Nebido (Testosterone Undecanoate)

Nebido is an androgen used in testosterone replacement therapy to address disorders of low endogenous testosterone.

• Male hypogonadism: restores normal testosterone concentrations and alleviates symptoms such as reduced libido, fatigue, and loss of muscle mass.
• Primary hypogonadism: compensates for testicular failure by providing exogenous testosterone.
• Secondary hypogonadism: replaces deficient gonadotropin‑stimulated testosterone production due to hypothalamic or pituitary dysfunction.

• Testosterone undecanoate is a long‑acting ester that, after intramuscular injection, is hydrolysed to testosterone. The liberated testosterone binds intracellular androgen receptors, modulating gene transcription that produces both anabolic effects (muscle growth, bone density) and androgenic effects (development of male secondary sexual characteristics). This restores physiological hormone levels in men with testosterone deficiency.

Nebido may cause a range of adverse reactions, varying from mild to serious.

Common Side Effects

• Injection site pain or erythema
• Acne or oily skin
• Increased red blood cell count (polycythemia)
• Fluid retention or peripheral edema
• Headache or dizziness
• Mood changes or irritability

Serious or Rare Side Effects

• Severe allergic reaction (anaphylaxis)
• Significant polycythemia leading to thrombosis
• Cardiovascular events such as myocardial infarction or stroke
• Liver function abnormalities
• Prostate enlargement or aggravation of existing prostate disease
• Testicular atrophy or infertility

Before initiating Nebido therapy, clinicians should consider several safety measures.

• Screen for prostate cancer: perform baseline PSA and digital rectal exam.
• Monitor hematocrit: check every 3–6 months to detect polycythemia.
• Assess cardiovascular risk: evaluate history of heart disease or stroke.
• Avoid use in patients with known hypersensitivity to testosterone products.
• Pregnancy and breastfeeding: not indicated; avoid exposure in women.
• Store at ambient temperature: keep in original packaging, protect from moisture and light.

Nebido can interact with several medicines, requiring careful management.

Major Interactions (Avoid)

• Warfarin: may increase anticoagulant effect and bleeding risk.
• Insulin or oral hypoglycemics: testosterone can alter glucose metabolism, necessitating dose adjustments.
• Strong CYP3A4 inhibitors (e.g., ketoconazole): can raise testosterone levels and increase adverse event risk.

Moderate Interactions (Monitor Closely)

• Other anticoagulants (e.g., apixaban): monitor coagulation parameters.
• Glucocorticoids: may exacerbate fluid retention.
• Statins: possible additive effect on liver enzymes; periodic liver function testing recommended.