What is the difference between hydrochloride (HCl) and chlorothiazide?

Hydrochloride vs. Chlorothiazide: Critical Distinction

These are completely different chemical entities: "hydrochloride" (HCl) is a salt form used to improve drug solubility and stability, while "chlorothiazide" is a specific thiazide diuretic medication used to treat hypertension and edema.

Understanding Hydrochloride (HCl)

• Hydrochloride is NOT a medication itself—it is a pharmaceutical salt form created by combining a drug molecule with hydrochloric acid 1, 2
• The HCl salt improves water solubility, stability, and absorption of many medications across all drug classes 2
• Examples include metoprolol hydrochloride, diltiazem hydrochloride, and countless other medications where "hydrochloride" simply indicates the chemical form 2

Understanding Chlorothiazide

• Chlorothiazide is a specific thiazide diuretic medication with the chemical formula C7H6ClN3O4S2 and molecular weight of 295.72 1
• It works by blocking sodium and chloride reabsorption in the distal tubule, increasing water excretion and lowering blood pressure 2
• Chlorothiazide is structurally distinct as 6-chloro-2H-1,2,4-benzothiadiazine-7-sulfonamide 1-dioxide 1

Common Source of Confusion

• The confusion likely arises from hydrochlorothiazide, which is a different thiazide diuretic that contains "hydro" in its name but is NOT related to "hydrochloride" salts 2
• Hydrochlorothiazide is the 3,4-dihydro derivative of chlorothiazide, making it a chemically modified version of chlorothiazide 2
• Despite the similar names, hydrochlorothiazide and chlorothiazide are distinct medications with different pharmacokinetic profiles 3, 4

Key Pharmacological Differences Between Chlorothiazide and Hydrochlorothiazide

• Potency: Chlorothiazide requires higher doses (500 mg) compared to hydrochlorothiazide (12.5-25 mg) for equivalent blood pressure effects 1, 2
• Duration: Both have similar mechanisms but different dosing requirements due to potency differences 3, 4
• Clinical use: Hydrochlorothiazide is far more commonly prescribed than chlorothiazide for hypertension management 5, 6

Critical Clinical Distinction

• When prescribers write "hydrochlorothiazide," they are ordering a specific diuretic medication, NOT a hydrochloride salt form of chlorothiazide 2
• Chlorothiazide and hydrochlorothiazide are separate drugs that should never be confused or substituted without dose adjustment 3, 4