Ionic agents

The third method of obviating precipitation of an ionic agent-ionic dye complex is to choose what effectively amounts to a modified ionic agent. Ethoxylated anionic and ethoxylated cationic agents are particularly useful in this respect. The ethoxylation tends to... 

Studies on non-ionic surfactants as effective drag-reducing additives have been submitted by Zakin (1972). He studied various effects on three non-ionic surfactants formed from straight-chain alcohols and ethyleneoxide. These surfactants have an upper and a lower temperature limit for solubility in water and prove effective drag reducers near their upper critical solubility temperature or clouding point. The clouding point is the point at which a solution of a non-ionic agent in water becomes turbid as the temperature is raised. 

Other parameters such as their physico-chemical properties, pharmacodynamics and the clinical application are very similar to the ionic agents gadopentetate and gadoterate [19]. 

In one US study of cardiac angiography, the incidence of adverse events was 32% with diatrizoate and 10% with iohexol it should be noted however that the diatrizoate used in that study (Renografin 76 ) causes calcium binding, which may have increased the rate of cardiac complications (19). The non-ionic agent iodixanol 320, which is virtually iso-osmolar, has been tested in cardiac angiography against iohexol and seemed to be better tolerated (20). 

In another survey, the incidence of contrast media reactions after intravenous administration was evaluated over 14 years (25). The incidence of all reactions to contrast media was 6-8% with high-osmolar contrast media and only 0.2% with low-osmolar non-ionic agents. Most of the reactions (over 90%) were aUergic-like, and severe reactions were rare (0.05%). One death was reported after the use of a low-osmolar agent. These data are compatible with previous reports, which showed that low-osmolar contrast media have a much better safety profile than high-osmolar media and that there is no significant difference in the incidence of acute adverse reactions between non-ionic dimeric and monomeric contrast media. 

When non-ionic agents are used, opinion is divided about the value of premedication... 

There was an increased risk of seizures in patients with a previous history of seizures and in association with anti-neoplastic therapy (97). Patients with thrombotic thrombocytopenic purpura also appear to be at greater risk of seizures during contrast examination. Fatal status epilep-ticus can occur during CT (98). The non-ionic agent iopa-midol appears to be less likely to cause seizures (76). 

An experimental study has suggested that intravenous injection of contrast media can cause increased mortality associated with severe pancreatitis (SEDA-19, 425). There was little difference between ionic and non-ionic agents. The authors argue that contrast-enhanced CT should be avoided in patients with severe pancreatitis as it can exacerbate it. 

Tubular Reabsorption Drugs are reabsorbed into the blood stream from the nephron tubule. Diffusion Process. Small, nonionic drugs pass more readily. because ionic agents are poorly reabsorbed, drug metabolites which are more ionic than the parent drug will be passed into the urine more easily. Urinary pH can be purposely altered to increase the rate of drug excretion (e.g., administration of bicarbonate). 

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