Delayed toxicity following acute ingestion of valpromide

As valpromide is a prodrug of valproic acid (valproate), the clinical presentation of overdoses with either valpromide or valproate sodium is generally considered similar. Whereas plasma peak levels and signs of central nervous system depression occur within a few hours after the acute ingestion of regular-release forms of valproate sodium, delayed toxicity and time to peak levels following valpromide ingestion can be seen as shown by the three reported cases. They were initially considered as mild because patients presented with no or only moderate symptoms and serum valproate levels were below or at therapeutic levels on admission more than 3 hours post-ingestion in two of the three patients. Serum valproate levels were not monitored until marked deterioration more than 10 hours after ingestion. At the time of deterioration, serum valproate was at toxic level in the three reported cases. Therefore, large intake of valpromide should be closely monitored because no or moderate symptoms together with low plasma levels in the first few hours after ingestion do not exclude a subsequent severe intoxication. Despite the usual favourable outcome and the poor correlation between plasma levels and toxic symptoms, patients should not be discharged until plasma levels are documented to remain at low levels for at least 10 hours after the ingestion of valpromide and the patient asymptomatic.     

Enzyme studies with human and hen autopsy tissue suggest omethoate does not cause delayed neuropathy in man

Levels of acetylcholinesterase and neurotoxic esterase were measured in brain autopsy material. In tissue from a fatal human poisoning and from hens given 4–8 × unprotected LD₅₀ AChE was highly inhibited and neurotoxic esterase uninhibited. The findings correlate with the inhibitory power of omethoate against these enzymes in vitro. It is concluded that omethoate has negligible potential to cause delayed neuropathy and a published report of human neuropathy due to omethoate is criticised.     

Interaction of methamidophos with hen and human acetylcholinesterase and neuropathy target esterase

Methamidophos causes acute cholinergic toxicity in several species, including man, and organophosphate-induced delayed polyneuropathy which has been reported in man but not in the hen. Acetylcholinesterase (AChE) and neuropathy target esterase (NTE) are thought to be the molecular targets of acute and delayed toxicity, respectively. The rate constants of inhibition (k_a) and reactivation (k₊₃) of human and hen brain AChE and NTE by methamidophos resolved optical isomers are here reported. NTE inhibition was progressive and irreversible. Human and hen NTE k_a (M^–1·m^–1) ford-(+) methamidophos was 88 and 59, respectively, and forl-(–) methamidophos 3.2 and 3.0, respectively. AChE spontaneously reactivates after inhibition.d-(+) methamidophos 10^–3·k_a (M^–1·m^–1) for human and hen AChE was 0.24 and 0.13; 10³·k₊₃ (m^–1) was 0.83 and 0.69, respectively,l-(–) Methamidophos 10^–3·k_a (M^–1·m^–1) for human and hen AChE was 5.7 and 2.8, whereas 10³ · k₊₃ (m^–1) was 6.50 and 1.52, respectively.l-(–)-Inhibited AChE reactivated to about 60% for human and 30% for hen enzymes, respectively.d-(+)-Inhibited AChE reactivated to about 10–20% for both species. Maximal reactivation occurred within 4–6 h when a plateau was reached. The larger and faster reactivation of human AChE inhibited in vitro byl-(–) methamidophos suggests that a corresponding effect might be possible in vivo and therefore explain, in part, the relatively higher susceptibility of man to delayed polyneuropathy induced by racemic methamidophos which occurs, however, with doses always causing severe cholinergic toxicity.Part of this work was presented at the 29th Annual Meeting of the Society of Toxicology, held in Miami FL, USA, February 1990.     

Reproductive, acute and subacute toxicity studies with nefopam in laboratory animals.

Nefopam hydrochloride, a compound with non-narcotic analgesic activity, was evaluated for its acute and subacute toxicity in mice, rats, and dogs. Potential teratogenic effects in mice and rabbits and its effect on general reproduction and postnatal development in rats were also studied. The LD50 by various routes of administration showed that in all three species oral LD50 values (80–178 mg/kg) were greater than im LD50 values (30–57 mg/kg) which were higher than iv LD50 values (20–45 mg/kg). A comparative oral acute toxicity study did indicate a strain difference in rats. Repeated daily administration of nefopam hydrochloride to rats and dogs at doses up to 10 mg/kg/day parenterally and 80 mg/kg/day orally revealed no toxic effects except for mild tissue irritation at injection sites and slight weight loss in some dogs receiving the high dose. Reproduction studies did not reveal any effects on fertility, lactation, or pup development and viability.     

Interaction of phosphamidon with neuropathy target esterase and acetylcholinesterase of hen brain

Phosphamidon (PSM) is an organophosphorus insecticide widely used in agriculture. This study was undertaken to examine the interaction of PSM with acetylcholinesterase (AChE) and neuropathy target esterase (NTE) of hen brain in vitro and in vivo. PSM was a potent inhibitor of AChE, with an I₅₀ of 2.9μM and second-order rate constant (k_a) of 1.2×10⁴ M^?1 min^?1 at 37°C. PSM-inhibited AChE aged rapidly (t_1/2=1.9h). Pyridinium oximes pralidoxime, trimedoxime, obidoxime and HI-6 were effective reactivators of PSM-inhibited AChE, providing up to 75% reactivation. PSM was one of the weakest inhibitors of NTE among organophosphorus compounds, with an I₅₀ of 19 mM and k_a of 1.8 M^?1 min^?1 at 37°C. Inhibited NTE did not reactivate spontaneously and KF-induced reactivation was not obtained even at the earliest tested moments, so it was not clear whether aging of PSM-inhibited NTE occurred very quickly or the KF molecule could not affect the stability of phosphoryl-NTE bond. From the ratio of k_as for NTE and AChE (0.00015) it was predicted that delayed neuropathic effects of PSM in vivo would appear only at doses far above the acute LD₅₀. The LD₅₀ value of PSM p.o. for hens was 9 mg/kg. Hens were treated with a single oral dose of PSM, combined with standard antidotal treatment which included atropine, physostigmine, pralidoxime and anticonvulsant midazolam. Doses of 90 and 250 mg/kg caused up to 27% and 45% NTE inhibition 48h after poisoning, respectively. Clinical signs of neuropathy were not seen up to 25 days after treatment, which could be expected, since the proposed level (>70%) of NTE inhibition necessary for the occurrence of delayed neuropathy was not achieved. The results suggest that PSM, at doses tested, has no ability to cause delayed neuropathy in hens without showing signs of severe cholinergic intoxication.     

Percutaneous toxicity and delayed neurotoxicity of organophosphates in the scaleless hen

The acute toxicity of tri-ortho-cresyl phosphate (TOCP) and the development of delayed neurotoxicity were characterized in the scaleless hen, a featherless mutant, and compared to the responses observed in normally feathered birds. Brain acetylcholinesterase (AChE) activity was comparable between scaleless and normal hens, but nonspecific cholinesterase (ChE) activities of brain and plasma were significantly higher in scaleless birds. The acute ID50 of TOCP for plasma ChE activity was 690 mg/kg for scaleless birds and 240 mg/kg for normal ones following sc administration. However, there was no difference in the ID50 for plasma ChE activity between normal and scaleless hens treated sc with the active metabolite of TOCP, 2-(o-cresyl)-4H-1:3:2-benzodioxaphosphoran-2-one, or parathion. The onset of clinical signs of delayed neurotoxicity in scaleless birds was 8 to 14 days after sc or dermal treatment with TOCP and caused typical axonal fragmentation in the sciatic nerve. Plasma creatine phosphokinase activity was significantly increased following the onset of delayed neurotoxicity in both lines of birds. Dermal application of TOCP to a 50-cm2 area on the backs of scaleless hens inhibited plasma ChE activity in a dose-related manner (ID50 = 115 mg/kg), and the lowest dose of TOCP, 114 mg/kg, did not produce delayed neurotoxicity. The results show that the scaleless hen can be used to determine a no-observable effect level for delayed neurotoxicity which regulatory agencies could use to extrapolate a safe level of human dermal exposure to organophosphates that produce delayed neurotoxicity.     

Innovative designs and practices for acute systemic toxicity studies

Over a four year period our laboratory has conducted 124 acute systemic toxicity studies (64 oral, 39 dermal, and 21 inhalation), altering study and program designs with the objectives of maximizing information while minimizing animal usage. By employing dose selection strategies, probes, lethality limits instead of LD50's, staggered sequential dosing, and by conducting studies in batteries, animal usage was reduced by 48% below the average number currently quoted as necessary for an LD50 study. Simultaneously, use of a neurobehavioral screen, adjunct studies and a flexible study design have led to a significant upgrading in the information generated by these studies. Additionally, the use of a decision tree approach for selecting tissues for histopathology was developed. The use of specific indicators (such as organ weights) for selecting organs for microscopic examination was also evaluated. Our efforts demonstrate that significantly more information can be generated by studies utilizing fewer animals than is now common practice.     

欧前胡素急性毒性和安全药理学研究

目的观察欧前胡素对大、小鼠的急性毒性,以及对小鼠神经系统和犬心血管系统、呼吸系统的影响。方法通过腹腔内注射给药（ip）和灌胃给药（培）研究欧前胡素对小鼠的急性毒性,以及培对大鼠的急性毒性实验。安全药理学实验中以50、100、200mg／kg分别单次培给予小鼠欧前胡素,观察对小鼠神经系统的影响（包括小鼠自发活动、爬杆能力、小鼠阈下剂量戊巴比妥钠催眠协同实验）;以25、50、100mg／kg分别单次口服给药（po）欧前胡素,观察对犬心血管系统和呼吸系统的影响（包括心电图、血压、心率,以及呼吸频率、幅度、节律等指标）。结果欧前胡素培对小鼠的LD50为988．5mg/kg;ip对小鼠的LD50为603．3mg／kg;ig对大鼠的LD50为3188．7mg／kg。欧前胡素单次ig对小鼠神经系统无明显影响;单次po对犬心血管系统指标和呼吸系统指标无明显影响。结论欧前胡素安全范围较大,毒性较容易控制,且对正常动物（包括小鼠、大鼠和犬）的降压作用不显著,因此具有较大的临床应用可能性。     

The toxicity of tetrahydrobiopterin: acute and subchronic studies in mice

Tetrahydrobiopterin (BH4) is presently being employed in clinical trials for the therapy of various neurological disorders. The toxicity of BH4 in mice was analyzed by acute and subchronic intraperitoneal and acute oral survival studies. Organ weight analysis and histopathology were performed after acute and subchronic i.p. administration. The effect of probenecid on BH4 toxicity was also tested. An LD50 of approximately 260 mg/kg was obtained from acute (14-day) intraperitoneal survival studies. A dose-dependent increase in kidney weights and histopathologic evidence of acute toxic tubular necrosis were noted in acute i.p. studies. Acute oral administration of up to 1318 mg/kg BH4 did not cause any significant morbidity or mortality, nor did subchronic (92-day) i.p. administration of 10 or 50 mg/kg BH4. Probenecid pretreatment did not decrease the toxicity of BH4. The importance of further evaluation of the potential toxicity of tetrahydrobiopterin in clinical utilization is emphasized.     

Delayed neuropathy by the organophosphorus nerve agents soman and tabun

The organophosphorus nerve agents soman and tabun were tested in the hen at doses 120–150 times higher than their acute LD₅₀, as it was assumed that these doses would produce delayed neuropathy. The animals were protected against the acute lethal effect of these agents by pretreatment with atropine, physostigmine, diazepam, and the oxime HI-6 or obidoxime.The surviving animals were followed for 30 days and the occurrence of delayed neuropathy was clinically diagnosed. Soman produced severe delayed neuropathy at a dose of 1.5 mg/kg, a dose which produced acute lethality in five animals out of six. Tabun elicited very mild neuropathic symptoms in one animal out of two at a dose of 6 mg/kg given on 2 consecutive days. Delayed neuropathy was not seen in the hens that survived the acute toxicity of a single dose of tabun, 12 mg/kg (three out of six) or 15 mg/kg (two out of six).     

犬和猴单次给药毒性试验终末处置的考虑

随着中国药品监管体系与国际接轨,国际人用药品注册技术协调会（ICH）指导原则在中国相继转化实施。在非临床安全性评价研究阶段,开展单次给药毒性试验研究,所使用的大动物犬和猴是否在试验结束时必须处死,在充分考虑试验的合规性时,更要从动物福利与伦理,试验的科学性、必要性及利益平衡进行综合评估。在保证试验能够获得预期的信息达到试验目的同时,能够保障动物生存权利。     

Hydroquinone: acute and subchronic toxicity studies with emphasis on neurobehavioral and nephrotoxic effects.

Hydroquinone (HQ) is a common water-soluble constituent of foods, an ingredient in skin lightening preparations, a photographic developer, and an antioxidant used in the preparation of industrial polymers. In this series of studies, aqueous solutions of HQ were given by gavage to male and female Sprague-Dawley rats to determine the acutely lethal dose, the clinical signs of behavioral toxicity associated with doses at or near a dose causing mortality, and the effects of the administration of dose levels resulting in acutely observable behavioral effects when administered 5 days/week for 13 weeks. The acute dermal toxicity of HQ in rabbits was also determined. For the acute oral toxicity study, groups of five male and five female rats were administered single oral doses of 375, 345, 315, or 285 mg/kg. At all dose levels, animals exhibited minor to moderate tremors and minor convulsions within the first hour after dosing. The acute oral LD50 value for both sexes combined was >375 mg/kg. Dermal application of 2000 mg/kg HQ to rabbits under an occlusive wrap for 24 h did not result in neurobehavioral effects or mortality. Subchronic exposure was accomplished by administration of doses of 200, 64, 20, or 0 mg/kg/day of HQ in water to groups of male and female rats study (10/sex/group). A functional observational battery (FOB) was used to detect neurobehavioral effects prior to HQ exposure and postexposure at 1, 6, and 24 h and 7, 14, 30, 60, and 91 days. Daily clinical observations were also recorded for each animal. Doses of 200 or 64 mg/kg HQ resulted in acutely observable behavioral effects including tremors and reduced activity. Tremors occurred within one hour of dosing and resolved by the 6-h examination. Brain weights were not altered by HQ administration, but mean terminal body weight was reduced approximately 7% for the 200 mg/kg males. Neuropathologic examination of the CNS and PNS, including special stains for myelin and axonal process, did not reveal any morphologic lesions associated with HQ administration or secondary to repetitive CNS stimulation by HQ. The nephrotoxic effects observed in Fischer 344 rats after HQ exposure was not observed in this study with Sprague-Dawley rats. Oral doses of >or=64/mg/kg HQ resulted in acute neurobehavioral effects indicative of CNS stimulation; however, subchronic exposure to dose levels that produced repetitive CNS stimulation by HQ did not result in an exacerbation of acute stimulatory effects over time or morphologic changes in the CNS or PNS or nephrotoxicity.     

Delayed behavioral toxicity of lead with increasing exposure concentration

Twenty-one-day-old male Long-Evans hooded rats were exposed chronically to drinking solutions containing 500 ppm sodium acetate (controls) or 50, 100, or 500 ppm lead acetate. Performance on a fixed interval 1-min schedule of food reinforcement was assessed over 155 sessions. Blood lead values were monitored serially and brain lead determinations made at the end of testing (335 days of lead exposure). The lowest concentration of lead in the drinking water was associated with increases in the rate of fixed-interval responding over the first 30 sessions. At the two higher concentrations, response rate values similar to controls over the first 40 sessions were followed by rate increases. The latency to maximum rate depended on concentration; the highest concentration was associated with the longest latency. Response rates of rats exposed to 50 ppm lead gradually returned to control levels after 120 sessions, while increased rates were sustained in rats at 100 and 500 ppm lead, even 100 days after lead exposure was terminated. Marked individual differences in susceptibility to lead-induced rate increases were observed in all treatment lead values also reflected exposure concentrations. Blood-brain ratios averaged 0.743 to 0.913, which agree with other data for the rat and human. These results confirm the vulnerability to lead of rats beyond the neonatal period, and extend the range of conditions under which such effects occur.     

Oral and intraperitoneal acute toxicity studies of yessotoxin and homoyessotoxins in mice.

The acute toxicity of yessotoxin (YTX), homoyessotoxin (homoYTX) and 45-hydroxy-homoyessotoxin (45-OH-homoYTX) has been studied in comparison to that of okadaic acid (OA), the main diarrhogenic toxin, both after intraperitoneal (i.p.) and oral administration. After i.p. administration, homoYTX and YTX showed similar lethality (LD(50)=444 microg/kg and 512 microg/kg), higher than that of OA (LD(50)=225 microg/kg), while 750 microg/kg of 45-OH-homoYTX did not cause death. OA induced the already known toxic signs: before death, mice were motionless and cyanotic; small intestine and liver damage were shown at post-mortem. Mice treated with YTX and homoYTX were restless and jumped before death; necroscopy did not show major changes. After oral treatment, 2 mg/kg of OA induced diarrhoea and body weight loss, causing 4/5 deaths; necroscopy and/or histology revealed degenerative lesions to small intestine, forestomach and liver (confirmed by increased plasma transaminase), but no myocardium alterations. On the contrary, the oral treatment with YTX (1 and 2 mg/kg) and its derivatives (1 mg/kg) did not cause any death or signs of toxicity, except some ultrastructural myocardiocyte alterations, adjacent to capillaries, such as cytoplasmic protrusions (YTX, 1 and 2 mg/kg), fibrillar alteration (YTX, 1 mg/kg) or mitochondria assemblage (45-OH-homoYTX). Altogether, our data show that YTX and its derivatives are less toxic than OA after acute oral and i.p. treatments, at doses which may represent up to 100 times of the possible human daily intake.     

Experimental studies on the acute cardiovascular toxicity of formalin and its antidotal treatment

Rats anesthetized with pentobarbital and ventilated artificially were infused with 0.01 ml formalin (= 0.12 mmol formaldehyde)/kg.min. They exhibited a sharp decline of arterial blood pressure, heart rate and peripheral resistance and a slower one of cardiac output and died after 59.9 +/- 6.0 min of infusion. Sinus bradycardia and, in some cases, AV-arrhythmia occurred in the ECG. The additional infusion with cysteine attenuated the cardiovascular failure and more than doubled the survival time of formalin-infused rats. Infusion of N-acetylcysteine or correction of formalin-induced metabolic acidosis with sodium bicarbonate, on the other hand, did not exert antidotal activity. On isolated rat atria in vitro, formalin decreased the rate and the contractility and cysteine antagonized these effects of formalin. In conclusion, the severe and often lethal incidents observed following the therapeutic administration of formalin are due to the cardiovascular-depressive activity of formaldehyde and may be antagonized by cysteine.     

Safety assessment of aditoprim acute,subchronic toxicity and mutagenicity studies

Aditoprim (ADP), a new developed dihydrofolate reductase (DHFR) inhibitor, has great potential in clinical veterinary medicine because of its greater pharmacokinetic properties than structural analogs. Preclinical toxicology studies were performed to assess the safety of ADP including an acute oral toxicity test, a subchronic toxicity test and five mutagenicity tests. In the acute oral toxicity test, ADP was administered singly by oral gavage to Wistar rats and Kunming mice. The LD₅₀ calculated was 1400 mg kg^–1 body weight (BW) day^–1 in rats and 1130 mg kg^–1 BW day^–1 in mice. In a subchronic study, Wistar rats were administered ADP at dose levels of 0, 20, 100 and 1000 mg kg^–1 diet for 90 days. Significant decreases were observed on body weight and food efficiency in the high‐dose group. Treatment‐related changes in clinical serum biochemistry were found in the medium‐ and high‐dose groups. Significant increases in the relative weights of livers and kidneys in females and testis in males in the 1000 mg kg^–1 diet, and significant decrease in relative weights of livers in males in the 100 mg kg^–1 diet were noted. Histopathological observations revealed that the 1000 mg kg^–1 ADP diet could induce lymphocytic infiltration and hepatocytic necrosis near the hepatic portal area. The genotoxicity of ADP was negative in tests, such as the bacterial reverse mutation assay, mice bone marrow erythrocyte micronucleus assay, in vitro chromosomal aberration test, in vitro cho/hgprt mammalian cell mutagenesis assay and mice testicle cells chromosome aberration. Based on the subchronic study, the no‐observed‐adverse‐effect level for ADP was a 20 mg kg^–1 diet, which is about 1.44‐1.53 mg kg^–1 BW day^–1 in rats. Copyright © 2015 John Wiley & Sons, Ltd.