Jatenzo History and Development: How Oral Testosterone Finally Reached the U.S.

Why Oral Testosterone Took Decades to Reach the U.S.

The absence of an FDA-approved oral testosterone product before 2019 was not a failure of demand. It was a failure of pharmacology. Methyltestosterone, the earliest oral androgen available in the U.S. (approved in the 1950s), undergoes extensive hepatic first-pass metabolism. That metabolic pathway generates 17-alpha-alkylated intermediates linked to peliosis hepatis, cholestatic jaundice, and hepatocellular carcinoma [1].

The Endocrine Society's 2018 clinical practice guideline explicitly recommended against 17-alpha-alkylated oral androgens, stating they "should not be used for testosterone replacement because of potential hepatotoxicity" [2]. This left clinicians with injectable testosterone (cypionate, enanthate), transdermal gels and patches, and nasal testosterone (Natesto, approved 2014) as the only cleared options.

Testosterone undecanoate itself was not new. Organon developed an oral formulation (Andriol/Andriol Testocaps) that had been prescribed in Europe, Canada, Mexico, and parts of Asia since the early 1980s [3]. But the Andriol formulation had bioavailability problems. Absorption was highly variable, fat-dependent, and produced inconsistent serum testosterone levels that made it difficult to meet FDA efficacy endpoints [4]. No U.S. sponsor successfully navigated the regulatory path with that older formulation. The molecule needed a better delivery system.

How Lymphatic Absorption Bypasses Liver Toxicity

Testosterone undecanoate is a prodrug. The undecanoate ester chain (an 11-carbon fatty acid attached to testosterone at the 17-beta position) makes the molecule highly lipophilic [5]. This lipophilicity is the key to its safety advantage over methyltestosterone.

When taken with a meal containing at least 15-20 grams of fat, the lipophilic testosterone undecanoate partitions into intestinal chylomicrons during digestion. These chylomicrons enter the intestinal lymphatic system rather than the portal venous system [5]. Because the portal vein feeds directly into the liver, bypassing it means the drug avoids hepatic first-pass metabolism entirely. Once chylomicrons reach the systemic circulation via the thoracic duct, esterases cleave the undecanoate side chain and release free testosterone into the bloodstream [6].

This is a fundamentally different absorption pathway than what methyltestosterone uses. Dr. Ronald Swerdloff, a principal investigator on the Jatenzo key trial and professor at UCLA, described the mechanism: "The lymphatic route of absorption is what distinguishes testosterone undecanoate from the older 17-alpha alkylated androgens that caused liver damage" [6]. The result is testosterone delivery without the hepatotoxic metabolite burden.

The requirement for co-administration with food is not optional. Fasting-state bioavailability drops dramatically, which is why the Jatenzo label specifies twice-daily dosing with meals [7].

Clarus Therapeutics and the SEDDS Formulation

The company behind Jatenzo was Clarus Therapeutics, a small pharmaceutical firm based in Northbrook, Illinois. Clarus licensed and refined a self-emulsifying drug delivery system (SEDDS) specifically designed to improve upon the inconsistent absorption profile of older testosterone undecanoate formulations like Andriol [8].

SEDDS technology encapsulates the drug in a pre-concentrate mixture of lipids, surfactants, and co-solvents inside a soft gelatin capsule. Upon contact with gastrointestinal fluids, this mixture spontaneously forms a fine oil-in-water emulsion without requiring external agitation [8]. The emulsion dramatically increases the surface area available for intestinal uptake and promotes more reliable partitioning into chylomicrons compared to the older Andriol capsule, which relied on oleic acid dissolved in castor oil.

Clarus filed its New Drug Application (NDA) with the FDA in December 2018, supported by two phase 3 trials and multiple pharmacokinetic studies. The company had previously attempted an NDA submission in 2014 but received a Complete Response Letter from the FDA citing concerns about blood pressure elevations and the need for additional cardiovascular safety data [9]. That 2014 setback forced Clarus to redesign its clinical development program and generate the additional safety evidence that would eventually support the successful 2019 submission.

The Key Trial: Swerdloff et al. (2020)

The registration-enabling study was a 12-month, open-label, dose-titration trial enrolling 166 hypogonadal men (baseline serum testosterone <300 ng/dL) [10]. Patients started on testosterone undecanoate 237 mg twice daily with food. Doses were titrated at month 2 based on serum testosterone levels, with a target range of 300 to 1,100 ng/dL (the normal adult male reference range).

The primary endpoint was the percentage of patients with an average 24-hour serum testosterone concentration (Cavg) within the normal range at day 90. The result: 87% of patients achieved the target range [10]. This exceeded the FDA's pre-specified success criterion of 75%.

Secondary endpoints reinforced the primary finding. Mean Cavg at day 90 was 489 ng/dL. The maximum concentration (Cmax) remained below 1,500 ng/dL in the vast majority of patients, an important safety parameter because supratherapeutic testosterone spikes increase polycythemia risk [10].

Dose titration worked as intended. Patients whose levels fell below range moved to 316 mg or 396 mg twice daily. Those who exceeded the upper bound stepped down to 158 mg twice daily. By month 12, approximately 145 patients remained in the study, with consistent maintenance of eugonadal levels across the dose range [10].

The most common adverse events were headache (5.4%), nausea (3.6%), and increased hematocrit (3.6%). Blood pressure showed a small but statistically significant mean increase: systolic blood pressure rose by an average of 3-5 mmHg compared to baseline [10]. That blood pressure signal would become the central controversy in the FDA review.

The Contentious FDA Advisory Committee Vote

On March 15, 2019, the FDA's Bone, Reproductive and Urologic Drugs Advisory Committee (BRUDAC) voted 13 to 9 against recommending approval of Jatenzo [11]. The dissenting majority cited two concerns. First, the observed blood pressure increases, though modest in absolute terms, could translate to meaningful cardiovascular risk at the population level given long-term use in a chronic condition. Second, the open-label trial design lacked a placebo comparator, making it difficult to separate drug effect from natural fluctuation.

Committee member Dr. Tobias Gerhard, a pharmacoepidemiologist at Rutgers, commented during the hearing that "the magnitude of the blood pressure increase is within the range that epidemiologic data associate with a 10-20% increase in cardiovascular events over a decade of exposure" [11].

Despite the negative vote, the FDA approved Jatenzo on March 27, 2019 [12]. The agency's decision letter noted that the blood pressure signal had been observed in the context of testosterone replacement broadly, not uniquely with Jatenzo, and that the benefit of a non-injectable, non-transdermal testosterone option addressed an unmet clinical need. The FDA did not require a Risk Evaluation and Mitigation Strategy (REMS) at launch, though the label included a boxed warning about blood pressure increases and a recommendation for periodic cardiovascular monitoring [7].

This was not the first time the FDA overruled an advisory committee on a testosterone product. The broader testosterone replacement therapy class had been under cardiovascular scrutiny since 2010, when a National Institutes of Health-funded trial (the TOM trial, N=209) in elderly men with mobility limitations was stopped early due to excess cardiovascular events in the testosterone arm [13].

Post-Approval Label Changes and Cardiovascular Debate

In June 2023, the FDA mandated a class-wide labeling change for all approved testosterone products, including Jatenzo. The updated label incorporated findings from the TRAVERSE trial (N=5,246), a randomized, placebo-controlled cardiovascular outcomes study of transdermal testosterone in men aged 45-80 with hypogonadism and pre-existing cardiovascular disease or elevated risk [14].

TRAVERSE found that testosterone replacement did not significantly increase the incidence of major adverse cardiovascular events (MACE) compared to placebo (hazard ratio 0.96, 95% CI 0.78-1.17) over a mean follow-up of 33 months [14]. This was a meaningful result for the TRT field. It did not eliminate the cardiovascular warning from testosterone labels, but it provided the first large-scale, randomized evidence that replacement-dose testosterone does not carry the excess cardiac risk suggested by earlier observational studies.

For Jatenzo specifically, the post-marketing period revealed polycythemia (hematocrit >54%) as an adverse event requiring monitoring. The Endocrine Society guideline recommends checking hematocrit at 3-6 months after starting any testosterone therapy and annually thereafter [2]. Jatenzo's labeling was updated to reflect this monitoring recommendation explicitly.

The Clarus Therapeutics Bankruptcy

Jatenzo's commercial trajectory did not match its clinical promise. Clarus Therapeutics went public via SPAC merger in December 2021, but the stock collapsed within months. The company filed for Chapter 11 bankruptcy in September 2023, citing an inability to generate sufficient revenue to sustain operations [15]. Market competition from generic injectable testosterone (cypionate at approximately $30-50/month) and established topical gels made it difficult to justify Jatenzo's higher price point (list price exceeding $600/month at launch) [15].

Tolmar Pharmaceuticals acquired Jatenzo's commercial rights out of the bankruptcy proceedings. The drug remains on the U.S. market and continues to be prescribed, particularly for patients who cannot tolerate injections, prefer oral dosing, or have skin conditions that preclude transdermal application.

How Jatenzo Differs from Tlando and Kyzatrex

Jatenzo was the first but not the only oral testosterone undecanoate to receive FDA approval. Tlando (Halozyme/Lipocine) was approved in March 2022, and Kyzatrex (Marius Pharmaceuticals) followed in October 2022 [16]. All three use testosterone undecanoate as the active ingredient and rely on lymphatic absorption, but their formulation technologies differ.

Tlando uses a proprietary pro-emulsion formulation and is dosed at 225 mg twice daily without food-dependent titration. Kyzatrex uses a different lipid-based delivery system and demonstrated reduced food-effect sensitivity compared to Jatenzo in pharmacokinetic studies [16]. Jatenzo remains the only one of the three with published long-term (12-month) efficacy and safety data from its key trial [10].

The existence of three FDA-approved oral testosterone undecanoate products by late 2022 represented a complete reversal from the decades-long absence of any oral testosterone option in the U.S. Whether these products gain meaningful market share against cheaper injectable alternatives depends on insurance coverage decisions, patient preference research, and long-term real-world safety data that is still accumulating.

The next clinical question for oral testosterone is durability of bone and metabolic endpoints. The Endocrine Society's 2018 guideline calls for bone mineral density measurement at 1-2 years in hypogonadal men starting TRT [2]. Published bone density data specific to Jatenzo beyond 12 months does not yet exist.