When to repeat testosterone level measurement after switching from Kystrax (naltrexone) to testosterone injections?

From the Guidelines

When switching from Kyzatrex to testosterone injections, you should typically check testosterone levels 4-6 weeks after starting the injection therapy, as this allows the body to reach a steady state with the new delivery method 1. This recommendation is based on the need to ensure that target testosterone levels have been achieved after changing the delivery method, as suggested by the American Urological Association guideline on the evaluation and management of testosterone deficiency 1. The specific timing of testosterone level checks may vary depending on the injection frequency, with measurements typically done midway between injections for twice-weekly or weekly schedules. It is essential to follow the healthcare provider's instructions, as they may adjust the monitoring schedule based on individual response, medical history, and symptoms. According to the guideline, testosterone levels should be measured every 6-12 months while on testosterone therapy to ensure that target levels are maintained 1. Additionally, the guideline suggests discussing the cessation of testosterone therapy if patients achieve target testosterone levels but do not experience sufficient improvement in symptoms 1. In patients with obesity, treatment with testosterone-replacement therapy should be considered when the morning free testosterone is frankly low on at least 2 separate assessments, and the hypogonadism workup has been completed to rule out an etiology of hypogonadism unrelated to obesity 1. The method of testosterone replacement should be individualized for each patient, with transdermal preparations suggested for most hypogonadal men due to their convenience and ability to produce normal serum testosterone concentrations 1. However, for patients receiving testosterone injections, levels should be measured midway between injections, targeting a mid-normal value (500-600 ng/dL) 1. It is crucial to monitor patients to determine that normal serum testosterone concentrations are being achieved, with testing done 2 to 3 months after treatment initiation, and/or after any dose change 1. Once stable levels are confirmed on a given dose, monitoring every 6 to 12 months is typically sufficient 1. The safety concerns regarding testosterone injections, such as the potential increased risk of cardiovascular events, should be considered, and patients should be closely monitored 1. In summary, the key to managing testosterone replacement therapy is individualized care, regular monitoring, and adjusting the treatment plan as needed to ensure optimal outcomes. Key points to consider when switching from Kyzatrex to testosterone injections include:

• Checking testosterone levels 4-6 weeks after starting injection therapy
• Measuring testosterone levels every 6-12 months while on therapy
• Discussing cessation of therapy if target levels are achieved but symptoms do not improve
• Individualizing the method of testosterone replacement
• Monitoring patients closely to ensure normal serum testosterone concentrations are achieved
• Adjusting the treatment plan as needed to minimize potential risks and optimize outcomes.

From the FDA Drug Label

DOSAGE AND ADMINISTRATION ... Injections more frequently than every two weeks are rarely indicated. Male hypogonadism: As replacement therapy, i.e., for eunuchism, the suggested dosage is 50 to 400 mg every 2 to 4 weeks.

The dosage and administration of testosterone enanthate injection will depend on the patient's response to treatment.

• The suggested dosage for male hypogonadism is 50 to 400 mg every 2 to 4 weeks.
• Injections more frequently than every two weeks are rarely indicated. Since the question is about when to repeat testosterone after changing from Kyzatrex to testosterone injections, the answer is to repeat the injection every 2 to 4 weeks, depending on the patient's response to treatment and the diagnosis of hypogonadism 2.

From the Research

Testosterone Replacement Therapy

When changing from Kyzatrex to testosterone injections, the timing of the next testosterone dose depends on various factors, including the specific formulation of testosterone used and individual patient needs.

• The study 3 suggests that for the treatment of testosterone deficiency in adult males, long-acting esters of testosterone, such as testosterone enanthate or testosterone cypionate, should be administered by intramuscular injection, with dosing intervals of 200 mg every two weeks or 300 mg every three weeks.
• Another study 4 compared different dosage regimens of testosterone enanthate and found that 200 mg every 2 weeks and 300 mg every 3 weeks were the most effective in suppressing serum LH concentrations to normal and had the infrequency of administration.
• A more recent study 5 compared the efficacy and safety of a novel long-acting testosterone undecanoate formulation with testosterone enanthate and found that administration of testosterone undecanoate every 12 weeks was at least as safe and efficacious as testosterone enanthate, with a substantially lower frequency of administration.
• Study 6 evaluated the efficacy and safety of a subcutaneous testosterone enanthate auto-injector administered weekly and found that dose adjustments were made at week 7 to 50,75, or 100 mg testosterone enanthate based on the week 6 total testosterone trough concentration.
• Study 7 assessed the effects of chronic testosterone cypionate therapy on circulating levels of testosterone and found that testosterone cypionate injections every 14 days did not appear to maintain increased testosterone concentrations for 2 full weeks, and other dosage/injection schedules were being evaluated.

Dosage and Administration

The optimal timing for repeating testosterone injections after changing from Kyzatrex will depend on the specific formulation and dosage used, as well as individual patient response.

• Testosterone enanthate or cypionate may be administered every 2-3 weeks 3, 4.
• Testosterone undecanoate may be administered every 12 weeks 5.
• Subcutaneous testosterone enanthate auto-injector may be administered weekly, with dose adjustments as needed 6.
• Testosterone cypionate may be administered every 14 days, but this may not maintain increased testosterone concentrations for 2 full weeks 7.