IRBESARTAN 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.
Irbesartan is an angiotensin II receptor antagonist that selectively blocks the binding of angiotensin II to AT1 receptors, inhibiting vasoconstriction and 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 | Irbesartan: primarily metabolized by CYP2C9 (glucuronidation and oxidation). Hydrochlorothiazide: not significantly metabolized; excreted unchanged in urine. |
| Excretion | Irbesartan: primarily biliary (80%) and renal (20%); Hydrochlorothiazide: renal (≥95% as unchanged drug). |
| Half-life | Irbesartan: 11-15 hours; Hydrochlorothiazide: 6-15 hours. Steady state achieved in 3-5 days. |
| Protein binding | Irbesartan: 90-95% (primarily albumin and alpha-1-acid glycoprotein); Hydrochlorothiazide: 40-68% (primarily albumin). |
| Volume of Distribution | Irbesartan: 53-93 L; Hydrochlorothiazide: 3-5 L/kg. Indicates extensive extravascular distribution for irbesartan and predominant extracellular distribution for HCTZ. |
| Bioavailability | Irbesartan: 60-80% (oral); Hydrochlorothiazide: 65-75% (oral). |
| Onset of Action | Irbesartan: 1-2 hours; Hydrochlorothiazide: 2 hours. Antihypertensive effect evident within 1-2 weeks, maximal at 4-6 weeks. |
| Duration of Action | Irbesartan: 24 hours; Hydrochlorothiazide: 6-12 hours. Once-daily dosing provides 24-hour blood pressure control. |
| Molecular Weight | 428.53 |
Oral: 1 tablet (irbesartan 150 mg / hydrochlorothiazide 12.5 mg or irbesartan 300 mg / hydrochlorothiazide 12.5 mg or irbesartan 300 mg / hydrochlorothiazide 25 mg) once daily, with or without food. Maximum: irbesartan 300 mg/hydrochlorothiazide 25 mg daily.
| Dosage form | TABLET |
| Renal impairment | GFR ≥30 mL/min: No adjustment. GFR <30 mL/min: Contraindicated due to thiazide ineffectiveness and risk of accumulation. |
| Liver impairment | Child-Pugh A: No dose adjustment. Child-Pugh B or C: Use with caution; hydrochlorothiazide may precipitate hepatic encephalopathy. No specific dose guidelines available; start with lowest dose if necessary. |
| Pediatric use | Not recommended for use in pediatric patients; safety and efficacy not established. |
| Geriatric use | Start at lower end of dosing range (e.g., irbesartan 150 mg/hydrochlorothiazide 12.5 mg daily) due to increased risk of hypotension, electrolyte imbalance, and renal impairment. Monitor blood pressure, electrolytes, and renal function closely. |
| 1st trimester | Avoid; risk of fetal malformations associated with ARBs and thiazide diuretics. |
| 2nd trimester | Avoid; fetal toxicity including oligohydramnios, renal dysfunction, and hypotension. |
| 3rd trimester | Avoid; risk of neonatal hypotension, anuria, and hyperkalemia. |
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 | Irbesartan crosses placenta; hydrochlorothiazide crosses minimally. |
| Breastfeeding | Hydrochlorothiazide passes into breast milk in small amounts; may suppress lactation. Irbesartan is excreted in rat milk, unknown in humans. Use with caution, especially in preterm infants. |
■ FDA Black Box Warning
No FDA black box warning.
| Common Effects | diabetic nephropathy |
| Serious Effects |
Hypersensitivity to irbesartan or hydrochlorothiazideAnuriaPregnancy (second and third trimesters)Severe renal impairment (CrCl <30 mL/min)Hypersensitivity to sulfonamide-derived drugs
| Precautions | Fetal toxicity (use in pregnancy, especially second and third trimesters, can cause injury and death to developing fetus; discontinue as soon as possible), Hypotension in volume- or salt-depleted patients, Impaired renal function (monitor serum creatinine and potassium), Electrolyte and fluid imbalances (hypokalemia, hyponatremia, hypomagnesemia, hypercalcemia, hyperuricemia), Acute angle-closure glaucoma (with hydrochlorothiazide), Sulfonamide allergy cross-reactivity (hydrochlorothiazide is a sulfonamide derivative), Exacerbation or activation of systemic lupus erythematosus (hydrochlorothiazide) |
| Food/Dietary |
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| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | First trimester: Limited data, but increased risk of cardiovascular and CNS defects suggested by ACE inhibitor data. Second and third trimesters: Irbesartan exposure associated with oligohydramnios, fetal renal dysfunction, skull ossification defects, hypotension, hyperkalemia, and death. Hydrochlorothiazide may cause neonatal thrombocytopenia, electrolyte disturbances, and hypoglycemia. |
| Fetal Monitoring | Monitor maternal blood pressure, serum electrolytes (potassium, sodium, chloride, bicarbonate), renal function (creatinine, BUN), and fetal ultrasound for amniotic fluid volume (oligohydramnios) and fetal growth in second and third trimesters. Consider serial fetal monitoring for renal function. |
| Fertility Effects | No specific human data. Animal studies with irbesartan showed no fertility impairment. Thiazides may cause transient impotence in males. Overall, likely minimal effect on fertility. |
| Avoid high-potassium foods (e.g., bananas, oranges, spinach, potatoes) if potassium levels are elevated; however, HCTZ may increase potassium loss, so maintain normal intake unless advised. Grapefruit juice may increase irbesartan absorption; avoid large quantities. Sodium intake should be moderate; do not use salt substitutes without checking potassium content. Alcohol may enhance hypotensive effect; limit consumption. |
| Clinical Pearls | Irbesartan is an ARB that inhibits angiotensin II, while HCTZ is a thiazide diuretic. Monitor serum potassium, especially in elderly or those with renal impairment; combination may cause hypokalemia due to HCTZ but hyperkalemia due to irbesartan. Check renal function and electrolytes within 2-4 weeks of initiation. Avoid in pregnancy (Category D). Use with caution in patients with severe renal impairment (CrCl <30 mL/min) as HCTZ may be ineffective. Onset of antihypertensive effect occurs within 2 weeks, maximal at 4-6 weeks. |
| Patient Advice | Take exactly as prescribed, usually once daily. · Avoid becoming dehydrated; drink adequate fluids unless fluid restricted. · If you miss a dose, take it as soon as remembered unless near next dose; do not double. · May cause dizziness; avoid driving until you know how the medication affects you. · Limit alcohol intake to avoid additive blood pressure lowering. · Notify your doctor if you experience signs of electrolyte imbalance: muscle cramps, weakness, irregular heartbeat, or excessive thirst. · Women of childbearing age: use contraception and notify doctor if pregnant or planning pregnancy. · Avoid potassium supplements or salt substitutes containing potassium without doctor approval. · Can cause increased urination; take early in day to avoid nighttime awakening. · Do not stop abruptly without consulting your doctor. |