Nebido (Testosterone Undecanoate)

Nebido is used in hormone replacement therapy to address testosterone deficiency in men.

• Male hypogonadism: restores normal serum testosterone levels, improving symptoms such as low libido, fatigue and loss of muscle mass.
• Testosterone replacement therapy: provides a long‑acting source of testosterone, reducing the frequency of injections compared with shorter‑acting esters.
• Secondary hypogonadism: compensates for inadequate endogenous production due to pituitary or hypothalamic dysfunction, supporting normal androgenic function.

• Testosterone undecanoate is a long‑acting ester of testosterone that acts as a prodrug. After intramuscular injection, the ester is slowly hydrolysed by tissue esterases, releasing testosterone into circulation. The liberated testosterone binds intracellular androgen receptors, modulating gene transcription that drives androgenic and anabolic effects in target tissues such as muscle, bone and the reproductive system, and contributes to the maintenance of secondary sexual characteristics.

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

Common Side Effects

• Injection site pain: mild to moderate discomfort, swelling or bruising at the injection site.
• Headache: transient headache that may appear within hours after the dose.
• Acne: increased sebaceous gland activity causing oily skin and acneiform lesions.

Serious or Rare Side Effects

• Polycythemia: elevated red blood cell count that can raise the risk of thrombosis and hypertension.
• Cardiovascular events: rare occurrences of myocardial infarction, stroke, or unstable angina in susceptible patients.
• Prostate abnormalities: rapid progression of existing prostate cancer, significant rise in prostate‑specific antigen (PSA), or urinary obstruction.

When prescribing Nebido, several precautions should be observed to ensure patient safety and product integrity.

• Patient assessment: evaluate baseline testosterone levels, hematocrit, liver function and prostate health before initiating therapy.
• Cardiovascular risk: avoid use in patients with uncontrolled hypertension, recent myocardial infarction or high thrombotic risk.
• Sleep apnea: screen for obstructive sleep apnea, as testosterone may worsen the condition.
• Monitoring: schedule regular follow‑up for hematocrit, lipid profile and PSA to detect adverse changes.
• Contraindications: do not use in individuals with known hypersensitivity to testosterone undecanoate or any component of the formulation.
• Store at 2-8°C: keep refrigerated, protect from light, do not freeze or shake the vial.

Nebido can interact with other medicines, affecting hormone levels or increasing the risk of adverse events.

Major Interactions (Avoid)

• Anticoagulants: testosterone may enhance erythrocytosis, potentially augmenting clotting risk when combined with warfarin or direct oral anticoagulants.
• Corticosteroids: concurrent use can exacerbate fluid retention and hypertension.
• 5α‑reductase inhibitors: may alter the conversion of testosterone to dihydrotestosterone, affecting efficacy.

Moderate Interactions (Monitor Closely)

• Insulin and oral hypoglycemics: testosterone can affect glucose metabolism, requiring dose adjustments.
• CYP3A4 inhibitors/inducers: may modify the metabolism of testosterone esters, influencing serum levels.