TELMISARTAN AND 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.
Telmisartan is an angiotensin II receptor blocker (ARB) that selectively inhibits the binding of angiotensin II to the AT1 receptor, leading to vasodilation and reduced aldosterone secretion. Hydrochlorothiazide is a thiazide diuretic that inhibits the sodium-chloride symporter in the distal convoluted tubule, increasing excretion of sodium and water.
| Metabolism | Telmisartan is primarily metabolized by glucuronidation via UGT1A3 and UGT2B7; minimal CYP450 metabolism. Hydrochlorothiazide is not metabolized and is excreted unchanged in urine. |
| Excretion | Telmisartan: >99% biliary-fecal as unchanged drug, <2% renal. Hydrochlorothiazide: ≥95% renal as unchanged drug; minimal biliary. |
| Half-life | Telmisartan: 24 hours (terminal); supports once-daily dosing with ~3-5 days to steady state. Hydrochlorothiazide: 6-15 hours (mean 10h); prolonged in renal impairment. |
| Protein binding | Telmisartan: >99.5% (primarily albumin and α1-acid glycoprotein). Hydrochlorothiazide: 40-68% (primarily albumin). |
| Volume of Distribution | Telmisartan: 500 L (approx 7 L/kg for 70 kg; extensive tissue binding). Hydrochlorothiazide: 0.83 L/kg (distributes into extracellular fluid; crosses placenta but minimal CNS entry). |
| Bioavailability | Telmisartan: 42-58% (oral); high-fat meal reduces AUC by 6%. Hydrochlorothiazide: 65-72% (oral); food may increase absorption. |
| Onset of Action | Telmisartan: 30-60 minutes (oral); peak effect 3-6 hours. Hydrochlorothiazide: 2 hours (oral); peak effect 4 hours. |
| Duration of Action | Telmisartan: 24 hours (antihypertensive); enables once-daily dosing. Hydrochlorothiazide: 6-12 hours (diuresis); antihypertensive effect persists >24 hours. |
| Molecular Weight | telmisartan: 514.6 Da; hydrochlorothiazide: 297.7 Da |
Oral, one tablet once daily. Initial: Telmisartan 40 mg/HCTZ 12.5 mg; titrate to max 80 mg/25 mg once daily.
| Dosage form | TABLET |
| Renal impairment | GFR ≥30 mL/min: No adjustment. GFR 15-29 mL/min: Not recommended (loop diuretics preferred). GFR <15 mL/min: Contraindicated. |
| Liver impairment | Child-Pugh A: No adjustment for telmisartan up to 40 mg; maximum HCTZ 25 mg. Child-Pugh B: Telmisartan 20 mg max; HCTZ 12.5 mg max. Child-Pugh C: Contraindicated. |
| Pediatric use | Safety and efficacy not established. Use not recommended. |
| Geriatric use | Start at lowest dose (40/12.5 mg). Monitor renal function and electrolytes closely. Titrate slowly. |
| 1st trimester | Avoid. Telmisartan is an angiotensin II receptor blocker (ARB) associated with teratogenic risk (oligohydramnios, fetal renal dysfunction, skull ossification defects). Hydrochlorothiazide (HCTZ) may cause fetal or neonatal jaundice, electrolyte disturbances, and thrombocytopenia. Use is contraindicated in pregnancy. |
| 2nd trimester | Avoid. ARBs are associated with fetal toxicity including oligohydramnios, fetal renal failure, and death. HCTZ decreases placental perfusion and may cause adverse fetal effects. |
| 3rd trimester | Avoid. ARBs can cause fetal renal dysfunction, oligohydramnios, and neonatal renal failure. HCTZ may cause neonatal electrolyte imbalance, hypoglycemia, and thrombocytopenia. |
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 |
| Placental transfer |
■ FDA Black Box Warning
Fetal toxicity: Drugs acting directly on the renin-angiotensin system can cause injury and death to the developing fetus. Discontinue as soon as possible once pregnancy is detected.
| Common Effects | Hyperkalemia |
| Serious Effects |
PregnancyAnuriaHypersensitivity to telmisartan, hydrochlorothiazide, or sulfonamide-derived drugs
| Precautions | Avoid use in pregnancy, Hypotension in volume-depleted patients, Monitor renal function and serum electrolytes, Worsening of renal function, Acute myopia and secondary angle-closure glaucoma (hydrochlorothiazide) |
| Food/Dietary | Avoid excessive salt intake to maximize antihypertensive effect. Grapefruit juice may reduce telmisartan absorption; avoid concurrent consumption. High-potassium foods (bananas, oranges, tomatoes, spinach) should be consumed consistently and not in excess. Hydrochlorothiazide may cause hypomagnesemia; consider magnesium-rich foods (nuts, dark leafy greens). Avoid liquorice as it may worsen hypokalemia. |
Loading safety data…
| Telmisartan: There is evidence of placental transfer in animals; likely crosses human placenta based on molecular weight (514.6 Da) and ARB class effects. Hydrochlorothiazide: Apparent placental transfer; known to cross human placenta (molecular weight 297.7 Da). |
| Breastfeeding | Telmisartan is excreted in human milk in trace amounts; effects on the infant are unknown. Hydrochlorothiazide is excreted in breast milk and may suppress lactation. Use during breastfeeding is not recommended due to potential for adverse effects in the infant, including electrolyte disturbances and dehydration. |
| Lactation Rating | L4 (Possibly Hazardous) |
| Teratogenic Risk | Telmisartan is an angiotensin II receptor blocker (ARB); use during second and third trimesters is associated with oligohydramnios, fetal renal dysfunction, skull hypoplasia, and death. First trimester exposure may increase risk of congenital malformations, though data are limited. Hydrochlorothiazide (HCTZ) does not appear to be major teratogen but can cause electrolyte disturbances and decreased placental perfusion. Overall, combination is contraindicated in pregnancy, especially after 20 weeks gestation. |
| Fetal Monitoring | Monitor maternal blood pressure, serum creatinine, potassium, and electrolytes. Fetal ultrasound to assess amniotic fluid volume and fetal growth if exposure occurs after 20 weeks. Monitor for signs of fetal hypotension or renal dysfunction. |
| Fertility Effects | No specific human studies; animal studies suggest telmisartan may alter renin-angiotensin system in fetal kidney development. No direct evidence of impaired fertility; HCTZ may cause maternal electrolyte imbalances that could theoretically affect ovulation, but data lacking. |
| Clinical Pearls | Monitor renal function and electrolytes within 2 weeks of initiation or dose titration due to risk of acute renal impairment and electrolyte disturbances. Avoid use if CrCl <30 mL/min; telmisartan component may cause hyperkalemia, especially in diabetics or those on potassium supplements. Hydrochlorothiazide may exacerbate gout; check uric acid in predisposed patients. Trough effect may underestimate 24-hour BP reduction; consider ambulatory BP monitoring. |
| Patient Advice | Take once daily, with or without food; do not skip doses. · Avoid potassium supplements or salt substitutes containing potassium without consulting your doctor. · Report signs of electrolyte imbalance: muscle cramps, weakness, irregular heartbeat, excessive thirst. · May cause dizziness; avoid driving or operating machinery until you know how you react. · Avoid excessive alcohol consumption as it may lower blood pressure too much. · Notify your doctor if you experience a dry cough, swelling of face/lips, or difficulty breathing. · Stay hydrated to prevent dehydration, especially in hot weather or during exercise. · Combination tablets cannot be split; use as prescribed. |