TESTOSTERONE ENANTHATE
Clinical safety rating: avoid
Contraindicated (not allowed)
Testosterone enanthate is a prodrug of testosterone, which binds to and activates androgen receptors (AR), modulating gene expression and exerting anabolic and androgenic effects. It also exhibits some affinity for estrogen receptors via aromatization.
| Metabolism | Testosterone enanthate is primarily metabolized in the liver via hydrolysis to testosterone, followed by further metabolism via conjugation (glucuronidation and sulfation) and reduction to androstanediol and androsterone. CYP450 enzymes play a minor role; specifically, CYP3A4 and CYP2D6 are involved in oxidative metabolism of testosterone. |
| Excretion | Primarily renal (90% as glucuronide and sulfate conjugates, 6% unchanged) and biliary/fecal (10%). |
| Half-life | Terminal elimination half-life is approximately 4-5 days (range 3.5-7 days) after intramuscular injection due to slow absorption from the oily depot; supports weekly to biweekly dosing intervals. |
| Protein binding | 97-99% bound primarily to sex hormone-binding globulin (SHBG) and albumin. |
| Volume of Distribution | Approximately 1.0 L/kg, indicating extensive distribution into tissues including muscle, fat, and prostate. |
| Bioavailability | Intramuscular injection: 100% (complete absorption from the oily depot); oral: negligible (<1% due to extensive first-pass metabolism); transdermal formulations: variable (10-20% depending on product). |
| Onset of Action | Intramuscular injection: 24-72 hours for initial effects (e.g., libido, mood), with maximal effects by 1-2 weeks. |
| Duration of Action | Intramuscular injection: 2-3 weeks after a single dose, but clinical effects may persist up to 4 weeks due to slow release from the oily depot. |
| Molecular Weight | 400.6 |
50-400 mg intramuscularly every 2-4 weeks
| Dosage form | INJECTABLE |
| Renal impairment | No specific adjustment required; use with caution in severe impairment (GFR <30 mL/min) due to potential fluid retention |
| Liver impairment | Contraindicated in Child-Pugh class B and C; in mild hepatic impairment (Child-Pugh class A) use with caution and reduce dose by 50% |
| Pediatric use | Not recommended for routine use in children; only for male hypogonadism under specialist guidance: 50 mg/m² intramuscularly every 2-4 weeks, adjust based on growth and bone age |
| Geriatric use | Initiate at lower doses (e.g., 50-100 mg intramuscularly every 4 weeks) and titrate based on serum testosterone levels and clinical response; monitor for prostate enlargement and cardiovascular risk |
| 1st trimester | Use contraindicated due to teratogenic effects, including masculinization of female fetus and potential for congenital anomalies. |
| 2nd trimester | Use contraindicated due to risk of virilization of female fetus and potential adverse effects on pregnancy. |
| 3rd trimester | Use contraindicated due to virilization of female fetus and potential for premature closure of epiphyses in fetus. |
Clinical note
Corticosteroids may increase edema risk and anticoagulants may have increased effects Can cause polycythemia and increased risk of cardiovascular events.
| Placental transfer | Crosses placenta; documented transfer leading to fetal exposure with risks of virilization and developmental effects. |
| Breastfeeding | Excreted in breast milk; may cause virilization in female infants and precocious sexual development in male infants. Use only if clearly needed and benefits outweigh risks. |
■ FDA Black Box Warning
WARNING: POSSIBILITY OF VIRILIZATION IN WOMEN AND PRECOCIOUS PUBERTY IN CHILDREN. Testosterone enanthate can cause serious adverse effects in women and children, including virilization and premature epiphyseal closure.
| Common Effects | Diarrhea Stomach discomfort Increased sweating Injection site reactions pain swelling redness Acne Voice change Breast enlargement in male |
| Serious Effects |
PregnancyBreastfeeding (relative contraindication depending on risk-benefit)Known hypersensitivity to testosterone enanthateProstate cancerMale breast cancerSevere renal or hepatic diseaseHypercalcemia (in immobile patients)
| Precautions | Monitor serum testosterone levels periodically., Risk of erythrocytosis (check hematocrit)., May cause prostate enlargement and exacerbate prostate cancer., Monitor liver function (risk of hepatotoxicity)., May increase risk of cardiovascular events (especially in elderly)., Risk of sleep apnea in patients with predisposing factors., Use with caution in patients with benign prostatic hyperplasia (BPH)., Testosterone can cause hypercalcemia in immobilized patients or those with metastatic breast cancer. |
Loading safety data…
| Lactation Rating | L4 |
| Teratogenic Risk | First trimester: Virilization of female fetus (clitoromegaly, labial fusion) if exposure occurs during sensitive period (8-12 weeks). Second and third trimesters: Continued risk of clitoral enlargement, and potential for accelerated skeletal maturation; masculinization of external genitalia irreversible. |
| Fetal Monitoring | Monitor maternal blood pressure, liver function, lipid profile, and signs of virilization (e.g., hirsutism, acne). Assess fetal growth and anatomy via ultrasound; exclude female pseudohermaphroditism if accidental exposure. |
| Fertility Effects | In males: exogenous testosterone suppresses endogenous LH and FSH, leading to reduced spermatogenesis and infertility; effects may be reversible upon discontinuation. In females: may cause menstrual irregularities, anovulation, and decreased fertility; use contraindicated in pregnancy. |
| Food/Dietary | Take with food to reduce gastrointestinal discomfort if oral methyltestosterone is used (not applicable to enanthate). No significant food interactions for injectable formulation. |
| Clinical Pearls | Administer intramuscularly; avoid inadvertent subcutaneous injection which can cause pain and sterile abscess. Monitor hematocrit and lipid profile; may exacerbate sleep apnea. Use with caution in patients with BMIs >30 due to increased aromatization to estradiol. Do not use for age-related hypogonadism in men without a confirmed pathologic cause per FDA labeling. Detect exogenous testosterone via LC-MS/MS; immunoassays are unreliable for monitoring. |
| Patient Advice | Rotate injection sites (gluteal, vastus lateralis) to prevent lipodystrophy or fibrosis. · Report symptoms of excessive erythrocytosis: headache, blurred vision, or shortness of breath. · Expect a delay of 1-2 weeks for full therapeutic effect; do not double doses if a dose is missed. · Store at room temperature away from light; do not freeze. · Use effective contraception if partner is of childbearing potential; testosterone can impair spermatogenesis. · Women should not handle the solution or use the product due to virilizing effects. |