IRBESARTAN 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.
Irbesartan is an angiotensin II receptor antagonist that selectively blocks AT1 receptors, inhibiting vasoconstriction and aldosterone secretion. Hydrochlorothiazide is a thiazide diuretic that inhibits sodium and chloride reabsorption in the distal convoluted tubule, reducing plasma volume.
| Metabolism | Irbesartan undergoes hepatic glucuronidation and oxidation via CYP2C9; Hydrochlorothiazide is not metabolized and excreted unchanged in urine. |
| Excretion | Irbesartan: primarily fecal (80%) via biliary excretion, with ~20% renal. Hydrochlorothiazide: primarily renal (≥95% as unchanged drug) via tubular secretion. |
| Half-life | Irbesartan: 11–15 hours terminal half-life; supports once-daily dosing with steady state by 3 days. Hydrochlorothiazide: 6–15 hours terminal half-life; prolonged in renal impairment (up to 20+ hours) requiring dose adjustment. |
| Protein binding | Irbesartan: 90% bound to serum proteins (mainly albumin and α1-acid glycoprotein). Hydrochlorothiazide: 40–68% bound to plasma proteins (primarily albumin). |
| Volume of Distribution | Irbesartan: 53–93 L (0.7–1.1 L/kg) indicating extensive extravascular distribution. Hydrochlorothiazide: 3–5 L/kg (210–350 L) reflecting wide tissue distribution, including placenta and breast milk. |
| Bioavailability | Irbesartan: oral bioavailability 60–80%; food does not affect absorption. Hydrochlorothiazide: oral bioavailability 65–75%; food may reduce absorption slightly. |
| Onset of Action | Irbesartan: 2 hours after oral administration (antihypertensive effect). Hydrochlorothiazide: 2 hours for diuresis; antihypertensive effect may take 3–4 days. |
| Duration of Action | Irbesartan: 24 hours (blood pressure reduction) with once-daily dosing; sustained trough effect. Hydrochlorothiazide: 6–12 hours for diuresis; antihypertensive effect persists 24 hours with chronic use. |
| Molecular Weight | 610.57 |
Oral, 150 mg irbesartan/12.5 mg hydrochlorothiazide once daily, titrated to 300 mg irbesartan/25 mg hydrochlorothiazide once daily based on BP response.
| Dosage form | TABLET |
| Renal impairment | Contraindicated if GFR < 30 mL/min. No adjustment for GFR 30-60 mL/min; monitor renal function. Not for use in dialysis. |
| Liver impairment | No adjustment required for mild-moderate hepatic impairment (Child-Pugh A or B). Avoid in severe hepatic impairment (Child-Pugh C) due to hydrochlorothiazide component. |
| Pediatric use | Not recommended for pediatric patients; safety and efficacy not established. |
| Geriatric use | Start at lowest dose (150/12.5 mg once daily); titrate cautiously. Monitor renal function and electrolytes due to age-related decline. |
| 1st trimester | Avoid during first trimester; may cause oligohydramnios and fetal renal dysfunction. Use only if potential benefit justifies risk. |
| 2nd trimester | Contraindicated in second trimester due to risk of fetal renal impairment, oligohydramnios, and skull ossification defects. |
| 3rd trimester | Contraindicated in third trimester due to high risk of fetal and neonatal morbidity including hypotension, anuria, and irreversible renal failure. |
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 | Both irbesartan and hydrochlorothiazide cross the placenta. Irbesartan: limited data, but likely crosses; hydrochlorothiazide: known to cross and is found in cord blood. |
■ FDA Black Box Warning
None.
| Common Effects | diabetic nephropathy |
| Serious Effects |
AnuriaHypersensitivity to irbesartan, hydrochlorothiazide, or sulfonamide-derived drugsPregnancy (second and third trimesters)Severe renal impairment (CrCl <30 mL/min)Refractory hypokalemia, hypercalcemia, or hyponatremiaConcurrent use with aliskiren in patients with diabetes mellitus
| Precautions | Fetal toxicity: discontinue if pregnancy detected, Hypotension in volume-depleted patients, Renal impairment: monitor renal function, Electrolyte disturbances: hyponatremia, hypokalemia, hyperkalemia, Acute angle-closure glaucoma (sulfonamide component), Non-melanoma skin cancer risk (HCTZ), Systemic lupus erythematosus exacerbation |
| Food/Dietary | Avoid high-potassium foods (bananas, oranges, tomatoes, spinach, potatoes with skin) in large amounts; irbesartan reduces aldosterone and can increase potassium. HCTZ may cause hyponatremia; limit excessive fluid intake if sodium is low. No grapefruit interaction known. Take with or without food; consistency matters. |
Loading safety data…
| Breastfeeding | Irbesartan is excreted into breast milk in low concentrations; hydrochlorothiazide may suppress lactation. Use with caution in nursing mothers, especially with premature infants. Monitor infant for hypotension, dehydration, and electrolyte disturbances. |
| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | First trimester: Possible increased risk of congenital malformations, particularly cardiovascular and central nervous system defects, based on limited human data for angiotensin receptor blockers. Second and third trimesters: Fetal toxicity including oligohydramnios, fetal renal dysfunction, skull ossification defects, and neonatal renal failure, hypotension, hyperkalemia. Risks are similar to ACE inhibitors. |
| Fetal Monitoring | Serial fetal ultrasound to assess amniotic fluid volume and fetal renal function; monitor maternal blood pressure and renal function (serum creatinine, potassium); assess for fetal growth restriction. In neonates, monitor for hypotension, oliguria, hyperkalemia. |
| Fertility Effects | No adverse effects on fertility reported in preclinical studies. No human data; theoretical impact via renin-angiotensin system blockade unlikely to impair fertility. |
| Clinical Pearls | Combination product: irbesartan 150/300 mg + HCTZ 12.5/25 mg. Contraindicated in anuria and sulfonamide allergy (HCTZ is a sulfonamide derivative). Monitor serum potassium, creatinine, and sodium; HCTZ can exacerbate hypokalemia, but irbesartan mitigates this. Avoid in pregnancy (ARB fetotoxicity) and severe renal impairment (CrCl <30 mL/min). Use with caution in hepatic impairment or biliary obstruction. May cause symptomatic hypotension, especially in volume-depleted patients. Dual blockade of RAAS (e.g., with ACE inhibitors) increases risk of hypotension, hyperkalemia, and renal impairment. |
| Patient Advice | Take this medication exactly as prescribed, usually once daily. Do not skip doses or double up. · Avoid potassium supplements or salt substitutes containing potassium unless directed by your doctor. · May cause dizziness or lightheadedness; rise slowly from sitting or lying down. Avoid driving if affected. · This drug can harm an unborn baby. Use effective contraception and notify your doctor immediately if pregnant or planning pregnancy. · Report signs of electrolyte imbalance: muscle cramps, weakness, irregular heartbeat, excessive thirst, or confusion. · Avoid alcohol, which can increase dizziness and blood pressure lowering effects. · Store at room temperature away from moisture and heat. Keep out of reach of children. |