Hydrochlorothiazide (HCT)

Hydrochlorothiazide is a diuretic and antihypertensive substance used to flush out edema and treat hypertension and chronic heart failure. The active substance, which belongs to the thiazide diuretics, is often combined with ACE inhibitors (drugs for high blood pressure).

Because hydrochlorothiazide has urine-thinning properties (which conceals the detection of doping), the use of the substance in competitive sports is prohibited in Switzerland according to the doping list.

Pharmacodynamics

Hydrochlorothiazide prevents the reabsorption of sodium and water from the kidney, resulting in increased urinary water excretion. Long-term use of the drug results in decreased calcium excretion, which can lead to hypercalcemia, an elevated level of calcium in the blood.

Pharmacokinetics

The diuretic is about 70% bioavailable, and absorption into the gastrointestinal tract after oral administration is about 80%. Ingestion during a meal decreases bioavailability by 10%.
Hydrochlorothiazid ist zu 40-68% im Plasma an Protein gebunden und wird unverändert im Urin ausgeschieden.
 Die Halbwertszeit ist bei einer eingeschränkten Nierenfunktion erhöht, bei normaler Nierenfunktion beträgt sie 6-8 Stunden.

Contraindications

Hydrochlorothiazide should not be used in cases of:

• Hypersensitivity to hydrochlorothiazide and other thiazides and sulfonamide derivatives.
• Low serum potassium or sodium levels
• Increased serum calcium or uric acid levels
• Pregnancy
• Renal dysfunction

Drug interactions

Drug interactions may occur with concomitant use with other blood pressure medications, lithium, insulin, cholestyramine, colestipol, steroid medications, and nonsteroidal anti-inflammatory drugs (aspirin, ibuprofen, naproxen, celecoxib, diclofenac, indomethacin, meloxicam).

An interval of 2 hours should be allowed between the intake of hydrochlorothiazide and gastric juice neutralizing medications and calcium or iron supplements.

Consumption of natural licorice should be avoided because licorice enhances the potassium-lowering effect of the antidiuretic. Potassium deficiency can be counteracted by increasing the consumption of potassium-containing foods (e.g. bananas, orange juice).

Side effects

The most common adverse reactions include:

• General disturbances in fluid and electrolyte balance.
• Low blood calcium levels
• low blood pressure
• Skin reactions
• Impaired ability to drive (especially when taken with alcohol)

Toxicological Data

The oral LD50 of hydrochlorothiazide is > 10 g/kg in mice and rats.