Iohexol

Intravascular Use

For most of the haemodynamic, clinical-chemical and coagulation parameters examined following intravenous injection of iohexol in healthy volunteers, no significant deviation from preinjection values has been found. The few changes observed in the laboratory parameters were minor and considered to be of no clinical importance.

A study was performed in 129 patients with diabetes and impaired renal function (serum creatinine levels from 115-308 μmol per litre) to compare a low osmolar (LOCM) and an isosmolar contrast medium (IOCM). Iohexol, as a representative of LOCM was compared to an IOCM in this high-risk population. The results showed 26% of the patients experiencing a rise in serum creatinine of >44.2 μmol per litre and 15% of patients with a rise of >88.4 μmol per litre, which is in line with expected incidence of CIN.

Iohexol provides opacification of blood vessels and permits radiographic visualisation until sufficient haemodilution occurs or sufficient contrast medium has left the site of injection.

Being a non-ionic compound, iohexol yields solutions of lower osmolality than the conventional ionic contrast media. Intravenous or intra-arterial injection of iohexol causes less pain and sensation of heat than conventional ionic media with similar iodine content. Iohexol solutions cause less cardiac and vascular disturbances on intravascular injection. The transit time of iohexol through the coronary vascular system is slightly increased compared with conventional ionic contrast media, probably due to the increased viscosity of iohexol at comparable iodine concentrations.

The period of maximal opacification of the renal vessels may begin as early as 30 seconds after i.v. injection. Urograms become apparent in about 1 to 3 minutes with optimal contrast occurring between 5 to 15 minutes. In nephropathic conditions, particularly when excretory capacity has been altered, the rate of excretion may vary unpredictably, and opacification may be delayed after injection. Severe renal impairment may result in a lack of diagnostic opacification of the collecting system.

Intrathecal Use

The initial concentration and volume of the medium, in conjunction with appropriate patient manipulation and the volume of CSF into which the medium is placed, will determine the extent of diagnostic contrast that can be achieved.

Following subarachnoid injection, iohexol will continue to provide good diagnostic contrast by conventional radiography for at least 30 minutes. Slow diffusion of iohexol takes place throughout the CSF as well as transfer into the circulation. At approximately 1 hour, contrast of diagnostic quality will not usually be available for conventional myelography. However, sufficient contrast for CT myelography will be available for several hours. If CT myelography is to follow, it should be deferred for several hours to allow the degree of contrast to decrease.

Following lumbar subarachnoid placement, irrespective of the position in which the patient is later maintained, slow upward diffusion of iohexol takes place throughout the CSF. CSF contrast enhancement for CT scanning may be expected in the thoracic region in about 1 hour, in the cervical region in about 2 hours and in the basal cisterns in 3 to 4 hours after administration into the lumbar subarachnoid space.

Intravascular Use

87-99 per cent of the intravenously injected iohexol is excreted unchanged through the kidneys within 24 hours in patients with normal renal function. The maximum urinary concentration of iohexol appears within approximately 1 hour after injection. The elimination half-life is approximately 2 hours in patients with normal renal function. No metabolites have been detected. The protein binding of iohexol is so low (less than 2%), that it has no clinical relevance and can therefore be neglected.

Intrathecal Use

Following injection into the lumbar subarachnoid space, iohexol is absorbed from CSF into the bloodstream and is eliminated by renal excretion.

After lumbar administration of 10-15 ml iohexol at a concentration of 180 mg I/ml to 6 patients, a mean maximum concentration of 0.024 mg I/ml was observed after a mean of 2.2 hours. The mean half-life of the initial rapid distribution phase from blood was 34 minutes and for the slower elimination phase was 3.4 hours.

Oral/Body Cavity Use

For most body cavities, the injected Iohexol is absorbed into the surrounding tissue and eliminated by the kidneys and bowel as described previously. Examinations of the uterus (hysterosalpingography) involve the most immediate drainage of contrast medium from the cavity upon conclusion of the radiographic procedure. Iohexol is well tolerated and readily absorbed if leakage into the peritoneal cavity occurs.

Visualisation of the joint spaces, uterus, fallopian tubes, peritoneal herniations, pancreatic and bile ducts can be accomplished by direct injection of contrast medium into the region to be studied. The use of appropriate iohexol concentrations assures diagnostic density.

Orally administered iohexol produces good visualisation of the gastrointestinal tract. Iohexol is particularly useful when barium sulphate is contraindicated as in patients with suspected bowel perforation or those where aspiration of contrast medium is a possibility.

Iohexol has a very low acute intravenous toxicity in mice and rats. Animal studies have shown that iohexol has a very low protein binding and is well tolerated by the kidneys. The cardiovascular and neurotoxicity are low. The histamine release ability and the anticoagulant activity have been shown to be less than for ionic contrast media.