M. T. Haroun, MD, FRCPC
Assistant Professor of Medicine, Division of Dermatology, University of Toronto, Sunnybrook and Women’s College Health Sciences Centre, Toronto, Canada
Acne vulgaris is a disease of the pilosebaceous follicle characterized by noninflammatory (open and closed comedones) and inflammatory lesions (papules, pustules, and nodules). Its pathogenesis is multifactorial, i.e., hormonal, bacterial and immunological (inflammatory)
factors are involved, and their interaction results in the production of acne lesions. Although it is not a life-threatening condition, it can have a detrimental effect on a patient’s quality of life. It is readily responsive to treatment with the goals being to clear the lesions, prevent scarring, and reduce the psychological distress.
Possible Causes of Acne
Hormones are known to affect sebum production, but may well play a role in follicular hyperkeratinization independent of the effect on the sebaceous gland. During adrenarche, an increase in adrenal androgens leads to:
- an increase in the size of sebaceous glands and a resulting increase in sebum production
- abnormal desquamation and greater adhesion of the shed keratinocytes in the sebaceous follicle, leading to obstruction in the follicle, and resulting in production of the microcomedo: the precursor of all acne lesions.
Colonization of the pilosebaceous apparatus by the anaerobic diphtheroid Propionibacterium acnes (P. acnes) occurs in this anaerobic environment where sebum provides the nutrition for its survival. This gram-positive bacterium contributes to the inflammation by
- releasing enzymes
- inducing cytokine release from other cells
- inducing immune response (e.g., antibody production).
Topical antibiotics have been used to treat acne for more than 40 years and are still widely used. Their efficacy is partly due to their reduction of the P. acnes population and partly due to the reduction of inflammatory mediators. The emergence of resistant strains has in some cases been associated with a failure to respond to antibiotic therapy. This resistance was first reported with the topical antibiotics clindamycin and erythromycin.[Crawford WW, et al. J Invest Dermatol 72:187-90 (1979).] The use of benzoyl peroxide (BP) helps to reduce the occurrence of resistance and can be effective in the treatment of both nonresistant and resistant P. acnes strains. BP does not promote antimicrobial resistance and has been shown to prevent such resistance when used concomitantly with topical erythromycin.
|Double-blind study of patients with mild-tomoderate
acne [Eady EA, et al. Br J Dermatol
|5% BP/3% erythromycin (BP/E)
gel vs. erythromycin alone applied
for 6 weeks
|The number of erythromycin-resistant
strains was signifi cantly reduced in the
BP/E group compared with the group who
received erythromycin alone.
|Open study of patients with erythromycin-resistant
strains of P. acnes. [Eady EA, et al. Br
J Dermatol 134:107-13 (1996).]
|5% BP/3% erythromycin (BP/E)
gel vs. erythromycin alone applied
for 6 weeks
|Highly signifi cant reductions were also
seen in acne grade and lesion counts with
the BP/E combination.
|Two double-blind randomized, parallel,
vehicle-controlled trials of acne patients
[Lookingbill DP, et al. J Am Acad Dermatol
|BP/clindamycin combination, BP,
clindamycin or vehicle gels applied
once nightly for 11 weeks
|The combination gel was signifi cantly
superior to the two individual agents in
global improvement and reduction of
infl ammatory lesions.
|Randomized, multicenter, single-blind trial
of moderate-to-severe acne patients [Leyden
JJ, et al. J Cutan Med Surg 5:37-42. (2001).]
|5% BP/1% clindamycin, 5% BP
or 5% BP/3% erythromycin applied
twice daily for 10 weeks
|Compared with BP, BP/clindamycin demonstrated
signifi cantly greater reductions
in infl ammatory lesions. BP/clindamycin
was comparable to BP/E.
|Table 1: Clinical trials demonstrating efficacy for combination treatments with BP and clindamycin or erythromycin|
Advantages of BP/Antibiotic Combination
- less irritation than BP alone
- increase tolerability to topical retinoid
- better efficacy than BP alone.
There are many acne grading systems, but it may be easier to use a descriptive grading system using the terms mild, moderate, and severe with descriptors of comedonal, inflammatory, nodular, and scarring acne.
Non-inflammatory (comedonal) acne is best treated with a topical retinoid. Options include tretinoin, adapalene, and tazarotene. Not only do retinoids inhibit comedo formation, they can usually clear all degrees of comedonal acne, but this may take a few months. BP has mild comedonal activity.
Acne that does not respond to topical therapy, causes scarring, or presents with nodular lesions should be treated orally. Options for oral therapies include antibiotics, hormonal therapy and isotretinoin. Isotretinoin is usually used as monotherapy. Both oral antibiotics and hormonal therapies should be used in combination with topical retinoids and BP.
Prescribing habits to minimize resistant strains of P. acnes
- Antibiotics should not be used as monotherapy, nor should they be used to treat mild acne.
- Avoid topical antibiotics if non-antibiotic topical preparations will suffice.
- Use alternatives to antibiotics for maintenance.
- Stop antibiotic treatment when the skin clears or if no further improvement is noted.
- If there is a failure to respond to oral antibiotics or a rapid relapse after discontinuation consider other therapy (e.g., systemic retinoid, anti-androgens [in women]).
- If the antibiotic is needed again, use the same antibiotic.
- Use full doses of antibiotics and do not taper.
- Avoid concomitant topical and systemic use of different antibiotics to reduce the risk of developing resistance to both.
- Do not switch or rotate antibiotics in nonresponders.
- Use BP during antibiotic therapy.
|Sebum overproduction||Estrogen, spironolactone, other anti-androgens, isotretinoin||None.|
|Follicular keratinization||Isotretinoin, antibiotics (indirect effect), anti-androgens||Tretinoin, adapalene, tazarotene,
Antibiotics and BP (indirect effects).
|P. acnes proliferation||Tetracycline, minocycline, doxycycline, erythromycin,
|Clindamycin, erythromycin, BP,
|Inflammation||Corticosteroids, isotretinoin, dapsone, antibiotics, NSAIDS||Intralesional corticosteroids, topical
antibiotics, BP/antibiotic combos, some
|Table 2: Major pathophysiologic features of acne and drugs that affect them|
Mild-to-moderate inflammatory acne can usually be managed with two topical drugs. Typically one is applied in the morning and the other at bedtime. A retinoid is used to deal with the precursor of all acne lesions, i.e., the microcomedo, and an antibacterial agent for its effects on P. acnes. Topical antibacterial options include BP or a BP/antibiotic combination. BP is extremely effective against P. acnes, but can be irritating. The irritation can be minimized by using the lowest concentration of BP in a water-based vehicle that does not reduce its efficacy. Another way to reduce the irritation induced by BP is to combine it with an antibiotic. BP/antibiotic combinations also reduce the irritation that can be induced by a topical retinoid. Only if a patient is allergic to BP (estimates range from 1%-2% of the population) should a topical retinoid be used with a topical antibiotic alone.
Since multiple factors are involved in the pathophysiology of acne, treatment that counteracts the majority of them can be expected to achieve the best results. When considering the options for reducing the P. acnes population, it is best to choose those that do not encourage resistance patterns.