MICARDIS HCT
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MICARDIS HCT (MICARDIS HCT).
Micardis HCT is a combination of telmisartan, an angiotensin II receptor blocker (ARB), and hydrochlorothiazide, a thiazide diuretic. Telmisartan selectively blocks the binding of angiotensin II to AT1 receptors in vascular smooth muscle and adrenal gland, leading to vasodilation and reduced aldosterone secretion. Hydrochlorothiazide inhibits sodium reabsorption in the distal convoluted tubule, increasing excretion of sodium and water, thereby reducing plasma volume.
| Metabolism | Telmisartan is primarily metabolized by glucuronidation via UGT1A1, UGT1A3, and UGT1A8; it is not metabolized by CYP450 enzymes. Hydrochlorothiazide is not extensively metabolized; it is eliminated unchanged in the urine. |
| Excretion | Primarily biliary excretion (≈60%) and renal excretion (≈40%) as unchanged drug. Telmisartan: renal <1%, fecal >97%. Hydrochlorothiazide: renal >95% unchanged. |
| Half-life | Telmisartan: terminal half-life ≈24 hours, allowing once-daily dosing. Hydrochlorothiazide: 6-15 hours (mean 10 hours). |
| Protein binding | Telmisartan: >99.5% bound primarily to albumin and α1-acid glycoprotein. Hydrochlorothiazide: 40-68% bound to albumin. |
| Volume of Distribution | Telmisartan: 500 L (≈7 L/kg), indicating extensive tissue distribution. Hydrochlorothiazide: 0.8-1.2 L/kg, confined to extracellular fluid. |
| Bioavailability | Telmisartan: absolute oral bioavailability ≈42-58% (dose-dependent). Hydrochlorothiazide: oral bioavailability ≈65-75%. |
| Onset of Action | Telmisartan: onset 2-4 hours for blood pressure reduction. Hydrochlorothiazide: diuresis onset 2 hours, peak at 4-6 hours. |
| Duration of Action | Telmisartan: >24 hours, enabling once-daily dosing. Hydrochlorothiazide: 6-12 hours with single dose, but antihypertensive effect persists up to 24 hours with combination. |
| Molecular Weight | Telmisartan: 514.62 Da; Hydrochlorothiazide: 297.74 Da |
One tablet orally once daily. Starting dose is 40 mg telmisartan / 12.5 mg hydrochlorothiazide; maximum 80 mg telmisartan / 25 mg hydrochlorothiazide.
| Dosage form | TABLET |
| Renal impairment | Contraindicated if GFR <30 mL/min. No adjustment needed for GFR 30-89 mL/min. Monitor renal function. |
| Liver impairment | Contraindicated in severe hepatic impairment (Child-Pugh C). Caution and possible dose reduction in mild-to-moderate impairment; maximum 40 mg/12.5 mg daily. |
| Pediatric use | Safety and efficacy not established in pediatric patients (<18 years). |
| Geriatric use | No initial dose adjustment required; monitor blood pressure and renal function, especially with concurrent diuretic therapy. |
| 1st trimester | Avoid. Angiotensin II receptor antagonists (ARBs) and thiazide diuretics are associated with teratogenic risk in the first trimester. Use alternative antihypertensive therapy. |
| 2nd trimester | Contraindicated. Exposure during the second trimester can cause fetal renal dysfunction, oligohydramnios, and skull ossification defects due to effects on the renin-angiotensin system. |
| 3rd trimester | Contraindicated. Third-trimester exposure increases risk of fetal hypotension, anuria, renal failure, and oligohydramnios. Thiazides may cause fetal electrolyte disturbances. |
Clinical note
Comprehensive clinical and safety monograph for MICARDIS HCT (MICARDIS HCT).
| Placental transfer | Telmisartan: Data limited; expected to cross placenta based on molecular weight and animal studies. Hydrochlorothiazide: Known to cross placenta, reaching fetal serum concentrations similar to maternal levels. |
| Breastfeeding |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to telmisartan or hydrochlorothiazidePregnancy (second and third trimesters)AnuriaSevere renal impairment (eGFR < 30 mL/min)Refractory hypokalemia or hypercalcemiaHepatic impairment with cholestasis or biliary obstructive disordersConcomitant use with aliskiren in patients with diabetes mellitus
| Precautions | Avoid use in pregnancy; can cause fetal harm when administered to a pregnant woman (discontinue as soon as possible when pregnancy is detected), May cause symptomatic hypotension in patients with volume or salt depletion, Monitor renal function; may cause acute renal failure, especially in patients with renal artery stenosis, Monitor serum electrolytes; risk of electrolyte imbalances (hypokalemia, hyponatremia, hypomagnesemia, hypercalcemia) due to hydrochlorothiazide, May exacerbate or activate systemic lupus erythematosus, May cause acute angle-closure glaucoma (due to hydrochlorothiazide), May cause hypersensitivity reactions, including anaphylaxis and angioedema (telmisartan), Use with caution in patients with hepatic impairment (telmisartan), Use with caution in patients with diabetes or impaired renal function; may increase risk of renal impairment when used with NSAIDs or COX-2 inhibitors, Monitor for hyperuricemia and gout, May cause photosensitivity reactions |
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| Telmisartan is excreted in breast milk in low amounts; hydrochlorothiazide is also present. Monitor infant for hypotension, electrolyte imbalances, and renal adverse effects. Avoid use in breastfeeding mothers, especially neonates/preterm infants, due to potential harm. |
| Lactation Rating | L4 (Possibly Hazardous) – Risk to infant outweighs benefits; consider alternative therapies. |
| Teratogenic Risk | First trimester: Increased risk of fetal malformations based on angiotensin II receptor antagonist (ARB) class effects. Second and third trimesters: Fetal renal dysfunction, oligohydramnios, skull ossification defects, hypotension, and anuria. Hydrochlorothiazide (HCTZ) may cause fetal or neonatal jaundice, thrombocytopenia, and electrolyte disturbances. |
| Fetal Monitoring | Monitor maternal blood pressure, renal function (serum creatinine, BUN), serum electrolytes (particularly potassium with telmisartan and sodium with HCTZ). Fetal monitoring includes ultrasound for amniotic fluid volume and fetal growth; assess for oligohydramnios if exposure occurs in second or third trimester. |
| Fertility Effects | Telmisartan: No specific human data; animal studies show no significant impact on fertility. Hydrochlorothiazide: No reported effects on fertility. Clinical significance unknown. |
| Food/Dietary | Avoid high-potassium foods (bananas, oranges, tomatoes, spinach, salt substitutes) due to telmisartan's potassium-sparing effect. Hydrochlorothiazide may cause hypomagnesemia and hypokalemia; ensure adequate intake of magnesium-rich foods (nuts, whole grains) and potassium-rich foods (if not contraindicated). Avoid excessive alcohol intake which can increase hypotensive effect. |
| Clinical Pearls | MICARDIS HCT (telmisartan/hydrochlorothiazide) is a fixed-dose combination for hypertension not controlled on monotherapy. Monitor renal function, electrolytes (especially potassium and sodium), and volume status. Avoid in severe renal impairment (CrCl <30 mL/min) and anuria. Assess for hypotension, particularly in volume-depleted patients. Use with caution in hepatic impairment, diabetes, and history of angioedema. May cause fetal harm in pregnancy; discontinue as soon as possible. Telmisartan is not dialyzable. |
| Patient Advice | Take exactly as prescribed; do not skip doses or take double doses. · Notify your doctor immediately if you become pregnant or plan to become pregnant. · Avoid alcohol, NSAIDs, and salt substitutes containing potassium. · May cause dizziness or lightheadedness; rise slowly from sitting or lying positions. · Report symptoms of electrolyte imbalance: muscle cramps, weakness, irregular heartbeat, confusion, or decreased urination. · This medication may increase blood sugar; monitor if you have diabetes. |