For a male patient with a prior pulmonary embolism, is intramuscular testosterone replacement appropriate, and if so, what low‑dose regimen and monitoring are recommended?

Testosterone IM in Patients with Prior Pulmonary Embolism

Intramuscular testosterone replacement can be used in men with a history of pulmonary embolism, but transdermal formulations (gel or patch) are strongly preferred due to lower risk of erythrocytosis and thrombotic events. If IM testosterone is necessary, use the lowest effective dose with more frequent administration intervals and implement intensive hematocrit monitoring.

Route Selection Priority

The choice of testosterone formulation is critical in patients with prior PE:

• Transdermal preparations (gel 1% or patches) are first-line because they produce more stable testosterone levels and significantly lower rates of erythrocytosis compared to IM injections 1, 2
• IM testosterone enanthate or cypionate causes erythrocytosis in 15-44% of patients versus only 2.8-5.5% with transdermal preparations 2
• The TRAVERSE trial (2023) demonstrated that while testosterone therapy overall was noninferior to placebo for major cardiovascular events, there was a higher incidence of pulmonary embolism in the testosterone group 3
• Recent 2025 pharmacovigilance data from FAERS showed no disproportionality signal for PE with testosterone cypionate, though serious outcomes occurred in older patients with complex medical histories 4

If IM Testosterone Must Be Used

When transdermal options are not feasible (cost, skin reactions, transfer concerns), implement this modified IM regimen:

Low-Dose Frequent Injection Protocol:

• Start with 50-100 mg testosterone enanthate or cypionate IM every 7-10 days (NOT the traditional 200-300 mg every 2-3 weeks) 5
• Alternative: 100 mg on days 1,11, and 21 of each month 5
• Target mid-normal testosterone levels (450-600 ng/dL) measured midway between injections 1, 6

The rationale: Smaller, more frequent doses minimize supraphysiologic testosterone peaks that drive erythropoiesis and maintain more stable levels similar to transdermal preparations 5, 2.

Mandatory Safety Monitoring

Given the PE history, implement this intensive surveillance protocol:

Hematocrit Monitoring (Critical):

• Baseline hematocrit before initiating therapy
• Recheck at 6 weeks (earlier than standard 3 months given PE history)
• Then at 3 months, 6 months, and every 3-6 months thereafter 1
• Stop testosterone immediately if hematocrit >54% until it decreases to safe levels 7, 1
• Evaluate for hypoxia and sleep apnea if erythrocytosis develops 7
• Reinitiate only with reduced dose or switch to transdermal 1

Testosterone Level Monitoring:

• Check at 2-3 months after initiation, measured midway between IM injections 7, 1
• Adjust if levels >700 ng/dL or <400 ng/dL 1
• Target mid-normal range (450-600 ng/dL) 6

Clinical Assessment:

• Evaluate at 3-6 months, then every 6-12 months 1, 6
• Screen for leg pain, swelling, chest pain, dyspnea at each visit
• Monitor for mood fluctuations specific to IM injections 1

Contraindications and Relative Contraindications

Absolute contraindications (do not use testosterone):

• Active thromboembolism
• Baseline hematocrit >50% (relative contraindication that becomes absolute >54%) 1, 5
• Prostate or breast cancer 5

Proceed with extreme caution if:

• Sleep apnea (increases PE risk and can worsen with testosterone) 5
• Chronic obstructive pulmonary disease (increases baseline hematocrit) 2
• Multiple cardiovascular risk factors
• Age >60 years with complex medication regimens 4

Key Clinical Pitfalls

1. Avoid traditional high-dose IM regimens (200-300 mg every 2-3 weeks) in PE patients—these create supraphysiologic peaks driving erythrocytosis 5, 2

2. The "early window" risk: Most observational data suggest VTE risk may be highest in the first 3-6 months after TRT initiation 8, making early hematocrit monitoring essential

3. Polypharmacy considerations: While recent data show no statistical association between polypharmacy and PE severity, patients on multiple cardiovascular medications require individualized risk assessment 4

4. Don't rely on absence of disproportionality signals: Even though recent pharmacovigilance studies show no increased PE signal, serious outcomes still occur, particularly in older patients 4

5. Testosterone undecanoate IM: While pulmonary oil microembolism (POME) is rare (<0.1% per injection), it mimics PE symptoms and requires specialized administration protocols 9, 10

Evidence Strength Considerations

The 2010 Endocrine Society guidelines 1 provide the most comprehensive monitoring framework and should guide practice. The landmark TRAVERSE trial 3 provides the highest-quality safety data but showed increased PE incidence with testosterone, reinforcing the need for caution. The 2025 FDA label update removed the boxed warning for major cardiovascular events but added warnings about blood pressure increases 8, reflecting evolving understanding of testosterone's cardiovascular effects.

Bottom line: Transdermal testosterone is safer for PE patients. If IM is necessary, use low-dose frequent injections (50-100 mg every 7-10 days), monitor hematocrit aggressively starting at 6 weeks, and maintain a low threshold for switching to transdermal formulations if hematocrit rises above 50%.