The most frequently reported adverse reactions following intrathecal administration of iopamidol are headache, nausea, vomiting, and musculoskeletal pain. These reactions usually occur 1 to 10 hours after injection, almost all occurring within 24 hours. They are usually mild to moderate in degree, lasting for a few hours and usually disappearing within 24 hours. Rarely, headaches may be severe or persist for days. Headache is often accompanied by nausea and vomiting, and tends to be more frequent and persistent in patients not optimally hydrated. Backache, neck stiffness, numbness and paresthesias, leg or sciatic-type pain occurred less frequently, often in the form of a transient exacerbation of preexisting symptomatology. Transient alterations in vital signs may occur and their significance must be assessed on an individual basis. 

The following table of incidence of reactions is based on clinical studies with ISOVUE-M (lopamidol Injection) in about 686 patients.

Other adverse effects reported in clinical literature for iopamidol include facial neuralgia, tinnitus, and sweating.   
Major motor seizures have been reported in the clinical literature and since market introduction in th eUnited States. Early onset of seizures (less than two hours) is indicative of early substantial intrcranial entry. Transitory EEG changes occur and usually take the form of slow wave activity.  
While not observed in controlled clinical studies with ISOVUE-M (Iopamidol Injection), the following adverse reactions may occur because they have been reported with ISOVUE-M and other nonionic water soluble contrast agents: cardiovascular (arrhythmias); pulmonary (apnea); bacterial meningitis, and aseptic meningitis syndrome; allergy or idiosyncrasy (chills, pruritus, nasal congestion, Guillain_Barre syndrome); CNS irritation (psycho-organic syndrome : mild and transitory perceptual aberrations such as depersonalization, anxiety, deppression, hyperreflexia or areflexia, hypertonia or flaccidity, restlessness, tremor, echoacousia,echolalia, asterixis or dysphasia have occurred). Profound mental disturbances have rarely been reported (various forms and degrees of aphasia, mental confusion or disorientation); the onset is usually at 8 to 10 hours and lasts for about 24 hours without aftereffects. However, occasionally they have been manifest as apprehension, agitation or progressive withdrawal to the point of stupor or coma. In a few cases, these have been accompanied by transitory hearing loss or other auditory symptoms and visual disturbances (believed subjective or delusional). Persistent cortical loss of vision in association with convulsions, and ventricular block have been reported. Rarely, persistent though transitory weakness in the leg or ocular muscles has been reported. Peripheral neuropathies have been rare and transitory. They include sensory and/or motor or nerve root disturbances, myelitis, persistent leg muscle pain or weakness, or sixth nerve palsy, or cauda equina syndrome. Muscle cramps, fasciculation or myoclonia, spinal convulsion, paralysis, or spasticity are unusual.  
  
General Adverse Reactions To Contrast MediaReactions known to occur with parenteral administration of iodinated ionic contrast agents (see the listing below) are possible with any nonionic agent. Approximately 95 percent of adverse reactions accompanying the use of other water-soluble intrvascularly administered contrast agents are mild to moderate in degree. However, life-threatening reactions and fatalities, mostly of cardiovascular origin, have occurred. Reported incidences of death from the administration of other iodinated contrast media range from 6.6 per 1 million (0.00066 percent) to 1 in 10,000 patients (0.01 percent). Most deaths occur during injection or 5 to 10 minutes later, the main feature being cardiac arrest with cardiovascular disease as the main aggravating factor. Isolated reports of hypotensive collapse and shock are found in the literature. The incidence of shock is estimated to be 1 out of 20,000 (0.005 percent) patients.  
Adverse reactions to injectable contrast media fall into two categories: chemotoxic reactions and idiosyncratic reactions. Chemotoxic reactions result from the physicochemical properties of the contrast medium, the dose, and the speed of injection. All hemodynamic disturbances and injuries to organs or vessels perfused by the contrast medium are included in this category. During intrathecal use, there is a lower incidence of electroencephalographic changes as well as neurotoxicity by virtue of the intrinsic properties of the iopamidol molecule.  
Idiosyncratic reactions include all other reactions. They occur more frequently in patients 20 to 40 years old. Idiosyncratic reactions may or may not be dependent on the amount of drug injected, the speed of injection, the mode of injection, and the radiographic procedure. Idiosyncratic reactions are subdivided into minor, intermediate, and severe. The minor reactions are self-limited and of short duration; the severe reactions are life-threatening and treatment is urgent and mandatory.  
The reported incidence of adverse reactions to contrast media in patients with a history of allergy is twice that for the general population. Patients with a history of previous reactions to a contrast medium are three times more susceptible than other patients. However, sensitivity to contrast media does not appear to increase with repeated examinations. Most adverse reactions to intravascular contrast agents appear within one to three minutes after the start of injection, but delayed reactions may occur (see PRECAUTIONS-GENERAL).  
Because measurable plasma levels are attained following the intrathecal administration of lopamidol, adverse reactions reported with the use of intravascular contrast agents are theoretically possible. These include:  
Cardiovascular: vasodilation (feeling of warmth), cerebral hematomas, hemodynamic disturbances, sinus brady cardia, transient electrocardiographic abnormalities, ventricular fibrillation, pentechiae.  
Digestive: nausea, vomiting, severe unilateral or bilateral swelling of the parotid and submaxillary glands.  
Nervous: paresthesia, dizziness, convulsions, paralysis, coma.  
Respiratory: increased cough, asthma, dyspnea, laryngeal edema, pulmonary edema, bronchospasm, rhinitis.  
Skin and Appendages: injection site pain usually due to extravasation and/or erythematous swelling, skin necrosis, urticaria.  
Urogenital: osmotic nephrosis of proximal tubular cells, renal failure, pain.  
Special Senses: perversion of taste; bilateral ocular irritation; lacrimation; itching; conjunctival chemosis, infection, and conjunctivitis.  
The following reactions may also occur: neutropenia, thrombophlebitis, flushing, pallor, weakness, severe retching and chocking, wheezing, cramps, tremors, and sneezing.