MICROZIDE

Clinical safety rating: caution

Comprehensive clinical and safety monograph for MICROZIDE (MICROZIDE).

How it works

Inhibits the sodium-chloride symporter (NCC) in the distal convoluted tubule of the nephron, reducing reabsorption of sodium and chloride, leading to increased excretion of water and electrolytes, and a decrease in blood volume and peripheral vascular resistance.

What the body does with it

Metabolism	Minimally metabolized; primarily excreted unchanged in urine; undergoes some hepatic metabolism via CYP450 enzymes, though specific isoenzymes are not well characterized.
Excretion	Primarily renal (approximately 70% unchanged drug; remainder as metabolites and conjugates); minimal biliary/fecal (<10%).
Half-life	Terminal elimination half-life: 8-12 hours (prolonged in renal impairment; up to 30 hours in severe insufficiency).
Protein binding	Approximately 40-80% bound to plasma proteins (mainly albumin).
Volume of Distribution	Vd: 1.5-2.5 L/kg (extensively distributed, indicating high tissue penetration).
Bioavailability	Oral bioavailability: 65-75% (reduced with food; increased in hepatic impairment).
Onset of Action	Oral: onset of diuresis within 1-2 hours; peak effect at 4-6 hours.
Duration of Action	Antihypertensive effect persists 24-48 hours; diuretic effect lasts approximately 16-24 hours.

Classification & Brands

Dosing & administration

12.5-25 mg orally once daily for hypertension; 25-100 mg orally once daily for edema.

Dosage form	CAPSULE
Renal impairment	Creatinine clearance 25-50 mL/min: 12.5 mg every 24 hours; <25 mL/min: not recommended (ineffective).
Liver impairment	Child-Pugh Class B or C: avoid use due to risk of electrolyte disturbances and hepatic encephalopathy.
Pediatric use	Not approved in children; safety and efficacy not established.
Geriatric use	Start at 12.5 mg orally once daily due to increased sensitivity to electrolyte disturbances and hypotension.

Use during pregnancy

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

Clinical note

Comprehensive clinical and safety monograph for MICROZIDE (MICROZIDE).

Breastfeeding	Excreted in breast milk in small amounts; M/P ratio not reported. Thiazides may suppress lactation. Use caution in nursing mothers; consider risk of infant electrolyte imbalance.
Teratogenic Risk	Pregnancy Category B. No evidence of teratogenicity in animal studies; however, thiazides cross the placental barrier and may cause fetal or neonatal jaundice, thrombocytopenia, and electrolyte disturbances. Use only if clearly needed, especially during first trimester.
Fetal Monitoring

Warnings & precautions

■ FDA Black Box Warning

None

Side Effect Profile

Serious Effects

Absolute Contraindications

["Anuria","Hypersensitivity to hydrochlorothiazide or other sulfonamide-derived drugs","Severe renal impairment (creatinine clearance <30 mL/min)","Hepatic coma or precoma"]

Clinical Precautions

Precautions

["May cause hypokalemia, hypomagnesemia, hyponatremia, and hypercalcemia","Risk of hyperuricemia and gout","May worsen renal function","Can cause photosensitivity","May precipitate hepatic encephalopathy in patients with liver disease","Caution in patients with diabetes mellitus (may increase blood glucose)","May cause systemic lupus erythematosus exacerbation","Electrolyte monitoring recommended"]

Clinical Tips & Counseling

Drug interactions

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MICROZIDE

Clinical safety rating: caution

Comprehensive clinical and safety monograph for MICROZIDE (MICROZIDE).

How it works

What the body does with it

Metabolism	Minimally metabolized; primarily excreted unchanged in urine; undergoes some hepatic metabolism via CYP450 enzymes, though specific isoenzymes are not well characterized.
Excretion	Primarily renal (approximately 70% unchanged drug; remainder as metabolites and conjugates); minimal biliary/fecal (<10%).
Half-life	Terminal elimination half-life: 8-12 hours (prolonged in renal impairment; up to 30 hours in severe insufficiency).
Protein binding	Approximately 40-80% bound to plasma proteins (mainly albumin).
Volume of Distribution	Vd: 1.5-2.5 L/kg (extensively distributed, indicating high tissue penetration).
Bioavailability	Oral bioavailability: 65-75% (reduced with food; increased in hepatic impairment).
Onset of Action	Oral: onset of diuresis within 1-2 hours; peak effect at 4-6 hours.
Duration of Action	Antihypertensive effect persists 24-48 hours; diuretic effect lasts approximately 16-24 hours.

Classification & Brands

Dosing & administration

12.5-25 mg orally once daily for hypertension; 25-100 mg orally once daily for edema.

Dosage form	CAPSULE
Renal impairment	Creatinine clearance 25-50 mL/min: 12.5 mg every 24 hours; <25 mL/min: not recommended (ineffective).
Liver impairment	Child-Pugh Class B or C: avoid use due to risk of electrolyte disturbances and hepatic encephalopathy.
Pediatric use	Not approved in children; safety and efficacy not established.
Geriatric use	Start at 12.5 mg orally once daily due to increased sensitivity to electrolyte disturbances and hypotension.

Use during pregnancy

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

Clinical note

Comprehensive clinical and safety monograph for MICROZIDE (MICROZIDE).

Breastfeeding	Excreted in breast milk in small amounts; M/P ratio not reported. Thiazides may suppress lactation. Use caution in nursing mothers; consider risk of infant electrolyte imbalance.
Teratogenic Risk	Pregnancy Category B. No evidence of teratogenicity in animal studies; however, thiazides cross the placental barrier and may cause fetal or neonatal jaundice, thrombocytopenia, and electrolyte disturbances. Use only if clearly needed, especially during first trimester.
Fetal Monitoring

Warnings & precautions

■ FDA Black Box Warning

None

Side Effect Profile

Serious Effects

Absolute Contraindications

["Anuria","Hypersensitivity to hydrochlorothiazide or other sulfonamide-derived drugs","Severe renal impairment (creatinine clearance <30 mL/min)","Hepatic coma or precoma"]