metyrapone: clinical use

Prescribing considerations

• Restrict diagnostic testing to referral hospital centres with appropriate supervision and biochemical facilities.
• Treatment should be supervised by clinicians experienced in managing hypercortisolism and hypocortisolism.
• Exercise caution with reduced adrenal reserve, severe hypopituitarism, liver dysfunction, hypertension, hypokalaemia, relevant cardiac disease or electrolyte disturbance.
• Use cortisol assays with minimal cross-reactivity from accumulating steroid precursors.

Contraindications and cautions

• Primary adrenocortical insufficiency.
• Hypersensitivity to metyrapone or any product excipient.

Monitoring

• Clinical and biochemical evidence of hypocortisolism.
• Cortisol, using a suitable assay.
• Potassium and correction of hypokalaemia.
• Blood pressure.
• ECG and electrolytes when cardiac risk exists or arrhythmia symptoms occur.
• Blood counts or liver enzymes when clinically indicated.

Clinical pharmacology

Metyrapone inhibits adrenal 11β-hydroxylase, decreasing cortisol and aldosterone synthesis. Reduced cortisol feedback increases ACTH and 11-deoxycortisol; metyrapol is the principal active metabolite.

Formulation and product differences

• The selected product is an oblong, yellowish-white, opaque soft gelatin capsule marked “M01” in red.
• The capsule contains gelatin and the parabens E215 and E217, which may cause delayed allergic reactions.
• It is essentially sodium-free and supplied in a child-resistant bottle that should be kept tightly closed to protect the capsules from moisture.

Capsule

Route: Oral

Strengths: 250 mg