Percutaneous absorption of organophosphorus insecticides in pigs--the influence of different vehicles.

In 40 experiments on 20 pigs three different organophosphorus insecticides (OPs), parathion (n = 6), phoxim (n = 7) and phosmet (n = 7), were administered both intravenously (i.v.) and dermally (d.) as 'pour-ons' in a crossover design in order to determine the dermal bioavailability of the OPs. As percutaneous absorption of drugs may be affected by the vehicle used, three chemically different vehicles--DMSO, 1-octanol and macrogol 400-were used for the dermal administration of each of the OPs. The pharmacokinetic parameters measured showed that 15-30% of dermally applied parathion is absorbed when administered in DMSO or octanol, but only 4-5% when administered in macrogol. Absorption was fastest with DMSO and slowest with macrogol. For the two ectoparasiticides, phoxim and phosmet, only between 0.5 and 3% of the dermal dose was absorbed with little difference in the absorption rate between the three vehicles. On the basis of the very limited dermal bioavailability for these two OPs it seems doubtful whether sufficient concentrations can reach the ectoparasites through the systemic route.