Pharmacokinetics and bioavailability of diisopropanolamine (DIPA) in rats following intravenous or dermal application

This study was conducted to determine the relative dermal bioavailability (absorption), distribution, metabolism, and excretion (ADME) of diisopropanolamine (DIPA), an alcohol amine used in a number of industrial and personal care products. Groups of 4 female Fischer 344 rats received either a single bolus i.v. dose of 19.0mg/kg (14)C-DIPA in water or a dermal application of 19.5mg/kg (14)C-DIPA in acetone to an area of 1cm(2) on the back and covered with a bandage. Time-course blood and excreta were collected and radioactivity determined. Urine was analyzed for DIPA and monoisopropanolamine (MIPA). Following i.v. administration, DIPA was rapidly cleared from the plasma and excreted into urine in a biexponential manner (t(1/2alpha), 0.4h; t(1/2beta), 2.9h). The levels of radioactivity in plasma dropped below the limit of detection 12h post-dosing. A total of 97+/-4% of the dose was actively excreted in urine by kidney, most ( approximately 71%) within 6h of dosing, virtually all as parent compound; renal clearance exceeded the glomerular filtration rate. Following dermal application, approximately 20% of the dose was absorbed in 48 h with the steady-state penetration rate of approximately 0.2%/h. Most (14.4%) of the applied radioactivity was excreted in urine at a relatively constant rate due to the presence of large amount of the (14)C-DIPA at the application site. Fecal elimination was <0.2% of the dose. The absorbed DIPA did not accumulate in tissues; only approximately 0.1% of the administered dose was found in liver and kidney. The absolute systemic dermal bioavailability (dose corrected AUC(dermal)/AUC(i.v.)) of (14)C-DIPA was 12%. The ADME of DIPA contrasts that of its diethanol analogue, diethanolamine, which displays a broad spectrum of toxicity in rats and mice. Toxicologically significant concentrations of DIPA are unlikely to be achieved in the systemic circulation and/or tissues as a result of repeated dermal application of products containing DIPA due to slow absorption from the skin, rapid unchanged elimination in urine, and majority of the products contain <or= 1% DIPA.

Effects of azimilide and d,l-sotalol on the heart rate and blood pressure response to isoproterenol in anesthetized rats

The novel class III antiarrhythmic agent, azimilide, provides antifibrillatory protection in a rat model of ischemia-reperfusion arrhythmias. In other species azimilide's antifibrillatory mechanism is thought to be mediated predominantly through blockade of both the rapid and slow components of the delayed rectifier potassium current in ventricular myocytes. However, the delayed rectifier potassium current does not appear to control cardiac repolarization in the rat. One possible mechanism for antiarrhythmic efficacy in rats is the compound's beta-adrenergic blocking effect, previously seen in isolated guinea pig hearts. The purpose of this study was to evaluate the beta-adrenergic antagonistic effect of azimilide in the rat. Beta-adrenergic blockade was evaluated in the intact anesthetized rat by studying the effects of intravenous azimilide (at or above the antifibrillatory dose) and d,l-sotalol (a known beta-adrenergic antagonist) on heart rate and blood pressure responses to isoproterenol (0.14 Mg/kg i.v.). d,l-Sotalol (6.0 mg/kg) reduced (p < 0.05) the tachycardic response to isoproterenol from 133 +/- 11 to 80 +/- 10 beats/min, and 3.0 mg/kg of d,l-sotalol reduced the hypotensive response from -74 +/- 4 to -43 +/- 5 mmHg. Azimilide (5.0, 10.0, and 20.0 mg/kg) did not have a statistically significant effect on either the heart rate or blood pressure changes caused by isoproterenol. These data demonstrate that azimilide does not have a beta-adrenergic antagonist effect in the rat at antifibrillatory doses. Therefore, the antiarrhythmic effect of azimilide in the rat is mediated through a mechanism other than beta-blockade.