Repository Corticotropin Injection for Persistently Active Systemic Lupus Erythematosus: Results from a Phase 4, Multicenter, Randomized, Double-Blind, Placebo-Controlled Trial

Response to Acthar Gel in sarcoidosis uveitis: A prospective open label study

PURPOSE

To investigate the response to Acthar Gel® in patients with moderate to severe sarcoidosis uveitis.

METHODS

This is a prospective open-label study that enrolled patients with moderate to severe sarcoidosis uveitis to receive 80 units daily of Acthar Gel for ten days followed by maintenance treatment with 80 units twice weekly. The primary outcome was the proportion of patients meeting at least one of the following variables 1) improved visual acuity, 2) resolution of intraocular inflammation, 3) ability to taper ocular or oral steroids by at least 50% or 4) reduction of cystoid macular edema, with no worsening of any single measure and no need for additional sarcoidosis therapies at 24 weeks.

RESULTS

A total of nine patients were enrolled in the study. Four patients completed the full 24-week course of Acthar Gel, and three of these met the primary endpoint. Among the five patients who did not complete the 24-week course of treatment, four discontinued the treatment due to worsening ocular inflammation. One patient discontinued treatment due to severe adverse effects. The most common adverse effects were fluid retention (77%), insomnia (44%), hypertension (44%) and hyperglycemia (44%).

CONCLUSIONS

We observed a clinical response to Acthar Gel in some patients with moderate to severe sarcoidosis uveitis, but a substantial proportion either failed to respond or did not tolerate the therapy. These observations may serve as preliminary data for controlled trials of Acthar Gel, but they do not support its role prior to failure of other agents.

Acthar® Gel Treatment for Patients with Autoimmune and Inflammatory Diseases: An Historical Perspective and Characterization of Clinical Evidence

Acthar® Gel (repository corticotropin injection) is a naturally sourced complex mixture of adrenocorticotropic hormone analogs and other pituitary peptides that is believed to have both steroidogenic and nonsteroidogenic immunomodulatory effects via activation of melanocortin receptors in various cells throughout the body. Since 1952, Acthar has been approved by the US Food and Drug Administration to treat a variety of autoimmune and inflammatory diseases. Since 2014, Mallinckrodt Pharmaceuticals has conducted a large number of preclinical, clinical, and real-world-evidence studies of Acthar for the treatment of rheumatoid arthritis, systemic lupus erythematosus, dermatomyositis and polymyositis, multiple sclerosis relapse, ophthalmic disorders, sarcoidosis, and nephrotic syndrome. To date, Acthar has been the subject of more than 500 publications, many of which demonstrate the safety and efficacy of Acthar in patients with inflammatory diseases for whom standard treatments were ineffective or intolerable. Here, we review the history of Acthar and the findings of studies that have investigated the mechanism of action, safety, efficacy, and real-world effectiveness of Acthar for the treatment of inflammatory diseases.

Acthar Gel (RCI): A Narrative Literature Review of Clinical and Economic Evidence

Acthar^® Gel (repository corticotropin injection [RCI]) is a naturally sourced complex mixture of adrenocorticotropic hormone analogs and other pituitary peptides used to treat patients with serious and rare inflammatory and autoimmune conditions. This narrative review summarizes the key clinical and economic findings among 9 indications: infantile spasms (IS), multiple sclerosis (MS) relapses, rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), dermatomyositis and polymyositis (DM/PM), ocular inflammatory diseases (primarily uveitis and severe keratitis), symptomatic sarcoidosis, and proteinuria in nephrotic syndrome (NS). Key studies of clinical efficacy and healthcare resource utilization and cost from 1956 to 2022 are discussed. Evidence supports the efficacy of RCI across all 9 indications. RCI is recommended as first-line treatment for IS and is associated with improved outcomes for the other 8 indications, including increased recovery rates in MS relapse; improved disease control in RA, SLE, and DM/PM; real-world effectiveness in patients with uveitis and severe keratitis; improved lung function and reduced corticosteroid use in symptomatic sarcoidosis; and increased rates of partial remission of proteinuria in NS. For many indications, RCI may improve clinical outcomes during exacerbations or when conventional treatments have failed to show a benefit. RCI is also associated with a reduction in the use of biologics, corticosteroids, and disease-modifying antirheumatic drugs. Economic data suggest RCI is a cost-effective, value-based treatment option for MS relapse, RA, and SLE. Other economic benefits have been demonstrated for IS, MS relapses, RA, SLE, and DM/PM, including reduced hospitalizations, lengths of stay, inpatient and outpatient services, and emergency department visits. RCI is considered safe and effective and features economic benefits for numerous indications. Its ability to control relapse and disease activity makes RCI an important nonsteroid treatment option that could help preserve functioning and well-being among patients with inflammatory and autoimmune conditions.

Cost-Effectiveness of Acthar Gel Versus Standard of Care for the Treatment of Exacerbations in Moderate-to-Severe Systemic Lupus Erythematosus

INTRODUCTION

Despite current standard of care (SoC), there is an unmet need for the treatment of active systemic lupus erythematosus (SLE). The study assessed the cost-effectiveness of Acthar^® Gel (repository corticotropin injection) versus SoC treatment in patients with active, moderate-to-severe SLE from the US payer and societal perspectives over 2 and 3 years.

METHODS

Cost-effectiveness model was developed using a probabilistic cohort-level state-transition approach. Patients received Acthar Gel in an exacerbation state, and the outcomes were assessed at the end of a 3-month cycle for response achievement based on the probability of treatment success with Acthar Gel. Patients may sustain the response or experience an exacerbation. For the base case scenario, moderate-to-severe SLE was defined as British Isles Lupus Assessment Group (BILAG)-2004 ≥ 20 or SLE Disease Activity Index 2000 (SLEDAI-2K) ≥ 10 and clinical response was based on SLE responder index (SRI)-4. Clinical response, productivity loss, and utility were derived from a phase 4 SLE trial; cost and disutility estimates were sourced from the literature.

RESULTS

From a payer perspective, Acthar Gel versus SoC resulted in an incremental cost-effectiveness ratio (ICER) of $133,110 per quality-adjusted life-year (QALY) and $94,818 per QALY over 2 and 3 years, respectively. From a societal perspective, Acthar Gel versus SoC results in an ICER of $70,827 per QALY and $32,525 per QALY over 2 and 3 years, respectively. Results from the sensitivity and scenario analyses are consistent with those of the base case model.

CONCLUSIONS

Acthar Gel is a cost-effective, value-based treatment option for appropriate patients with moderate-to-severe SLE at a willingness-to-pay threshold of $150,000 over 2-3 years from the US payer and societal perspectives. Acthar Gel results in the reduction of direct medical and indirect costs.

FDA-APPROVED INDICATIONS OF ADRENOCORTICOTROPIC HORMONE (ACTH) AS A DRUG: DOES IT HAVE A PLACE IN DISEASE MANAGEMENT TODAY?

ACTH is a pituitary hormone important for proper function of adrenal glands, cortisol production as well as human physiology in general.  It is involved in the pathogenesis of several endocrine disorders like Cushing syndrome and can be a useful diagnostic tool for diseases like primary adrenal insufficiency.  Although popular as a hormone in endocrine system physiology and testing, ACTH has been used as a drug since the 1950s.  Except for steroid-releasing properties, its mechanism of action involves a steroid-independent anti-inflammatory and possible immune-modulatory effect.  Pharmaceutic ACTH has a wide range of indications approved by FDA and usually comes in the form of subcutaneous injections.  In this narrative review, we accumulated what we considered as important data from reviews, cases and trials involving the most basic FDA-approved ACTH indications.  A special emphasis was given on rheumatologic indications of ACTH.  More large data studies need to be performed to assess ACTH usefulness, efficacy, safety and cost-effectiveness as a drug.  

Results from a Prospective, Open-Label, Phase 4 Pilot Study of Repository Corticotropin Injection for Moderate and Severe Dry Eye Disease

INTRODUCTION

There is a substantial unmet need for effective therapies to treat patients with refractory dry eye disease (DED). The goal of this open-label pilot study was to investigate the efficacy and safety of repository corticotropin injection (RCI; Acthar® Gel; Mallinckrodt Pharmaceuticals) in subjects with DED, most of whom did not experience adequate response to standard-of-care therapies.

METHODS

Adults with moderate or severe-acute DED received 80 U of subcutaneous RCI twice weekly for 12 weeks. Primary efficacy outcomes were improvements in corneal fluorescein staining of superficial punctate keratitis (SPK) lesions and Symptom Assessment in Dry Eye (SANDE) scores. Secondary outcomes included changes in Schirmer's test scores, conjunctival lissamine green staining, erythema, intraocular pressure (IOP), and best corrected visual acuity (BCVA). Adverse events (AEs) were assessed continuously throughout the study.

RESULTS

Fifteen subjects received at least 1 dose of RCI, and 12 subjects completed the study. Compared to baseline (day 1), significantly fewer fluorescein-stained SPK lesions were detected at day 14 (p = 0.0250) and day 84 (p = 0.0240) after RCI treatment. Mean SANDE scores progressively declined from 62.0 at baseline to 46.9 at day 84. Erythema (p = 0.0046), conjunctival lissamine green staining of SPK lesions (p = 0.0317), and IOP (p = 0.0052) were all significantly improved after 12 weeks of RCI therapy. Schirmer's test scores and BCVA showed no significant changes throughout the study. No ocular AEs or deaths occurred, and no new safety signals were identified for RCI.

CONCLUSIONS

These results suggest that RCI may be a safe and effective treatment for moderate and severe DED.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT03287635.

A Narrative Review of Repository Corticotropin Injection for the Treatment of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disorder that affects multiple organ systems. The most prevalent manifestations include constitutional symptoms, arthritis, and rash. An SLE flare is defined as a measurable increase in disease activity that may prompt a change in treatment. According to the European Alliance of Associations for Rheumatology guidance, SLE treatments should be aimed at reducing disease activity and flares, as well as preventing organ damage. Standard-of-care treatment of SLE includes glucocorticoids, but their long-term use is associated with damage accrual. Repository corticotropin injection (RCI; Acthar^® Gel) is a naturally sourced complex mixture of adrenocorticotropic hormone analogs and other pituitary peptides that has anti-inflammatory and immunomodulatory effects beyond its steroidogenic effect, and has been US Food and Drug Administration–approved for the treatment of SLE flares and as a maintenance therapy. This review summarizes data from three clinical trials that evaluated the efficacy and safety of RCI in the treatment of patients with moderate–severe refractory SLE. These clinical trials confirmed that RCI improved global disease activity scores and some SLE clinical manifestations. Analysis of pooled data from these trials showed that RCI treatment significantly improved the British Isles Lupus Assessment Group 2004 (BILAG-2004) index scores after 8 weeks of treatment, and tender and swollen joint counts after 4 weeks. These clinical trials demonstrated an acceptable safety profile with few serious adverse events reported. The distinct mechanisms of action from standard-of-care therapies and the favorable safety and good efficacy profiles support the use of RCI as therapy for patients with refractory SLE.

Pain and Fatigue Improvements in Patients Treated with Repository Corticotropin Injection Across Five Indications: A Narrative Review

Repository corticotropin injection (RCI; Acthar^® Gel) is approved by the US Food and Drug Administration (FDA) for use in 19 indications, including for the treatment of selected patients with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), symptomatic sarcoidosis, uveitis, and keratitis. Despite treatment with disease-modifying antirheumatic drugs, many patients with RA, SLE, and other chronic inflammatory rheumatic diseases continue to be affected by severe pain and fatigue, indicating a need for other therapies. To examine the clinical data regarding the impact of RCI treatment on pain and fatigue in selected populations, this review included English-language peer-reviewed publications of clinical trials of any size and cohort studies with more than 10 patients that included pain and/or fatigue based on patient-reported outcomes (PROs) and/or physician-assessed measures in adults following treatment with RCI for RA, SLE, symptomatic sarcoidosis, uveitis, or keratitis. Literature searches identified eight studies that met these criteria. Four studies (reported in five publications) were in patients with RA or SLE, two in patients with sarcoidosis, one in patients with uveitis, and one in patients with noninfectious keratitis. Across the different types of studies assessed (clinical trials, chart reviews, real-world evidence), the results were consistent with respect to the impact of RCI treatment on improving pain and fatigue. As summarized in this review, data from patient- and physician-reported outcome measures in eight studies demonstrate that, in addition to improving more traditional efficacy measures, RCI may also improve pain and fatigue in patients with RA, SLE, symptomatic sarcoidosis, uveitis, and noninfectious keratitis.

Rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) are chronic autoimmune diseases. Clinical studies of drugs for these diseases do not often ask patients how they feel after treatment. Despite treatment, many people with these diseases have pain and feel tired. Repository corticotropin injection (RCI) is a prescription drug for patients with RA, SLE, and other chronic immune diseases. We reviewed the results of published studies with data on pain and fatigue from patients treated with RCI. Four studies were in patients with RA or SLE. Two studies were in patients with symptomatic sarcoidosis. One study was in patients with uveitis. One study was in patients with noninfectious keratitis. These eight studies show that adding RCI to standard treatment lowers pain and fatigue in some patients. It would be helpful to measure pain and fatigue in future clinical studies of drugs for patients with chronic immune diseases.

Repository Corticotropin Injection for the Treatment of Pulmonary Sarcoidosis: A Narrative Review

Although corticosteroids are the standard first-line therapy for pulmonary sarcoidosis, long-term and high-dose use of these drugs are associated with increased risk of adverse events and high healthcare utilization costs. Treatment guidelines for pulmonary sarcoidosis indicate that off-label immunomodulators and biologics may be warranted for severe disease. Repository corticotropin injection (RCI, Acthar^® Gel), a complex mixture of adrenocorticotropic hormone analogs and other pituitary peptides, is one of only two therapies approved by the US Food and Drug Administration for symptomatic pulmonary sarcoidosis and is recommended by current European Respiratory Society treatment guidelines for use on a case-by-case basis. With its unique anti-inflammatory and immunomodulatory mechanism of action through activation of melanocortin receptors in various cell types, RCI has demonstrated steroid-sparing properties. RCI has a long history of use in autoimmune and inflammatory disorders, with proven safety and efficacy for pulmonary sarcoidosis. In this narrative review, we present the clinical evidence for the safety and efficacy of RCI in the treatment of pulmonary sarcoidosis, identify where RCI falls within the current treatment guidelines, and describe the unique mechanism of action of RCI for promoting anti-inflammatory and immunomodulatory effects.

Repository Corticotropin Injection (Acthar® Gel) for Refractory Severe Noninfectious Keratitis: Efficacy and Safety from a Phase 4, Multicenter, Open-Label Study

Introduction

Noninfectious keratitis is a painful corneal inflammation treated with topical cyclosporine and other immunosuppressants. Additional treatment options are needed for keratitis that does not improve with standard therapies. Repository corticotropin injection (RCI; Acthar^® Gel) is approved to treat severe acute and chronic allergic and inflammatory processes involving the eye and its adnexa, including keratitis. This phase 4, multicenter, open-label study assessed the efficacy and safety of RCI for refractory severe noninfectious keratitis.

Methods

Patients were ≥ 18 years old with persistent severe keratitis despite treatment with topical immunosuppressants. Patients received 80 U of RCI subcutaneously twice weekly for 12 weeks followed by a 4-week taper. Assessments included all domains of the Impact of Dry Eye on Everyday Life (IDEEL) Questionnaire, Ocular Discomfort and 4-Symptom Questionnaire, and Visual Analog Scale (VAS). Corneal fluorescein and conjunctival lissamine green staining, Conjunctival Redness Scale, tear production (Schirmer’s test), visual acuity, slit lamp examination, and intraocular pressure were also assessed. Safety was evaluated via treatment-emergent adverse events. Analyses were performed using the modified intent-to-treat (mITT) population (patients who received ≥ 1 dose of RCI and contributed any post-baseline efficacy data).

Results

In the mITT population (N = 35), 50.0% (95% confidence interval, 33.2% to 66.8%) of patients experienced clinically important improvements in the symptom bother domain of the IDEEL Questionnaire at week 12 of RCI therapy. All domains of the IDEEL and the Ocular Discomfort and 4-Symptom Questionnaire showed improvements at week 12 of RCI treatment. The most pronounced improvements in the VAS at week 12 were for eye dryness and eye discomfort. Corneal staining, conjunctival staining, conjunctival redness, and tear production showed early improvements that were sustained through week 12. No new safety signals for RCI were identified.

Conclusions

RCI is safe and effective for refractory severe noninfectious keratitis that has not improved with other approved therapies.

Trial registration number

ClinicalTrials.gov NCT04169061.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40123-021-00400-y.

Measurement of specific organ domains in lupus randomised controlled trials: a scoping review

OBJECTIVE

Randomised controlled trials (RCTs) in systemic lupus erythematosus (SLE, lupus) typically adopt composite responder definitions as primary efficacy endpoints, however outcomes within individual organ domains are also important to understand. The aim of this scoping review was to evaluate how organ-specific disease activity and therapeutic responses have been measured and reported in lupus RCTs.

METHODS

We searched MEDLINE, EMBASE, Cochrane registry and clinicaltrials.gov. Eligible studies were RCTs investigating efficacy of an immune-directed drug therapy in active SLE, published January 2000-March 2021, excluding studies limited to lupus nephritis. Data were extracted independently in duplicate into a template and summarised descriptively.

RESULTS

Thirty-four RCTs were included, of which 32 (94%) reported activity and/or responses in at least one organ domain. Study populations had a high, although variable, frequency of baseline musculoskeletal and mucocutaneous activity and low but also variable representation of other domains. Definitions of organ-specific responses were inconsistent, even within individual instruments. Response in most organ domains were evaluated using BILAG and SLEDAI components but meaningful comparison between treatment arms was limited by small subgroups analysed in a post hoc fashion. Specific mucocutaneous and arthritis instruments were also used, including within pre-specified organ-specific endpoints, which discriminated between treatment arms in some studies.

CONCLUSION

Mucocutaneous and musculoskeletal manifestations predominate in SLE RCTs. Organ-specific outcome measures are commonly reported, but definitions of involvement and response are inconsistent. Research into the development of new outcome measures for key organ domains, and validation and comparison of response definitions using existing instruments, is needed.

Pharmacokinetics and Pharmacodynamics of Repository Corticotropin Injection Compared With Synthetic ACTH1-24 Depot and Methylprednisolone in Healthy Subjects

Repository corticotropin injection (RCI; Acthar Gel) is a naturally sourced complex mixture of adrenocorticotropic hormone (ACTH) analogs and other pituitary peptides. This phase 1, single-center, open-label, randomized parallel study directly compared the pharmacokinetics and pharmacodynamics of RCI and synthetic ACTH_1-24 depot. Methylprednisolone was included to estimate the steroidogenic exposure of RCI and synthetic ACTH_1-24 depot when used to treat nephrotic syndrome. A total of 48 healthy subjects aged 18 to 50 years were randomly assigned 1:1:1 to RCI (80 IU subcutaneously twice weekly on study days 1 and 4), synthetic ACTH_1-24 depot (1 mg subcutaneously twice weekly on study days 1 and 4), or methylprednisolone (32 mg orally once daily on study days 1 through 6). After 2 doses, RCI induced about 5-fold lower free cortisol exposure and an estimated 4-fold lower steroidogenic exposure than synthetic ACTH_1-24 depot. The lower endogenous cortisol response of RCI was achieved despite higher observed mean plasma concentrations of N25-deamidated porcine ACTH_1-39 (the pharmacokinetic marker for RCI) than of ACTH_1-24 . The different pharmacodynamic properties demonstrated by RCI and synthetic ACTH_1-24 depot in this study suggest that these products in the ACTH class are not interchangeable.

Post Hoc Biomarker Analyses from a Phase 4, Multicenter, Randomized, Double-Blind, Placebo-Controlled Trial of Repository Corticotropin Injection (Acthar® Gel) for Persistently Active Systemic Lupus Erythematosus

INTRODUCTION

We conducted post hoc analyses of biomarker results from a multicenter, randomized, double-blind, placebo-controlled study of repository corticotropin injection (RCI; Acthar® Gel) in patients with persistently active systemic lupus erythematosus (SLE) despite treatment with moderate-dose glucocorticoids.

METHODS

Adults with active SLE and moderate to severe rash and/or arthritis were enrolled in the primary study. Patients had active SLE despite treatment with stable glucocorticoids, antimalarials, and nonsteroidal anti-inflammatory drugs and/or immunosuppressants. Patients were randomly assigned to 80 U of RCI or placebo subcutaneously every other day for 4 weeks and then twice weekly through week 24. Blood samples were analyzed for serum cytokines and complement proteins using enzyme-linked immunosorbent or Luminex assays and for circulating leukocytes using flow cytometry. Biomarker levels were reported as percentages of the baseline and were further evaluated in subgroups stratified by baseline SLE Disease Activity Index-2000 (SLEDAI-2K) scores (< 10 vs. ≥ 10), baseline anti-double-stranded DNA levels (< 15 IU/mL vs. ≥ 15 IU/mL), and BILAG-based Combined Lupus Assessment (BICLA) responses at week 20 and 24.

RESULTS

RCI treatment resulted in reduced levels of B cell-activating factor and interleukin-6 cytokines in all subgroups compared with placebo. RCI treatment also resulted in lower levels of CD19⁺ B cells and CD19⁺IgD^-CD27^-CD95⁺ atypical activated memory B cells than did placebo in the higher baseline disease activity subgroups and in BICLA non-responders. Furthermore, RCI treatment led to greater increases in complement component (C)3 and C4 levels than did placebo in the higher baseline disease activity subgroups and in BICLA responders.

CONCLUSIONS

RCI may reduce inflammation through B cell immunomodulation in patients with persistently active SLE, particularly in those with higher disease activity.

TRIAL REGISTRATION

ClinicalTrials.gov identifier NCT02953821.

Patient-Reported Outcomes from a Phase 4, Multicenter, Randomized, Double-Blind, Placebo-Controlled Trial of Repository Corticotropin Injection (Acthar® Gel) for Persistently Active Systemic Lupus Erythematosus

Introduction

We assessed patient-reported outcomes from a multicenter, randomized, double-blind, placebo-controlled study of repository corticotropin injection (RCI; Acthar^® Gel) in patients with persistently active systemic lupus erythematosus (SLE) despite treatment with moderate-dose glucocorticoids.

Methods

The trial enrolled adults with active SLE and moderate-to-severe rash and/or arthritis despite use of stable glucocorticoids (7.5 mg/day to 30 mg/day prednisone equivalent), antimalarials, and nonsteroidal anti-inflammatory drugs for ≥ 4 weeks and/or immunosuppressants for ≥ 8 weeks before screening. Patients were randomly assigned to 80 U of RCI or placebo subcutaneously every other day through week 4, then twice weekly through week 24. Primary analyses evaluated the change from baseline to week 24 in the Lupus Quality of Life (QoL) and Work Productivity and Activity Impairment (WPAI)-Lupus questionnaires. Post hoc analyses stratified results by baseline disease activity (SLE Disease Activity Index-2000 [SLEDAI-2K] < 10 or ≥ 10; Cutaneous Lupus Erythematosus Disease Area and Severity Index [CLASI]-Activity < 11 or ≥ 11; and British Isles Lupus Assessment Group [BILAG]-2004 < 20 or ≥ 20) and by BILAG-based Combined Lupus Assessment (BICLA) response at weeks 20 and 24.

Results

RCI treatment resulted in greater improvement in the LupusQoL pain domain at week 16 and planning domain at week 24 compared with placebo. Post hoc analyses demonstrated greater improvements with RCI in the pain, planning, and fatigue domains than with placebo at multiple time points in patients with higher disease activity by baseline SLEDAI-2K ≥ 10, CLASI-Activity ≥ 11, and BILAG-2004 ≥ 20 and/or in BICLA responders. Compared with placebo, RCI also resulted in greater improvements in percentage work time missed at week 24 in patients with baseline CLASI-Activity < 11 and in percentage impairment while working at week 16 in BICLA responders.

Conclusions

RCI may improve QoL and work productivity in patients who have persistently active SLE despite treatment with standard SLE therapy.

Trial Registration

ClinicalTrials.gov identifier NCT02953821.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40744-021-00294-z.

Comparison of Steroidogenic Exposure Following the Administration of Repository Corticotropin Injection With a Synthetic ACTH1-24 Depot and Methylprednisolone in Healthy Subjects

The pharmacokinetics (PK) and pharmacodynamics (PD) of clinically relevant doses of repository corticotropin injection (Acthar Gel) and synthetic ACTH_1‐24 depot have not been fully characterized. We compared the steroidogenic exposure of repository corticotropin injection and synthetic ACTH_1‐24 depot in healthy adults at therapeutic doses using data from 2 separate phase 1 studies. Subjects were randomly assigned to repository corticotropin injection 40 or 80 IU subcutaneously twice weekly or 80 IU subcutaneously 3 times weekly for 15 days or to daily synthetic ACTH_1‐24 depot doses of 0.5 mg subcutaneously, 0.75 mg subcutaneously, 1 mg subcutaneously, or 1 mg intramuscularly for 5 days. A population PK/PD model was developed to simulate the free cortisol exposure of a clinically relevant dose of synthetic ACTH_1‐24 depot (1 mg subcutaneously twice weekly). Study drug doses were converted to methylprednisolone‐equivalent doses using the steroidogenic exposure of methylprednisolone 16 mg daily as a conversion factor. Doses were also converted to prednisone equivalents using a coefficient of 1.25. These analyses revealed that the steroidogenic exposure of repository corticotropin injection at clinically relevant doses was substantially lower than that for synthetic ACTH_1‐24 depot. The 3 repository corticotropin injection regimens were equivalent to approximately 5, 8, and 16 mg of daily prednisone, respectively. On the basis of simulated free cortisol exposure, synthetic ACTH_1‐24 depot 1 mg subcutaneously twice weekly was comparable to 57 mg of daily prednisone. These results suggest that repository corticotropin injection has pharmacological effects that cannot be considered identical to synthetic ACTH_1‐24 depot.