Nebido (Testosterone Undecanoate)

Nebido (testosterone undecanoate) is used in hormone replacement therapy to address conditions caused by insufficient endogenous testosterone.

• Male hypogonadism: restores normal serum testosterone levels, improving symptoms such as low libido, fatigue, and reduced muscle mass.
• Testosterone deficiency syndrome: alleviates biochemical deficiency and associated clinical signs in adult men.
• Delayed puberty in males: provides exogenous testosterone to initiate and support normal pubertal development.

• Testosterone undecanoate is a long‑acting ester of testosterone that, after intramuscular administration, is hydrolyzed to testosterone. The liberated testosterone binds intracellular androgen receptors, modulating gene transcription and promoting anabolic processes. This restores physiological androgenic activity in tissues, normalizing the hypothalamic‑pituitary‑gonadal feedback loop in men with deficient endogenous production. The increased circulating testosterone also undergoes peripheral conversion to dihydrotestosterone and estradiol, contributing to its diverse physiological effects.

Nebido may be associated with a range of adverse reactions, varying from mild to serious.

Common Side Effects

• Injection site pain: discomfort or soreness at the injection site.
• Headache: mild to moderate head pain.
• Acne: increased skin oiliness leading to pimples.
• Fluid retention: mild edema, especially in lower extremities.
• Gynecomastia: breast tissue enlargement in men.
• Mood changes: irritability or emotional fluctuations.

Serious or Rare Side Effects

• Polycythemia: elevated red blood cell count that may increase clot risk.
• Cardiovascular events: potential for myocardial infarction or stroke.
• Liver toxicity: abnormal liver function tests or hepatitis.
• Sleep apnea worsening: exacerbation of pre‑existing sleep‑disordered breathing.

Before initiating Nebido therapy, clinicians should consider several precautionary measures to ensure patient safety.

• Baseline assessment: obtain serum testosterone, hematocrit and prostate-specific antigen levels prior to treatment.
• Cardiovascular risk: evaluate history of heart disease, as therapy may affect lipid profile and blood viscosity.
• Prostate health: monitor for signs of prostate enlargement or cancer during therapy.
• Hematocrit monitoring: check hematocrit periodically to detect polycythemia.
• Pregnancy contraindication: avoid use in women; drug is teratogenic (Category X).
• Store at ambient temperature: keep vials below 25 °C, protect from light and moisture, and do not freeze.

Nebido can interact with other medicines, altering its efficacy or safety profile.

Major Interactions (Avoid)

• Anticoagulants: increased risk of thrombosis due to elevated hematocrit.
• Corticosteroids: may exacerbate fluid retention and hypertension.
• 5‑alpha‑reductase inhibitors: can affect conversion of testosterone to dihydrotestosterone.

Moderate Interactions (Monitor Closely)

• Insulin and oral hypoglycemics: testosterone may affect glucose metabolism.
• Lipid‑lowering agents: potential changes in cholesterol levels.
• Hormonal therapies: concurrent use may lead to hormonal imbalance.