Hydrochlorothiazide
MICROZIDE
Pronunciation: hye-droe-klor-oe-THYE-a-zide
“Micro-sized Hydrant, tie-dyed”
Bananas dispersing → ↓ serum potassium
What it isNCC-inhibiting thiazide diuretic; hypertension and edema.
Why this oneLowers urinary calcium, but a large trial found no recurrence benefit for calcium stones; chlorthalidone lasts longer.
What limits itCheck sodium, potassium, glucose and uric acid. Hyponatremia often ends treatment, and lithium exposure can rise sharply.
Hydrochlorothiazide prescription history
Animated chart of estimated U.S. prescriptions per year, Antihypertensives (1953–2026). Hydrochlorothiazide enters in 1959 (estimated).
FDA-approved for
- hypertension/edema (~1959)
Principal riskHyponatremia and hypokalemia
Sulfonamide
Sulfonamide-derived drug (non-antibacterial) — label warns
No N4 aromatic amine, no N1 heterocycle: cross-reactivity after a sulfonamide-antimicrobial reaction is unlikely — sulfa-allergic patients reacted to sulfonamide non-antibiotics at 9.9% vs 1.6%, less often than to penicillin. The label warns anyway.
Open the sulfonamide hypersensitivity presentation → · sources [n] are on its References slide.
Classes and tags
Clinical profile
Legacy pregnancy categoryB
Defining liabilityHyponatremia, hypokalemia and substantial elevation of lithium concentrations.
FDA label
Read the full label on DailyMed ↗
NO BOXED WARNINGS
| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Edema | Adults | 25 mg QD | 25-100 mg/day QD or divided BID | 100 mg/day |
| Hypertension | Adults | 25 mg QD | 25-50 mg/day QD or divided BID | 50 mg/day (doses >50 mg often cause marked hypokalemia) |
| Diuresis and hypertension | Infants and children <2 y | 1-2 mg/kg/day (0.5-1 mg/lb) QD or divided BID | 1-2 mg/kg/day QD or divided BID | 37.5 mg/day |
| Diuresis and hypertension | Children 2-12 y | 1-2 mg/kg/day (0.5-1 mg/lb) QD or divided BID | 1-2 mg/kg/day QD or divided BID | 100 mg/day |
| Diuresis and hypertension | Infants <6 months | 1-2 mg/kg/day divided BID | Up to 3 mg/kg/day (1.5 mg/lb) divided BID may be required | 37.5 mg/day |
Renal Undefined
Hepatic Undefined
Patients usually do not require more than 50 mg/day when hydrochlorothiazide is used with other antihypertensives.
Instructions
- Individualize therapy to patient response; use the smallest dose necessary to achieve the required response.
- For edema, intermittent therapy (alternate days, or 3-5 days per week) makes excessive response and electrolyte imbalance less likely.
- Reduce the thiazide dose or withdraw therapy whenever adverse reactions are moderate or severe.
- Doses above 50 mg/day are often associated with marked reductions in serum potassium — monitor electrolytes.
Available strengths
- tab 12.5, 25, 50 mg
Contraindications
- Anuria
- Hypersensitivity to other sulfonamide-derived drugs
Cautions
- Electrolyte imbalance — hypokalemia especially above 50 mg/day; also hyponatremia and hypochloremic alkalosis. Monitor serum electrolytes.
- Hypotension including orthostatic hypotension; may be aggravated by alcohol, barbiturates, narcotics, or other antihypertensives.
- Non-melanoma skin cancer — increased risk, predominantly squamous cell carcinoma, in white patients on large cumulative doses.
- Renal dysfunction, renal failure, and interstitial nephritis.
- Metabolic effects: hyperglycemia, glycosuria, hyperuricemia.
- Hypersensitivity reactions including anaphylaxis, necrotizing angiitis, pneumonitis/pulmonary edema, and photosensitivity.
- Serious dermatologic reactions: erythema multiforme/Stevens-Johnson syndrome and exfoliative dermatitis/toxic epidermal necrolysis.
- Hematologic: aplastic anemia, agranulocytosis, leukopenia, hemolytic anemia, thrombocytopenia.
Adverse reactions
- Cardiovascular: hypotension including orthostatic hypotension.
- Metabolic: electrolyte imbalance, hyperglycemia, glycosuria, hyperuricemia.
- GI: nausea, anorexia, cramping, constipation, diarrhea, vomiting, gastric irritation, sialadenitis, pancreatitis, intrahepatic cholestatic jaundice.
- CNS: dizziness, vertigo, headache, paresthesias, restlessness; weakness; muscle spasm.
- Skin/hypersensitivity: photosensitivity, rash, urticaria, purpura, fever, anaphylaxis, necrotizing angiitis, Stevens-Johnson syndrome, toxic epidermal necrolysis, alopecia.
- Hematologic: aplastic anemia, agranulocytosis, leukopenia, hemolytic anemia, thrombocytopenia.
- Renal: renal failure, renal dysfunction, interstitial nephritis. Urogenital: impotence.
- Special senses: transient blurred vision, xanthopsia.
- Postmarketing: increased risk of non-melanoma skin cancer (~1 extra SCC per 16,000 patients/year overall; ~1 per 6,700/year in white patients with cumulative dose >=50,000 mg).
Pregnancy No adequate, well-controlled studies in pregnant women; no evidence of fetal harm in mice or rats. Thiazides cross the placenta and appear in cord blood — risk of fetal/neonatal jaundice and thrombocytopenia. Use only if clearly needed.
Lactation Undefined
Cost
Generic entry1982
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Self-check
- How does hydrochlorothiazide affect urinary calcium?
Lowers it. - How can hydrochlorothiazide affect lithium exposure?
Raise it sharply.