The effect of skin thickness and time in the absorption of dexamethasone in human tendons using iontophoresis.
METHODS
Experimental laboratory study.


OBJECTIVE
To measure the transmission of dexamethasone sodium phosphate (DEX-P) using iontophoresis as a function of skinfold tissue thickness and time elapsed between treatment and tissue extraction.


BACKGROUND
Iontophoresis is a modality used in physical therapy with the intent to drive medications through the skin to underlying tissues using a direct electrical current. DEX-P is the most commonly used medication with iontophoresis and is used to treat a variety of connective tissue conditions.


METHODS
Sixteen adults undergoing anterior cruciate ligament reconstructive surgery using the semitendinosis/gracilis autograft received a 40-mA-min dose of iontophoresis with 0.4% DEX-P superficial to a slip of the distal semitendinosis tendon prior to surgery. The tendon slip was extracted within 4 hours. Time between treatment and tissue extraction and skinfold thickness were measured. Analysis was performed on the slip of the semitendinosis using high-performance liquid chromatography mass spectrum.


RESULTS
Of the 16 subjects (10 female, 6 male; mean age, 33 years), 7 had measurable amounts of DEX-P in the tendon slip (4 female, 3 male; mean age, 34 years). The average concentration in the 16 subjects was 2.9 ng/g of tendon tissue. There was no correlation between DEX-P absorbed and skinfold thickness (r = -0.08, P = .79) or time elapsed (r = 0.25, P = .38). In a subset of the 7 individuals that showed measurable levels of DEX-P absorbed, the average concentration of DEX-P was 6.6 ng/g of tendon tissue, and there was a relationship between DEX-P concentrations and time elapsed that did not reach statistical significance (r = 0.71, P = .11).


CONCLUSIONS
Iontophoresis appears to facilitate the transmission of dexamethasone to connective tissues in humans with skinfold thickness up to at least 30 mm. The absorption of the dexamethasone seemed to continue to occur for up to 4 hours after delivery. It is not clear why DEX-P was measured in only 7 of the 16 subjects.


METHODS
Therapy, level 5.
Gurney
Burke
B
University of New Mexico, Physical Therapy Program, Albuquerque, NM 87131-0001, USA. BGurney@salud.unm.edu
Wascher
Daniel
D
Eaton
Leslie
L
Benesh
Errin
E
Lucak
Joseph
J
D000328:Adult; D016118:Anterior Cruciate Ligament / Q000601:surgery; D000070598:Anterior Cruciate Ligament Injuries; D002851:Chromatography, High Pressure Liquid; D003907:Dexamethasone / Q000008:administration & dosage / Q000493:pharmacokinetics*; D005260:Female; D005938:Glucocorticoids / Q000008:administration & dosage / Q000493:pharmacokinetics; D006801:Humans; D007478:Iontophoresis / Q000379:methods*; D007718:Knee Injuries / Q000378:metabolism / Q000628:therapy*; D008297:Male; D011300:Preoperative Care / Q000379:methods; D012867:Skin / Q000033:anatomy & histology*; D012869:Skin Absorption / Q000502:physiology*; D013710:Tendons / Q000378:metabolism* / Q000637:transplantation; D013997:Time Factors
D005938:Glucocorticoids; D003907:Dexamethasone