Chlorthalidone
THALITONE
Pronunciation: klor-THAL-i-doen
“Cooler thiazide, lid on”
Bananas dispersing → ↓ serum potassium
What it isThiazide-like NCC inhibitor; hypertension and edema.
Why this oneIts longer action and stronger outcomes evidence distinguish it from hydrochlorothiazide.
What limits itHyponatremia and hypokalemia are more pronounced than with hydrochlorothiazide; monitor electrolytes and renal function.
Chlorthalidone prescription history
Animated chart of estimated U.S. prescriptions per year, Diuretics (1953–2026). Chlorthalidone enters in 1960 (estimated).
FDA-approved for
- hypertension/edema (~1960)
Principal riskHyponatremia and hypokalemia; longer-acting than hydrochlorothiazide
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 categoryC
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 |
|---|---|---|---|---|
| Hypertension | Adults | 15 mg QD with food | 25 mg QD after 2 weeks if more BP reduction needed | 25 mg QD (doses >25 mg not expected to add BP reduction) |
| Edema | Adults | 50–100 mg QD or 100 mg every other day | 50–200 mg QD or alternate days | 200 mg/day |
Titration Increase after a suitable trial if response insufficient
Renal Undefined
Hepatic Undefined
Instructions
- Single dose in the morning with food
- Divided daily doses are unnecessary
- Maintenance doses may be lower than initial; titrate to response
Available strengths
- tab 12.5, 15, 25, 50 mg
Contraindications
- Anuria
- Hypersensitivity to sulfonamide-derived drugs
Cautions
- Electrolyte imbalance (hypokalemia, hyponatremia); monitor serum electrolytes
- Increases serum uric acid and blood glucose (dose-related)
- Orthostatic hypotension, aggravated by alcohol/barbiturates/narcotics
- Idiosyncratic reactions, photosensitivity, hypersensitivity
Adverse reactions
- GI: anorexia, gastric irritation, nausea, vomiting, cramping, pancreatitis, cholestatic jaundice
- CNS: dizziness, vertigo, paresthesias, headache
- Hematologic: leukopenia, agranulocytosis, thrombocytopenia, aplastic anemia
- Metabolic: hyperglycemia, glycosuria, hyperuricemia; impotence
Pregnancy Category B; use only if clearly needed — thiazides cross placenta (risk fetal/neonatal jaundice, thrombocytopenia)
Lactation Undefined
Cost
Generic entry1982
Open Chlorthalidone in the interactive console ↗
Memory aids: interaction avatars
Open Chlorthalidone in the interactive console ↗
Self-check
- How does chlorthalidone duration compare with hydrochlorothiazide?
Longer. - Which electrolyte disturbances are more pronounced than with hydrochlorothiazide?
Hyponatremia and hypokalemia.