Testosterone isocaproate

Table of contents

• What is testosterone isocaproate?
• How does testosterone isocaproate work?
• Which conditions is it used or studied for?
• How is testosterone isocaproate given?
• What do the clinical trials show?
• What side effects are known?

What is testosterone isocaproate?

Testosterone isocaproate is a chemically synthesised ester of testosterone, the main male sex hormone. It is one of four testosterone esters in the fixed combination product Sustanon 250, solution for injection, alongside testosterone propionate, testosterone phenylpropionate and testosterone decanoate.^[1] The product is authorised as a medicine in Belgium under authorisation record BE012704, held by Aspen Pharma Trading Limited.^[1] The electronic medicines compendium (emc) lists Sustanon 250 as the only product containing testosterone isocaproate.^[4] In the clinical trial register, the substance appears under the combined registry name of all four testosterone esters.^[1]

How does testosterone isocaproate work?

Testosterone is the principal androgen hormone in men. It supports the development and maintenance of male sexual characteristics, muscle strength, bone density and red blood cell production. NHS shared care guidance describes testosterone treatment for male hypogonadism, a condition in which the body does not produce enough testosterone, and notes that treatment aims to restore testosterone levels to the normal range.^[2] The different esters in Sustanon 250 are absorbed at different rates after injection, which allows a sustained release of testosterone over time. The trial record does not provide further detail on the mechanism of action in palliative care.^[1]

Which conditions is it used or studied for?

• Androgen deficiency: Testosterone products are commissioned in NHS formularies for hypogonadism due to androgen deficiency in adult men.^[5]
• Palliative care: The registered trial studies testosterone supplementation in male patients in best supportive care who have no therapeutic options left and do not wish to be resuscitated.^[1]
• Transgender hormone treatment: NHS formulary guidance lists testosterone preparations for transgender patients requiring virilising endocrine therapy.^[5]
• Low sexual desire in menopausal women: Testosterone gel has been approved in some NHS areas for low sexual desire in women experiencing menopausal symptoms when HRT alone is not effective.^[3]

How is testosterone isocaproate given?

Testosterone isocaproate is given as a solution for injection. The trial record for Sustanon 250 lists the route of administration as intravenous use, although the product is more commonly given by deep intramuscular injection in clinical practice.^[1] The Bradford Teaching Hospitals formulary lists Sustanon 250 as an injection and also lists other testosterone formulations including transdermal gels (Testavan, Testogel, Tostran) and the long-acting injection Nebido.^[3] The Norfolk and Waveney formulary describes testosterone gel products for transdermal application and testosterone injection Sustanon 250 for male androgen deficiency in adults.^[5]

What do the clinical trials show?

One clinical trial is registered for testosterone isocaproate as part of Sustanon 250. It is a Phase 2 interventional study in 25 participants with androgen deficiency in palliative care.^[1] The trial is currently authorised, meaning it has received regulatory approval to proceed. It evaluates the impact of testosterone supplementation on the quality of life of male patients in best supportive care with no therapeutic options left and who do not wish to be reanimated.^[1]

The primary outcome measures two aspects of quality of life. The first is the best improvement over time in independence using the ADL independence scale, covering personal hygiene, dressing, going to the toilet, locomotion, continence and eating. The second is the best improvement over time in symptoms of pain, fatigue, sadness, anxiety, drowsiness, appetite, sense of well-being, shortness of breath, bowel movements and strength, measured with the Edmonton Symptom Assessment Scale.^[1]

The study population is male patients in best supportive care with androgen deficiency. The trial does not report comparator arms; the intervention is Sustanon 250, solution injectable.^[1]

What side effects are known?

The shared care protocol from the Leicester, Leicestershire and Rutland prescribing committee lists monitoring requirements for testosterone treatment in male hypogonadism. These include baseline and follow-up measurement of testosterone level, full blood count (FBC), liver function tests (LFTs), lipid profile and, for men aged 40 years and over, prostate-specific antigen (PSA).^[2] The protocol also mentions monitoring for adverse drug reactions during the titration period and annual monitoring of the same parameters once care is shared with the general practitioner.^[2] The formulary sources do not provide a list of common or serious side effects for testosterone isocaproate specifically, and the trial record does not report side effect data.^[1][5]