HYDROCHLOROTHIAZIDE; IRBESARTAN
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.
Hydrochlorothiazide is a thiazide diuretic that inhibits the sodium-chloride symporter in the distal convoluted tubule, reducing sodium and water reabsorption. Irbesartan is an angiotensin II receptor blocker (ARB) that selectively inhibits the AT1 receptor, blocking vasoconstriction and aldosterone secretion.
| Metabolism | Hydrochlorothiazide is not extensively metabolized; it is eliminated unchanged in urine. Irbesartan undergoes hepatic metabolism via glucuronidation and oxidation by CYP2C9. |
| Excretion | Renal: 70% (irbesartan, unchanged and metabolites); 95% (hydrochlorothiazide, unchanged). Fecal: 30% (irbesartan). |
| Half-life | Hydrochlorothiazide: 6-15 hours (prolonged in renal impairment); Irbesartan: 11-15 hours (supports once-daily dosing). |
| Protein binding | Hydrochlorothiazide: 64%; Irbesartan: 90% (primarily albumin and alpha-1 acid glycoprotein). |
| Volume of Distribution | Hydrochlorothiazide: 3.6 L/kg (extensive tissue distribution); Irbesartan: 53-93 L (0.7-1.2 L/kg) (moderate tissue binding). |
| Bioavailability | Hydrochlorothiazide: 65-75% (oral); Irbesartan: 60-80% (oral, increased with food). |
| Onset of Action | Oral: Hydrochlorothiazide diuresis within 2 hours; Irbesartan antihypertensive effect within 2-4 hours, peak at 6-8 hours. |
| Duration of Action | Hydrochlorothiazide: 6-12 hours (diuretic); Irbesartan: >24 hours (antihypertensive) due to once-daily dosing with steady-state after 3-5 days. |
Hydrochlorothiazide 12.5-25 mg and irbesartan 150-300 mg orally once daily. Maximum dose: hydrochlorothiazide 25 mg/day; irbesartan 300 mg/day.
| Dosage form | TABLET |
| Renal impairment | Contraindicated if GFR <30 mL/min. For GFR 30-50 mL/min, maximum hydrochlorothiazide dose is 12.5 mg/day; irbesartan dose adjustment not required but monitor renal function. For GFR <30 mL/min, do not use hydrochlorothiazide-containing products. |
| Liver impairment | No specific dose adjustment required for mild to moderate hepatic impairment (Child-Pugh A/B). For severe impairment (Child-Pugh C), use with caution; no established dose recommendation, avoid if possible. |
| Pediatric use | Not approved in pediatric patients. Safety and efficacy not established. |
| Geriatric use | Start at lowest dose (hydrochlorothiazide 12.5 mg/irbesartan 150 mg) once daily; titrate slowly. Monitor renal function, electrolytes, and blood pressure closely due to increased risk of hypotension, electrolyte imbalances, and renal impairment. |
| 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 | Irbesartan is excreted in human milk in small amounts (M/P ratio not available). Hydrochlorothiazide is excreted in breast milk (M/P ratio ~1.3). Combination may suppress lactation based on thiazide effect. Use caution; monitor infant for hypotension, electrolyte imbalance, and dehydration. |
| Teratogenic Risk |
■ FDA Black Box Warning
Drugs that act directly on the renin-angiotensin system (e.g., irbesartan) can cause fetal harm and death when used during pregnancy. Discontinue as soon as pregnancy is detected.
| Common Effects | diabetic nephropathy |
| Serious Effects |
["Pregnancy (especially second and third trimesters)","History of hypersensitivity to sulfonamide-derived drugs (hydrochlorothiazide) or ARBs","Anuria (hydrochlorothiazide)","Concomitant use with aliskiren in patients with diabetes or renal impairment (creatinine clearance <60 mL/min)"]
| Precautions | ["Avoid use in pregnancy (may cause fetal harm)","Monitor renal function and electrolytes; risk of hypotension in volume-depleted patients","May cause hyperkalemia when combined with other agents affecting the RAAS","Exacerbation of systemic lupus erythematosus (hydrochlorothiazide)","Use with caution in severe renal impairment (creatinine clearance <30 mL/min)"] |
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| First trimester: Angiotensin II receptor antagonists (irbesartan) are associated with increased risk of fetal renal dysplasia, oligohydramnios, and skull ossification defects. Second and third trimesters: Exposure during second and third trimesters causes oligohydramnios, fetal hypotension, anuria, renal failure, skull hypoplasia, and death. Hydrochlorothiazide has been associated with neonatal thrombocytopenia, electrolyte disturbances, and jaundice. |
| Fetal Monitoring | Monitor maternal blood pressure, renal function (serum creatinine, BUN), electrolytes (sodium, potassium, chloride), and urine output. Fetal monitoring includes amniotic fluid index (oligohydramnios detection) and fetal renal ultrasound. Neonatal monitoring for hypotension, renal function, and electrolyte disturbances. |
| Fertility Effects | Irbesartan may reduce fertility by affecting the renin-angiotensin system in reproductive tissues. Hydrochlorothiazide may cause reversible erectile dysfunction in males. Clinical impact on female fertility is unknown. |
| Food/Dietary |
| Avoid high-potassium foods (e.g., bananas, oranges, potatoes, spinach, salt substitutes) unless directed by clinician. Limit alcohol intake to reduce hypotensive effects. Maintain normal dietary sodium but avoid excessive intake. |
| Clinical Pearls | Monitor serum potassium and renal function within 2 weeks of initiation. Avoid in severe renal impairment (CrCl <30 mL/min). Combination reduces hypokalemia risk from HCTZ alone. Maximum antihypertensive effect may take 4 weeks. Use with caution in diabetes (HCTZ may increase glucose and irbesartan may decrease insulin sensitivity). |
| Patient Advice | Take this medication exactly as prescribed, usually once daily with or without food. · Avoid salt substitutes containing potassium unless approved by your doctor. · Drink adequate fluids to prevent dehydration, especially during hot weather or exercise. · Report persistent dizziness, muscle cramps, weakness, irregular heartbeat, or signs of allergic reaction (rash, swelling). · This medication may cause dizziness or lightheadedness; avoid driving until you know how it affects you. · Do not use this medication during pregnancy; notify your doctor immediately if you become pregnant. |