seborrhea and psoriasis. Foam formulations are par-
ticularly useful for diseases of the scalp due to the nature of the
formulation. A novel foam formulation with enhanced betameth-
asone valerate bioavailability has been shown to be superior in
efficacy when compared with a lotion in the treatment of scalp
psoriasis, without an associated increase in toxicity.[6-9] Psoriasis
is a chronic relapsing skin disorder that affects about 2% of the
US population, approximately half of these occurrences involv-
ing the scalp. Therefore, one can gauge the usefulness of this type
of dosage form in clinical practice.
72 Purdon et al.
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A study has been performed comparing the ability of a foam
formulation to release the active ingredient (betamethasone ben-
zoate) with ointment, gel, and cream formulations.[5] It was found
that the release of betamethasone benzoate from the ointment,
gel, and foam formulations was similar, but better than the release
from the cream. This was one of the first investigations into the
use of foams in dermatology and illustrates the usefulness of this
type of formulation. A foam formulation of the superpotent corti-
costeroid, clobetasol propionate, has demonstrated anti-inflam-
matory, antipruritic, and vasoconstrictive properties.[9,11] In pa-
tients with moderate to severe scalp psoriasis, topical application
of clobetasol propionate foam (0.05%) twice daily for 2 weeks
resulted in significant improvement of all signs and symptoms of
the disease compared with placebo and clobetasol propionate so-
lution (0.05%). Furthermore, patients who received clobetasol pro-
pionate foam demonstrated greater improvement of scaling after
2 weeks of treatment, and after 2 weeks of follow-up.
There are only a limited number of reports in the literature
concerning the use of foam formulations in other fields of derma-
tology or nondermatological fields. Nonsteroidal anti-inflammatory
and antifungal agents are among the other drug families that have
been formulated into foam products, while nonoxynol-9 foam[12]
has been used vaginally as a contraceptive, and chlorhexidine
gluconate foam has been used as a preoperative application.[13]
If one considers that drug delivery to the alimentary canal and
mucosae may be classified as ‘topical’ delivery in the classical
sense, then one may include rectal foam products in this discus-
sion of dermatological foams.
Prednisolone, hydrocortisone, beclomethasone dipropion-
ate, and mesalazine foams have been applied rectally in ulcerative
colitis and the treatment of postepisiotomy pain and erythema. A
report on a 28-day trial evaluated the efficacy and tolerability of
beclomethasone dipropionate in a rectal foam formulation during
the treatment of patients with ulcerative colitis, evaluating endo-
scopic, histologic, clinical, and tolerability parameters.[14] Sixty
male and female patients aged between 20 and 81 years, with
proctosigmoiditis (47%) and ulcerative rectocolitis (53%) were
evaluated in the study. Endoscopic parameters showed an im-
provement in 75% of patients after 28 days of treatment, and clinical
improvement was achieved in 65% of patients. Eighty-two per-
cent of patients judged the treatment to be good/excellent with
regard to tolerability, emphasizing the validity of the use of foam
formulations in the treatment of ulcerative colitis and procto-
sigmoiditis.[14]
Similarly, a comparison of the efficacy, tolerability, and overall
acceptability of a new mesalazine rectal foam with mesalazine
enema in the treatment of active distal ulcerative colitis has been
reported.[15] A multicenter study was carried out in patients with
active proctitis, proctosigmoiditis, and left-sided ulcerative coli-
tis. Patients were randomly assigned to receive either mesalazine
foam (2g twice daily) or mesalazine enema (2g/60ml twice daily)
for 3 weeks.[15] The mesalazine foam and enema were found to
be equally effective for the treatment of proctitis, proctosigmoid-
itis and left-sided ulcerative colitis, and the new foam preparation
was well tolerated and accepted as a therapeutic alternative to
conventional mesalazine enema formulations.
Eczematous contact dermatitis is a serious work-related skin
disease. Reimbursement by insurance companies for the treat-
ment of skin diseases has become a significant cost source in some
countries.[16] An aerosol foam skin protectant has been evaluated[16]
in the prevention of contact dermatitis caused by sodium lauryl
sulfate and urushiol, the resinous sap of poison ivy and poison oak.
Table I. A representative list of foam products that are currently commercially available[10]
TradenameaManufacturer Active drug Indications
BactoshieldAmsca 4% chlorhexidine gluconate Surgical scrub, skin cleanser, skin wound cleanser
BetadinePurdue Federick Povidone iodine Shampoo for temporary relief of scaling and itching due
to dandruff
DesenexCiba Consumer 10% undecylenate Antifungal and antibacterial agent for tinea pedis
Epifoam aerosol foam Schwarz Pharma 1% hydrocortisone; 1% pramoxine Relief of inflammation and pruritic manifestations of
corticosteroid-responsive dermatoses
LuxiqConnetics Betamethasone valerate Relief of inflammation and pruritic manifestations of
corticosteroid-responsive dermatoses
OperandRedi-Products Povidone iodine Shampoo for temporary relief of scaling and itching due
to dandruff
ProctoFoam-HC aerosol foam Reed and Carnrick 1% hydrocortisone; 1% pramoxine Relief of inflammation and pruritic manifestations of
corticosteroid-responsive dermatoses
Sarna anti-itch Stiefel 0.5% camphor; 0.5% menthol Antipruritics, mild local anesthetics and counter-irritants
SeptisolCalgon Vestal 0.23% hexachlorophene Surgical scrub and bacteriostatic skin cleanser
a The use of tradenames is for product identification purposes only and does not imply endorsement.
Foam Drug Delivery in Dermatology 73
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This evaluation demonstrated that the foam product was effective
in reducing the irritation from sodium lauryl sulfate, but did not
prevent the allergic reaction to urushiol.
A study in 25 children and infants was conducted to assess the
efficacy of a chlorhexidine, prednisolone, and nystatin-containing
antifungal foam formulation on candida skin infections of the diaper
region.[17] It was found that all infections, even the most severe,
were cured within a maximum of 13 days. Similarly, 61 patients
with pityriasis versicolor were treated with a single application
of ketaconazole foam in a clinical trial conducted in France.[18]
The trial was double-blind and placebo-controlled, with 28 pa-
tients in the ketaconazole group. Of the patients who received
ketoconazole, 21 demonstrated a negative mycologic examina-
tion 30 days after the single application.
Ibuprofen, ketoprofen, and diclofenac foams have been ap-
plied topically as anti-inflammatory and analgesic agents.[19-21]
A recently published report examined the in vitro permeation of
ibuprofen from commercially available formulations, purchased
in the UK, through a silastic silicone membrane monitored over
a period of 72 hours using modified Franz cell apparatus.[22] In-
dividual and mean apparent release constants were obtained by
linear regression analysis of plots of cumulative amount of re-
leased drug versus square root of time. The release constants and
linear correlation coefficients for ibuprofen-containing topical
formulations using the Franz diffusion cell apparatus are shown
in table II.
The plot of cumulative amount of released drug versus time
for ibuprofen-containing topical formulations is depicted in fig-
ure 1.[22] The profiles obtained for the three formulations are
similar between 0 and 8 hours, but diverge markedly thereafter.
The initial release rates of the formulations were shown to stead-
ily increase from 0–8 hours, with a further increase from 8–48
hours. This is indicative of a biphasic release pattern, and is pos-
sibly an example of metamorphosis of the delivery vehicle with
time. Drug penetration is dependent upon the influence of the
vehicle on the thermodynamic activity of the active ingredient.
The cream and gel appeared to present an ideal combination of
solubility and physical diffusivity through the vehicle, yielding
higher ibuprofen release rates and apparent release constants than
the mousse formulation. This data exemplifies the observation
that nonstandard drug release kinetics may be obtained in con-
ventional in vitro drug diffusion studies, especially those where
foam vehicles are evaluated. Metamorphosis of the delivery ve-
hicle may change drug delivery potential markedly with time, a
factor that topical formulation developers need to take into ac-
count at the preformulation stage of development.
3. Conclusions
It is evident that there are only a small number of reports in
the literature concerning the use of foam formulations in derma-
tology and nondermatological fields. Most of the foam dosage
forms used in dermatology to date have incorporated corticoster-
oids, although the literature does describe products used to de-
liver antiseptics, antifungal agents, anti-inflammatory agents, lo-
cal anesthetic agents, skin emollients, and protectants.
The type of delivery vehicle or the formulation excipients
can markedly affect the percutaneous absorption of a drug. Phar-
maceutical and cosmetic products are developed in terms of sta-
bility and compatibility of excipients and active agents, cosmetic
acceptability, usage criteria of the vehicle, and bioavailability of
the incorporated drug. Thus, the ideal topical delivery vehicle
should be easy to apply and remove, nontoxic, nonirritant, non-
allergenic, chemically stable, homogeneous, bacteriostatic, cos-
metically acceptable, pharmacologically inert, and should readily
release the drug to the stratum corneum. Foam formulations are
commonplace in the cosmetic industry; in that sphere manufac-
turers are prepared to produce the higher cost formulations, and
consumers are prepared to pay the premium for the convenience
and elegance of the specialized product. The same cannot be said
for the dermatologic sphere. Presumably, cost-containment to the
Table II. Release constants and correlation coefficients (r 2) for ibuprofen-
containing topical formulations (reproduced from Purdon,[22] with permis-
sion)
Tradename Apparent release constant
(µg/cm2/h1⁄2)
r 2
Deep Relief gel 155.81 0.9627
Ibuleve gel241.87 0.9794
Ibuleve mousse 114.46 0.9931
Proflex cream 312.91 0.9803
0
2500
Cumulative amount released (µg/cm
2
)
024 2448
Time (h)
8
1500
1000
500
2000
72
Proflex cream
Ibuleve gel
Ibuleve mousse
Fig. 1. Diffusion profiles of commercially available ibuprofen-containing
products (reproduced from Purdon,[22] with permission)
74 Purdon et al.
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patient has caused pharmaceutical manufacturers to shy away
from foam delivery systems.
It would appear that foam products may be an extremely
useful addition to the range of formulations available for topical
use, but as yet only a few are available. In addition to the cost
factor, this may well be due to the fact that studies have shown
that there is generally little improvement in drug release from a
foam dosage form when compared with cream, lotion, ointment,
and gel formulations. Even for use on the scalp, it has been shown
that there is no significant clinical advantage (and considerable
container and manufacturing disadvantage) gained by the use of
a foam formulation compared with a lotion or scalp application
solution. Probably the most convincing argument for the use of
foams is ease of use by the patient and the low-shear spreading
and application that is possible with these products – the latter
being the most significant physical property of this formulation
type. However, advances are constantly being made in drug de-
livery technology, e.g. the employment of penetration enhancers
and supersaturation delivery techniques. The use of a foam for-
mulation appears to be an ideal medium for using delivery vehicle
metamorphosis technology in the future to improve drug delivery
profiles for the patient.
Acknowledgements
No sources of funding were used to assist in the preparation of this
manuscript. The authors have no conflicts of interest that are directly relevant
to the content of this manuscript.
References
1. Ansel HC, Allen LV, Popovich NG. Pharmaceutical dosage forms and drug deliv-
ery systems. 7th ed. Baltimore (MD): Lippincott Williams & Wilkins, 1999
2. Sciarra JJ, Sciarra CJ. Aerosols. In: Gennaro AR, editor. Remington: the science
and practice of pharmacy. 20th ed. Baltimore (MD): Lippincott Williams &
Wilkins, 2000: 963-79
3. Surber C, Smith E. The vehicle: the pharmaceutical carrier of dermatological
agents. In: Gabard B, Elsner P, Surber C, et al., editors. Dermato-pharmacology
of topical preparations. Berlin: Springer-Verlag, 2000: 5-22
4. Schwarb FP, Imanidis G, Smith EW, et al. Effect of concentration and degree of
saturation of topical fluocinonide formulations on in vitro membrane transport
and in vivo availability on human skin. Pharm Res 1999; 16: 909-15
5. Woodford R, Barry BW. Bioavailability and activity of topical corticosteroids
from a novel drug delivery system: the aerosol quick break foam. J Pharm Sci
1977; 66: 99-103
6. Feldman SR, Sangha N, Setaluri V. Topical corticosteroids in foam vehicle offers
comparable coverage compared with traditional vehicles. J Am Acad Dermatol
2000; 42: 1017-20
7. Feldman SR, Ravis SM, Fleischer Jr AB, et al. Betamethasone valerate in foam
vehicle is effective with both daily and twice daily dosing: a single-blind, open-
label study in the treatment of scalp psoriasis. J Cutan Med Surg 2001; 5: 386-9
8. Franz TJ, Parsell DA, Halualani RM, et al. Betamethasone valerate foam 0.12%:
a novel vehicle with enhanced delivery and efficacy. Int J Dermatol 1999; 38:
628-32
9. Melian EB, Spencer CM, Jarvis B. Clobetasol propionate foam 0.05%. Am J Clin
Dermatol 2001; 2: 89-92
10. Cada DJ, Covington TR, Generdli JA, et al., editors. Drug facts and comparisons.
St Louis (MO): Facts and Comparisons, 2000: 1597-722
11. Lebwohl M, Sherer D, Washenik K, et al. A randomized, double-blind, placebo-
controlled study of clobetasol propionate 0.05% foam in the treatment of non-
scalp psoriasis. Int J Dermatol 2002; 41 (5): 269-74
12. Barditch-Crovo P, Witter F, Hamzeh F, et al. Quantitation of vaginally adminis-
tered nonoxynol-9 in premenopausal women. Contraception 1997; 55 (4): 261-3
13. Beeuwkes H, Rooij SH. Microbiological tests on operating-theatre staff of a new
disinfectant foam based on 1% chlohexidine gluconate. J Hosp Infect 1986; 8
(2): 200-2
14. Arcidiacono R, Zanasi G, Pirone Z, et al. The topical therapy of ulcerative colitis:
a multicenter study with beclomethasone dipropionate foam. Minerva Chir
1999; 54 (9): 635-44
15. Ardizzone S, Doldo P, Ranzi T, et al. Mesalazine foam (Salofalk foam) in the
treatment of active distal ulcerative colitis: a comparative trial vs Salofalk en-
ema. The SAF-3 study group. Ital J Gastroenterol Hepatol 1999; 31 (8): 677-84
16. Patterson SE, Williams JV, Marks JG. Prevention of sodium lauryl sulphate irritant
contact dermatitis by Pro-Q aerosol foam skin protection. J Am Acad Dermatol
1999; 40: 783-5
17. Pillwein K, Rauschmeier W, Berger H. Clinical experiences with an antimycotic
foam preparation with added prednisolone. Padiatr Padol 1986; 21: 75-80
18. Rekacewicz I, Guillaume JC, Benkhraba F, et al. A double-blind placebo-control-
led study of a 2% foaming lotion of ketaconazole in a single application in the
treatment of pityriasis versicolor. Ann Dermatol Venereol 1990; 117: 709-11
19. Daffonchio L, Bestetti A, Clavenna G, et al. Effects of a new foam formulation of
ketoprofen lysine salt in experimental models of inflammation and hyperalge-
sia. Arzneimittel Forschung 1995; 45 (5): 590-4
20. Parrini M, Cabitza P, Arrigo A, et al. Efficacy and tolerability of ketoprofen lysine
salt foam for topical use in the treatment of traumatic pathologies of the loco-
motor apparatus. Clin Ther 1992; 141 (9): 199-204
21. Muller M, Rastelli C, Ferri P, et al. Transdermal penetration of diclofenac after
multiple epicutaneous administration. J Rheumatol 1998; 25 (9): 1833-6
22. Purdon CH. In vitro passage of ibuprofen through synthetic and biological mem-
branes [thesis]. Grahamstown: Rhodes University, 2002
Correspondence and offprints: Dr E.W. Smith, College of Pharmacy, Univer-
sity of South Carolina, Columbia, SC 29208, USA.
E-mail: esmith@cop.sc.edu
Foam Drug Delivery in Dermatology 75
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