Toxicity antagonistic effect

Another agent of this general type is nalmefene (47) Despite their useful characteristics, opiates display tolerance, addiction, abuse, and some toxic side effects Antagonists combat some of these effects, most notably respiratory depression and addiction Nalmefene reputedly has significant oral activity as a narcotic antagonist The synthesis of nalmefine concludes by Wittig olefination of naltrexone (46) to nalmefene (47) This molecular transformation resulted in a significant increase in oral potency as well (141... 

Abstract The characterization of toxicological impact of chemicals and mixtures from environmental matrices is a critical point in the assessment of adverse effects induced in human and ecological targets. In fact, the toxicity of most of the environmental mixtures is still under investigation due to the possibility of synergic or antagonistic effects of the components. Moreover, in some cases, the toxicity of identified chemicals is not already well known and it could be an additional matter of concern. 

Several papers discuss the effects of oxygen alone or with other compounds on cyanide toxicity. Oxygen alone results in minimal antagonism in mice injected with potassium cyanide and only slightly enhances the antagonistic effects of sodium nitrite (Sheehy and Way 1968). The antidotal effect of sodium thiosulfate alone or in combination with sodium nitrite, was enhanced by oxygen. 

Any treatment process that can remove the toxicity-causing constituents can reduce whole-effluent toxicity of a discharge. If the primary cause of effluent toxicity can be identified through the TIE or TRE procedures, specific treatment processes can be incorporated into the existing treatment system to control the toxicity. However, for a complex wastewater such as that from refinery and petrochemical facilities, the cause of toxicity may not be easily identified. The toxicity can be caused by a combination of constituents that exhibit synergistic or antagonistic effects. 

This lack of complete effectiveness led to the hypothesis that a second type of histamine receptor existed. In 1972, Black et al. (55) discovered a new series of antagonists which they called H2 receptor blockers. Burimamide was the first highly effective H2 blocker, but it was poorly absorbed orally. The modified compound, metiamide, had better absorption but was found to cause granulocytopenia (57.58). Finally, cimetidine was tested and found to be a potent and relatively non-toxic antagonist (59). Cimetidine is now widely used clinically to treat duodenal ulcers, Zollinger-Ellison Syndrome and other gastric hypersecretory diseases (32). 

Lithium intoxication can be precipitated by the use of diuretics, particularly thiazides and metola-zone, and ACE inhibitors. NSAIDs can also precipitate lithium toxicity, mainly due to NSAID inhibition of prostaglandin-dependent renal excretion mechanisms. NSAIDs also impair renal function and cause sodium and water retention, effects which can predispose to interactions. Many case reports describe the antagonistic effects of NSAIDs on diuretics and antihypertensive drugs. The combination of triamterene and indomethacin appears particularly hazardous as it may result in acute renal failure. NSAIDs may also interfere with the beneficial effects of diuretics and ACE inhibitors in heart failure. It is not unusual to see patients whose heart failure has deteriorated in spite of increased doses of frusemide who are also concurrently taking an NSAID. 

The high resolution power provides for a good profile analysis of the sample with a clear pattern and minor peak overlap compared to packed column GC. Furthermore, in view of the possible toxic, synergestic or antagonistic effects of the individual PAH, it is important to quantify each compound separately. The chromatograms also demonstrate the application of 0V-73 to PAH analysis, a stationary phase similar to SE-52, but with improved temperature stability. 

Naltrexone Nonselective competitive antagonist of opioid receptors Reduced risk of relapse in individuals with alcoholism Available as an oral or long-action parenteral formulation Toxicity Gastrointestinal effects and liver toxicity will precipitate a withdrawal reaction in individuals physically dependent on opioids and will prevent the analgesic effect of opioids... 

The initial species present, their relative concentrations, the induction of their enzymes, and their ability to acclimate once exposed to a chemical are likely to vary considerably, depending upon such environmental parameters as temperature, salinity, pH, oxygen concentration (aerobic or anaerobic), redox potential, concentration and nature of various substrates and nutrients, concentration of heavy metals (toxicity), and effects (synergistic and antagonistic) of associated microflora (Howard and Banerjee, 1984). Many of the parameters affect the biodegradation of chemicals in the environment as well as in biodegradation test systems used to simulate the environment. 

An antagonistic effect occurs when the toxic effect of the combination of chemical substances is less than what would be predicted from the individual toxicities. The antagonistic effect or antagonism is like adding 1 + 1 and getting 1 as the result. 

Methotrexate is a valuable drug in the treatment of many rapidly growing tumors, such as those in acute leukemia and choriocarcinoma, a cancer derived from placental cells. However, methotrexate kills rapidly replicating cells whether they are malignant or not. Stem cells in bone marrow, epithelial cells of the intestinal tract, and hair follicles are vulnerable to the action of this folate antagonist, accounting for its toxic side effects, which include weakening of the immune system, nausea, and hair loss. 

The most significant finding of this phase of the study was that very low concentrations of the cations studied could produce both synergistic and antagonistic effects. Thus it is clear why previously reported results on cation toxicity in this field have differed qualitatively from those obtained by biologists. Undoubtedly, since strict control over the ionic constituents of media was not exercised, synergistic and antagonistic effects were overlooked. 

Zinc is known to compete with cadmium, lead, copper, iron, and calcium for similar binding sites (109). In the future, a potential use of zinc may be to alleviate toxic effects of cadmium and lead in human subjects. Use of zinc as an antisickling agent is an example of its antagonistic effect on calcium, which is known to produce irreversible sickle cells by its action on red-cell membrane. 

Tertiary mixtures of NO2, CO2, and HCN. Earlier work indicated that the presence of 5% CO2 with either HCN or NO2 produced a more toxic environment than would occur with either gas alone. The antagonistic effects of NO2 on HCN indicate that the presence of one LC50 concentration of NO2 ( 200 ppm) will protect the animals from the toxic effects of HCN during the 30 min exposures, but not from the postexposure effects of the combined HCN... 

Frequently, diazepam overdoses are adequately managed with clinical observation and supportive care. However, coingestion of ethanol and other CNS depressants which may exacerbate toxicity are common and warrant investigation in the patient history. Flumazenil, a benzodiazepine antagonist, effectively reverses symptoms of CNS toxicity, but is hazardous with the coingestion of other substances such as antidepressants. Therefore, it should not be used routinely. 

The PAHs, like many other groups of envirotoxicants, constitute an immense number of different substances, each one expressing its own toxicity (Bispo et al., 1999). However, certain PAHs express planar structures and affinity for the Ah-receptor and thus interact with certain PCDDs and planar PCBs, adding toxicity equivalents (TEQs) to the overall impact on the receptor. Also, for different PAHs, additive effects towards the Ah-receptor have been documented, as have competition and antagonistic effects from naphthalene in combination with benzo[a]pyr-ene (White, 2002). Exposure to PAHs gives rise to a panorama of different toxic... 

The presence of organic acids can lead to intracellular production of H202 and is toxic for a bacteria cell. Resistance to H202 can be induced by ethanol and could explain antagonistic effects that may result when using ethanol in combination with organic acids (Barker and Park, 2001). 

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