Thanks for asking your question.
You asked the following:
"If acne is a virus, how come doctors prescribe antibiotics such as
tetracycline and doxycycline for treatment of moderate to severe acne,
rather than an antiviral medication?"
Acne vulgaris is the most common cutaneous disorder in the United
States. It affects more than 17 million Americans, accounting for over
10 percent of all patient encounters with primary care physicians and
over 4.8 million patient visits per year (1).
I have to dispute your claim that acne is a virus. The primary
organism involved is a bacteria, Propionibacterium acnes. Here are
several sources detailing the pathogenesis of acne.
"Acne vulgaris is a disease of pilosebaceous follicles. Four factors
1) Retention hyperkeratosis
2) Increased sebum production
3) Propionibacterium acnes (a bacteria) within the follicle
The earliest change in the pilosebaceous unit is follicular
hyperkeratinization, which is associated with both increased
proliferation and decreased desquamation of keratinocytes lining the
follicular orifice. The result is formation of a hyperkeratotic plug
composed of sebum and keratin (the microcomedo) in the follicular
canal. Why this process occurs is not known.
Sebaceous glands enlarge with adrenarche and sebum production
increases. Sebum provides a growth medium for Propionibacterium acnes,
an anaerobic diphtheroid that is a normal component of skin flora.
Microcomedones provide an anaerobic lipid-rich environment that allows
these bacteria to thrive; they utilize triglycerides as a nutrient
source by hydrolyzing them into free fatty acids and glycerol.
Inflammation results from the proliferation of P. acnes.
Proinflammatory lipids and keratins are thereby extruded into the
surrounding dermis, leading to papule or nodule formation.
Depending upon the degree of follicular hyperkeratinization, sebum
production, P. acnes growth, and inflammation, the microcomedo evolves
into a noninflammatory closed comedo, an open comedo, or an
inflammatory pustule, papule, or nodule." (1)
The bottom line is that the major organism that plays a role in acne
is a bacteria, Propionibacterium acnes.
Another viewpoint can be found from the Merck Medicus:
"The pathogenesis of acne includes several factors: (1) abnormal
keratinization of the sebaceous follicles of the face, chest, and back
that leads to filling of the follicle with keratin, sebum, and
bacteria; (2) increased bacterial colonization by the anaerobe
Propionibacterium acnes, a ubiquitous organism that thrives on sebum;
(3) excessive immune response to the bacterial colonization, possibly
genetically determined, producing inflammation; and (4) hormonal
influences, especially those of androgens that enhance sebum
production at the time of puberty. Although there appears to be a
genetic predisposition to severe acne, other factors modify disease
expression, and the severity of disease in a specific individual
cannot be accurately predicted based on the family history of acne."
Here is some information as to why the oral antibiotics you mentioned
(tetracycline and doxycycline) is used to treat acne. From UptoDate:
"Oral antibiotics improve inflammatory acne by inhibiting the growth
of P. acnes within the pilosebaceous unit. The tetracyclines also have
direct antiinflammatory properties; they inhibit the neutrophil
chemotaxis and granuloma formation that are instrumental in the
pathogenesis of severe acne. Systemic antibiotics produce more rapid
clinical improvement than topical preparations, but may induce vaginal
candidiasis, decrease the efficacy of concomitantly administered oral
contraceptive pills, and cause gastrointestinal distress. Oral
antibiotics are prescribed for daily use over four to six months, with
subsequent tapering and discontinuation as acne improves. Antibiotics
may be continued at the lowest effective dose indefinitely in those
with persistent acne, although this practice can lead to antibiotic
Antibiotics used in the treatment of acne include tetracycline,
doxycycline, minocycline, erythromycin, trimethoprim-sulfamethoxazole
and clindamycin. Tetracycline is the preferred oral antibiotic due to
its low cost and high efficacy. It is initiated at a dose of 500 mg
twice daily, although 250 mg twice daily may also be effective." (1)
I can give a detailed approach to all of the therapeutic options of
treating acne in a seperate question if you wish.
Please use any answer clarification before rating this answer. I will
be happy to explain or expand on any issue you may have.
Internet search strategy:
No internet search engine was used in this research. All sources were
from objective physician-written and peer reviewed sources.
1) Wirth, F. Approach to acne vulgaris. UptoDate, 2002.
Merck Medicus - Acne
Medline PLUS - Acne