TENORETIC 50
Clinical safety rating: caution
Comprehensive clinical and safety monograph for TENORETIC 50 (TENORETIC 50).
Atenolol is a cardioselective beta-1 adrenergic receptor antagonist that reduces heart rate, myocardial contractility, and blood pressure. Chlorthalidone is a thiazide-like diuretic that inhibits sodium-chloride symporter in the distal convoluted tubule, increasing excretion of sodium and water, reducing plasma volume.
| Metabolism | Atenolol is primarily excreted unchanged by the kidneys, with minimal hepatic metabolism. Chlorthalidone is excreted unchanged in urine, with some metabolism in the liver via glucuronidation. |
| Excretion | Renal: atenolol 40-50% unchanged, chlorthalidone >95% unchanged; biliary/fecal minimal |
| Half-life | Atenolol: 6-7 hr (up to 20 hr in renal impairment); chlorthalidone: 40-60 hr (prolonged in renal impairment) |
| Protein binding | Atenolol: <5% bound to albumin; chlorthalidone: 75% bound to albumin and erythrocytes |
| Volume of Distribution | Atenolol: 0.7-1.2 L/kg (low, reflects hydrophilicity); chlorthalidone: 4.8 L/kg (extensive tissue distribution) |
| Bioavailability | Oral: atenolol ~50% (first-pass metabolism minimal); chlorthalidone ~65% |
| Onset of Action | Oral: 1-2 hr for atenolol, 2-3 hr for chlorthalidone diuretic effect |
| Duration of Action | Atenolol: 24 hr (once-daily dosing); chlorthalidone: 24-72 hr (effective for 24 hr with once-daily dosing) |
| Molecular Weight | Atenolol: 266.34 Da; Chlorthalidone: 338.77 Da. Combined product: not applicable. |
1 tablet (atenolol 50 mg / chlorthalidone 25 mg) orally once daily, may increase to 2 tablets once daily if needed.
| Dosage form | TABLET |
| Renal impairment | CrCl 35-50 mL/min: maximum atenolol 50 mg daily; CrCl 15-34 mL/min: maximum atenolol 25 mg daily; CrCl <15 mL/min: contraindicated. |
| Liver impairment | No specific adjustment for mild-to-moderate impairment. Severe impairment: use with caution, consider dose reduction. |
| Pediatric use | Not recommended for use in children; safety and efficacy not established. |
| Geriatric use | Start at lower dose (e.g., atenolol 25 mg / chlorthalidone 12.5 mg) and titrate carefully; monitor for hypotension and electrolyte imbalance. |
| 1st trimester | Atenolol: Associated with IUGR when used in second and third trimesters; first trimester exposure may carry risk of congenital anomalies, though data are conflicting. Chlorthalidone: Thiazide diuretics are generally avoided in first trimester due to potential teratogenic effects, though risk appears low. |
| 2nd trimester | Atenolol: Continued use may cause fetal bradycardia and IUGR. Chlorthalidone: Associated with decreased placental perfusion, fetal electrolyte disturbances, and oligohydramnios; generally avoided. |
| 3rd trimester | Atenolol: Risk of neonatal bradycardia, hypotension, hypoglycemia, and respiratory depression; use near term may cause prolonged labor due to beta-blockade. Chlorthalidone: May cause neonatal thrombocytopenia, hyperbilirubinemia, and electrolyte abnormalities; use is contraindicated in pregnancy-induced hypertension. |
Clinical note
Comprehensive clinical and safety monograph for TENORETIC 50 (TENORETIC 50).
| Placental transfer | Both atenolol and chlorthalidone cross the placenta. Atenolol: readily crosses, with fetal serum concentrations similar to maternal. Chlorthalidone: crosses the placental barrier, but data are limited. |
■ FDA Black Box Warning
None
| Serious Effects |
Sinus bradycardiaHeart block greater than first degreeCardiogenic shockOvert cardiac failureAnuriaHypersensitivity to atenolol, chlorthalidone, or sulfonamide-derived drugs
| Precautions | Exacerbation of angina and myocardial infarction upon abrupt withdrawal; bradycardia; heart failure; bronchospasm in asthmatic patients; hypotension; electrolyte disturbances (hypokalemia, hyponatremia, hypomagnesemia); hyperuricemia; diabetes mellitus (may mask hypoglycemia); renal impairment; peripheral vascular disease; thyrotoxicosis; anaphylactic reactions. |
| Food/Dietary | Avoid excessive alcohol and high-sodium foods. Use caution with high-potassium foods (bananas, oranges, potatoes) if on potassium-sparing diuretics or with renal impairment. |
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| Breastfeeding | Atenolol accumulates in breast milk with a milk-to-plasma ratio of ~4.6, potentially causing bradycardia, cyanosis, and hypothermia in infants. Chlorthalidone is excreted in breast milk in low amounts; however, thiazides may suppress lactation. Use is generally not recommended during breastfeeding; consider alternative agents. |
| Lactation Rating | L4 (Hazardous) |
| Teratogenic Risk | First trimester: No adequate studies; risk cannot be ruled out. Second/third trimester: Atenolol (beta-blocker) may cause fetal bradycardia, intrauterine growth restriction, and placental hypoperfusion. Chlorthalidone (thiazide diuretic) may cause fetal electrolyte disturbances and neonatal hypoglycemia. Avoid use in pregnancy unless no alternative. |
| Fetal Monitoring | Maternal: Blood pressure, heart rate, serum electrolytes (K+, Na+), renal function, uric acid, and glucose. Fetal: Ultrasound for growth restriction, fetal heart rate monitoring (bradycardia risk), and amniotic fluid assessment. |
| Fertility Effects | Beta-blockers may impair male fertility due to reduced sperm motility. No established effects on female fertility. Thiazide diuretics have no known significant impact on fertility. |
| Clinical Pearls | TENORETIC 50 combines atenolol (cardioselective beta-blocker) and chlorthalidone (thiazide diuretic). Avoid abrupt cessation due to risk of rebound hypertension and angina. Monitor serum potassium, magnesium, and uric acid. Use with caution in asthma, COPD, and diabetes (may mask hypoglycemia). Reduce dose in renal impairment (CrCl <35 mL/min). |
| Patient Advice | Take exactly as prescribed; do not stop suddenly without consulting your doctor. · May cause dizziness or lightheadedness; avoid driving if affected. · Rise slowly from sitting or lying position to prevent falls. · Report unusual weight gain, swelling, or shortness of breath. · Limit alcohol and avoid potassium supplements or salt substitutes unless directed. |