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.

Diethylphosphorus metabolites in serum and urine of persons poisoned by phosalone

The presence and elimination rate of phosalone and its diethylphosphorus metabolites in blood serum and urine were studied in persons who had ingested a concentrated phosalone solution. Phosalone was detected only in serum samples. As it was rapidly hydrolysed and eliminated from the body, its diethylphosphorus metabolites were a more sensitive indicator of exposure. The concentration decrease of phosalone in serum and of total diethylphosphorus metabolites in serum and urine followed the kinetics of a biphasic reaction. The faster elimination half-times in serum, calculated for two persons, were 2.3 and 3.4 h for phosalone and 3.4 and 38.6 h for total diethylphosphorus metabolites. In the faster phase the average elimination half-time of total urinary metabolites in five persons was 25 +/- 17 h. The kinetic data for total urinary metabolites in a person occupationally exposed to phosalone indicated an early and very fast elimination phase (elimination half-time 1.3 h), which was overlooked in poisoned persons. The proportions of single metabolites in total urinary metabolites in poisoned persons depended on whether the total amount of diethylphosphorus metabolites was above 1000 or below 1000 nmol/mg creatinine. Diethylphosphorodithioate predominated at high and diethylphosphate at low concentrations of total metabolites. The correlation between the maximum concentrations of total metabolites, measured in urine of poisoned persons on the day of admission to hospital or a day later, and the initial depression of serum cholinesterase (EC 3.1.1.8) and erythrocyte acetylcholinesterase (EC 3.1.1.7) activities was poor (r = 0.6).

[Exposure to DMTP by sprayers and the urinary excretion of metabolites]

Exposure in vinyl hothouses to DMTP (0,0-dimethyl-s-(2-methoxy-1,3,4-thiadiazol-5(4H)-onyl-(4)-m ethyl)- dithiophosphate) was studied in 5 spray-operators and one assistant worker. To determine the level of exposure to DMTP, concentrations in the atmosphere, concentration in atmosphere near the operators breathing zone, skin levels from penetration through the operator's clothing, and urinary excretion of metabolites of DMTP (2,3-dihydro-5-methoxy-3-methyl-sulphonyl methyl-1,3,4-thiadiazol-2-one and 2,3-dihydro-5-methoxy-3-methyl-sulphinyl methyl-1,3,4-thiadiazol-2-one) were measured. The results were as follows; 1. DMTP concentrations in the atmosphere were 10.0-18.0 micrograms/m3, and concentrations in the atmosphere near the operators breathing zone were 5.4-33.6 micrograms/m3 during spraying. 2. Metabolites of DMTP were detected in all sprayers. Levels were 1.5 to 31.6 micrograms/day for the sulphonyl-metabolite. But it was not detected in the assistant sprayer. 3. Urinary concentrations of the DMTP metabolite were maximum 15-20 h after spraying. 4. Amount of DMTP adherent on the skin was estimated to be 0.4 to 71.3 micrograms for spray-operators. Variations resulted from differences in condition of protective clothing. 5. DMTP appeared to be absorbed not only through the respiratory system, but also through the skin.

In vivo and in vitro percutaneous absorption and skin evaporation of isofenphos in man

Studies were done to determine the percutaneous absorption of isofenphos in human volunteers from whom informed consent had been obtained. In vivo absorption in man was 3.6 +/- 3.6% of applied dose for 24-hr exposure and 3.6 +/- 0.5% for 72-hr exposure. Skin wash recovery data show that isofenphos evaporates from in vivo skin during the absorption process; the surface dose is minimal (< 1%) by 24 hr. Skin stripping showed no residual isofenphos in stratum corneum. This explains the similar absorption for 24 and 72-hr dose prewash exposures. Skin surface recovery in vivo with soap and water was 61.4 +/- 10.4 for the first dosing time (15 min). Time-recovery response declined with time to 0.5 +/- 0.2% at 24 hr. In vitro absorption utilizing flow-through diffusion methodology with human cadaver skin and human plasma receptor fluid gave 2.5 +/- 2.0% dose absorbed, an amount similar to in vivo studies. An additional 6.5 +/- 24% was recovered in the skin samples (total of 9%). Skin surface wash at 24 hr recovered 79.7 +/- 2.2% and skin content was 6.5 +/- 2.4% (total dose accountability of 88.7 +/- 4.6%). Thus, isofenphos was available for absorption during the whole dosing period. Neither in vitro absorption nor in vitro evaporation studies predicted the potential skin evaporation of isofenphos. Published dermal studies in the rat had predicted isofenphos absorption at 47% of applied dose (12-fold greater than actual in man). Subsequent toxicokinetic modeling predicted possible concern with the use of isofenphos.(ABSTRACT TRUNCATED AT 250 WORDS)

Organ distribution and stability of phosphorothioated oligodeoxyribonucleotides in mice

Results of recent studies in our laboratory have suggested a potential role for antisense oligodeoxyribonucleotides (oligo(dN)s) as therapeutic agents in the treatment of human hepatitis B virus infection. As a first step towards assessing the potential utility of oligo(dN) in therapy, we have examined the organ distribution, stability and toxicity of a phosphorothioated oligo(dN) (S-oligo) of 20 nucleotides in length which was administered to mice via different routes. Among the various organs analysed, the liver retained the highest amount of S-oligo (1.3-2 per cent of the total injection) at the peak time (10-30 min) regardless of the route of injection. However, the S-oligo appeared to be degraded in the liver to about 40 per cent of its original length within 30 min of injection, presumably by the action of 3' exonucleases. Injection of doses of up to 5 mg kg-1 of S-oligo had no apparent toxic effects on the mice.

Bioavailability and toxicological potential of wheat-bound pirimiphos-methyl residues in rats

1. Wheat-bound residues of 14C-pirimiphos-methyl were fed to albino rats at 1.17 and 7.5 ppm in the diet for 3.5 months. 2. In toxicological tests, 1.17 ppm of bound residues caused an increase of rat alkaline phosphatase activity and blood urea nitrogen, and reduction in lymphocyte and monocyte counts. A dietary level of 7.5 ppm showed a significant decrease in serum cholinesterase activity and in lymphocytes and monocytes, and an increase in alkaline phosphatase activity and of urea nitrogen. 3. Bioavailability data indicate that wheat-bound pirimiphos-methyl residues are absorbed by rat.

The effect of pyridostigmine pretreatment on oxime efficacy against intoxication by soman or VX in rats

This study was done to assess the effects of pyridostigmine (PYR) on a) the accumulation of labelled VX and soman within the brain, b) the therapeutic efficacy of atropine and oxime (2-PAM or HI-6) against intoxication by VX and soman and c) oxime-induced reactivation of inhibited acetylcholinesterase (AChE). In all experiments, rats were given PYR (131 micrograms/kg, im; I70 dose for whole blood AChE) or vehicle 30 min prior to nerve agent. In estimating 3H-agent the accumulation in the brain or estimating blood AChE activity, sufficient soman (47 micrograms/kg, iv) or VX (21.3 micrograms/kg, iv) was given to inhibit 50% of brain AChE activity. In assessing therapeutic efficacy and oxime-induced reactivation of blood AChE, rats were pretreated with PYR, challenged with agent and treated with atropine (16 mg/kg, im) and HI-6 or 2-PAM (100 umoles/kg, im) 30 sec post agent. Whole blood was collected by tail bleeding to monitor peripheral AChE activity at various time points before and after PYR and challenge. Pyridostigmine failed to alter covalent binding of labelled VX or soman in the brain. The 24-hr survival data showed that PYR reduced the therapeutic benefit of atropine and oxime against VX intoxication (but not soman). Protective ratios in VX-challenged rats given vehicle or PYR and treated with atropine + 2-PAM decreased slightly from 2.5 to 2.1 (p > .05), whereas with atropine + HI-6 they decreased significantly from 3.8 to 2.4. Also, AChE reactivation by HI-6 in VX-challenged rats was greater (p < .05) in vehicle- than in PYR-pretreated rats. HI-6 significantly reactivated AChE activity in both pretreatment groups (PYR or vehicle) given soman. The data suggest that PYR decreases the overall recovery of inhibited AChE in VX-challenged rats given HI-6; under the conditions used, this adverse effect decreases atropine+oxime efficacy against VX-induced lethality.

Pharmacokinetics of propetamphos following intravenous administration in the F344 rat

Propetamphos [(E)-1-methylethyl 3-[[(ethylamino)methoxyphosphinothioyl]oxy]-2-butenoate], the active ingredient in Safrotin, is an organophosphate developed by Sandoz, Ltd. (Switzerland) as an insecticide (1). Although metabolism of propetamphos has been previously investigated (2,3), there is no pharmacokinetic data available in the literature. The current studies were undertaken to investigate the pharmacokinetics of propetamphos following intravenous administration in male and female Fischer 344 (F344) rats. Rats were dosed via an indwelling jugular cannula at a dose of 12 mg/kg (one-tenth the oral LD-50). Blood samples were withdrawn via the cannula at predetermined timepoints to quantitate plasma concentrations of propetamphos over time. Propetamphos is highly bound to plasma proteins (free fraction = 0.06). Free propetamphos concentration in plasma vs. time data were analyzed by noncompartmental methods. The terminal elimination rate constant, lambda, was significantly different for males versus females (0.015 min-1 for males and 0.037 min-1 for females, p = 0.001). Plasma was cleared of unbound propetamphos at rates of 0.559 +/- 0.069 and 0.828 +/- 0.181 L/min/kg for males and females (mean +/- standard error). Mean residence times (MRTs) for propetamphos in the body for males and females were 28.3 +/- 5.7 and 14.4 +/- 3.5 min, and the volume of distribution at steady state (Vss) was 14.7 +/- 2.6 and 12.3 +/- 4.5 L/kg. The differences in these parameters, clearance (CI), MRT, and Vss, were not statistically significant at the p < 0.05 level for males versus females, but MRT was nearly significantly different (p = 0.08).(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue distribution and urinary excretion of 14C-ethion in goats

Tissue concentration and elimination and urinary excretion were followed after intravenous injection of 14C-ethion in 12 goats. Tissue levels were determined in two goats after 8 hr and on each of days 1, 3, 7, 14 and 28 after exposure. During the four-week period plasma and all tissues examined (liver, kidney, fat, muscle, lung, heart and brain) had detectable 14C-residues, the highest values being found in liver, kidney and fat. Elimination of 14C-residues was faster in the first 3 days than in the later part of the experiment, where the elimination half-life for most tissues was approximately 2 weeks. During the first two weeks after exposure, 77% of the administered dose was eliminated in urine (55%) and faeces (22%). TLC of urine collected over the first 15 hr after exposure showed at least 8 bands of metabolites, five of which accounted for about two thirds of the dose excreted in urine.

Acute poisoning with methidathion: a case

An acute poisoning in a 50-year-old man who ingested approximately 6.2 g of the phosphorus ester methidathion is described. The patient was treated with three haemoperfusions 23, 44 and 115 h after ingestion, with continuous gastric lavage, atropine and pralidoxime administration and with prolonged mechanical ventilation. Haemoperfusion was an ineffective epuration technique since it removed only 0.22% of the ingested methidathion. The clinical course wavered because of a probable redistribution of phosphorus ester from fat to blood. A plasma level higher than 100 micrograms l-1 was associated with the most serious phases. Methidathion was present in the plasma until the sixth day, in the urine until the seventh and in the gastric juice until the eighth. Its absence in the fat biopsy made on the tenth day was an aid to therapy. The phosphorus ester did not inhibit lymphocyte neuropathy target esterase (NTE), neither did it induce development of delayed polyneuropathy.

Evaluation of the carcinogenic potential of pesticides. 2. Methidathion

The carcinogen potential of methidathion, a dimethoxyorganic phosphorus pesticide and cholinesterase inhibitor, was evaluated by the Health Effects Division of the Office of Pesticide Programs using a consensus peer review process and the EPA's guidelines for risk assessment. Methidathion was categorized as a Group C (possible human) carcinogen based upon evidence of an increased incidence of benign and malignant hepatocellular tumors, alone and in combination, in a single study involving male Chr-CD-1 mice. The compound was not carcinogenic in female Chr-CD-1 mice in the same study or in Sprague-Dawley rats of either sex in a second study. Methidathion was not genotoxic in a variety of in vitro or in vivo tests designed to detect DNA damage, chromosome aberrations, gene mutations, and sister chromatid exchange. Although methidathion was identified as being structurally similar to two other organophosphate insecticides, prothidathion and lythidathion, no toxicological data were available on either of these agents for comparative purposes. The biological information on methidathion was reviewed by the agency's FIFRA Scientific Advisory Panel who agreed with the category C designation for methidathion. The data were not found to be sufficient to quantify human risk to methidathion.

Fate of ethion in goats after intravenous, oral and dermal administration

Toxicokinetic parameters and cumulative excretion were studied in goats after intravenous, oral and dermal administration of unlabelled and 14C-ethion. Plasma concentration-time data was subjected to non-compartmental analysis. IV injection studies showed an effective half-life (t1/2) of 2 hr, a total body clearance (ClT) of 3.21.kg-1.hr-1 and a volume of distribution (Vd(ss) of 9.4 1.kg-1. Plasma levels of 14C-ethion (ethion + metabolites) were much higher and more persistent than those of unchanged ethion. Cumulative excretion of 14C-ethion was 78% of the dose with 66% in urine, 8% in faeces and 4% in milk. Oral administration resulted in low plasma levels of unchanged ethion, an absorption half-life (t1/2 abs) of 10 hr and a bioavailability of less than 5%. Cumulative excretion was 80% of the dose with 64% in urine, 14% in faeces and 1.7% in milk. Dermal application showed a t1/2 abs of 85 hr and a bioavailability of 20%. Only 0.05% of the dose was excreted unchanged in milk. It is concluded that (1) orally administered ethion is extensively metabolized in the GIT, (2) dermal application results in prolonged and limited absorption and (3) absorbed ethion is rapidly eliminated through metabolism.

Disposition of the radioprotector ethiofos in the rhesus monkey. Influence of route of administration

Plasma concentrations of ethiofos [S-2-(3-aminopropylamino)ethyl phosphorothioic acid, WR-2721] were compared following iv, ip, intraduodenal, and portal administration to the rhesus monkey. Plasma samples were analyzed for ethiofos, free WR-1065, [2-(3-aminopropylamino)ethanethiol], and total material convertible to WR-1065 (total WR-1065). In separate experiments, total radioactivity in plasma was compared following iv, ip, and intraduodenal administration of [14C]ethiofos; excretion of the radiolabel was measured in urine and in feces. Intraduodenal administration of unlabeled ethiofos rarely gave measurable levels of unchanged drug in plasma. In contrast, intraduodenal administration of [14C]ethiofos produced an average AUC for total radioactivity that was 62% of that for a 10-min iv infusion of [14C]ethiofos. Urinary excretion of radioactivity following iv and intraduodenal administration of [14C]ethiofos was 78.9 +/- 14.0% and 43.8 +/- 12.4%, respectively, whereas 1.9 +/- 0.5% and 9.7 +/- 6.3% was excreted in feces. After an ip dose of either labeled or unlabeled ethiofos, absorption of the dose was prolonged, but AUC values for total radioactivity or ethiofos and total WR-1065 were similar to those observed after the corresponding 10-min iv experiments. For either iv or portal routes, increases in ethiofos AUC values were observed for the same total dose when the infusion rate was increased from 1.25 to 15 mg/kg/min.(ABSTRACT TRUNCATED AT 250 WORDS)

Toxicological studies on the organophosphorous insecticide methyl-ISP

Methyl-ISP, a newly developed organophosphorous insecticide, is used in China to treat and protect plants from pest infestation. Our studies demonstrated that methyl-ISP is metabolized rapidly in rat and mouse. Its toxicity was low, no obvious accumulative toxicity, chronic toxicity, teratogenicity, mutagenicity, reproductive toxicity or delayed neurotoxicity could be observed. It is therefore concluded that methyl-ISP is relatively safe to animals and human subjects. methyl-ISP is now employed to replace the other commonly used insecticide hexachlorobenzene (666) in agriculture. A preliminary study was performed to elucidate the mechanism of intoxication at subcellular levels.

Competition for polyamine uptake into rat lung slices by WR2721 and analogues

The objective of these studies was to determine whether a series of structurally related radioprotective agents could act as substrates for the recently identified polyamine system in the lung. We have shown that WR2721 (S-2(3-aminopropylamino)ethyl phosphorothioate), S-2(4-aminobutylamino)ethyl phosphorothioate (S-ABEP or WR2822) and S-2(7-aminoheptylamino)ethyl phosphorothioate (S-AHEP) competitively inhibit the uptake of putrescine into rat lung slices. The ability of the radioprotectors to act as substrates for the polyamine uptake system was expressed as the Ki for each compound. The Ki values for WR2721, S-ABEP and S-AHEP in the absence of dithiothreitol were 48, 57 and 7 mumol dm-3 compared to 155, 88 and 15 mumol dm-3 in the presence of dithiothreitol, indicating that the disulphide form may have a higher affinity for the transport system. By analogy with other substrates for the polyamine uptake system we have concluded that it should be possible to target radioprotectors to the alveolar epithelial type I and II cells and the Clara cells in the lung, as they prossess this uptake system, and thus protect these cells from oxidative stress.

The disposition of ethiofos (WR-2721) in the isolated perfused rat liver

We have investigated the disposition of ethiofos (20 mg, 4 microCi [14C]ethiofos) in the isolated perfused rat liver preparation to determine the hepatic contribution to the poor oral bioavailability of the drug. Ethiofos clearance (10.6 +/- 3.3 ml h-1) was only a small fraction (1.2 +/- 0.03%) of the perfusate flow rate. The elimination half-life was calculated at 7.1 +/- 1.9 h. The area under curve, AUC0-4 h, for ethiofos (2858 +/- 314 nM h ml-1) was not significantly different from that of 14C (3038 +/- 692 nM h ml-1) or total material convertible to WR-1065 (total WR-1065, 3324 +/- 612 nM h ml-1), indicating a low level of metabolism. The AUC0-4 h for free WR-1065 (37.5 +/- 23.3 nM h ml-1) was less than 2% of ethiofos. Biliary elimination of ethiofos, WR-1065, and 14C was below 1%. At 4 h postdose, 7.9 +/- 1.9% of the dose of radioactivity remained in the liver. Less than 1.5% could be identified as ethiofos (0.12 +/- 0.09%) or total WR-1065 (1.09 +/- 0.05%). Ethiofos, 14C, and total WR-1065 were approximately evenly distributed between the 10,000-g pellet and supernatant. However, significantly more ethiofos, WR-1065, and 14C were recovered from the 105,000-g supernatant compared with the pellet. In summary, both the metabolism and biliary elimination of ethiofos and its derivatives were sparing. Hence it is likely that in the rat, the contribution of the liver to the presystemic biotransformation and poor bioavailability of ethiofos is relatively minor.

[Circadian rhythm of blood acetylcholinesterase after administration of organophosphate compounds during hypokinesia]

Circadian and ultradian rhythms of blood acetylcholinesterase (ACE) and rectal temperature were investigated during hypokinesia and administration of a toxic organic phosphate compound in various doses. Hypokinesia was found to produce a strong desynchronizing effect on ACE and thermal regulation. It is maintained that the use of chemicals with a well documented mechanism of action may yield reliable information about biorhythm restructuring in response to exogenous effects. It is emphasized that biorhythm changes should be taken into consideration when arranging work schedules in hypokinetic conditions.

Determination of phosacetim in rabbit tissues and blood by TLC

A sensitive and rapid method for analysis of phosacetim in rabbit tissues and blood has been developed. It requires extraction from biological materials followed by TLC. The assay allows good reproducibility, high recoveries (about 80%), excellent linearity in the range of 0.1 to 20 micrograms with r equal to 0.999, and a low detection limit, 0.05 microgram. The results from TLC were in conformity with those from HPLC. In addition, the assay was applied to study the distribution of phosacetim in rabbit tissues.

WR-2721 entry into the brain across a modified blood-brain barrier

Radioprotection of the CNS by WR-2721 has not been possible because of its inability to cross the blood-brain barrier (BBB) and so gain access to the neural tissue. Modification of the BBB using hypertonic arabinose (1.8 m), injected via the internal carotid artery (ica), permitted entry of ip-injected [14C]WR-2721 into the ipsilateral cerebral hemisphere. The BBB-modified hemisphere had a 5.34-fold increased uptake compared to nonmodified controls. Delivery as a bolus via the ica further enhanced uptake after BBB opening; WR-2721 was 3.73 times greater than by ip injection. A 20-fold increase of WR-2721 brain uptake has been calculated for ica administration with the BBB opened as compared to the ip route without BBB modification. Toxicity of ip-administered WR-2721 with the BBB open was only 1.4 times greater than non-modified controls and 1.96 times more toxic when delivered via the ica. These data demonstrate significant uptake of WR-2721 into the CNS, a previously unprotected organ, and provide a model for future radioprotective studies.