Jatenzo Pediatric (<12) Transition to Adult Care

Why Jatenzo Is Not Approved for Children Under 12

Jatenzo received FDA approval in March 2019 exclusively for adult males with conditions associated with a deficiency or absence of endogenous testosterone [1]. The drug's prescribing information explicitly states it has not been studied in pediatric patients, and its use in children under 12 carries documented risks of serious harm including premature closure of epiphyseal growth plates [2].

The Pharmacology Problem in Pre-Pubertal Bone

Testosterone acts on androgen receptors in growth plate chondrocytes. In children under 12, circulating testosterone above physiological pre-pubertal concentrations (typically below 10 ng/dL) accelerates bone age advancement [3]. Jatenzo produces mean serum testosterone concentrations of approximately 400 to 600 ng/dL in adults taking the standard 237 mg twice-daily dose [1]. Exposing a pre-pubertal skeleton to those concentrations, even briefly, may permanently shorten final adult height.

A 2020 review in the Journal of Clinical Endocrinology and Metabolism confirmed that supraphysiological androgen exposure in boys under 12 consistently advanced bone age by 1 to 3 years beyond chronological age [4]. That acceleration is rarely fully reversible once the physis begins to fuse.

Regulatory Context and Off-Label Risk

The FDA's 2019 approval letter for Jatenzo (NDA 022488) required a specific warning about pediatric misuse and mandated that the label include a statement against use in anyone under 18 except under specialist direction [1]. Off-label prescribing in children under 12 therefore carries heightened medico-legal and clinical risk. Any practitioner considering such use must document a clear risk-benefit analysis, obtain informed consent or assent, and coordinate with a board-certified pediatric endocrinologist.

What Conditions Bring Pediatric Patients Near Jatenzo

Young children rarely require testosterone replacement, but several diagnoses create the clinical pathway that eventually leads toward adult TRT and, potentially, Jatenzo.

Congenital Hypogonadotropic Hypogonadism

Congenital hypogonadotropic hypogonadism (CHH), including Kallmann syndrome, affects approximately 1 in 10,000 to 1 in 86,000 males [5]. Diagnosis in infancy is possible when micro-penis or cryptorchidism prompts hormonal workup revealing undetectable LH, FSH, and testosterone. Short-course neonatal testosterone (typically intramuscular testosterone enanthate 25 mg monthly for 3 months) is used to stimulate penile growth, but this is a time-limited intervention, not chronic replacement [6].

These patients do not restart testosterone therapy until the age when puberty would normally begin, usually around age 12 to 14, at which point the transition framework described in later sections of this article applies directly.

Klinefelter Syndrome (47,XXY)

Klinefelter syndrome occurs in approximately 1 in 500 to 1,000 male births [7]. Testosterone levels in childhood are often normal, declining progressively through adolescence as Leydig cell function deteriorates. Most boys with Klinefelter syndrome do not require testosterone replacement before age 11 to 12, but early identification is critical for timely transition planning [8].

Disorders of Sexual Development (DSD)

Some children assigned male at birth with 46,XY DSD have partial androgen insensitivity or biosynthetic defects in testosterone production. These patients require individualized decisions about androgen therapy, often deferred until puberty, and are managed under multi-disciplinary DSD teams per the 2006 Chicago Consensus and its 2016 update [9].

The Transition Framework: From Pediatric to Adult Care

Transition from pediatric to adult endocrine care is not a single appointment. It is a process lasting 12 to 24 months, ideally beginning between ages 12 and 14 for most testosterone-deficient diagnoses and culminating in a stable adult provider relationship by age 18 [10].

Phase 1: Pre-Transition Preparation (Ages 10 to 12)

The pediatric endocrinology team should:

• Confirm the underlying diagnosis with updated laboratory testing, including morning total testosterone, LH, FSH, and karyotype if not previously obtained [4].
• Obtain a bone age radiograph of the left hand and wrist to document skeletal maturity relative to chronological age [3].
• Begin education with the patient and family about the eventual need for lifelong androgen replacement and the options available, including injectable, transdermal, and oral formulations.
• Screen for comorbidities that will affect adult formulation choice. Hypertension, for example, is a specific concern with Jatenzo: the FDA label requires blood pressure assessment prior to initiation and monitoring thereafter because oral testosterone undecanoate produced a mean increase of 3 to 5 mmHg in systolic blood pressure in clinical trials [1].

Bone mineral density assessment via DXA scan is appropriate at this stage for any child with more than 12 months of documented testosterone deficiency, given that testosterone is the primary driver of male skeletal accrual [11].

Phase 2: Pubertal Induction (Ages 12 to 14 Typically)

For patients with CHH, Klinefelter syndrome, or primary testicular failure, pubertal induction uses low-dose testosterone with gradual titration over 18 to 24 months to mimic normal pubertal tempo [6]. The Endocrine Society 2018 guidelines recommend starting testosterone at approximately 25 to 50 mg/month intramuscularly and increasing the dose every 6 months [12].

Jatenzo is not appropriate during this phase. The capsule's minimum available dose of 158 mg twice daily delivers far more testosterone than a pubertal-induction protocol requires. Intramuscular or transdermal formulations allow the fine-grained dosing control needed to move a child through Tanner stages 2 through 5 without accelerating bone age inappropriately.

Phase 3: Adult Dose Establishment and Handoff (Ages 16 to 18)

Once the patient has completed pubertal development and reached skeletal maturity (bone age 18 years or epiphyseal closure confirmed radiographically), the conversation about adult formulations is appropriate [10]. This is the window when Jatenzo becomes a legitimate option, provided the patient:

• Has a blood pressure below 130/80 mmHg at baseline, or well-controlled hypertension [1].
• Can reliably take the capsule twice daily with a meal containing at least 30% of calories from fat (required for adequate absorption) [1].
• Has no contraindications including prostate cancer, breast cancer, or polycythemia with hematocrit above 54% [2].

The formal transfer of care to an adult endocrinologist or TRT-competent internist should include a complete summary document covering diagnosis, pubertal induction history, all testosterone formulations used, laboratory trends, bone density data, and any adverse events.

Jatenzo Pharmacokinetics Relevant to Transition Planning

Understanding how Jatenzo behaves pharmacokinetically helps clinicians anticipate what young adult patients transitioning to this formulation will experience.

Absorption and the Fat Requirement

Oral testosterone undecanoate is absorbed via the intestinal lymphatic system, bypassing first-pass hepatic metabolism [13]. This mechanism requires dietary fat for adequate chylomicron formation. In the key TLANDO trial (a separate formulation study), absorption varied significantly when subjects took the capsule with low-fat meals [14]. For Jatenzo specifically, the prescribing information reports a mean Cmax of approximately 1,083 ng/dL and mean Cavg of approximately 489 ng/dL when taken twice daily with food in adult males [1].

Young adults transitioning from pediatric care may have irregular eating patterns. Counseling on consistent high-fat meal timing is not optional. It directly determines whether the patient achieves therapeutic testosterone levels.

Blood Pressure Signal

Across the Jatenzo clinical development program, mean increases in systolic blood pressure of 3.9 mmHg and diastolic blood pressure of 2.1 mmHg were observed [1]. In a population of young adults who have had lifelong hypogonadism and may have developed metabolic comorbidities (common in Klinefelter syndrome, for example), this signal warrants careful monitoring [15].

The American Heart Association considers even a 2 mmHg population-level increase in systolic blood pressure to correspond to a measurable increase in cardiovascular event risk [16]. Baseline and 3-month blood pressure checks are the minimum standard.

Hematocrit and Erythrocytosis

Testosterone stimulates erythropoiesis. Jatenzo trials reported hematocrit elevations above 54% in approximately 5.7% of subjects [1]. In adolescents transitioning to adult dosing, baseline hematocrit should be documented and rechecked at 3 and 6 months after initiating any new formulation [12].

Laboratory Monitoring Schedule During and After Transition

Monitoring is not uniform across all patients. The schedule below applies to patients transitioning from pediatric pubertal induction to adult-dose therapy, including Jatenzo.

First 6 Months on Adult Formulation

• Total testosterone (mid-dose, approximately 4 to 6 hours post-dose for Jatenzo) at weeks 4, 12, and 24 [1].
• Hematocrit and hemoglobin at weeks 12 and 24 [12].
• Blood pressure at every clinical contact.
• Lipid panel at week 24, given that oral androgens may modestly reduce HDL cholesterol [17].
• PSA is not routine in males under 40 but should be obtained if the patient has any urologic symptoms [12].

Ongoing Monitoring After Stabilization

Once testosterone levels are confirmed within the reference range (typically 300 to 1,000 ng/dL per most laboratory platforms [18]) and no adverse signals are present, monitoring can shift to every 6 to 12 months. Bone density reassessment by DXA is appropriate every 1 to 2 years in the first decade of adult therapy, given that patients with hypogonadism starting from childhood may never fully close the gap with age-matched controls [11].

Special Populations Within the Pediatric Under-12 Transition Group

Patients With Klinefelter Syndrome

Men with Klinefelter syndrome have higher rates of metabolic syndrome, type 2 diabetes, and venous thromboembolism than the general population [7]. A 2013 meta-analysis in Genetics in Medicine (N=1,506 patients) found a twofold increased risk of type 2 diabetes in this population [19]. These comorbidities affect the risk calculus for Jatenzo specifically, because oral testosterone undecanoate's blood pressure effects may compound existing cardiovascular risk. Injectable testosterone, which allows precise dose titration and avoids the fat-meal requirement, may be preferable in Klinefelter patients with established metabolic disease.

Patients With CHH Seeking Fertility

Testosterone replacement of any kind, including Jatenzo, suppresses endogenous LH and FSH secretion and renders the patient azoospermic [5]. Young men with CHH who desire fertility in adulthood should be counseled that Jatenzo is incompatible with concurrent gonadotropin therapy for spermatogenesis. Transitioning to adult care must include a documented fertility counseling session with documentation of the patient's reproductive goals [6].

Patients With Prior Prolonged Androgen Deprivation

Any child who had significantly delayed or absent puberty (for example, a patient not diagnosed until age 14 with CHH) may have entered adulthood with below-normal bone mineral density. A 2016 study in the Journal of Bone and Mineral Research found that men with onset of hypogonadism before puberty had lumbar spine Z-scores averaging minus 1.4 compared with age-matched eugonadal controls [20]. These patients need aggressive bone health management alongside testosterone replacement, including calcium, vitamin D, and periodic DXA.

Practical Counseling Points for Patients and Families

Patients under 12 and their families need age-appropriate education long before any adult formulation is considered.

Keep the language concrete. A child does not need to understand pharmacokinetics, but a 10-year-old can understand that "your body does not make enough of a hormone called testosterone, and when you are older we will give it to you as a medicine."

Discuss formulation options early. By age 14 to 16, most patients can meaningfully participate in choosing between injections, gels, patches, and oral capsules like Jatenzo. Research consistently shows that patient participation in formulation decisions improves adherence [21].

Address stigma directly. Testosterone deficiency in young males carries psychological weight. A 2019 study in Hormone Research in Paediatrics found that adolescent males with delayed puberty secondary to hypogonadism had significantly higher rates of anxiety and social withdrawal than age-matched controls, with 38% meeting criteria for clinically significant anxiety [22]. Referral to a psychologist familiar with chronic endocrine conditions should be routine, not reactive.

The Endocrine Society's position statement on transition of care states: "Transition from pediatric to adult endocrine care should be a planned, purposeful process that addresses the medical, psychosocial, and educational needs of adolescents and young adults" [10].

A HealthRX-affiliated board-certified pediatric endocrinologist notes: "The biggest failure point I see is the gap year, typically age 17 to 18, when the pediatric team has stepped back and the adult team has not yet taken ownership. That is when young men stop taking testosterone, lose bone density, and regress psychologically. Someone must own that 12-month window."

Contraindications and Red Flags Specific to This Population

Before Jatenzo is ever initiated in a young adult who has transitioned from pediatric care, the following contraindications must be screened [1] [2]:

• Active or suspected prostate or male breast cancer.
• Hematocrit above 54%.
• Uncontrolled hypertension (systolic above 165 mmHg or diastolic above 100 mmHg at baseline).
• Hypersensitivity to any component of the Jatenzo capsule, including the castor oil and benzyl benzoate excipients.
• Concurrent use of strong CYP3A4 inhibitors (e.g., ketoconazole, ritonavir), which can dramatically increase testosterone exposure [1].

If any of these are present, an alternative testosterone formulation should be selected and Jatenzo reconsidered only after the contraindication resolves.

The Role of Telehealth in Transition Care

Many pediatric endocrinology centers are located in academic medical centers distant from patients' homes. The transition to adult TRT care, including Jatenzo management, is increasingly supported by telehealth platforms that can order laboratory tests, review results, and adjust dosing remotely [23].

For Jatenzo specifically, telehealth providers must ensure that blood pressure monitoring can be performed accurately at the patient's location, either at a local pharmacy kiosk, a primary care office, or with a validated home blood pressure device. A single telehealth visit without documented blood pressure is insufficient for safe Jatenzo prescribing under the FDA label requirements [1].

Telehealth transition programs should include a minimum of four synchronous visits in the first year of adult-dose therapy: at baseline, at 3 months, at 6 months, and at 12 months [24].