Testosterone decanoate, isocaproate, phenylpropionate and propionate

How it works

After intramuscular injection the esters are gradually hydrolysed to release testosterone, the principal endogenous androgen, which acts on androgen receptors to maintain male secondary sexual characteristics, libido, muscle and bone, and to support spermatogenesis.

Prescribing in practice

• It is contraindicated in known or suspected prostate or breast carcinoma in men, and prostate assessment (including PSA where appropriate) and haematocrit should be checked before starting, as androgens can stimulate existing prostate cancer.
• Polycythaemia can develop, so the haematocrit should be monitored periodically during therapy.
• It should be avoided in pregnancy because of the risk of virilisation of a female foetus, and the oily injection must be given by deep intramuscular injection.

Monitoring

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

Counselling the patient

• This treatment is given as a deep injection into a muscle by a healthcare professional.
• Report difficulty passing urine, breast tenderness or swelling, or persistent headache.
• Mood, libido, and energy may take some weeks to stabilise after starting.

Evidence & guidelines

Use is supported by long-standing clinical experience and endocrine society guidance on testosterone replacement in confirmed male hypogonadism.