Closed-chamber inhalation pharmacokinetic studies with hexamethyldisiloxane in the rat.

Gas uptake methods together with physiologically based pharmacokinetic (PBPK) modeling have been used to assess metabolic parameters and oral absorption rates for a wide variety of volatile organic compounds. We applied these techniques to study the in vivo metabolism of hexamethyldisiloxane (HMDS), a volatile siloxane with low blood/air (partition coefficient PB approximately 1.00) and high fat/blood partitioning (partition coefficient PF approximately 300).

Physiological modeling of inhalation kinetics of octamethylcyclotetrasiloxane in humans during rest and exercise.

In a recent pharmacokinetic study, six human volunteers were exposed by inhalation to 10 ppm (14)C-D(4) for 1 h during alternating periods of rest and exercise. Octamethylcyclotetrasiloxane (D(4)) concentrations were determined in exhaled breath and blood. Total metabolite concentrations were estimated in blood, while the amounts of individual metabolites were measured in urine.

Metabolites of hexamethyldisiloxane and decamethylcyclopentasiloxane in Fischer 344 rat urine--a comparison of a linear and a cyclic siloxane.

Hexamethyldisiloxane (MM or HMDS) and decamethylcylclopentasiloxane (D(5)) are examples of a linear and a cyclic siloxane, respectively. These volatile low molecular weight siloxanes are of significant commercial importance. To aid in the pharmacokinetic investigations, major metabolites of MM and D(5) were identified in urine collected from Fischer (F-344) rats administered [(14)C]MM and [(14)C]D(5) orally and via intravenous injection.