INTRODUCTION
The Consensus Guidelines for acne management suggest
that enhanced therapeutic benefits may be obtained by combining
therapeutic agents with different but complementary
mechanisms of action.1 The topical combination of a an antibiotic/
antimicrobial plus a retinoid targets ductal hypercornification,
bacterial proliferation, and inflammation. The
addition of benzoyl peroxide (BP) may help minimize the development
of Propionibacterium acnes’ (P. acnes) resistance to
the antibiotics that are typically used to treat it.1-3 It also confers
significant activity against inflammatory acne lesions and
exhibits a moderate ability to reduce comedonal lesions.4,5
Numerous studies have demonstrated increased efficacy with
the combination of BP and a topical antibiotic over either
agent alone.1-3,6 For example, Cunliffe et al showed that topical
therapy with BP 5%/clindamycin 1% (BP/C) in a waterbased
vehicle reduced P. acnes counts significantly compared
to clindamycin 1% monotherapy. Unlike topical clindamycin
monotherapy, which was associated with a progressive increase
in P. acnes resistant strains after 8 weeks of use, the
combination of BP/C obviated the emergence of clindamycin
resistance.3
In addition to the therapeutic effects of the active ingredients,
the efficacy and safety of topical formulations can be influenced
by excipients. The BP/C gel used in this study is
formulated in a water-based, fragrance-free vehicle and does
not contain alcohol. The vehicle contains glycerin, a humectant,
and dimethicone, an emollient with occlusive properties.
These ingredients are known to reduce irritation and
dryness and may obviate the need for an additional noncomedogenic
moisturizer. These excipients may affect local
tolerability and efficacy, particularly when the antibiotic gel
is used in combination with topical retinoids.7,8 In a study
comparing 2 gel formulations of BP/C, the formulation containing
glycerin and dimethicone was shown to be both better
tolerated and preferred by patients.7
Adapalene (AP) is a third-generation synthetic retinoid that
has been shown to be less irritating than tretinoin. In addition
to having efficacy equivalent to that of tretinoin, adapalene has
been shown to have potent anti-inflammatory activity of its
own.5,9 Because of its reduced irritation potential, AP is well
suited for use in combination regimens particularly in topical
regimens such as BP, which is also potentially irritating.10 Besides
the fact that topical retinoids add comedolytic activity to
the BP/C regimen, they have also been shown to increase the
penetration of topical antibiotics.11
A recent single-blind, parallel-group, multicenter study in the
UK compared the use of BP/C gel and AP 0.1% gel in the
management of mild to moderate acne. The BP/C combination
was found to produce significantly superior reductions in
inflammatory lesion counts beginning at week 1 and continuing
through the 12 weeks of the study (P=.001). In addition,
the BP/C combination had a more rapid onset of
action compared to AP, and was associated with markedly
fewer local tolerability reactions. The authors of the study
concluded that greater efficacy, more rapid onset of clinical
effect, and better tolerability of the BP/C topical gel formulation
is likely to result in better patient compliance with
therapy and thus better treatment outcomes.12
In a study of BP/C gel and tazarotene cream13 versus tazarotene
alone, the combination regimen was shown to enhance efficacy
and demonstrated a trend toward improved tolerability.
The combination therapy was at least as well tolerated as
tazarotene cream monotherapy. The authors noted that the
addition of BP/C gel to the topical retinoid also conferred increased
comedolytic activity. While this study found no significant
intergroup differences in pruritus, burning, dryness,
or erythema, there were significant intergroup differences in
peeling at week 4. At this time point, a higher number of subjects
in the BP/C plus tazarotene group (67% vs. 57%) had no
peeling or only a trace of peeling. This suggested that BP/C
gel containing the excipients glycerin and dimethicone may
