Sorry, you need to enable JavaScript to visit this website.

ALDACTAZIDE® (spironolactone, hydrochlorothiazide) Clinical Pharmacology

ACTIONS / CLINICAL PHARMACOLOGY

Mechanism of action

ALDACTAZIDE is a combination of two diuretic agents with different but complementary mechanisms and sites of action, thereby providing additive diuretic and antihypertensive effects. Additionally, the spironolactone component helps to minimize the potassium loss characteristically induced by the thiazide component.

The diuretic effect of spironolactone is mediated through its action as a specific pharmacologic antagonist of aldosterone, primarily by competitive binding of receptors at the aldosterone-dependent sodium-potassium exchange site in the distal convoluted renal tubule. Hydrochlorothiazide promotes the excretion of sodium and water primarily by inhibiting their reabsorption in the cortical diluting segment of the distal renal tubule.

ALDACTAZIDE is effective in significantly lowering the systolic and diastolic blood pressure in many patients with essential hypertension, even when aldosterone secretion is within normal limits.

Both spironolactone and hydrochlorothiazide reduce exchangeable sodium, plasma volume, body weight, and blood pressure. The diuretic and antihypertensive effects of the individual components are potentiated when spironolactone and hydrochlorothiazide are given concurrently.

Pharmacokinetics

Spironolactone is rapidly and extensively metabolized. Sulfur-containing products are the predominant metabolites and are thought to be primarily responsible, together with spironolactone, for the therapeutic effects of the drug. The following pharmacokinetic data were obtained from 12 healthy volunteers following the administration of 100 mg of spironolactone (ALDACTONE film-coated tablets) daily for 15 days. On the 15th day, spironolactone was given immediately after a lowfat breakfast and blood was drawn thereafter.

Accumulation Factor:
AUC (0–24 hr, day 15)/AUC (0–24 hr, day 1) Mean Peak Serum Concentration Mean (SD) Post-Steady State Half-Life
7-α-(thiomethyl) spirolactone (TMS) 1.25 391 ng/mL at 3.2 hr 13.8 hr (6.4) (terminal)
6-β-hydroxy-7-α-(thiomethyl) spirolactone (HTMS) 1.50 125 ng/mL at 5.1 hr 15.0 hr (4.0) (terminal)
Canrenone (C) 1.41 181 ng/mL at 4.3 hr 16.5 hr (6.3) (terminal)
Spironolactone 1.30 80 ng/mL at 2.6 hr Approximately 1.4 hr (0.5) (β half-life)

The pharmacological activity of spironolactone metabolites in man is not known. However, in the adrenalectomized rat the antimineralocorticoid activities of the metabolites C, TMS, and HTMS, relative to spironolactone, were 1.10, 1.28, and 0.32, respectively. Relative to spironolactone, their binding affinities to the aldosterone receptors in rat kidney slices were 0.19, 0.86, and 0.06, respectively.

In humans, the potencies of TMS and 7-α-thiospirolactone in reversing the effects of the synthetic mineralocorticoid, fludrocortisone, on urinary electrolyte composition were 0.33 and 0.26, respectively, relative to spironolactone. However, since the serum concentrations of these steroids were not determined, their incomplete absorption and/or first-pass metabolism could not be ruled out as a reason for their reduced in vivo activities.

Spironolactone and its metabolites are more than 90% bound to plasma proteins. The metabolites are excreted primarily in the urine and secondarily in bile.

The effect of food on spironolactone absorption (two 100 mg ALDACTONE tablets) was assessed in a single dose study of 9 healthy, drug-free volunteers. Food increased the bioavailability of unmetabolized spironolactone by almost 100%. The clinical importance of this finding is not known.

Hydrochlorothiazide is rapidly absorbed following oral administration. Onset of action of hydrochlorothiazide is observed within one hour and persists for 6 to 12 hours. Hydrochlorothiazide plasma concentrations attain peak levels at one to two hours and decline with a half-life of four to five hours. Hydrochlorothiazide undergoes only slight metabolic alteration and is excreted in urine. It is distributed throughout the extracellular space, with essentially no tissue accumulation except in the kidney.

What's New

No Current Announcements.

Therapeutic Area

Contact Pfizer Medical

Report an Adverse Event
1-800-438-1985

Contact Pfizer

Need to report an Adverse Event, Side Effect or Product Quality Concern?

Contact Pfizer Safety to report an adverse event, side effect or concern about the quality of a Pfizer product: (800) 438-1985

You may also contact the U.S. Food and Drug Administration (FDA) directly to report adverse events or product quality concerns at 1-800-FDA-1088 or www.fda.gov/MedWatch

Have a Medical Question on a Pfizer Prescription Medicine?
Contact Pfizer Medical Information to speak with a professional regarding your medical question on a Pfizer prescription product: (800) 438-1985
Have a Question on a Pfizer Over-the-Counter Product?
For Pfizer Consumer Healthcare non-prescription or over-the-counter products such as Advil, Centrum, Nexium or Thermacare, call (800) 322-3129
Have a Question about Pfizer Clinical Trials?
If you are looking for information about Pfizer studies currently recruiting new patients in your area, you can begin your search on our website. For questions about a Pfizer Clinical Trial, call (800) 718-1021 or email [email protected]
Need Information on Pfizer’s Patient Assistance Programs?

Pfizer RxPathways® connects eligible patients, regardless of their insurance status, to a range of assistance programs that offer insurance support, co-pay help, and medicines for free or at a savings. For more information, please call (844) 989-7284 or visit www.PfizerRxPathways.com.

Eligible patients can register for valuable savings offers for nearly 40 brand name medications. Visit www.MyPfizerBrands.com for more information.