Subchronic oral and intravenous (iv) safety evaluation and pharmacokinetics in rats and dogs of ipazilide fumarate (Win 54,177-4), an antiarrhythmic agent

Ipazilide fumarate (Win 54,177-4) is a chemically novel antiarrhythmic agent that prolongs ventricular refractoriness and possesses antiectopic activity. Subchronic (29 days) nonclinical safety evaluation of ipazilide was conducted following oral and iv administration in Sprague-Dawley rats (20–320 mg/kg oral and 1.25 – 10 mg/kg iv) and 14 and 28 days in beagle dogs (3–30 mg/kg oral and 2.5–20 mg/kg iv). The pharmacokinetic parameters of ipazilide indicate that ipazilide is absorbed (t_max ≤ 1 hr) in fasted rats and dogs following single and repeated oral administrations. The apparent elimination half-life in the two species is approximately 1 hr (except in rats at a dosage of 320 mg/kg), suggesting rapid clearance. Increases in liver weights (rats 320 mg/kg) accompanied by the observation of centrilobular hypertrophy of hepatocytes were considered an expression of an adaptive metabolic response of the liver to ipazilide and may be associated with the induction of microsomal enzymes. Duodenal villous atrophy and epithelial hyperplasia (rats, 80 and 320 mg/kg) were interpreted to represent an irritant response to the drug. Local irritation was also observed at the injection site in rats and dogs. Dogs tolerated the oral and the iv administration of ipazilide at dosages of up to 30 and 20 mg/kg, respectively. Despite emesis (oral dogs), which was reduced in frequency following repeated treatment over several weeks, plasma levels in treated dogs (i.e., C_max 4–5 μg/ml) were approximately twice that required to convert spontaneous arrhythmias in the conscious dog model 24 hr after myocardial infarction. Moreover, plasma levels (C_max 6–7 μg/ml) of iv-treated dogs were approximately three times higher than the efficacious levels in the dog model and did not cause adverse effects except emesis. Electrocardiographic changes (i.e., increased P wave and QRS durations, and T wave alterations) in dogs were transient and represented an extension of the pharmacological effects of ipazilide. In summary, since ipazilide, at multiple therapeutic dosages, was well tolerated in rats and dogs, it may be considered an appropriate drug for clinical evaluation of safety and efficacy in humans as a potential antiarrhythmic agent. The safety profile of ipazilide in clinical trials is currently ongoing.     

Comparative Toxicokinetics of Methanol in the Female Mouse and Rat

The toxicokinetics of methanol in female CD-1 mice and Sprague-Dawleyrats were examined to explore the possibility of species differencesin the disposition of the compound. Mice received a single doseof 2.5 g/kg methanol either po (by gavage) or iv (as a 1-mminfusion). Rats received a single oral dose of 2.5 g/kg methanol.As expected, the disposition of methanol was nonlinear in bothspecies. Data obtained after iv administration of methanol tomice were well described by a one-compartment model with Michaelis-Mentenelimination. Blood methanol concentration-time data after oraladministration could be described by a one compartment (mice)or two-compartment (rats) model with Michaelis-Menten eliminationfrom the central compartment and biphasic absorption from thegastrointestinal tract Kinetic parameters (V_max for elimination,apparent volume of the central compartment [V_e first-order rateconstants for intercompartmental transfer [k₁₂ and k₂₁ and first-orderabsorption rate constants for fast [k_AF] and slow [k_AS] absorptionprocesses) were compared between species. When normalized forbody weight, mice evidenced a higher maximal elimination ratethan rats (V_max=117±3 mg/hr/kg vs 60.7±1.4 mg/hr/kgfor rats). The contribution of the fast absorption process tooverall methanol absorption also was larger in the mouse thanin the rat.     

Toxicity of the Protein Kinase C Inhibitor Safingol Administered Alone and in Combination with Chemotherapeutic Agents

Safingol [(2S,3S)-2-amino-1,3-octadecanediol] potentiates thetoxicity of doxorubicin (DOX) and cisplatin (CIS) against tumorcells in vitro and in vivo. The present studies were conductedin rats and dogs to evaluate safingol toxicity when administerediv as a single agent and to evaluate safingol's ability to potentiatethe toxicity of established chemotherapeutic agents to normaltissues in vivo. In an escalating dose study, dogs were administeredsafingol iv at 5, 10, 20, 30, 40, and 75 mg/kg on Days 1 through6. Necropsies were performed on Day 7. Red urine was observedat 10 mg/kg and higher. Icterus was observed following 40 mg/kgwith additional signs of hypoactivity and anorexia occurringafter 75 mg/kg. Clinical and microscopic pathology revealedmarked hepatotoxicity, venous degeneration and necrosis at injectionsites, and evidence of intra-vascular hemolysis. Doses of 5,20, or 40 mg safingol/kg were utilized in single iv dose ratand dog studies. No evidence of adverse systemic toxicity wasseen up to 20 mg/kg in either species [for rats: C_max = 12,600(males) or 17,133 (females) ng/ml, AUC = 3853 (males) or 4365(females) ng x hr/ml; for dogs: C_max = 2533 ng/ml, AUC = 2851ng x hr/ml (no sex differences)]. Local effects of venous irritationor intravascular hemolysis were observed at all doses in ratsand at 20 and 40 mg/kg in dogs. A dose of 40 mg/kg [for rats:C_max = 31,233 (males) or 91,300 (females) ng/ml, AUC = 11,519(males) or 18,620 (females) ng x hr/ml; for dogs: C_max = 9033ng/ml, AUC = 11,094 ng x hr/ml (combined sex)] was associatedwith clinical pathologic and renal histomorphologic changesconsidered consequent to intravascular hemolysis in both species,lethality and testicular toxicity in rats, and clinical biochemicalchanges indicative of hepatobiliary injury in dogs. Studiesindicated that hemolysis occurred during infusion, was not causedby circulating levels of safingol, and was a function of doseconcentration and vein of delivery. Safingol at 10 or 20 mg/kgwas administered iv to rats 30–60 min prior to myelosuppressiveiv doses of DOX, CIS, or cyclophosphamide (CYP). Hematology,plus renal function and morphology for CIS-treated animals,was assessed 4 and 14 days later. Safingol did not potentiateDOX-, CIS-, or CYP-mediated leukopenia/thrombocytopenia. A minimalenhancement of CIS-mediated decrease in GFR and increase increatinine was observed at 20 mg safingol/kg. Dogs were administered20 mg safingol/kg iv followed 60 min later by 0.5 or 1.25 mgDOX/kg or 0.75 or 2.0 mg CIS/kg. A complete toxicologic assessment4 and 29 days postdose failed to show potentiation of DOX toxicityby safingol or vice versa. A renal lesion was inferred in dogsadministered 20 mg/kg safingol and 2 mg/kg CIS based on minimalto slight renal tubular regeneration observed 4 weeks post-treatment.There were no effects of safingol on the pharmacokinetic profilesof DOX or CIS or vice versa.     

Preliminary Toxicity Findings in Dogs and Rodents Given the Iron Chelator Ethylenediamine-N,N'-bis(2-hydroxyphenylacetic acid) (EDHPA)

Preliminary Toxicity Findings in Dogs and Rodents Given theIron Chelator Ethylenediamine N,N'-bis(2-hydroxyphenylaceticacid) (EDHPA). ROSENKRANTZ, H., METTERVILLE, J. J., AND FLEISCHMAN,R. W. (1986). Fundam. Appl. Toxicol 6, 292–298. Becauseof a projected pilot study with EDHPA in Cooley's anemia patients,animal studies with emphasis on reversibility of potential toxicsigns were performed. Young dogs were treated iv with 6–18mg/kg or orally with 30–240 mg/kg for 14 days followedby a 16-day recovery period. Drug-induced emesis, elevated BUNchanges in kidney, spleen, and thymus weights diminished duringrecovery. One deceased dog exhibited nephrotoxicity consistingof tubular necrosis and deposition of the iron—EDHPA complex.The latter was observed in the excreta of survivors but kidneydamage was not evident. Atrophy of the spleen and thymus inthe deceased dog was consistent with less intense organ weightchanges in recovered survivors. In the absence of morphologicchanges after recovery, the precise effect on the immune systemis unknown. The iv LD50 was 53 mg/kg for rats and mice. No rodentdeaths occurred at an oral dose of 6000 mg/kg An elevated BUNand changes in kidney, spleen, and thymus weights were confirmedin rodents given iv doses of 5–20 mg/kg or oral dosesof 150–600 mg/kg for 5 days. It is cautioned that duringthe use of EDHPA derivatives that the functions of the renaland immune systems be monitored.     

Nonclinical Toxicology Studies with Zidovudine: Acute, Subacute, and Chronic Toxicity in Rodents, Dogs, and Monkeys

In single dose acute toxicity studies in CD-1 mice and CD rats,the median lethal dose (MLD) for zidovudlne (ZDV) was >750mg/kg after iv dosing and >3000 mg/kg after po administration(recommended human dose is 100 mg every 4 hr while awake). Becauseof the short half-life in rats (0.8 hr), dogs (1.0 hr), andmonkeys (0.8 hr), the daily dose of ZDV in most studies wasgiven in two equal portions approximately 6 hr apart. Intravenousadministration of ZDV was well tolerated in beagle dogs at doselevels up to 42.5 mg/kg bid for 2 weeks and in CD rats at doselevels up to 75 mg/kg bid for 4 weeks. In a 2-week dose range-findingstudy in beagle dogs, cytostatic effects were noted at po doselevels of 62.5 to 250 mg/kg bid in certain tissues with rapidcell replication rates. In contrast, in 3-to 12-month oral toxicitystudies in CD rats and cynomolgus monkeys, the principal toxicologicfinding was reversible macrocytic normochromic anemia whichoccurred at 225–250 mg/kg bid in rats and 17.5–150mg/kg bid in monkeys. In the 12-month rat study, RBC was decreasedat 25 and 75 mg/kg bid. In the 12-month monkey study WBC wasslightly decreased at 150 mg/kg bid.     

Vitamin A Potentiation of Vinylidene Chloride Hepatotoxicity in Rats and Precision-Cut Rat Liver Slices

Pretreatment of large doses of vitamin A (VA) is known to potentiatethe hepatotoxicity of carbon tetrachloride. Therefore the effectsof 1-day VA pretreatment on VDC hepatotoxicity was examinedboth in vivo and in an in vitro system of precision-cut ratliver slices. Male Sprague-Dawley rats were pretreated with250,000 IU/kg VA by oral gavage. After 24 hr rats were administered50, 100, or 200 mg/kg VDC ip. Precision-cut liver slices wereprepared from VA pretreated rats 24 hr later and the liver sliceswere exposed for 2–8 hr to 0.025–1.0 µl VDCevaporated into the gas phase of the incubation vials. VA pretreatmentresulted in an enhancement of VDC toxicity, both in vivo andin vitro. There was a dose-dependent increase in plasma ALT24 hr after VDC treatment of rats and an increase in K⁺ leakagefrom liver slices after VDC exposure. Histological analysisof the liver or the liver slices revealed that VA+VDC treatmentresulted in centrilobular necrosis of the liver. When GdCl₃(10 mg/kg iv) was administered just before VA pretreatment ofrats, VDC toxicity was partially reversed as observed by a decreasein ALT in vivo and a decrease in the loss of K⁺ in vitro. Theseresults indicated that Kupffer cells, the resident macrophagesof the liver, were partially responsible for the VA-potentiatedVDC hepatotoxicity. One-day pretreatment of VA induced cytochromeP450IIE1 protein content as well as its enzymatic activity asmeasured by p-nitrophenol hydroxylation. Because VDC is bioactivatedby cytochrome P450IIE1, the increase in VDC hepatotoxicity afterVA may be due to an increased bioactivation of VDC in the liverand in precision-cut liver slices. Thus, more than one mechanismmay be involved in the VA enhancement of VDC hepatotoxicity.     

4,4'-Methylenebis(2-chloroaniline) (MOCA): The Effect of Multiple Oral Administration, Route, and Phenobarbital Induction on Macromolecular Adduct Formation in the Rat

The effect of multiple oral administration of MOCA, a suspecthuman carcinogen, was studied in the adult male rat. As manyas 28 consecutive daily doses of [¹⁴C]MOCA at 28.1µmol/kgbody wt (5 µC1/day) were administered and rats were euthanizedat weekly intervals for 7 weeks. MOCA adduct formation for globinand serum albumin was evaluated by determination of [¹⁴C]MOCAcovalent binding. The covalent binding associated with globinshowed a linear increase over the 28-day exposure period with342 fmol/mg globin 24 hr after the final dose. More extensivecovalent binding was detected for albumin with 443 fmol/mg albuminafter the final dose, but increases were not linear. After cessationof dosing, the albumin adduct levels decreased rapidly (t _1/2=4.6 days) in relation to globin adduct levels (t _1/2 =16.1days). The MOCA-globin adduct t _1/2 is consistent with thatdetermined after a single 281 µmol/kg oral dose of MOCA.Significant differences related to route of administration weredetected for 24-hr globin covalent binding with ip > po >dermal. Distribution of undifferentiated [¹⁴C]MOCA was highestin the liver at 24 hr with tissue levels for liver > kidney> lung > spleen > testes > urinary bladder. Inductionof cytochrome P450 enzymes by administration of phenobarbital(100 mg/kg/day/3 days) resulted in a significant (p < 0.05)increase in MOCA-globin adduct formation detected with 33.5pmol/ mg globin for induced rats versus 13.6 pmol/mg globinfor control rats. Although MOCA-globin and albumin adducts showdiffering stability, quantification of such MOCA adducts maybe useful for long-term industrial biomonitoring of MOCA.     

Oral Toxicity of Carbon Tetrachioride: Acute, Subacute, and Subchronic Studies in Rats

Oral Toxicity of Carbon Tetrachloide: Acute, Subacute, and SubchronicStudies in Rats. BRUCKNER, J. V., MACKENZIE, W. F., MURALIDHARA,S., LUTHRA, R., KYLE, G. M., AND ACOSTA, D. (1986). Fundam.Appl. Toxicol. 6, 16–34. This investigation was conductedto characterize the acute, subacute, and subchronic toxic potencyof ingested carbon tetrachloride (CCl₄) In the first acute andsubacute toxicity study, male Sprague-Dawley rats of 300–350g were gavaged with 0, 20, 40, or 80 mg CCl₄/kg once daily for5 consecutive days, rested for 2 days, and dosed once dailyfor 4 additional days. Rats of 200–250 g were gavagedwith 0, 20, 80, or 160 mg CCl₄/kg according to the same dosageregimen in the second acute and subacute study. In the firstand second studies one group of rats at each dosage level wassacrificed for clinical chemistry and histopathological evaluationat 24 hr, 4 days, and 11 days after initiation of dosing. Single20- and 40-mg/kg doses had no apparent toxic effect at 24 hr,although 80 mg/kg caused mild hepatic centrilobular vacuolizationand significant increases in some serum enzyme levels. In general,there was progressively severe hepatic injury at each dosagelevel over the 11-day period. CCl₄ was more hepatotoxic to the200–250-g rats than to the 300–350-g rats. In thesubchronic study, rats initially 200–250 g were gavaged5 times weekly for 12 weeks with 0, 1, 10, or 33 mg CCl4/kgBody weight and clinical chemistry indices were monitored duringthe 12 weeks of dosing and 2 weeks after cessation of dosing,A dose of 1 mg/kg had no apparent adverse effect; 10 mg/kg producedslight, but statistically significant increases in sorbitoldehydrogenase activity and mild hepatic centrilobular vacuolization;33 mg/kg caused marked hepatotoxicity. Serum enzyme levels remainedelevated during the 12-week dosing period, but returned towardnormal within 13 days of cessation of CCl₄ exposure. Microscopicexamination of livers of the 33-mg/kg rats revealed cirrhosis,characterized by bile duct proliferation, fibrosis, lobulardistortion, parenchymal regeneration, hyperplastic nodules,and single-cell necrosis. The fibrosis was not reversed withinthe 13-day recovery period.     

Sublethal Acute Toxicity of Carbosulfan [2,3-dihydro-2,2-dimethyl-7-benzofuranyl(di-n-butylaminosulfenyl)(methyl)carbamate] in the Rat after Intravenous and Oral Exposures

Sublethal Acute Toxicity of Carbosulfan [2,3-dihydro-2,2-dimethyl-7-benzofuranyl(di-n-butylaminosulfenyl)(methyl)carbamate]in the Rat after Intravenous and Oral Exposures. RENZI, B. E.,AND KRIEGER, R. I. (l986). Fundwn. Appl. Toxicol. 6, 7–15.Sublethal toxicity of carcarbosulfan, 2,3-dihydro-2,2-dimethyl-benzofuranyl(di-n-butylaminosulfenyl)(methyl)carbamate,was evaluated in female Sprague-Dawley rats. Erythrocyte acetylcholinesterase(AChE) activity was maximally inhibited 1 min after iv administration(38, 23, and 15% of pretreatment activity after 86, 250, and690 µg/kg, respectively) and recovered by 4 hr. MaximumAChE inhibition (63% of pretreatment activity) was measured45 min after oral dosing (690 µg/kg) and activity recoveredafter 5 hr. Signs included urination, defecation, facial musclefasciculations, salivation, and tremors. Carbosulfan was lesstoxic when given orally. Metabolic activation of carbosulfanto carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranol methylcarbamate)was in vestigated by measuring plasma concentrations 4, 30,and 240 min after iv (80–120 or 620–640 µg/kg)and oral (540–700 or 2030–2190 µ/kg) dosagesof [carbonyl-¹⁴C]carbosulfan. Peak plasma concentrations weremeasured at 4 and 30 min after iv and oral exposure, respectively.Carbosulfan was rapidly activated to carbofuran. Reduction inAChE activity was better correlated (r = 0.97) with plasma concentrationof [carbosulfan + carbofuran] and plasma carbofuran (r = 0.96)than with plasma carbosulfan (r = 0.73). Signs generally occurredwhen AChE activity was less than 65% of pretreatment levels,corresponding to 40 pmol/ml [carbosulfan + carbofuran] in plasma.Based on regression analysis and metabolic studies, both carbosulfanand carbofuran contributed to the observed AChE inhibition;however, carbofuran, a more potent in vitro inhibitor and theusual predominant inhibitor in plasma, was responsible for mostof the erythrocyte AChE inhibition.     

Carbofuran Metabolism and Toxicity in the Rat

Carbofuran Metabolism and Toxicity in the Rat. FERGUSON, P.W., DEY, M. S., JEWELL, S. A., AND KRIEGER, R. I. (1984). Fundam.Appl. Toxicol. 4, 14–21. The influence of carbofuran metabolismon acetylcholinesterase inhibition has been defined after lowdose (50 µg/kg, iv and oral) [carbonyl-¹⁴C]carbofuranexposures to male Sprague–Dawley Rats. Red blood cellacetylcholinesterase (RBC AchE) inhibition (83% at 2 min, 37%at 15 min for iv and oral, respectively, with recovery by 3hr), was correlated with carbofuran plasma concentrations (r= 0.97). Eight-hour sample collection indicated that ultimatecarbofuran fate (41–47% ^l4CO₂, 14–15% urine, <1%feces, and 30–31% carcass) was independent of exposureroute. Carbofuran absorption (peak plasma levels < 7 min),distribution, and elimination (t? = 29 ? 5 min) occurred rapidly.3-Hydroxycarbofuran, a significant oxidative metabolite of carbofuranwith anticholinesterase activity, was rapidly formed and subjectto enterohepatic circulation (plasma t? = 64 ? 5 min). Resultsindicated that rapid RBC AchE recovery closely paralleled carbofuranmetabolism and the primary in vivo disposition of 3-hydroxycarbofuranwas metabolic conjugation.     

Hypocalcemia Induced by Foscarnet (Foscavir) Infusion in Dogs

Hypocalcemia Induced by Foscarnet (Foscavir) Infusion in Dogs.RYRFELDT, ., NORDGREN, T., AND LUNDSTRM, J. (1992). Fundam.Appl. Toxicol. 18, 126–130. Foscarnet (Foscavir) is an antiviral drug for intravenous (iv)treatment of cytomegalovirus (CMV) retinitis in immunocompromisedpatients. The drug forms complexes with divalent metal ionssuch as Ca²⁺ and serum calcium levels may be affected duringits iv infusion. In this study, the effect on calcium homeostasiswas investigated during daily 8-hr infusions of foscarnet indogs. After priming infusions of 40 or 80 mg/kg administeredduring 0.5 hr, maintenance infusion rates were 46 or 91 mg/kg/hr(total daily doses of 410 or 810 mg/kg). At the low infusionrate, foscarnet was administered for 5 consecutive days. Themean plateau serum concentration was 0.56 mmol/liter and themain clinical sign was vomiting. Total serum calcium was reducedfrom about 2.5 to 2.0 mmol/liter and ionized calcium from 1.3to 0.9 mmol/liter. Parathyroid hormone (PTH) levels in serumwere elevated three to six times while calcitriol (1,25- (OH)₂D₃)levels were unaffected. At the high infusion rate, treatmentwas discontinued after 1–2 days of dosing due to pronouncedadverse clinical signs such as extensive vomitings, apathy,ataxia, and muscle spasms. The mean serum plateau concentrationof foscarnet at this dose level was 1.2 mmol/liter. Total serumcalcium was reduced from 2.5 to 1.6 mmol/liter and ionized calciumfrom 1.3 to 0.7 mmol/liter. PTH as well as 1,25-(OH)₂D₃ levelsin serum were elevated. Total and ionized calcium levels werenormalized within 16 hr after stopping drug treatment. The resultsshowed that foscarnet infusion affects calcium homeostasis andthat calcium monitoring might be considered in the clinicaluse of the drug.     

Preclinical Toxicology Studies with Acyclovir: Acute and Subchronic Tests

Preclinical Toxicology Studies with Acyclovir: Acute and SubchronicTests. Tucker, W.E., Jr., Macklin, A.W., Szot, R.J., Johnston,R.E., Elion, G.B., de Miranda, P. and Szczech, G.M. (1983).Fundam. Appl. Toxicol. 3:573–578. Acyclovir (ACV), a newantiherpes drug, was evaluated for toxicity in a series of acuteand subchronic toxicity tests. Oral LD₅₀ values were greaterthan 10 000 mg/kg in male ICR mice and greater than 20 000 mg/kgin male Long Evans rats. When ACV was given iv, the LD₅₀ was405 mg/kg for male mice and greater than 600 mg/kg for malerats. Additionally, LD₅₀ values for male rats treated sc were1070, 790, 678, and 650 mg/kg in rats that were respectively,3, 10, 28 and 71 days old indicating that very young rats werenot more sensitive to acute toxic effects of ACV. There wereno signs of toxicosis in CD-1 mice given ACV by gavage at doselevels of 50, 150 and 450 mg/kg/day for 1 month. Obstructivenephropathy occurred in rats given 20, 40 and 80 mg/kg/day onceeach day by rapid iv injection for 3 weeks. Both 5 and 10 mg/kg/daywere no effect dose levels. Renal damage caused by precipitationof drug crystals in renal tubules and collecting ducts in ratsgiven ACV by rapid iv injection was readily reversible within2 weeks. Beagle dogs were given doses of 10, 20, 25, 50 and100 mg/kg b.i.d. by rapid iv injection for 1 month. All 8 dogsgiven 100 mg/kg b.i.d. died by the 8th day of treatment; 5 of8 dogs given 50 mg/kg b.i.d. died after 21 to 31 days of treatment.At 50 and 100 mg/kg b.i.d. the clinical signs of toxicosis werenumerous and mainly resulted from the underlying morphologicaland functional changes associated with hypoplasia of the esophagealand gastrointestinal mucosa, lymphoid tissue, and bone marrow.At the 20 and 25 mg/kg b.i.d. dose levels the kidney was thetarget organ; the principal indications of altered renal functionwere increased water intake and hyposthenuria. The dose levelof 10 mg/kg b.i.d. was a no effect level for Beagle dogs treatediv. Thus, in subchronic experiments, the rapid iv injectionof acyclovir caused precipitation of crystals in the renal tubules,resulting in obstructive nephropathy in rats and dogs. Primarytoxicity occurred only in the dog where high doses of acyclovircaused hypoplasia of certain tissues with rapid cell turnover.     

Acute Cardiotoxicity of the Anti-HIV Dideoxynucleoside, F-ddA, in the Rat

2'-ß-Fluoro-2',3'-dideoxyadenosine (F-ddA), an acid-stable,pu-rine dideoxynucleoside with in vitro anti-HIV activity, hasbeen selected by the NCI as a clinical trial candidate. A recentreport that high, single doses of F-ddA produce cardiotoxicityin rats prompted the present investigation whose objective wasto quantitate this effect and establish a relationship betweenthis toxicity and F-ddA plasma concentrations. Microscopic examinationof cardiac tissues for degenerative lesions established theeffects of F-ddA and ddA on three iv schedules [daily x 1 (2.5–250mg/kg); daily x 5 (125, 250 mg/kg), and BID x 1 (250 mg/kg)]as well as one oral schedule [BID x 1 (500 mg/kg)] using 8-to 12-week-old female Sprague-Dawley rats. For both F-ddA andddA, the group mean severity of the cardiac lesions was dose-dependentand proportional to the measured plasma concentrations of theundeaminated parent drugs. F-ddl and ddI, the respective deaminatedcatabolites of F-ddA and ddA, were essentially nontoxic in thisstudy (iv, 250 mg/kg, daily x 1 and daily x 5), since plasmaconcentrations exceeding 2 mM produced only minimal cardiaclesions. The cardiomyopathy of F-ddA was minimal to mild forall iv doses except 250 mg/kg (daily x 1) and usually was greaterthan that of ddA at any given dose. This is a consequence ofthe fact that F-ddA is deaminated 20 times more slowly thanddA, resulting in higher plasma concentrations of F-ddA relativeto ddA at any given time for any given dose. Neither F-ddA norddA was more cardiotoxic on a repeated iv schedule (daily x5) than when administered only once, suggesting that rat cardiotoxicityis related to C_max, rather than total exposure. In this mostsensitive species, the formation of cardiac lesions above thebackground level is associated with iv F-ddA administrationwhen the F-ddA plasma concentration approaches 300 µM,30–50 times the anticipated therapeutic level in humans.     

Adrenocortical Toxicity of 3-Methylsulfonyl-DDE in Mice: II. Mitochondrial Changes following Ecologically Relevant Doses

Transmission electron microscopy was used to characterize earlyultrastructural lesions in the adrenal zona fasciculata of femaleC57BL mice given a single ip injection of the adrenocorticolyticDDT-metabolite 3- methylsulfonyl-DDE (MCSO₂-DDE Following 3mg/kg, mitochondrial changes were observed 6 hr after dosing.At 12 and 24 hr the mitochondrial changes were conspicuous,with disorganization and disappearance of central cristae. Atdoses of 6, 12, and 25 mg/kg body wt initial (6 hr) mitochondrialvacuolization was observed, followed by disappearance of mitochondria(6–12 mg/kg) or cellular necrosis (25 mg/kg). The metabolicactivation and binding of MeSO₂-[¹⁴C]DDE in adrenal homogenateswere determined in vitro. The irreversible binding of MeSO₂-[¹⁴C]to the mitochondria-containing adrenal S-9 pellet fraction was50 times higher than that to the postmitochondrial S-12 supernatantfraction. The apparent K_m was 2.1 µM and the apparentV_max was 104 pmol/mg protein/30 mm for the binding of MeSO₂-[¹⁴C]to S-0.3 supernatants. The irreversible protein binding wasinhibited by metyrapone (K₁=1 µM) and 11-deoxycorticosterone(K₁=3 µM). In conclusion, the adrenal metabolic activationof MeSO₂-[¹⁴C]DDE is suggested to be mediated by a mitochondrialcytochrome P450 form, presumably P450 (11ß). A primarymitochondrial lesion develops and subsequently leads to degenerationand necrosis of the zona fasciculata.     

meso-2, 3-Dimercaptosuccinic Acid and Prevention of Arsenite Embryotoxicity and Teratogenicity in the Mouse

meso-2,3-Dimercaptosuccinic Acid and Prevention of ArseniteEmbryotoxicity and Teratogenicity in the Mouse. DOMINGO, J.L., BOSQUE, M. A., AND PIERA, V. (1991). Fundom. Appl. To. 17,314–320. meso2,3-Dimercaptosuccinic acid (DMSA), an antidotefor the treatment of experimental and human poisoning by a numberof heavy metals, has been reported to reduce the lethality ofanimals poisoned with arsenic more effectively than 2,3-dimercaptopropanol.In the present study, the effcct of DMSA on arsenite-inducedembryotoxic and teratogenic effects was evaluated in mice. Ina first experiment, a series of four DMSA injections was administeredsc to pregnant Swiss mice immediately after a single i p injectionof 12 mg/kg of sodium aresenite (NaAsO₂) given on Day 10 ofgestation, and at 24, 48, and 72 hr thereafter. DMSA effectivenesswas assessed at dosage levels of 0, 80, 160, and 320 mg/kg/day.Treatment with DMSA significantly reduced the embryolethalityand the incidence of gross external and skeletal malformationsand variations provoked by NaAsO₂. Based on these findings,the effect of increasing the time interval between acute arseniteexposure and mitiation of DMSA therapy was invmgated in a secondexperiment. On Day 10 of gestation, DMSA (320 mg/kg) was administeredsc to pregnant mice at 0, 0.25, 0.50, 1, 4, or 12 hr after a12-mg/kg ip dose of NaAsO₂. Embryotoxicity and teratogenicityderived from NaAsO₂ exposure were significantly reduced whenDMSA was given during the first hour aRer NaAsO₂ injection.According to these results, a delay between acute arsenite intoxicationand DMSA treatment should be avoided to have a practical beneficialeffect on the arsenite exposed conceptus.     

Nonclinical Toxicology Studies with Zidovudine: Reproductive Toxicity Studies in Rats and Rabbits

Zidovudine (ZDV) was evaluated for adverse effects on reproductionand fetal development in animal test species. Standard preclinicaltests for reproduction and fertility, developmental toxicity,and postnatal toxicity were conducted in CD (Sprague-Dawley)rats and a developmental toxicity study was conducted in NewZealand white rabbits. In an additional study, reproductiveoutcome was characterized in female rats given ZDV before, during,or after mating and drug levels in the plasma and milk of lactatingrats were determined. Finally, drug exposure data includingobserved peak plasma concentrations (C_max) and area under theconcentration-time curve (AUC) were evaluated for pregnant ratsand rabbits. In a reproduction/fertility study in CD rats, toxicityto the early rat embryo, manifested as an increase in earlyresorptions and a decrease in litter size, was noted followingdosage of the parental animals with 75 or 225 mg ZDV/kg bid.A dose of 25 mg/kg bid was a no-effect level in rats. At thetime of mating, male rats had been dosed for 85 days, and femaleshad been dosed for 26 days. To further evaluate the effectsof ZDV on reproduction, dosing of male rats was continued to149 days when they were mated a second time to virgin, untreatedfemales. All reproductive parameters were normal in the untreatedfemales from this second mating, indicating that the embryotoxiceffect of the drug was not likely mediated by a genotoxic orother effect in the male. A separate study in female CD ratsgiven 225 mg/kg bid for various periods pre- or postconceptionsuggests that the toxic effect of ZDV is primarily to the earlyrodent embryo. Early embryo death did not occur in rats or rabbitsin standard developmental (teratology) studies; however, pregnantNew Zealand white rabbits given 250 mg/kg bid during gestationDays 6–18 showed reduced weight gain, anemia, and an increasein late fetal deaths. No other evidence of developmental toxicitywas noted in either species, and ZDV was not teratogenic inrats or rabbits given up to 250 mg/kg bid during the periodof major organogenesis. At this dose, C_max, values in rats andrabbits were approximately 234 and 150 times higher, respectively,than the mean steady-state serum concentration in adults followingchronic oral administration of 250 mg every 4 hr. In both thereproduction/fertility study and a periand postnatal study inrats, liveborn offspring showed no adverse effects on survival,growth, or developmental measurements.     

Evaluation of Valproic Acid (VPA) Developmental Toxicity and Pharmacokinetics in Sprague--Dawley Rats

Evaluation of Valproic Acid (VPA) Developmental Toxicity andPharmacokinetics in Sprague-Dawley Rats.BINKERD, P. E., ROWLAND,J. M., NAU, H., and HENDRICKX, A. G. (1988). Fundam Appl. Toxicol.11, 485—493. This study was undertaken to assess the pharmacokinetics and developmental toxicity of the anticonvulsant,valproic acid (VPA), a human teratogen, in Sprague-Dawley rats.Oral administration of 200-800 mg/kg VPA (5-20X human 3 therapeuticdose) from Gestational Days (GD) 8 to 17 resulted in increasingmaternal toxicity at the higher doses with 100% maternal lethalityat 800 mg/kg. Although there was an increased incidence of resorptionsat 600 mg/kg (48 ? 43%) compared to controls (18 ? 24%), itwas not statistically significant. Fetal examination on GD 20revealed dose-dependent fetal growth retardation (p 0.05) asevidenced by decreased fetal weight and length in addition tounderossi-fication of both the axial and appendicular skeleton.The incidence of skeletal defects, including abnormal vertebrae,ribs, and craniofacial dysmorphia, also increased with higherdoses of VPA. Cardiac anomalies observed in the two highesttreatment groups consisted of great vessel malformations withor without associated ventricular septal defects (VSDs). Urogenitaldefects were 3 also noted in the 600 mg/kg group. The plasmaelimination half-life on GD 8 was 1.0 ? 0.3 hr at 200 mg/kgand 2.3 ? 0.7 hr at 600 mg/kg. Maximal concentrations of totaland free drug were 341 ? 18 µg/ml and 181 ? 11 µg/ml,respectively, in the low-dose group and 911 ? 379 µg/mland 542 ? 224 µ%/ml in the high-dose group. No significantchanges in any pharmacokinetic 3 parameters (t1/2, AUC, C_max,t_max) were observed over the 10-day treatment period at eitherdose level.     

Effects of Chlorpyrifos on High-Affinity Choline Uptake and [3H]Hemicholinium-3 Binding in Rat Brain

High, subcutaneous doses of the organophosphorus insecticidechlorpyrifos (CPF) in adult male rats can be well-tolerateddespite extensive and persistent acetylcholinesterase (AChE)inhibition. We propose that changes in acetylcholine synthesiscould modulate the toxicity associated with extensive AChE inhibitionfollowing CPF exposure. High-affinity choline uptake (HACU,the rate-limiting step in acetylcholine synthesis) and bindingto [³H]-hemicholinium-3 (HC-3, a specific ligand for the cholinetransporter) were chosen as indicators of acetylcholine synthesis.Female, Sprague-Dawley rats (220–280 g) were treated witheither vehicle (peanut oil, 2 ml/kg, sc) or CPF (280 mg/kg,2 ml/kg, sc), examined daily for clinical signs of toxicity,and sacrificed 1, 2, or 7 days later for neurochemical measurements{AChE inhibition, muscarinic receptor binding using [³H]quinuclidinylbenzilate (QNB) and [³H]cis-methyldioxolane (CD) as ligands,HACU and [³H]HC-3 binding} in frontal cortex. Despite extensiveAChE inhibition (90–93%) at all time points, relativelyminor degrees of overt toxicity were noted in CPF-treated rats.Binding to the non-selective muscarinic antagonist [³H]QNB wasreduced (10–34%), whereas binding to the putative m2-selectiveagonist [³H]CD was increased (15–23%) at all three timepoints. HACU was reduced (20%) in crude synaptosomes preparedfrom CPF-treated rats 1 day following exposure but no significantchanges were noted at 2 or 7 days after treatment. CPF-oxon,the active oxidative metabolite of CPF, was a weak inhibitorof HACU in vitro (IC₅₀>200 µM). Binding to [³H]HC-3was reduced in a dose-related manner 1 day after CPF exposure.Kinetic analyses of [³H]HC-3 binding 1 day after CPF (280 mg/kg)indicated a significant reduction in density {B_max: control,187±18 fmol/mg protein; CPF, 104±12 fmol/mg protein)with no apparent change in binding affinity (K_d: control, 25±3nM; CPF, 19±3 nM). These results suggest that a reductionin HACU/acetylcholine synthesis may contribute, along with compensatorychanges in cholinergic receptors, to the diminished toxicityfollowing extensive AChE inhibition by CPF.     

Acute, Distribution, and Subchronic Toxicological Studies of Succinate Tartrates

The estimated single-dose oral toxicity (50% lethality) of succinatetartrates (ST) was 2–3 g/kg in rats. ST produced minimalto moderate dermal irritation but no evidence of systemic toxicityin a standard acute percutaneous toxicity test in rabbits. STwas not an eye irritant in a standard rabbit low-volume eyeirritation test ST was not genotoxic in a series of six genotoxicitytests. A 14-day oral gavage study in rats at a dose range of0.05–1.0 g ST/kg/day produced only gastric irritation.The no-observed-effect level (NOEL) for gastric irritation was0.1 g/kg for males and 0.05 g/kg for females. A 28-day percutaneoustoxicity study in rabbits produced minimal to moderate dermalirritation and no adverse systemic effects at a high dose of450 mg ST/kg/day. Single-dose absorption, distribution, andelimination (ADE) studies in male rats showed that 10–15%of an oral dose and 1–3% of a dermal dose were absorbed.Approximately 98% of the orally administered ST was eliminatedas ¹⁴C in urine, feces, or expired CO₂ after 72 hr. Approximately80% of the dermally absorbed ¹⁴C dose was eliminated in urine,feces, or expired CO₂ after 72 hr. In conclusion, no adverseeffects were noted in acute toxicity, genotoxicity, or subchronictoxicity studies conducted with ST.     

Pharmacokinetic Fate of14C-Labeled Deoxynivalenol in Swine

Pharmacokinetic Fate of ¹⁴C-Labeled Deoxynivalenol in Swine.PRELUSKY, D. B., HARTIN, K. E., TRENHOLM, H. L., AND MILLER,J. D. (1988). Fundam. Appl Toxicol. 10,276-286. The pharmacokineticsof the trichothecene mycotoxin deoxynivalenol (DON) was investigatedin swine following intravenous (0.30 mg, 0.35 µCi/kg)and intragastric (0.60 mg, 0.60 µCi/kg) administrationof the ¹⁴C-labeled toxin. After iv dosing, plasma concentrationdata favored a three-compartment open model with half-life valuesfor the rapid distribution (), slower distribution (ß),and terminal elimination () phases of 5.8, 96.7, and 510.0 min,respectively. The apparent volume of distribution (V') was 1.34liter/kg, the volume of the central compartment (K_c) was 0.166liter/kg, and the plasma clearance was 1.81 ml/min/kg. DON wasrapidly cleared essentially unchanged (>95%), and was excretedprimarily in unne (86–104%), with minor elimination inbile (3–5%). Following intragastric dosing DON was veryrapidly absorbed, reaching near peak plasma levels within 15–30min. Levels remained elevated (63-325 ng/ml) for approximately9 hr, and began declining slowly (t ß= 7.1 hr) thereafter.The calculated systemic bioavailability (F) was between 48 and65%, although urinary and biliary recoveries indicated marginallygreater absorption actually occurred (54–85%). Overall,although DON was eliminated rapidly and completely within 24hr following a single iv or intragastric dose, data suggestthat residues may undergo temporary sequestration in a tissuedepot.