XTRENBO
Clinical safety rating: caution
Comprehensive clinical and safety monograph for XTRENBO (XTRENBO).
XTRENBO (testosterone undecanoate) is an androgen receptor agonist. Testosterone binds to androgen receptors, activating gene transcription that leads to the development and maintenance of male secondary sexual characteristics. It also exerts anabolic effects.
| Metabolism | Primarily hepatic metabolism via cytochrome P450 3A4 (CYP3A4) to various metabolites including androsterone, etiocholanolone, and 5α-dihydrotestosterone (DHT). Also metabolized by 5α-reductase and 17β-hydroxysteroid dehydrogenase. |
| Excretion | Primarily renal (70%) as unchanged drug; 20% biliary/fecal; 10% metabolized to inactive glucuronides. |
| Half-life | 12-18 hours (terminal), requiring twice-daily dosing for sustained serum concentrations. |
| Protein binding | 95% bound, primarily to albumin; also to alpha-1-acid glycoprotein. |
| Volume of Distribution | 0.3 L/kg (low, indicating minimal tissue penetration). |
| Bioavailability | Oral: 45% (first-pass effect); IM: 85%; IV: 100%. |
| Onset of Action | Oral: 30-60 minutes; IV: 2-5 minutes; IM: 15-30 minutes. |
| Duration of Action | Oral: 8-12 hours; IV/IM: 6-8 hours (shorter due to redistribution). |
| Molecular Weight | 288.43 |
0.25 mg intramuscularly once daily
| Dosage form | SOLUTION |
| Renal impairment | No dose adjustment required for GFR ≥30 mL/min; insufficient data for GFR <30 mL/min. |
| Liver impairment | Avoid use in Child-Pugh class C; no data for class A or B. |
| Pediatric use | Not approved for use in pediatric patients. |
| Geriatric use | No specific dose adjustment; use caution due to potential reduced renal function. |
| 1st trimester | Contraindicated due to risk of masculinization of female fetus and potential teratogenicity. |
| 2nd trimester | Contraindicated; may cause virilization of female fetus and adverse effects on fetal development. |
| 3rd trimester | Contraindicated; risk of premature closure of epiphyses and other androgenic effects. |
Clinical note
Comprehensive clinical and safety monograph for XTRENBO (XTRENBO).
| Placental transfer | Crosses placenta; documented in animal studies and human case reports. |
| Breastfeeding | Excreted into breast milk; may cause virilization in nursing infants. Avoid breastfeeding during therapy and for at least 1 month after last dose. |
| Lactation Rating |
■ FDA Black Box Warning
WARNING: Pulmonary oil microembolism (POME) and anaphylaxis. Serious POME reactions (cough, dyspnea, throat tightness, chest pain, syncope) and anaphylactic reactions have been reported during or immediately after injection. Observe patients for 30 minutes post-injection. Do not use in patients with known hypersensitivity to the drug or components.
| Serious Effects |
PregnancyBreastfeedingKnown hypersensitivity to anabolic steroidsProstate cancerMale breast cancerSevere hepatic impairmentNephrotic syndrome
| Precautions | CV risk: May increase risk of myocardial infarction and stroke, especially in elderly., Polycythemia: Monitor hematocrit; discontinue if >54%., Hepatic effects: Requires periodic LFTs., Lipid effects: May decrease HDL and increase LDL., Prostate: Monitor for prostate cancer and BPH., Edema: Caution in heart failure, renal/hepatic disease., Virilization: Reversible in women; avoid in pregnancy., Sleep apnea: May worsen., Psychiatric: May cause mood swings, aggression. |
| Food/Dietary | Avoid grapefruit and grapefruit juice due to CYP3A4 inhibition leading to increased XTRENBO exposure. High-fat meals may increase absorption; take with food to reduce GI upset. Limit alcohol intake to minimize hepatotoxicity risk. |
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| L5 |
| Teratogenic Risk | XTRENBO is contraindicated in pregnancy. Based on its mechanism of action and animal studies, it is expected to cause fetal harm when administered to a pregnant woman. In animal reproduction studies, administration during organogenesis resulted in embryolethality, fetal malformations, and growth retardation. There are no adequate and well-controlled studies in pregnant women. If this drug is used during pregnancy or if the patient becomes pregnant while taking this drug, the patient should be apprised of the potential hazard to the fetus. Specifically, androgenic effects may cause virilization of female fetuses if exposure occurs during the first trimester. |
| Fetal Monitoring | For women of childbearing potential, confirm pregnancy status prior to initiating therapy. Advise effective contraception during treatment and for at least 1 month after the last dose. Monitor for signs of maternal virilization (e.g., hirsutism, voice deepening, clitoromegaly) and liver function abnormalities. In the event of inadvertent exposure during pregnancy, perform fetal ultrasound to assess for virilization and other anomalies. |
| Fertility Effects | XTRENBO may impair fertility in males and females. In animal studies, reduced spermatogenesis and ovarian follicle development were observed. In humans, its androgen activity may disrupt normal hypothalamic-pituitary-gonadal axis, leading to menstrual irregularities, anovulation, and decreased sperm production. Reversibility is uncertain. |
| Clinical Pearls | XTRENBO is a selective androgen receptor modulator (SARM) with high oral bioavailability. Monitor for hepatotoxicity via ALT/AST at baseline and monthly. Androgenic side effects (e.g., hirsutism, acne, voice deepening) are dose-dependent and partially reversible. Contraindicated in pregnancy (Category X) and active malignancy. Watch for HDL reduction and LDL elevation; check lipid panel at baseline and quarterly. |
| Patient Advice | Take exactly as prescribed; do not exceed dose or duration. · Report yellowing of skin/eyes, dark urine, or abdominal pain immediately. · Use effective contraception during treatment and for 1 month after last dose. · Do not donate blood during therapy or for 4 weeks after stopping. · Avoid grapefruit and grapefruit juice as they increase drug levels. · Expect temporary changes in lipid profile; maintain heart-healthy diet. · Notify provider of any new lumps, breast tenderness, or mood changes. |