Core pharmacology

Class Group

Diuretic – Aldosterone antagonist

Legacy Cicm Level

Level 3

Introduction

A synthetic steroid

Indications Uses

Oedema – CHF, cirrhosis with ascites, refractory. HTN, Nephrotic syndrome. With loop/thiazide to conserve K+, diagn of Conn's syndr

Presentation

25/100mg tablets

Mechanism of action

Acts in the DCT.
It is a competitive antagonist of aldosterone at the receptors in the DCT.
Decreased Na reabsorption and increased K reabsorption
= Increased Na loss and Diuresis.

Physiological effects

Sedation and muscle weakness (due to electrolyte abnm)
Antihypertensive,
Diuresis (in 3-4 days)
Potassium retention
Anti-androgenic effect- inhbn of ovarian androgen secretion
↑renal Ca excr, ↑plasma urea
Reversible hyperchloraemic MA

Adverse Effects Toxicity

↑K+(esp in renal failure). N/V and GI disturbances
Menstr irreg, Gynaecomastia
↑digoxin conc.
↓pressor response
↑effects of CVS depressants

Absorption

PO - BA 70%, extensive 1st pass metb. Onset 3-4hrs, dur upto 3 days

Protein binding

90%

Metabolism

Hepatic: Rapidly and extensively metabolised by deacetylation and dethiolation. Active metab: canrenone and 7-alpha-spirolactone

Excretion

Urine and faeces

Half-life

1-2hours, metab upto 24hrs

Route And Dose

PO. 25-200mg/day