Testosterone undecanoate

How it works

The ester is hydrolysed to release testosterone, which acts on androgen receptors to maintain male secondary sexual characteristics, libido, muscle and bone, and spermatogenesis; the oral form is absorbed partly via the lymphatic system, reducing first-pass metabolism.

Prescribing in practice

• The depot injection carries a recognised risk of pulmonary oil microembolism and anaphylactic reactions, so it must be injected very slowly and deeply, with observation of the patient afterwards.
• It is contraindicated in known or suspected prostate or breast carcinoma in men, so prostate status, PSA where appropriate, and haematocrit should be assessed before and during treatment.
• Polycythaemia can occur and the haematocrit should be monitored, while pregnancy is a contraindication because of the risk of virilising a female foetus.

Monitoring

Monitor serum testosterone to guide dosing intervals, together with haematocrit, prostate status, PSA, lipids, and liver function during long-term replacement.

Counselling the patient

• The depot injection is given slowly into a muscle, and you may be observed afterwards for any breathing or fainting reaction.
• Report difficulty passing urine, breast swelling, or persistent headache.
• Take the oral form with food as advised, since this affects how it is absorbed.

Evidence & guidelines

Its use is supported by clinical trials and endocrine guidance on long-acting testosterone replacement in confirmed male hypogonadism.