Reduced systemic availability of an antiarrhythmic drug, bidisomide, with meal co-administration: relationship with region-dependent intestinal absorption.

PURPOSE: The aim of this research was to determine the mechanism by which a co-administered meal decreases the oral absorption of bidisomide and does not influence the oral absorption of the chemically-related antiarrhythmic agent, disopyramide. METHODS: Bidisomide plasma levels, following oral administration and intravenous infusion in the fasted state and with various meal treatments, were determined in human subjects. A dialysis technique was employed to examine the potential for drug binding to meal homogenates. Plasma levels, following drug administration through duodenal and jejunal intestinal access ports and following various meal treatments with oral drug co-administration, were compared for bidisomide and disopyramide in a canine model. RESULTS: Bidisomide plasma AUC was significantly reduced following oral drug co-administration with breakfast compared to fasted-state controls in human subjects and in dogs independent of the composition of the solid cooked breakfast. While intravenous bidisomide infusion in human subjects showed a statistically significant reduction in AUC 15 minutes after oral administration of a high fat breakfast as compared to drug infusion in the fasted state, the reduction (-13%) was substantially smaller than the reduction (from -43% to -63%) observed with oral bidisomide meal co-administration. The percentages of bidisomide and disopyramide lost by binding to homogenates of cooked breakfast were 25.0 +/- 5.7% and 23.7 +/- 7.7%, respectively, as determined by dialysis at 4 hours. In dogs, the extent of absorption of disopyramide was comparable from oral, duodenal and mid-jejunal administration while the extent of bidisomide absorption from mid-jejunal administration was significantly lower than for oral or duodenal administration. Non-viscous liquid meals decreased Cmax but not AUC, while viscous homogenized solid meals decreased both Cmax and AUC for bidisomide with oral drug-meal co-administration. Oral non-caloric hydroxypropyl methylcellulose meals decreased bidisomide to the same extent as homogenized solid meals but did not lower disopyramide AUC. CONCLUSIONS: The significant reduction in bidisomide plasma levels observed with meal co-administration in human subjects was predominantly mediated through a reduction in drug absorption and was independent of solid meal composition. The difference in meal effect on the absorption of the two drugs in humans did not appear to be a function of drug binding to cooked meal components over typical human upper gastrointestinal residence times. In dogs, the high-viscosity medium generated by oral co-administration of a solid meal reduced the upper intestinal absorption of bidisomide and disopyramide. Bidisomide AUC was decreased since it was well absorbed in the upper but not lower small intestine. Disopyramide AUC was not significantly affected since it was well absorbed from both regions. A similar mechanism may play a role in drug plasma level reductions following oral co-administration with solid meals for drugs showing similar regionally-dependent absorption profiles.

30-day oral toxicity study of domoic acid in cynomolgus monkeys: lack of overt toxicity at doses approaching the acute toxic dose.

Domoic acid was orally administered to 3 cynomolgus monkeys at doses of 0.5 mg/kg for 15 days and then at 0.75 mg/kg for another 15 days. After the 30-day dosing period, the treated monkeys were killed. Parameters monitored as markers for toxicity included body weight, food and water consumption, clinical observations, hematology, serum chemistry, light microscopy of all major organs (including brain and retina), and glial fibrillary acid protein immunohistochemistry. Domoic acid in serum and 24-hour urine samples was measured at several time points. All parameters measured remained unremarkable. Domoic acid concentrations measured in the 24-hour urine samples indicated that gastrointestinal absorption in the monkey was approximately 4-7 percent of the administered dose, which is at least twice that previously reported for the rat.

Subchronic toxicity study of domoic acid in the rat.

Male and female Sprague-Dawley rats were dosed by gavage for 64 days with 0, 0.1 or 5 mg/kg/day domoic acid. Treated animals showed no clinical abnormalities. Terminal values in haematology and clinical chemistry did not reveal differences between treated and control groups. Findings in histopathology and immunohistochemistry were unremarkable. The 24-hr urinary excretion rate for domoic acid determined at three time points was approximately 1.8% of the dose and remained unchanged during the study.

Chronic feeding study of deoxynivalenol in B6C3F1 male and female mice.

A 2 year feeding study was conducted with male and female B6C3F1 mice that consumed diets containing 0, 1, 5, or 10 ppm deoxynivalenol (DON). Survivability was good and, while the test animals gained less weight with increasing levels of DON in the diet, there were no consistent toxic manifestations associated with DON consumption. There was some evidence for an increase in serum IgA and IgG in females, and there were sporadic changes noted in the clinical chemistry and hematology parameters conducted at the terminal sacrifice. However, these changes were not considered to be biologically significant. The pathology results provided statistically significant dose-related evidence for a decrease in liver preneoplastic and neoplastic lesions as the dose level of DON increased. This negative trend probably results from the known positive correlation between body weight and the appearance of spontaneous hepatic neoplasms in this strain of mouse.

Comparison of high-performance liquid chromatography with radioimmunoassay for the determination of domoic acid in biological samples.

A reversed-phase liquid chromatographic method employing UV absorption detection at 242 nm was compared to a radioimmunoassay technique for the determination of the marine toxin, domoic acid, in several types of seafood and biological samples. Agreement between the two methods for spiked samples of mussels and rat serum was very good over a range of concentrations of 0.15-7.3 micrograms/g domoic acid. Also, a very good correlation was observed between the two methods for naturally incurred residues of domoic acid in razor clams, anchovies and crab meat over a concentration range of 0.6-43 micrograms/g domoic acid.

An incident of elevated levels of unsaturated free fatty acids in mussels from Nova Scotia and their toxic effect in mice after intraperitoneal injection.

Methanol extracts of the hepatopancreas of mussels (Mytilus edulis) harvested at two locations (Ship Harbour and Wine Harbour) in eastern Nova Scotia, Canada, were found to be toxic to mice after intraperitoneal injection. The commonly known toxins, such as those associated with diarrhetic shellfish poison (DSP), paralytic shellfish poison, and domoic acid, were not present in the extracts. However, they were found to contain elevated levels of free fatty acids. Using a modified DSP extraction procedure the quantities of free fatty acids determined (by latroscan TLC/FID) in the hepatopancreases of mussels were 2.9 mg/g (Ship Harbour 1), 2.2 mg/g (Ship Harbour 2), 1.2 mg/g (Wine Harbour), and 0.15 mg/g (Prince Edward Island, control). After further investigation it was determined that certain unsaturated fatty acids were mainly responsible for the toxicity. These included palmitoleic, linoleic, linolenic, octadecatetraenoic, and eicosapentenoic acids. Artificial mixtures of pure standards of these acids prepared in the same concentrations as found in the shellfish samples were also toxic to mice. These results indicate that elevated levels of free fatty acids in mussel hepatopancreas from locations in eastern Canada can lead to mouse deaths when using the DSP mouse bioassay procedure.

Toxicology and seafood toxins: domoic acid.

Marine and terrestrial food sources are susceptible to contamination by various industrial chemicals and microbial pathogens. Both types of hazard are amenable to regulatory assessment using a single toxicology data base, along with some knowledge of contaminant levels and consumption figures for food. On the other hand, regulatory problems persist with acutely toxic naturally occurring phycotoxins, which may accumulate unpredictably to toxic levels in seafood. However, a scarce supply of pure toxin often precludes the availability of acceptable toxicology studies describing their biological effects. An exception to this situation is domoic acid, a neurotoxin phycotoxin that produced numerous cases of severe human intoxication which demanded extensive toxicological study. This paper describes a series of ongoing studies initiated in the wake of the outbreak of domoic acid toxicity that occurred in 1987 in Eastern Canada.

Toxicological consequences of Aroclor 1254 ingestion by female rhesus (Macaca mulatta) monkeys. Part 1B. Prebreeding phase: clinical and analytical laboratory findings.

A group of 80 menstruating rhesus (Macaca mulatta) monkeys, with an average estimated age of 11.1 +/- 4.1 yr SD were first randomly allocated to four similar test rooms (20 monkeys/room), and then randomly allocated to one of five dose groups (four females/dose group/room). Each day, the monkeys self-ingested capsules containing doses of 0, 5, 20, 40 or 80 micrograms Aroclor 1254/kg body weight. After 25 months of daily dosing, approximately 90% of the treated females attained a qualitative pharmacokinetic steady state with respect to the concentration of polychlorinated biphenyl (PCB) in their adipose tissue. Subsequently, oestrogen and progesterone concentrations in serum were determined for one complete oestrous cycle and various immunological tests were conducted, while the monkeys continued to receive their daily dose of PCB. During the prebreeding phase of the study, blood for clinical and analytical monitoring including haematology, serum biochemistry, serum hydrocortisone, serum proteins (alpha 1, alpha 2, beta and gamma-globulins), serum immunoglobulins (A, G and M) and thyroid variables (thyroxine/triiodothyronine (T3) uptake ratio, percentage T3 uptake and free thyroxine index), were obtained monthly, as were specimens to ascertain the concentration of PCB in the blood, adipose tissue and faeces. Major findings among treated monkeys included the following: changes in haematology (decreased erythrocyte count, haematocrit, reticulocyte count, and mean platelet volume), serum biochemistry (decreased cholesterol and total bilirubin), immunotoxicity (decreased antibody production to sheep red blood cells and alterations in the percentage of T helper and T suppressor cells) and pathology (the number of regions of sebaceous gland lobules per unit of histological length was significantly reduced). These effects were observed at PCB doses lower than those previously reported for non-human primates.

Effect of polychlorinated biphenyls on several endocrine reproductive parameters in the female rhesus monkey.

Female rhesus monkeys (Macaca mulatta) ingested gelatin capsules containing daily doses of 0 (control), 5, 20, 40, or 80 micrograms of Aroclor 1254/kg/day (PCB) which was dissolved in corn oil plus glycerol. After approximately two years of dosing and when the monkeys were near an adipose tissue PCBs equilibrium, each dose group of 16 animals was randomly divided into two test groups. Daily blood samples from both groups were acquired for estrogen and progesterone analysis during one menstrual cycle. Test group 1 was sampled during February-March and test group 2 during August-September. Serum estrogen and progesterone concentrations in monkeys dosed with PCBs were equivalent to control values with the exception of the luteal phase progesterone levels in the 20 and 80 micrograms/kg/day dosed monkeys in test group 1. There was no difference in menstrual cycle length between control and treated monkeys for the month sampled, however, menses duration was marginally longer in the 80 micrograms/kg/day dose group. There were no apparent treatment related differences in the incidence of anovulatory cycles nor on the temporal relationship between the estrogen peak and menses onset, menses end or the progesterone peak.

Experimental oral toxicity of domoic acid in cynomolgus monkeys (Macaca fascicularis) and rats. Preliminary investigations.

A recent outbreak of marine food poisoning in humans was attributed to the consumption of blue mussels (Mytilus edulis L.) contaminated with domoic acid (DA) that was produced by the diatom Nitzschia pungens. The clinical and morphological effects of single oral doses of extracts of mussels contaminated with DA or of DA isolated from toxic mussels were investigated in small groups (one to six) of cynomolgus monkeys (Macaca fascicularis; 0.5-10 mg DA/kg body weight) and of Sprague-Dawley rats (60 to 80 mg DA/kg body weight). Control animals were either given saline or were not treated. To test whether monosodium glutamate, present in the food consumed by some affected humans, and dimethylsulphoxide, suspected of being present in the plankton, enhanced the response, monosodium glutamate (at 0.25% of mussel extract bolus) or dimethylsulphoxide (at 1 g per bolus) were co-administered to two (one each) of the DA-treated monkeys. DA-treated monkeys developed transient excitation characterized by vomiting. DA-treated rats showed withdrawal followed by hyperexcitation and death (in one case). Mild to moderate central nervous system lesions consistent with neuroexcitation were present in both monkeys and rats. The addition of monosodium glutamate and dimethylsulphoxide had no significant effect on the appearance and severity of central nervous system clinical signs and lesions. The wide variations in the response of test animals to orally administered DA were attributed to the protective effect of vomiting, and to suspected incomplete or slow gastro-intestinal absorption of the toxic agent. The results reinforce the view that DA is an emetic and that under appropriate conditions may also inflict excitotoxic central nervous system damage.

Acute neurotoxicity of domoic acid in the rat.

A recent outbreak of human food poisoning, characterized by severe gastrointestinal and neurologic abnormalities, with a fatal outcome in 3 patients, was attributed to the consumption of poisonous mussels containing domoic acid at an abnormally high concentration. The purpose of the present study was to determine if domoic acid, a glutamate analogue extracted from poisonous mussel, was neurotoxic to rats. Groups of female Sprague-Dawley rats were dosed once intraperitoneally with 0, 1, 2, 4, or 7.5 mg domoic acid/kg of body weight and observed for a maximum period of 24 hr. Clinically, control rats and rats in the 1 mg/kg group were unremarkable. Seventy-five percent of the animals in the 2 mg/kg group had equivocal transient behavioral signs. One that was given 2 mg/kg and all rats given in excess of 4 mg/kg of body weight developed unequivocal behavioral and neurologic signs culminating in partial seizures and status epilepticus. Histopathologically, severely affected rats developed selective encephalopathy characterized by neuronal degeneration and vacuolation of the neuropil in the limbic and the olfactory systems, and retinopathy characterized by neuronal hydropic degeneration of the inner nuclear layer and vacuolation of the external plexiform layer. The results of this study suggest that domoic acid is excitotoxic and causes a characteristic syndrome with clinical signs and histopathologic lesions similar to those reported for kainic acid.

Acute parenteral neurotoxicity of domoic acid in cynomolgus monkeys (M. fascicularis)

To study the CNS effects of domoic acid (D.A.), 6 adult Cynomolgus monkeys (M. fascicularis) were dosed intraperitoneally (4 mg/kg) or intravenously (0.025-0.5 mg/kg) with D.A. obtained from cultured mussels contaminated with this neurotoxin. Clinical signs of neurotoxicity were preceded by a short presymptomatic period (2-3 min) and an even shorter prodromal period (0.5-1 min). The symptomatic period proper was characterized by persistent chewing with frothing, varying degrees of gagging, and vomit. Monkeys in the higher dose regimen exhibited additional signs including abnormal head and body positions, rigidity of movements and loss of balance, and tremors. The duration of the symptomatic period was dose dependent. Excitotoxic lesions consisting of vacuolation of the neuropil, astrocytic swelling, and neuronal shrinkage and hyperchromasia were detected in the area postrema, the hypothalamus, the hippocampus, and the inner layers of the retina in monkeys given D.A. at 0.5 mg/kg intravenously and 4 mg/kg intraperitoneally. It was concluded that D.A., administered intravenously, is neuroexcitatory and a powerful emetic at doses of 0.025 to 0.2 mg/kg. At higher doses (0.5 mg/kg intravenously and 4 mg/kg intraperitoneally), D.A. is strongly excitotoxic.

Domoic acid poisoning and mussel-associated intoxication: preliminary investigations into the response of mice and rats to toxic mussel extract.

Consumption of cultivated blue mussels from Prince Edward Island was recently associated with episodes of gastro-intestinal and neurological distress. Extracts of the toxic mussels, tested in the mouse bioassay for paralytic shellfish poison, caused an atypical response characterized by scratching, convulsions and death. The present investigation shows that the domoic acid present in toxic mussels can produce in mice and rats signs identical to those induced by mussel extracts. These studies, preliminary in nature by virtue of the scarcity of domoic acid, gave ip no-effect levels in mice of 0.59 mg/kg body weight based on the behavioural response (scratching) and 2.4 mg/kg for death. These levels correspond to levels of 24 and 94 ppm in mussels. When administered orally doses of between 35 and 70 mg domoic acid/kg body weight were required to produce toxicity in mice and rats. This reduced toxicity is consistent with a lack of absorption from the gastro-intestinal tract: faecal excretion accounted for 102 +/- 17% and 98 +/- 12% (mean +/- SE) of the domoic acid administered to mice and rats, respectively. Since human intoxication occurred at an estimated 1-5 mg domoic acid/kg body weight, susceptible individuals appear to be more sensitive than rodents to the oral toxicity of domoic acid.

A 12-week study of BHA in the cynomolgus monkey.

Butylated hydroxyanisole (BHA) given by gavage to female cynomolgus monkeys on 5 days/wk for 84 days produced transient changes in selected serum chemistry and haematology parameters. Terminal observations revealed increased liver size, decreased hepatic monooxygenase activity and an increase in the mitotic index of the oesophageal epithelium. Several of these observations are similar to those reported for rodents also given BHA at or near the maximum tolerated dose. Gastroscopic evaluation of the stomach and oesophagus at monthly intervals and extensive gross and histopathological examination failed to reveal the proliferative effects seen in the forestomach of rats fed diets containing BHA.

Hydrolysis of leucine enkephalin in the nasal cavity of the rat--a possible factor in the low bioavailability of nasally administered peptides.

In order to investigate the utility of intranasal administration of peptides for systemic medication, the nasal absorption of the model peptide, leucine enkephalin (Tyr-Gly-Gly-Phe-Leu), was studied in the rat. At a concentration of 60 micrograms/ml in Ringer's buffer the pentapeptide was found to undergo, extensive hydrolysis in the nasal cavity. The hydrolysis rather than the polarity of the pentapeptide appears responsible for limiting the nasal absorption of this model compound. In the presence of dipeptides, the hydrolysis of leucine enkephalin was significantly inhibited. These results suggest that the nasal administration of peptides may become an important route for drug administration provided that the peptidases in the nasal mucosa can be transiently inhibited via coadministration of pharmacologically inactive peptidase substrates.