Nebido (Testosterone Undecanoate)

• Nebido is used in androgen replacement therapy to address conditions associated with low endogenous testosterone.
• Male hypogonadism: restores normal testosterone levels, improving fatigue, libido and muscle mass.
• Secondary hypogonadism: provides exogenous testosterone when pituitary or hypothalamic dysfunction reduces hormone production.
• Testosterone replacement therapy: maintains physiological testosterone concentrations in men requiring long‑acting supplementation.
• Age‑related testosterone decline: helps alleviate symptoms of low testosterone in older men.

• Testosterone undecanoate is a lipophilic ester of testosterone that, after intramuscular injection, is slowly hydrolysed by esterases to release free testosterone. The liberated testosterone binds to intracellular androgen receptors, modulating gene transcription and promoting anabolic processes such as protein synthesis, while also exerting androgenic effects on secondary sexual characteristics. It also influences the hypothalamic‑pituitary‑gonadal axis by providing negative feedback, reducing luteinizing hormone secretion, which helps stabilize endogenous production.

Nebido may be associated with a range of adverse reactions, which are generally classified by frequency and severity.

Common Side Effects

• Injection site pain: mild discomfort or bruising at the injection site.
• Acne: increased sebaceous gland activity leading to breakouts.
• Fluid retention: mild edema, especially in lower extremities.
• Increased hematocrit: rise in red blood cell mass causing thicker blood.
• Headache: transient mild to moderate headache.

Serious or Rare Side Effects

• Cardiovascular events: rare cases of myocardial infarction or stroke.
• Severe allergic reaction: anaphylaxis, urticaria, or angioedema.
• Prostate abnormalities: rapid growth of existing prostate cancer or significant PSA rise.

Before initiating Nebido therapy, several precautions should be considered to ensure safe use.

• Screen for prostate cancer: perform baseline PSA and digital rectal exam.
• Assess cardiovascular risk: evaluate history of heart disease, stroke, or thrombosis.
• Monitor hematocrit: regular blood tests to detect polycythemia.
• Avoid in patients with untreated severe sleep apnea.
• Contraindicated in known hypersensitivity to testosterone undecanoate or excipients.
• Store at 2-8°C: keep refrigerated, protect from light, do not freeze or shake.

Nebido can interact with several medications, altering its efficacy or safety profile.

Major Interactions (Avoid)

• Anticoagulants (e.g., warfarin): increased risk of thrombosis due to elevated hematocrit.
• Insulin or oral hypoglycemics: testosterone may enhance insulin resistance, requiring dose adjustment.
• CYP3A4 inhibitors (e.g., ketoconazole): may increase testosterone levels, raising risk of adverse effects.
• 5α‑reductase inhibitors: may reduce conversion to dihydrotestosterone, affecting efficacy.

Moderate Interactions (Monitor Closely)

• Glucocorticoids: may exacerbate fluid retention.
• Thiazide diuretics: can potentiate blood pressure changes.
• Estrogen therapy: may counteract androgenic effects.