Potassium Iodide - Adverse Reactions

Adverse Reactions

There is reason for caution with prescribing the ingestion of high doses of potassium iodide and iodate, as their unnecessary use can cause conditions such as the Jod-Basedow phenomena, and the Wolff-Chaikoff effect, trigger and/or worsen hyperthyroidism and hypothyroidism, and ultimately cause temporary or even permanent thyroid conditions. It can also cause sialadenitis (an inflammation of the salivary gland), gastrointestinal disturbances, allergic reactions and rashes. Potassium iodide is also not recommended for those who have had an allergic reaction to iodine, and people with dermatitis herpetiformis and hypocomplementemic vasculitis, conditions that are linked to a risk of iodine sensitivity.

There have been some reports of potassium iodide treatment causing swelling of the parotid gland (one of the three glands which secrete saliva), due to its stimulatory effects on saliva production.

A saturated solution of KI (SSKI) is typically given orally in adult doses of about 250 mg iodide several times a day (5 drops of SSKI assumed to be ⅓ ml) for thyroid blockade (to prevent the thyroid from excreting thyroid hormone) and occasionally this dose is also used, when iodide is used as an expectorant (the total dose is about one gram KI per day for an adult). The anti-radioiodine doses used for I-131 uptake blockade are lower, and range downward from 100 mg a day for an adult, to less than this for children (see table). All of these doses should be compared with the far lower dose of iodine needed in normal nutrition, which is only 150 μg per day (150 micrograms, not milligrams).

At maximal doses, and sometimes at much lower doses, side effects of iodide used for medical reasons, in doses of 1000 times the normal nutrional need, may include: acne, loss of appetite, or upset stomach (especially during the first several days, as the body adjusts to the medication). More severe side effects which require notification of a physician are: fever, weakness, unusual tiredness, swelling in the neck or throat, mouth sores, skin rash, nausea, vomiting, stomach pains, irregular heartbeat, numbness or tingling of the hands or feet, or a metallic taste in the mouth.

The administration of known goitrogen substances can also be used as a prophylaxis in reducing the bio-uptake of iodine, (whether it be the nutritional non-radioactive iodine-127 or radioactive iodine, radioiodine - most commonly iodine-131, as the body cannot discern between different iodine isotopes). perchlorate ions, a common water contaminant in the USA due to the aerospace industry, has been shown to reduce iodine uptake and thus is classified as a goitrogen. Perchlorate ions are a competitive inhibitor of the process by which iodide, is actively deposited into thyroid follicular cells. Studies involving healthy adult volunteers determined that at levels above 0.007 milligrams per kilogram per day (mg/(kg·d)), perchlorate begins to temporarily inhibit the thyroid gland’s ability to absorb iodine from the bloodstream ("iodide uptake inhibition", thus perchlorate is a known goitrogen). The reduction of the iodide pool by perchlorate has dual effects – reduction of excess hormone synthesis and hyperthyroidism, on the one hand, and reduction of thyroid inhibitor synthesis and hypothyroidism on the other. Perchlorate remains very useful as a single dose application in tests measuring the discharge of radioiodide accumulated in the thyroid as a result of many different disruptions in the further metabolism of iodide in the thyroid gland.

Treatment of thyrotoxicosis (including Graves' disease) with 600-2,000 mg potassium perchlorate (430-1,400 mg perchlorate) daily for periods of several months or longer was once common practice, particularly in Europe, and perchlorate use at lower doses to treat thryoid problems continues to this day. Although 400 mg of potassium perchlorate divided into four or five daily doses was used initially and found effective, higher doses were introduced when 400 mg/day was discovered not to control thyrotoxicosis in all subjects.

Current regimens for treatment of thyrotoxicosis (including Graves' disease), when a patient is exposed to additional sources of Iodine, commonly include 500 mg potassium perchlorate twice per day for 18–40 days.

Prophylaxis with perchlorate containing water at concentrations of 17 ppm, which corresponds to 0.5 mg/kg-day personal intake, if one is 70 kg and consumes 2 litres of water per day, was found to reduce baseline radioiodine uptake by 67% This is equivalent to ingesting a total of just 35 mg of Perchlorate ions per day. In another related study were subjects drank just 1 litre of perchlorate containing water per day at a concentration of 10 ppm, i.e. daily 10 mg of Perchlorate ions were ingested, an average 38% reduction in the uptake of Iodine was observed.

However when the average perchlorate absorption in perchlorate plant workers subjected to the highest exposure has been estimated as approximately 0.5 mg/kg-day, as in the above paragraph, a 67% reduction of iodine uptake would be expected. Studies of chronically exposed workers though have thus far failed to detect any abnormalities of thyroid function, including the uptake of iodine. this may well be attributable to sufficient daily exposure or intake of healthy Iodine-127 among the workers and the short 8 hr Biological half life of Perchlorate in the body.

To completely block the uptake of Iodine-131 by the purposeful addition of perchlorate ions to a populaces water supply, aiming at dosages of 0.5 mg/kg-day, or a water concentration of 17 ppm, would therefore be grossly inadequate at truly reducing radioiodine uptake. Perchlorate ion concentrations in a regions water supply, would need to be much higher, at least 7.15 mg/kg of body weight per day or a water concentration of 250 ppm,assuming people drink 2 liters of water per day, to be truly beneficial to the population at preventing bioaccumulation when exposed to a radioiodine environment, independent of the availability of Iodate or Iodide drugs.

The continual distribution of perchlorate tablets or the addition of perchlorate to the water supply would need to continue for no less than 80–90 days, beginning immediately after the initial release of radioiodine was detected, after 80–90 days had passed released radioactive iodine-131 would have decayed to less than 0.1% of its initial quantity at which time the danger from biouptake of iodine-131 is essentially over.

In the event of a radioiodine release the ingestion of prophylaxis potassium iodide, if available, or even iodate, would rightly take precedence over perchlorate administration, and would be the first line of defense in protecting the population from a radioiodine release. However in the event of a radioiodine release too massive and widespread to be controlled by the limited stock of iodide & iodate prophylaxis drugs, then the addition of perchlorate ions to the water supply, or distribution of perchlorate tablets would serve as a cheap, efficacious, second line of defense against carcinogenic radioiodine bioaccumulation.

The ingestion of goitrogen drugs is, much like potassium iodide also not without its dangers, such as hypothyroidism. In all these cases however, despite the risks, the prophylaxis benefits of intervention with iodide, iodate or perchlorate outweigh the serious cancer risk from radioiodine bioaccumulation in regions were radioiodine has sufficiently contaminatated the environment.