Nebido (Testosterone Undecanoate)

Nebido (testosterone undecanoate) is used in testosterone replacement therapy to address androgen deficiency.

• Male hypogonadism: restores normal testosterone levels and alleviates symptoms such as low libido, fatigue, and loss of muscle mass.
• Testosterone deficiency: improves energy, mood, and bone density in men with documented low testosterone.
• Secondary hypogonadism: supports endogenous hormone production when pituitary or hypothalamic dysfunction reduces testosterone output.

• Testosterone undecanoate is a long‑acting prodrug that is enzymatically hydrolyzed after intramuscular injection to release testosterone. The liberated testosterone binds to intracellular androgen receptors, modulating gene transcription and promoting anabolic effects in target tissues such as muscle, bone, and the reproductive system, thereby correcting the hormonal deficit.

Nebido may cause a range of adverse reactions, most of which are dose‑related and reversible upon discontinuation.

Common Side Effects

• Injection site pain: mild to moderate discomfort at the injection site.
• Acne: increased sebaceous gland activity leading to skin eruptions.
• Fluid retention: mild edema, especially in the lower extremities.
• Elevated hematocrit: rise in red blood cell concentration.

Serious or Rare Side Effects

• Polycythemia: excessive increase in red blood cells that may require therapeutic phlebotomy.
• Liver toxicity: abnormal liver function tests or hepatic injury.
• Cardiovascular events: increased risk of thrombosis, myocardial infarction, or stroke in susceptible individuals.

Before initiating Nebido therapy, clinicians should evaluate patient history and monitor specific parameters.

• Hematocrit monitoring: check levels periodically to detect polycythemia.
• Prostate assessment: perform baseline PSA and digital exam, then monitor regularly.
• Cardiovascular risk: assess for hypertension, dyslipidemia, or prior thrombotic events.
• Liver function: evaluate hepatic enzymes before and during treatment.
• Hypersensitivity: discontinue if allergic reactions such as rash or anaphylaxis occur.
• 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): may increase bleeding risk.
• 5α‑Reductase inhibitors (e.g., finasteride): can reduce conversion of testosterone to dihydrotestosterone, affecting therapeutic outcomes.

Moderate Interactions (Monitor Closely)

• CYP3A4 inhibitors (e.g., ketoconazole): may raise testosterone levels.
• Glucocorticoids: can exacerbate fluid retention and hypertension.
• Insulin or oral hypoglycemics: testosterone may affect glucose metabolism, requiring dose adjustments.