CHOLOXIN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for CHOLOXIN (CHOLOXIN).
Choloxin (dextrothyroxine sodium) is a synthetic isomer of thyroxine that reduces serum cholesterol levels by increasing hepatic cholesterol catabolism and excretion, likely through enhanced LDL receptor activity and increased conversion of cholesterol to bile acids.
| Metabolism | Primarily hepatic; undergoes deiodination and conjugation to glucuronides and sulfates. Hepatic clearance involves CYP450 enzymes, with a half-life of approximately 12-24 hours. |
| Excretion | Primarily renal excretion of conjugated metabolites (70-80% of dose); biliary/fecal excretion accounts for 10-20%; less than 5% excreted unchanged. |
| Half-life | Terminal elimination half-life is approximately 1-2 hours in euthyroid patients; may be prolonged in hypothyroidism or hepatic impairment. |
| Protein binding | Highly bound (>99%) to thyroxine-binding globulin (TBG), transthyretin, and albumin. |
| Volume of Distribution | Apparent volume of distribution is 0.10-0.20 L/kg, reflecting extensive tissue binding and distribution. |
| Bioavailability | Oral bioavailability is 50-80%, reduced by food, bile acid sequestrants, and certain drugs. |
| Onset of Action | Oral: clinical effects begin within 24-48 hours; intravenous: onset within 6-12 hours. |
| Duration of Action | Duration of action is 2-3 weeks following discontinuation due to slow tissue redistribution and conversion to liothyronine. |
| Molecular Weight | 776.87 Da |
50-250 mcg/kg orally once daily, adjusted to maintain T4 within normal range.
| Dosage form | TABLET |
| Renal impairment | No dose adjustment required for renal impairment as drug is hepatically cleared. |
| Liver impairment | Child-Pugh A: no adjustment. Child-Pugh B: reduce dose by 25-50%. Child-Pugh C: reduce dose by 50-75% and monitor T4 closely. |
| Pediatric use | Neonates: 10-15 mcg/kg/day orally. Infants: 5-10 mcg/kg/day. Children: 2-5 mcg/kg/day. Adjust based on T4 levels. |
| Geriatric use | Start at 25 mcg/day orally, titrate slowly (every 4-6 weeks) due to increased sensitivity and risk of cardiac adverse effects. |
| 1st trimester | Contraindicated. Choloxin is a Category X drug with known teratogenic effects in animals; risk of fetal harm outweighs any potential benefit. |
| 2nd trimester | Contraindicated. Continued risk of fetal harm, including potential effects on fetal thyroid function and development. |
| 3rd trimester | Contraindicated. May cause fetal goiter and hypothyroidism; avoid use during pregnancy. |
Clinical note
Comprehensive clinical and safety monograph for CHOLOXIN (CHOLOXIN).
| Placental transfer | Dextrothyroxine crosses the placenta. Animal studies have demonstrated teratogenic effects; human data are limited but suggest placental transfer with potential for fetal thyroid suppression. |
| Breastfeeding | Choloxin (dextrothyroxine) is excreted in human milk. Due to potential for adverse effects on thyroid function in the nursing infant, use is not recommended. Monitor infant thyroid function if exposure occurs. |
■ FDA Black Box Warning
None specified in FDA labeling.
| Serious Effects |
Hypersensitivity to dextrothyroxine or any component of the formulationPregnancyLactationThyrotoxicosisAcute myocardial infarctionUncontrolled hypertensionUncorrected adrenal insufficiency
| Precautions | Cardiac toxicity: Increased risk of arrhythmias, angina, and myocardial infarction, especially in patients with pre-existing cardiovascular disease., Hyperthyroidism: Can induce thyrotoxicosis if dose is too high or in patients with iodine deficiency., Drug interactions: Enhances effect of oral anticoagulants (reduce warfarin dose); decreases effect of antidiabetic medications; alters response to digitalis., Use in pregnancy: Category X – contraindicated due to teratogenic effects. |
| Food/Dietary | High-fiber foods (e.g., bran, whole grains) may reduce absorption; take levothyroxine separately. Soy-containing products (e.g., tofu, soy milk) and grapefruit juice can alter absorption. Consume these at least 4 hours apart from dosing. Avoid taking with walnuts, cottonseed meal, or concentrated iron-rich foods. |
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| Lactation Rating | L5 - Contraindicated |
| Teratogenic Risk | CHOLOXIN (dextrothyroxine) is not recommended during pregnancy. In animal studies, high doses caused fetal resorptions and anomalies. First trimester exposure may increase risk of congenital defects; second and third trimester exposure may impair fetal thyroid function and development. Risk cannot be excluded. |
| Fetal Monitoring | Monitor maternal thyroid function (TSH, free T4) and cardiac status (heart rate, blood pressure, ECG). Monitor fetal growth and development via ultrasound and fetal heart rate monitoring. Assess newborn for thyroid dysfunction at birth. |
| Fertility Effects | May reduce fertility by altering thyroid hormone levels and metabolic state. Normalization of thyroid function with appropriate therapy may improve fertility. Dextrothyroxine use may interfere with ovulation and menstrual cycle regularity. |
| Clinical Pearls | CHOLOXIN (sodium levothyroxine) is a synthetic T4 thyroid hormone. Monitor TSH levels 6-8 weeks after dose changes; target TSH 0.5-2.5 mIU/L for most adults. Administer on empty stomach, 30-60 minutes before breakfast, with water. Avoid concurrent calcium, iron, or antacids within 4 hours. Dose adjustments needed in pregnancy, with T4 dose increase by 30-50% typically. Check for drug interactions with amiodarone, oral contraceptives, and tyrosine kinase inhibitors. |
| Patient Advice | Take levothyroxine on an empty stomach, at least 30-60 minutes before breakfast. · Take with a full glass of water, not with other beverages. · Do not take within 4 hours of calcium or iron supplements, antacids, or sucralfate. · Consistency is key: take the same brand and dose daily; do not switch brands without consulting your provider. · Report symptoms of hyperthyroidism (palpitations, anxiety, weight loss) or hypothyroidism (fatigue, cold intolerance, constipation) promptly. · Do not stop or change dose without talking to your doctor; lab monitoring is required. · If you miss a dose, take it as soon as remembered, but skip if near next dose; do not double. · Inform all healthcare providers you are taking this medication, especially before surgery or starting new meds. |