TELMISARTAN; HYDROCHLOROTHIAZIDE

Clinical safety rating: avoid

NSAIDs may diminish the antihypertensive effect Lithium levels may be increased Use in pregnancy can cause injury and death to the developing fetus.

How it works

Telmisartan is an angiotensin II receptor antagonist that selectively blocks the AT1 receptor, inhibiting the vasoconstrictor and aldosterone-secreting effects of angiotensin II. Hydrochlorothiazide is a thiazide diuretic that inhibits the sodium-chloride symporter in the distal convoluted tubule, reducing sodium and water reabsorption.

What the body does with it

Metabolism	Telmisartan: primarily metabolized by glucuronidation; minor CYP2C9 involvement. Hydrochlorothiazide: not significantly metabolized; eliminated renally.
Excretion	Telmisartan: predominantly biliary/fecal (≥97%), renal <1%. Hydrochlorothiazide: predominantly renal (≥95%) as unchanged drug.
Half-life	Telmisartan: ~24 hours (range 18–24 h), enabling once-daily dosing. Hydrochlorothiazide: 6–15 hours (average ~9 h); prolonged in renal impairment.
Protein binding	Telmisartan: ≥99.5%, primarily to albumin and α1-acid glycoprotein. Hydrochlorothiazide: 40–68%, primarily to albumin.
Volume of Distribution	Telmisartan: 500 L (≈7.1 L/kg for 70 kg), indicating extensive extravascular distribution. Hydrochlorothiazide: 3–5 L/kg, distributed in extracellular fluid.
Bioavailability	Telmisartan: oral bioavailability ~42–58%, dose-dependent; food slightly reduces absorption. Hydrochlorothiazide: oral bioavailability ~65–75%; food may increase absorption.
Onset of Action	Telmisartan: antihypertensive effect within 2–4 weeks of continuous therapy. Hydrochlorothiazide: diuresis begins within 2 hours, peak at 4–6 hours.
Duration of Action	Telmisartan: 24 hours, supporting once-daily dosing. Hydrochlorothiazide: 6–12 hours; antihypertensive effect may persist ≥24 hours with chronic dosing.

Classification & Brands

Dosing & administration

Initial dose: 40 mg telmisartan/12.5 mg hydrochlorothiazide orally once daily. Titrate up to 80 mg telmisartan/25 mg hydrochlorothiazide once daily as tolerated.

Dosage form	TABLET
Renal impairment	Contraindicated in anuria. For GFR 30-60 mL/min: caution due to thiazide efficacy; monitor electrolytes. For GFR <30 mL/min: not recommended for initial therapy; if used, monitor renal function and electrolytes.
Liver impairment	Child-Pugh A: No adjustment. Child-Pugh B: Maximum telmisartan dose 40 mg daily; avoid initiating combination. Child-Pugh C: Contraindicated.
Pediatric use	Safety and efficacy not established in pediatric patients.
Geriatric use	Initiate at lower dose (e.g., 40 mg/12.5 mg) and titrate slowly; monitor electrolytes, renal function, and orthostatic hypotension.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

NSAIDs may diminish the antihypertensive effect Lithium levels may be increased Use in pregnancy can cause injury and death to the developing fetus.

FDA category	Contraindicated
Breastfeeding	Telmisartan: Present in human milk in low amounts; M/P ratio unknown. Hydrochlorothiazide: Excreted in human milk in low amounts; may suppress lactation. Use with caution, monitor infant for hypotension and electrolyte disturbances.
Teratogenic Risk	First trimester: Limited data; potential risk of congenital malformations based on drugs acting on RAAS. Second and third trimesters: Fetal toxicity including oligohydramnios, fetal renal dysfunction, skull ossification defects, hypotension, and anuria. Hydrochlorothiazide may cause fetal or neonatal jaundice, thrombocytopenia, and electrolyte imbalances.

Warnings & precautions

■ FDA Black Box Warning

No black box warning.

Side Effect Profile

Common Effects	Hyperkalemia
Serious Effects

Absolute Contraindications

["Pregnancy","History of angioedema with ARBs","Anuria (HCTZ)","Severe renal impairment (CrCl <30 mL/min)","Hypersensitivity to sulfonamide-derived drugs (HCTZ)"]

Clinical Precautions

Precautions

["Avoid use in pregnancy (fetal toxicity)","Monitor renal function and electrolytes","Hypotension in volume-depleted patients","Exacerbation of angioedema","Acute myopia/angle-closure glaucoma (with HCTZ)","Electrolyte disturbances (hypokalemia, hyponatremia)"]

Clinical Tips & Counseling

Drug interactions

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TELMISARTAN; HYDROCHLOROTHIAZIDE

Clinical safety rating: avoid

NSAIDs may diminish the antihypertensive effect Lithium levels may be increased Use in pregnancy can cause injury and death to the developing fetus.

How it works

What the body does with it

Metabolism	Telmisartan: primarily metabolized by glucuronidation; minor CYP2C9 involvement. Hydrochlorothiazide: not significantly metabolized; eliminated renally.
Excretion	Telmisartan: predominantly biliary/fecal (≥97%), renal <1%. Hydrochlorothiazide: predominantly renal (≥95%) as unchanged drug.
Half-life	Telmisartan: ~24 hours (range 18–24 h), enabling once-daily dosing. Hydrochlorothiazide: 6–15 hours (average ~9 h); prolonged in renal impairment.
Protein binding	Telmisartan: ≥99.5%, primarily to albumin and α1-acid glycoprotein. Hydrochlorothiazide: 40–68%, primarily to albumin.
Volume of Distribution	Telmisartan: 500 L (≈7.1 L/kg for 70 kg), indicating extensive extravascular distribution. Hydrochlorothiazide: 3–5 L/kg, distributed in extracellular fluid.
Bioavailability	Telmisartan: oral bioavailability ~42–58%, dose-dependent; food slightly reduces absorption. Hydrochlorothiazide: oral bioavailability ~65–75%; food may increase absorption.
Onset of Action	Telmisartan: antihypertensive effect within 2–4 weeks of continuous therapy. Hydrochlorothiazide: diuresis begins within 2 hours, peak at 4–6 hours.
Duration of Action	Telmisartan: 24 hours, supporting once-daily dosing. Hydrochlorothiazide: 6–12 hours; antihypertensive effect may persist ≥24 hours with chronic dosing.

Classification & Brands

Dosing & administration

Initial dose: 40 mg telmisartan/12.5 mg hydrochlorothiazide orally once daily. Titrate up to 80 mg telmisartan/25 mg hydrochlorothiazide once daily as tolerated.

Dosage form	TABLET
Renal impairment	Contraindicated in anuria. For GFR 30-60 mL/min: caution due to thiazide efficacy; monitor electrolytes. For GFR <30 mL/min: not recommended for initial therapy; if used, monitor renal function and electrolytes.
Liver impairment	Child-Pugh A: No adjustment. Child-Pugh B: Maximum telmisartan dose 40 mg daily; avoid initiating combination. Child-Pugh C: Contraindicated.
Pediatric use	Safety and efficacy not established in pediatric patients.
Geriatric use	Initiate at lower dose (e.g., 40 mg/12.5 mg) and titrate slowly; monitor electrolytes, renal function, and orthostatic hypotension.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

NSAIDs may diminish the antihypertensive effect Lithium levels may be increased Use in pregnancy can cause injury and death to the developing fetus.

FDA category	Contraindicated
Breastfeeding	Telmisartan: Present in human milk in low amounts; M/P ratio unknown. Hydrochlorothiazide: Excreted in human milk in low amounts; may suppress lactation. Use with caution, monitor infant for hypotension and electrolyte disturbances.
Teratogenic Risk	First trimester: Limited data; potential risk of congenital malformations based on drugs acting on RAAS. Second and third trimesters: Fetal toxicity including oligohydramnios, fetal renal dysfunction, skull ossification defects, hypotension, and anuria. Hydrochlorothiazide may cause fetal or neonatal jaundice, thrombocytopenia, and electrolyte imbalances.

Warnings & precautions

■ FDA Black Box Warning

No black box warning.

Side Effect Profile

Common Effects	Hyperkalemia
Serious Effects

Absolute Contraindications

["Pregnancy","History of angioedema with ARBs","Anuria (HCTZ)","Severe renal impairment (CrCl <30 mL/min)","Hypersensitivity to sulfonamide-derived drugs (HCTZ)"]