Metazolone Pharmacology
Critical Clarification: Metazolone vs. Metolazone
There is no medication called "Metazolone" in clinical practice. The question likely refers to either metolazone (a thiazide-like diuretic) or methandrostenolone (an anabolic steroid), which are entirely different drug classes with distinct pharmacology and clinical applications.
If Referring to Metolazone (Diuretic)
Mechanism of Action
- Metolazone is a thiazide-like diuretic that inhibits sodium reabsorption in the distal convoluted tubule, promoting diuresis even in patients with impaired renal function 1
Therapeutic Uses
Severe Refractory Heart Failure:
- Metolazone (1.25-10 mg daily) is highly effective for severe refractory congestive heart failure (NYHA class IV) when conventional diuretics fail, with 15 of 17 patients in one study improving sufficiently for hospital discharge 1
- Average weight loss of 8.3 kg was achieved in responders, with improvement to NYHA class II or III 1
- Failure to respond to metolazone may indicate especially poor prognosis 1
Ascites Due to Liver Disease:
- In patients with chronic liver disease and ascites, metolazone controlled fluid retention in 8 of 20 patients as monotherapy, while 10 required additional amiloride or spironolactone 2
- Initial dosing of 5 mg daily is recommended, though much higher doses may be required 2
Critical Precautions and Adverse Effects
Electrolyte Disturbances (Major Concern):
- Hypokalaemia occurs in 80% of patients with liver disease when metolazone is used alone, necessitating concurrent potassium-sparing diuretics 2
- Hypochloraemia develops in 35% of patients 2
- Mild transient hypokalaemia occurred in 7 of 17 heart failure patients 1
Hepatic Encephalopathy Risk:
- Encephalopathy occurred in 35% of liver disease patients, indicating metolazone should be used with extreme caution in this population 2
- This risk can be mitigated by preventing hypokalaemia through simultaneous administration of amiloride or spironolactone 2
Renal Function:
- Hyponatraemia and renal impairment may occur, requiring dose reduction 1
- Low incidence of azotaemia (5%) suggests potential utility when renal function is impaired 2
Dosing Algorithm
- Start with 1.25-5 mg daily 1, 2
- Titrate upward based on response, with maximum doses up to 10 mg daily 1
- Always combine with potassium-sparing diuretics (amiloride or spironolactone) in liver disease to prevent life-threatening hypokalaemia 2
- Monitor electrolytes, renal function, and mental status closely 1, 2
If Referring to Methandrostenolone (Anabolic Steroid)
Mechanism of Action
- Methandrostenolone is a 17α-alkylated anabolic-androgenic steroid with potent anabolic effects but significant androgenic and hepatotoxic properties 3
Endocrine Effects
- Large doses (nearly ten times therapeutic levels) cause marked depression of testosterone levels in urine and blood, with some suppression of gonadotrophin excretion 3
- This represents significant hypothalamic-pituitary-gonadal axis suppression 3
Contraindications and Precautions
Absolute Contraindications:
Relative Contraindications/Use with Extreme Caution:
- Patients particularly sensitive to side effects 4
- Conditions where fluid retention must be prevented 4
- Liver diseases (due to hepatotoxicity risk) 4
- Skeletal metastases of mammary carcinoma 4
- Incomplete longitudinal growth 4
Hepatotoxic Effects
- 17α-alkylated steroids like methandrostenolone cause hepatic alterations ranging from abnormal liver function tests to life-threatening liver tumours 4
- This is a domain almost exclusively of 17α-alkylated preparations 4
Androgenic Side Effects
- Virilization in females and children, ranging from voice disturbances to severe reproductive derangement 4
- Effects occur in both sexes depending on individual sensitivity, dosage, and drug androgenicity 4
Cardiovascular and Metabolic Effects
- Atherogenic changes in lipid-lipoprotein balance may increase coronary heart disease risk 4
- At excessive doses, can create prediabetic conditions and polycythaemia 4
Psychobehavioral Effects
- Normal doses generally produce positive effects on psyche and behavior 4
- Excessive doses can cause grave psychic and behavioral disturbances and possibly dependence 4
Clinical Pitfall to Avoid
Never confuse metolazone (diuretic) with anabolic steroids—they have completely different indications, mechanisms, and safety profiles. Clarify which medication is intended before prescribing or counseling patients.