Neurotolerability of nonionic X-ray contrast media. The role of chemotoxicity

Seizures: An Unusual Complication of Intrapleural Povidone–Iodine Irrigation

Objective:

To report a case of seizures that probably developed because of the disinfectant and antiseptic agent povidone iodine (PVI).

Case Summary:

A 67-year-old healthy white man developed pleural empyema that was treated with drainage and intrapleural PVI irrigation. Within 10 minutes, complex partial seizures with secondary generalization lasting several minutes were documented. Several hours later, the patient developed a similar episode. Both events resolved spontaneously and, in 10 months of follow-up, there was no recurrence.

Discussion:

The adverse effects of iodine are known; however, little has been reported about seizures following the administration of PVI. This complication is thought to be due to either the osmotic and hydrophilic qualities or the presence of ionic changes and lipid solubility of PVI.

Conclusions:

Intracavitary PVI should be considered in the differential diagnosis of localized and generalized seizures.

Is contrast medium osmolality a causal factor for contrast-induced nephropathy?

The exact pathophysiology of contrast-induced nephropathy (CIN) is not fully clarified, yet the osmotic characteristics of contrast media (CM) have been a significant focus in many investigations of CIN. Osmotic effects of CM specific to the kidney include transient decreases in blood flow, filtration fraction, and glomerular filtration rate. Potentially significant secondary effects include an osmotically induced diuresis with a concomitant dehydrating effect. Clinical experiences that have compared the occurrence of CIN between the various classes of CM based on osmolality have suggested a much less than anticipated advantage, if any, with a lower osmolality. Recent animal experiments actually suggest that induction of a mild osmotic diuresis in association with iso-osmolar agents tends to offset potentially deleterious renal effects of high viscosity-mediated intratubular CM stagnation.

Malignant Cerebral Edema following CT Myelogram Using Isovue-M 300 Intrathecal Nonionic Water-Soluble Contrast: A Case Report

Lumbar myelogram utilizing nonionic contrast is a commonly performed procedure to identify spinal pathology. Complication rates are low. Cerebral edema has been shown to occur following intrathecal injection of ionic contrast; however, no current literature has documented this complication relating to the ubiquitously used nonionic contrast medium. We report a case of a patient who developed malignant cerebral edema following a lumbar myelogram with Isovue-M 300 nonionic water-soluble intrathecal contrast. We believe this is the first reported case of cerebral edema resulting from the use of a nonionic contrast.

Conjugates of Gadolinium Complexes to Bile Acids as Hepatocyte-Directed Contrast Agents for Magnetic Resonance Imaging

A series of structurally different Gd(III) conjugates incorporating a bile acid moiety have been prepared. Polyaminopolycarboxylic ligands such as diethylenetriaminepentaacetic acid (DTPA) and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetracetic acid (DOTA) have been selected as chelating subunit for the Gd(III) ion. Cholic acid, cholylglycine, and cholyltaurine have been incorporated as the bile acid moieties. In first generation conjugates the Gd(III) complex is linked to the carboxyl group of cholic acid. Second generation conjugates feature the attachment of the Gd(III) complex to the 3 position of the steroidic backbone of the bile acid. Finally, in third generation conjugates the Gd(III) complex is attached to the epsilon nitrogen atom of cholyllysine. The conjugates are eliminated through the biliary route to a various extent (7.5 to 77% in rats) according to their structural features. Among the most promising terms, a second generation conjugate in which the Gd(III) complex is linked to cholic acid through the 3alpha hydroxy group seems to enter hepatocytes using the Na(+)/taurocholate transporter. Noticeably, some of the second generation conjugates are characterized by very high tolerabilities (LD(50) up to 9.5 mmol/kg) after intravenous administration in mice.

Contrast enhancement and contrast extravasation on computed tomography after intra-arterial thrombolysis in patients with acute ischemic stroke

BACKGROUND AND PURPOSE

The goal of this study was to determine the CT findings and clinical consequences of contrast enhancement and contrast extravasation on CT scans obtained after intra-arterial thrombolytic therapy for treatment of acute ischemic stroke.

METHODS

Sixty-two patients were treated with intra-arterial thrombolysis. All patients underwent nonenhanced CT scans immediately and 24 hours after thrombolytic therapy. Contrast enhancement was defined as a hyperdense lesion that disappeared on a 24-hour follow-up CT scan. Contrast extravasation was defined as a hyperdense lesion with maximum Hounsfield unit >90 that persisted on a follow-up CT scan. We evaluated the differences in the clinical and radiological data between 3 groups: contrast enhancement, contrast extravasation, and control groups.

RESULTS

Contrast enhancement was found in 14 of 62 patients (22.6%); contrast extravasation was seen in 7 (11.3%). Compared with the control group, the contrast enhancement group had a lower recanalization grade (64.3% versus 34.1%, P=0.048) and a lower incidence of hemorrhagic transformation (14.3% versus 43.9%, P=0.047). The contrast extravasation group had a higher incidence of both hemorrhage (100% versus 43.9%, P=0.006) and symptomatic hemorrhage (100% versus 14.6%, P<0.001) than the control group. Poor outcomes were more frequent in the contrast extravasation group (100% versus 38.9%, P=0.003) than the control group.

CONCLUSIONS

Contrast enhancement on CT scans obtained after intra-arterial thrombolysis is usually not associated with hemorrhagic complications. However, contrast extravasation is highly associated with parenchymatous hematoma and should be considered a negative prognostic sign.

Effect of iomeprol on rat hippocampal slice synaptic transmission: comparison with other X-ray contrast agents

RATIONALE AND OBJECTIVES

All contrast agents should be neurologically safe because although some are not indicated for procedures, such as myelography, just the same they may come in contact with nervous tissue during contrast-enhanced imaging. This is because even when they are intravascularly injected, the presence of undiagnosed blood-brain barrier damage may allow them to penetrate the brain barrier. In the present study, we investigated the neurologic safety of iomeprol by studying in vitro its potential effects on the central nervous system (CNS) synaptic transmission. Other widely used x-ray contrast agents were also assessed for comparative purposes.

METHODS

CNS synaptic transmission was evaluated in terms of evoked field potentials recorded from the pyramidal region of rat hippocampal slices. The field potentials were evoked by electrical stimulation of the Schaffer collateral pathway. The effects of the contrast agents were evaluated in terms of number and amplitude of population spikes (PS) and as the maximal slope of the excitatory postsynaptic potentials (EPSP). The contrast agents were tested at final concentrations of 3, 10, and 30 mg(iodine)/mL in iso-osmolal condition with respect to artificial cerebrospinal fluid (CSF).

RESULTS

Iomeprol, like ioversol, principally exerted a mild inhibitory effect on CNS synaptic transmission, an effect that was preceded by a weak, transient excitation. Iopentol exerted a rapid and complete inhibition of synaptic transmission without showing any excitatory effects. Iobitridol, though belonging to the nonionic monomeric class, exerted, surprisingly, an epileptogenic action at the highest concentration, whereas its inhibitory action was slow and mild. Diatrizoate, as expected, exerted an epileptogenic activity even at the lowest concentration, followed by a marked inhibitory action. Ioxaglate, as expected because it is an ionic though dimeric contrast agent, exerted an epileptogenic action at the intermediate concentration, whereas it barely demonstrated an inhibitory effect at all. All the contrast agent effects observed in the study reversed or tended to reverse during washout.

CONCLUSIONS

Even taking in account the limitation because of the use of an in vitro approach and high contrast agent concentrations, we can conclude that the positive neuro-tolerability of iomeprol is further confirmed by this model as it proved to be devoid of epileptogenic activity and, among the contrast agents exhibiting inhibitory action, it was the contrast agent with the least amount of activity. In addition, contrary to that generally reported in the literature, nonionic, low osmolal contrast agents are not all identical in their neuro-tolerability when assessed in the rat hippocampal slice model.

Comparative study between gadobenate dimeglumine and gadobutrol in rats with brain ischemia: evaluation of somatosensory evoked potentials

RATIONALE AND OBJECTIVES

The present study had two main objectives: to validate a rat model of brain ischemia in terms of somatosensory evoked potentials (SEPs) and to compare, using the validated model, the potential activity on the somatosensory function of the new, approved contrast agent gadobenate dimeglumine with that of gadobutrol, a specific contrast agent, for magnetic resonance imaging of the brain.

METHODS

Rats were prepared for SEP recording at least 5 days before ischemia induction. Ischemia was induced by 30-minute right middle cerebral artery occlusion and 3-day reperfusion. The SEP responses, evoked contralaterally to the stimulated upper limb, were recorded from the primary somatosensory cortical area. Model validation, on day 3 after occlusion, was performed using iopromide, an iodinated contrast agent poorly neurotolerated in rats, intravenously injected at 7 g I/kg. The comparative study between gadobenate dimeglumine and gadobutrol was performed at an intravenously injected dose of 2 mmol/kg. Somatosensory evoked potential responses were measured as peak latencies (P2 and N2) and peak-to-peak amplitude (P2N2). The brain concentration of iopromide was measured by high-performance liquid chromatography, whereas that of the gadolinium contrast agent was measured by inductively coupled plasma-atomic emission spectrometry analysis; given the absence of metabolism for both contrast agents, the gadolinium content values can be interpreted as representing unmetabolized contrast agent.

RESULTS

In the ischemic rats, the SEP responses of the lesioned hemisphere showed significant increases in P2, N2, and interpeak N2-P2 latencies and a significant reduction in peak-to-peak (P2N2) amplitude. In the validation experiments, iopromide dramatically increased the P2N2 amplitude of the SEP responses recorded from both hemispheres of ischemic rats without affecting the P2, N2, and interpeak N2-P2 latencies. The iopromide effect was coupled with high concentrations of the contrast agent in the brain. Iopromide had no effect on healthy rats. In the comparative study, gadobenate dimeglumine did not induce any alteration in SEP components of either the lesioned or unlesioned hemisphere of ischemic rats. In fact, no significant difference was found between responses obtained before and after gadobenate dimeglumine injection. Gadobutrol, administered at the same dose, on the whole showed the same behavior as gadobenate dimeglumine, although a slight but significant decrease in the P2 latency, a sign of excitatory activity, was observed 2 hours after injection. Analytic data indicated higher levels of contrast agent in the lesioned hemisphere versus the unlesioned hemisphere 2 hours after injection.

CONCLUSIONS

Based on these results, three conclusions can be drawn: (1) the evaluation of SEPs in ischemic rats is a useful tool for assessing the potential neurological effects of a new contrast agent because ischemic and contrast agent effects can be clearly differentiated; (2) the experimental conditions used allow the contrast agents to penetrate into the brain, where their activity can be manifested and evaluated; and (3) the complete absence of neurological activity of gadobenate dimeglumine shows its safety profile and confirms its suitability for use in neurological diseases for which contrast-enhanced magnetic resonance imaging is indicated.

Neurotolerability of contrast agents in rats with brain ischemia induced by transient middle cerebral artery occlusion: EEG evaluation

RATIONALE AND OBJECTIVES

Because contrast agent (CA) formulations are injected intravenously to patients who may have a disrupted blood-brain barrier, their neurotolerability should be tested by using appropriate animal models. In the present study, a model of rat brain ischemia evaluated in terms of the electroencephalogram (EEG) was validated and then used to compare the neurotolerability of gadobenate dimeglumine to that of gadodiamide, a well-documented CA for brain MRI.

METHODS

Rats were prepared for EEG recording about 15 days before ischemia induction. Ischemia was induced in the right hemisphere by 2-hour middle cerebral artery (MCA) occlusion and 3-day reperfusion. Model validation in terms of EEG, on day 3 after MCA occlusion, was performed by using iopromide, a poorly neurotolerated iodinated CA in rats, intravenously injected at 7 g iodine/kg. The EEG recording was analyzed for pathological tracings and for changes in spectral content in terms of the frequency index (FI) at 1, 2, and 3 hours after test compound injection. The comparative study between gadobenate dimeglumine and gadodiamide was performed at 2.0 mmol/kg. D-Mannitol was used as a control compound. The presence of CA in the rat brain was verified by measuring the total gadolinium content by using inductively coupled plasma-atomic emission spectrometry analysis. Given the absence of metabolism for both CAs, the values of gadolinium content can be interpreted as representing unmetabolized CA.

RESULTS

On days 1, 2, and 3 after transient MCA occlusion, the lesioned hemisphere of rats presented a decreased FI value with respect to the basal value. The unlesioned hemisphere, after a slight, nonsignificant decrease in the FI value on the first 2 days, presented a normal FI value on day 3. Thus, ischemic rats on day 3 after transient MCA occlusion were chosen for these neurotolerability studies. Iopromide injected intravenously into ischemic rats at a dose 10 times higher than the maximum clinical dose caused bilateral spikes on the EEG and increases in FI values for the unlesioned hemisphere without affecting the lesioned hemisphere. Gadobenate dimeglumine, like gadodiamide when injected into ischemic rats, did not cause spikes or further changes in the FI value of the lesioned hemisphere and did not modify the normal FI value of the unlesioned hemisphere. Furthermore, no significant differences between gadobenate dimeglumine, gadodiamide, and D-mannitol were found when postinjection FI values were compared. Finally, higher levels of gadolinium were found in the lesioned hemisphere with respect to the unlesioned hemisphere after both gadobenate dimeglumine and gadodiamide administration.

CONCLUSIONS

We can therefore conclude that (1) on the EEG, ischemia induced by transient MCA occlusion is an appropriate model for evaluating CA neurotolerability because ischemic and CA effects can be clearly differentiated; (2) the higher level of CA in the lesioned hemisphere compared with the unlesioned one (two to three times), even 3 hours after injection, demonstrates that the CA effectively penetrated the brain; if it were neurotoxic, any negative effects would have been detected; and (3) gadobenate dimeglumine, like gadodiamide, injected intravenously at a dose 20 times higher than the intended clinical dose for brain MRI is well tolerated and, also like gadodiamide, is suitable for use in neurological diseases for which contrast-enhanced MRI is indicated.