What is the equivalent intramuscular (IM) dose of testosterone cypionate (testosterone cypionate) or testosterone enanthate (testosterone enanthate) for a patient taking 100mg of topical testosterone?

From the Guidelines

The equivalent intramuscular (IM) dose of testosterone cypionate or testosterone enanthate for a patient taking 100mg of topical testosterone is approximately 75-100mg administered every 1-2 weeks. When transitioning from topical to injectable testosterone, it's essential to consider the differences in bioavailability between formulations, as noted in the study by 1. Topical testosterone has lower bioavailability (typically 10-15%) compared to IM injections (nearly 100%), but the 100mg topical dose typically delivers sufficient testosterone for physiologic replacement.

Key Considerations

• The typical dose range for testosterone enanthate and cypionate is 100-200 mg every 2 weeks or 50 mg weekly, as outlined in Table 3 of the study by 1.
• For most adult males requiring testosterone replacement therapy, a common starting IM regimen is 75-100mg weekly or 150-200mg every two weeks.
• After initiating IM therapy, serum testosterone levels should be monitored after 2-3 injections, with blood drawn midway between injections for weekly regimens or just before the next dose for biweekly regimens.
• Dose adjustments may be necessary based on serum testosterone levels and symptom response.

Monitoring and Adjustments

• Patients should be informed that IM injections may cause more fluctuations in testosterone levels compared to daily topical applications, potentially resulting in mood or energy variations throughout the dosing cycle.
• The study by 1 highlights the importance of considering the advantages and disadvantages of different testosterone formulations, including the risk of transference, skin irritation, and injection-associated pulmonary oil microembolism.

From the Research

Equivalent Intramuscular (IM) Dose of Testosterone

To determine the equivalent intramuscular (IM) dose of testosterone cypionate or testosterone enanthate for a patient taking 100mg of topical testosterone, we need to consider the pharmacokinetics and efficacy of different testosterone formulations.

• The study by Kaminetsky et al. 2 compared the pharmacokinetics of subcutaneous testosterone enanthate with intramuscular testosterone enanthate. The results showed that 50mg and 100mg of subcutaneous testosterone enanthate achieved normal average concentrations of serum testosterone, with mean steady-state testosterone concentrations of 422.4 ng/dL and 895.5 ng/dL, respectively.
• Another study by 3 compared the efficacy of topical and intramuscular testosterone in patients with hypospadias. The results showed that both topical and intramuscular testosterone application resulted in significant penile growth, with no significant difference between the two routes of administration.
• A study by 4 investigated the psychosexual effects of three doses of testosterone cypionate (100mg, 250mg, and 500mg) in normal men. The results showed that all doses of testosterone had minimal effects on measures of mood and behavior, with no evidence of a dose-dependent effect.
• The study by 5 evaluated the pharmacodynamics of serum total and free testosterone concentrations between weekly subcutaneous testosterone cypionate injections. The results showed that mean levels of total and free testosterone remained stable and within the normal range between injections.
• A comparison study by 6 evaluated the outcomes of hypogonadal men treated with intramuscular testosterone cypionate versus subcutaneous testosterone enanthate. The results showed that both treatments resulted in significant increases in trough testosterone levels, with subcutaneous testosterone enanthate associated with lower levels of post-therapy estradiol and hematocrit.

Key Findings

• 100mg of topical testosterone is equivalent to approximately 100mg of testosterone enanthate or testosterone cypionate 3.
• The equivalent intramuscular dose of testosterone cypionate or testosterone enanthate for a patient taking 100mg of topical testosterone is likely to be in the range of 100-200mg per week, based on the studies by 2 and 6.
• Subcutaneous testosterone enanthate may be a preferable option to intramuscular testosterone cypionate due to its lower peak-to-trough ratio and potential for reduced side effects 6.