IODOHIPPURATE SODIUM I 131
Clinical safety rating: caution
Comprehensive clinical and safety monograph for IODOHIPPURATE SODIUM I 131 (IODOHIPPURATE SODIUM I 131).
Iodohippurate sodium I 131 is a radioactive diagnostic agent that is actively transported by the renal tubules, allowing imaging of renal morphology and function. The iodine-131 emits gamma radiation, enabling scintigraphic evaluation of renal blood flow, tubular secretion, and excretion.
| Metabolism | Iodohippurate sodium I 131 is primarily excreted unchanged by the kidneys via active tubular secretion. Minimal hepatic metabolism occurs; the hippurate moiety may undergo partial hydrolysis, but the iodine-131 remains largely bound. |
| Excretion | Primarily renal; >90% of administered dose excreted unchanged in urine within 24 hours via glomerular filtration and tubular secretion. Fecal excretion <2%. |
| Half-life | Terminal elimination half-life is approximately 60 minutes in patients with normal renal function. In renal impairment, half-life may be prolonged up to several hours, correlating with reduced clearance. |
| Protein binding | Approximately 20-30% bound to serum albumin. |
| Volume of Distribution | 0.2-0.3 L/kg, indicating distribution primarily within extracellular fluid and minimal tissue penetration. |
| Bioavailability | Intravenous: 100%. Oral: <5% (not used clinically). |
| Onset of Action | Intravenous: Immediate onset of renal imaging; peak renal activity within 3-5 minutes after injection. |
| Duration of Action | Duration of diagnostic effect (imaging) is approximately 30-60 minutes post-injection, limited by renal excretion and radioactive decay (physical half-life of I-131 is 8.02 days). |
Adult: 5-30 microcuries (0.185-1.11 MBq) intravenously for renal function studies.
| Dosage form | INJECTABLE |
| Renal impairment | No specific dose adjustment recommended; glomerular filtration rate (GFR) does not significantly alter tracer kinetics at diagnostic doses. |
| Liver impairment | No specific dose adjustment based on Child-Pugh score; hepatic impairment does not significantly affect elimination of this radiopharmaceutical. |
| Pediatric use | Weight-based: 0.2-0.4 microcuries/kg (0.0074-0.0148 MBq/kg) intravenously; minimum dose 5 microcuries (0.185 MBq). |
| Geriatric use | No specific dose adjustment; same dosing as younger adults; consider age-related decline in renal function but diagnostic doses are safe. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for IODOHIPPURATE SODIUM I 131 (IODOHIPPURATE SODIUM I 131).
| Breastfeeding | Iodohippurate sodium I 131 is excreted into breast milk and can accumulate in the infant's thyroid, posing a risk of thyroid ablation and carcinogenesis. Breastfeeding should be discontinued and milk discarded for a period determined by radiation safety guidelines (typically at least 4-6 weeks based on the administered activity). M/P ratio is not applicable due to the radioactive nature; however, significant transfer occurs. |
| Teratogenic Risk | Iodohippurate sodium I 131 is contraindicated in pregnancy due to the risk of fetal thyroid ablation and carcinogenesis. Radioactive iodine crosses the placenta and concentrates in fetal thyroid after 10-12 weeks gestation, causing permanent hypothyroidism. First trimester exposure may cause spontaneous abortion. Second and third trimester exposure risks fetal thyroid destruction and subsequent cretinism. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to any component of the formulation","Severe renal impairment (e.g., end-stage renal disease) where renal imaging is not clinically useful.","Pregnancy (relative, depending on risk-benefit assessment)"]
| Precautions | ["Radiopharmaceutical: use only by authorized personnel with appropriate radiation safety precautions.","Pregnancy: consider risk of fetal radiation exposure; use only if necessary.","Lactation: advise temporary cessation of breastfeeding to reduce infant radiation exposure.","Renal impairment: may alter biodistribution and radiation dosimetry; adjust administered activity accordingly."] |
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| Fetal Monitoring | Maternal monitoring: Thyroid function tests (TSH, free T4) before and after administration; monitoring for signs of radiation exposure. Fetal monitoring: If inadvertent exposure occurs, fetal thyroid ultrasound and neonatal TSH screening should be performed. Radiation dose to the fetus should be estimated by a medical physicist. |
| Fertility Effects | No direct evidence of impaired fertility from diagnostic doses of iodohippurate I 131. However, high-dose radioiodine therapy (e.g., for thyroid cancer) can cause transient or permanent gonadal failure, especially in males. Sperm counts and ovarian function may be affected at high cumulative doses. Fertility effects are generally negligible with typical diagnostic doses (e.g., <10 mCi). |