Biomedical Engineering Reference
In-Depth Information
antibiotic prophylaxis
The use of antibiotic prophylaxis for cutaneous laser resurfac-
ing remains a controversial issue. A number of studies have
found antibiotics to be effective in the prevention of infection
after cutaneous laser resurfacing.
Bernstein et al. observed no infections in a series of 50 patients
who underwent full-face resurfacing and were treated with
250 mg of dicloxacillin q.i.d., starting the day before resurfacing
and continuing for 1 week (146). Nanni et al. reported no bacte-
rial infections in 500 consecutive cases of full-face cutaneous
laser resurfacing, using 1 g intravenous (IV) cefazolin intraop-
eratively followed by 500 mg of azithromycin on postoperative
day 1 and 250 mg for at least 4 days (147). Waldorf et al. found
three instances of clinical infection in a series of 47 patients
undergoing facial laser resurfacing that were prescribed 250 mg
of dicloxacillin q.d. or 333 mg of erythromycin b.i.d. for 1 week
throughout the reepithelialization period. The patients who
developed infection were not taking antibiotics nor receiving
aggressive wound care (148). Ross et al. reported that two
of four patients without antibiotic prophylaxis undergoing
full-face laser resurfacing developed
Staphylococcus aureus
infection, whereas none of four patients with gram-positive
antibiotic prophylaxis developed infection. Notably, they also
reported a gram-negative infection in a patient who had
received gram-positive antibiotic prophylaxis (46).
Gaspar et al. performed a randomized prospective study of
31 patients undergoing full-face CO
2
laser resurfacing and
found four culture-positive clinical infections in the group of
patients not receiving antibiotic prophylaxis (
n
= 14) and no
cases of infection in the group of patients (
n
= 17) treated with
cephalexin 500 mg PO b.i.d. started the day before surgery and
continued for 5-10 days. The most common pathogen found
in this study was
S. aureus
. An occlusive dressing was used
postoperatively in their patients (149). Sriprachya-Anunt et al.
retrospectively found a 4.3% rate of culture-positive infection
in a series of 395 patients undergoing facial skin laser resurfac-
ing. However, the rate of infection increased sevenfold (from
1.35% to 9.82%) with a change from oral antibiotic prophy-
laxis (azithromycin 250 mg q.d. or a similar antibiotic for
7 days) to intranasal mupirocin and gentamicin otic solution,
and the use of occlusive dressings rather than an open wound
care technique postoperatively. The most common organism
found was
Pseudomonas aeruginosa
, followed by
S
.
aureus
and
S
.
epidermidis
. Several combinations of gram-positive and
gram-negative organisms were found in their study. Prophy-
lactic ciprofl oxacin (500-750 mg) b.i.d. for 5-7 days, starting
the morning of surgery, was recommended by these authors,
especially when an occlusive dressing technique was used (43).
Manuskiatti et al. reported on the infection rates of a large
series of 356 patients who underwent facial skin resurfacing
with the CO
2
laser. They observed an 8.2% bacterial infection
rate when antibiotic prophylaxis was not given and a closed
wound care technique was utilized. The infection rate
decreased to 4.3% in the group of patients who received anti-
biotic prophylaxis with ciprofl oxacin. Of note, infections in
the group of patients who received prophylaxis occurred
almost exclusively after discontinuation of ciprofl oxacin (45).
The “pseudo-tissue culture” environment maintained by
occlusive dressings is an ideal growth medium not only for
host cells that will carry out reepithelialization but also for
Hydroquinone inhibits tyrosinase, a key enzyme in the mela-
nin synthesis pathway, and is directly toxic to melanocytes. Tret-
inoin promotes melanosome transfer and keratinocyte turnover
and decreases epidermal melanin content. Azelaic acid, kojic
acid, and glucosamine also inhibit tyrosinase and pigment syn-
thesis. Reported benefi ts of alfa-hydroxy acids (i.e., glycolic
acid) include increased epidermal thickness, decreased stratum
corneum thickness, and reversal of basal cell layer atypia.
Despite their widespread use, currently there is a great
debate over whether pretreatment with these skin bleaching
agents helps prevent hyperpigmentation after cutaneous laser
resurfacing (Table 6.5). Data from several studies suggest that
these agents are ineffective in the prophylaxis of hyperpigmen-
tation after cutaneous laser resurfacing. West et al. randomized
100 consecutive CO
2
laser skin resurfacing patients (skin pho-
totypes I-III) to receive pretreatment with 10% glycolic acid
cream b.i.d. or a combination of tretinoin 0.025% cream b.i.d.
and hydroquinone 4% q.h.s. or no pretreatment at all. The
overall incidence of postinfl ammatory hyperpigmentation
was 11.1%, 32.3%, and 50% in patients with skin phototypes I,
II, and III, respectively. Most importantly, they observed no
signifi cant difference in the incidence of postinfl ammatory
hyperpigmentation between those patients who received pre-
treatment and those who did not (54).
Postinfl ammatory hyperpigmentation is largely caused by
the migration of melanocytes from deep within the adnexal
epithelium or from cutaneous wound edges after resurfacing.
Because of their limited penetration depths, topical bleaching
agents may not exert any effect on these deeply situated mela-
nocytes. Instead, they most likely affect superfi cially located
melanocytes that are generally removed by the initial passes of
the resurfacing laser. Topical bleaching agents such as tretinoin
and hydroquinone may be most effective, not as prophylactic
agents during the preoperative period, but rather as therapeu-
tic agents during the postoperative period once melanocyte
and keratinocyte migration has taken place (3-4 weeks post-
operatively) and hyperpigmentation has manifested itself clin-
ically (54,55).
To reduce the risk of hyperpigmentation, patients are
encouraged to avoid having a suntan at the time of the laser
resurfacing procedure. Daily application of a full-spectrum
sunscreen containing broad-spectrum physical blockers such
as micronized zinc is an important, noncontroversial, aspect
of the pre- and postoperative care of the cutaneous resurfacing
patient.
Table 6.5
Agents to Treat Hyperpigmentation
Agent
Mechanism of Action
Hydroquinone
Cytotoxic to melanocytes
Azelaic acid
Inhibits tyrosinase and pigment
synthesis
Kojic acid
Inhibits tyrosinase and pigment
synthesis
Glucosamine
Inhibits tyrosinase and pigment
synthesis
Tretinoin
Promotes melanosome transfer and
keratinocyte turnover
Alfa-hydroxy acids
Promotes keratinocyte turnover
