Where do adult males with hypogonadism (low testosterone levels) inject testosterone?

Injection Sites for Testosterone in Adult Males with Hypogonadism

Adult males with hypogonadism inject testosterone intramuscularly into large muscle groups, most commonly the gluteal (buttock) muscles or the vastus lateralis (lateral thigh), with injections typically administered every 2-3 weeks using testosterone cypionate or enanthate. 1

Standard Intramuscular Injection Sites

The traditional approach involves intramuscular (IM) administration into:

• Gluteal muscles (buttocks): The upper outer quadrant is the most common site for IM testosterone injections 1
• Vastus lateralis (lateral thigh): An alternative site that allows for self-administration 1
• Deltoid muscle (shoulder): Less commonly used due to smaller muscle mass and injection volume limitations

These injections achieve peak serum testosterone levels 2-5 days after administration, with return to baseline typically occurring 10-14 days post-injection, supporting the standard 2-4 week dosing interval 1

Emerging Alternative: Subcutaneous Administration

Subcutaneous (SC) injection into abdominal fat tissue is an effective and increasingly preferred alternative to traditional IM injections. 2 This approach offers several advantages:

• Injection site: Lower abdominal wall subcutaneous tissue 2
• Efficacy: Achieves serum testosterone levels within the normal male range in all patients studied, with doses of 50-150 mg weekly 2
• Patient preference: Among 22 patients who switched from IM to SC, all had either mild (n=2) or marked (n=20) preference for SC injections; none preferred IM 2
• Tolerability: Minor and transient local reactions occurred in only 9 out of 63 patients (14.3%) 2
• Effectiveness across body types: Therapy was effective across a wide BMI range (19.0 to 49.9 kg/m²) 2

The subcutaneous route involves significantly less discomfort and allows easier self-administration compared to IM injections 2

Pellet Implantation Sites

For patients choosing long-acting testosterone pellets:

• Subdermal fat tissue of the lower abdominal wall is the standard implantation site 3
• Pellets provide the longest biological action of any testosterone formulation, with therapeutic levels maintained for approximately 180 days 3
• However, local infections occurred in 5.4% of implantations, leading to pellet extrusion in some cases 3

Clinical Decision-Making Algorithm

When selecting injection sites, consider:

1. Cost considerations: IM injections are significantly more economical ($156.24 annually) compared to transdermal preparations ($2,135.32 annually), making them the preferred choice when cost is a barrier 4, 5

2. Patient preference and convenience:

   • 53% of patients initially chose injectable testosterone over gel-based or pellet regimens primarily due to lower cost 4
   • However, among patients who tried multiple formulations, 71% preferred topical gel over injections for convenience, ease of use, and non-staining of clothes 4

3. Stability of testosterone levels: Transdermal preparations provide more stable day-to-day testosterone levels compared to the peak-and-trough pattern of IM injections 1

4. Risk of erythrocytosis: Injectable testosterone carries a higher risk of erythrocytosis (up to 44%) compared to transdermal preparations (3-18%) 5

Important Clinical Caveats

• Monitoring injection site: For IM injections, testosterone levels should be measured midway between injections, targeting a mid-normal value (500-600 ng/dL) 1
• Avoid fertility compromise: Testosterone therapy is absolutely contraindicated in men seeking fertility preservation, as it suppresses spermatogenesis and causes azoospermia; gonadotropin therapy must be used instead 1, 5
• Subcutaneous administration is off-label: While highly effective and preferred by patients, SC testosterone administration is not FDA-approved and represents off-label use 2
• Weekly vs. biweekly dosing: SC injections typically use weekly dosing (50-150 mg) to maintain more stable levels, whereas IM injections use biweekly or triweekly dosing (100-200 mg every 2 weeks) 1, 2