First-pass Metabolism Research Articles

Intraoperative contrast-enhanced cone beam CT allows visualization of the ‘dark side’ of the clot and improves mechanical thrombectomy performance

BackgroundVisualization of the clot is key to the endovascular treatment of ischemic stroke, but identification of the distal part of the clot and distal arteries during mechanical thrombectomy (MT) remains...

Enabling oral novel Taxanes-based Chemotherapy with Lipophilic prodrug Self-nanoemulsifying drug delivery system

Larotaxel (LTX) and SB-T-1214 (SBT), two new synthetic experimental toxoids, have shown broad-spectrum antitumor activity, especially against tumors that are resistant to other drugs. However, their poor solubility, membrane permeability, and first-pass effect limits their use in oral administration. We designed and synthesized two long-chain triglyceride-mimic prodrugs of LTX (LTXSSTG) and SBT (SBTSSTG), which are bridged by disulfide bonds and efficiently incorporated them into Self-nanoemulsifying drug delivery system (SNEDDS). These prodrugs can bypass hepatic metabolism by entering the blood through intestinal lymphatic transport, following a similar oral absorption pathway to dietary lipids. It was found that LTXSSTG and SBTSSTG significantly improved oral bioavailability (about 4.5-fold for LTX and 3.4-fold for SBT) compared to their solution forms. Moreover, with LTXSSTG and SBTSSTG incorporating reduction stimulus-responsive spacer were much more effective in suppressing tumor growth in vivo with eliminated adverse effects than solution form. To sum up, this strategy provides a new avenue to enhance oral delivery of new toxoids.

Lymphatic targeting of cilnidipine by designing and developing a nanostructured lipid carrier drug delivery system

Objective The objective of current research is to design, develop, and optimize a cilnidipine (CLN) nanostructured lipid carrier (NLC)-based drug delivery system for the effective treatment of hypertension (HT). Significance Oral administration of CLN-loaded NLC (CLN NLC) containing glyceryl monostearate (GMS) as a solid and isopropyl myristate (IPM) as a liquid lipid may show remarkable lymphatic uptake through payer patches. Methods The emulsification probe sonication technique was used followed by optimization using 32 factorial designs. Results The optimized batch showed a mean particle size of 115.4 ± 0.22 nm with encapsulation efficiency of 98.32 ± 0.23%, polydispersity index (PDI) of 0.342 ± 0.03, and zeta potential (ZP, ζ) was −60.5 ± 0.24 which indicate excellent physical stability. In vitro studies showed a controlled release of CLN NLCs. Pharmacokinetics studies determined the C max of NLCs (373.47 ± 15.1) indicates 2.3-fold enhancement compared with plain drug (160.64 ± 7.63). Pharmacodynamic studies indicated that CLN NLCs were maintaining systolic blood pressure in a controlled manner without any signs of side effects. Conclusion CLN NLCs significantly improved lymphatic delivery and proved to be effective in the treatment and management of HT. It has been proved that CLN NLCs are found to be better than any traditional CLN dosage form due to enhancement in solubility, absorption, bioavailability, intestinal permeability, avoidance of first-pass metabolism, P-glycoprotein efflux and reduction in dose-related side effects, achievement of controlled and sustained release action.

Intestine vs. Liver ？ Uncovering the Hidden major Metabolic organs of Silybin in Rats.

Silybin, extracted milk thistle, was a flavonolignan compound with hepatoprotective effect. Now it is commonly used in dietary supplements, functional foods, and nutraceuticals. However, the metabolism of silybin has not been systematically characterized in organisms to date. Therefore, we established a novel HPLC-Q-TOF/MS method to analyze and identify the prototype and metabolites of silybin in rats. Totally, 29 (out of 32) new metabolic pathways and 56 (out of 59) unreported metabolite products were detected. Moreover, we found that the liver had a high first-pass effect of 63.30%{plus minus}13.01 for silybin and only one metabolite was detected. And the metabolites identified in gastrointestinal tract possessed 88% of all (52 out of 59). At the same time, the high concentration of silybin in the livers also indicated large amounts of silybin may be accumulated in liver instead of being metabolized. These results indicated the primary metabolizing organ of silybin in rats was intestine rather than liver, which would also offer solid chemical foundation for exploring more promising health care products of silybin. Significance Statement This study confirmed the main metabolism place of silybin in rats were gastrointestinal tracts instead of livers and the intestinal microbes were closely involved. Then 29 (out of 32) metabolism pathways and 56 (out of 59) metabolites were identified for the first time in rats. And to further study the liver disposition of silybin, its hepatic first-pass effect was determined for the first time.

Prognostic impact of intracranial arteriosclerosis subtype after endovascular treatment for acute ischaemic stroke.

The influence of intracranial arteriosclerosis (ICAR) on acute ischaemic stroke (AIS) prognosis is unclear. This study explored its impact, focusing on ICAR subtypes categorized by intracranial carotid artery calcification (ICAC) patterns: intimal or atherosclerotic versus internal elastic lamina calcification or non-atherosclerotic. The aim was to determine their effect on AIS prognosis in patients undergoing endovascular treatment (EVT). This prospective cohort study included consecutive AIS patients with anterior circulation large vessel occlusion undergoing EVT. ICAC, the hallmark of ICAR, was assessed using non-contrast computed tomography to quantify volume and establish the predominant ICAR subtype. The primary outcome was long-term functional outcome, measured by the 90-day modified Rankin Scale score. Secondary outcomes included first-pass effect, revascularization degree, symptomatic intracranial haemorrhage and 24-h infarct volume. Multivariate-adjusted linear and logistic regression models were used to assess the association of ICAC volume and subtype with these outcomes. From January 2021 to February 2022, 181 patients were included, of whom 172 (95%) had ICAC. Internal elastic lamina calcification was the predominant subtype in 103 (57%), intimal in 52 (29%) and mixed in 17 (9%). The intimal or atherosclerotic ICAC pattern was linked to poorer functional outcomes (adjusted odds ratio 2.12, 95% confidence interval [CI] 1.10-4.09), decreased first-pass effect probability (adjusted odds ratio 0.42, 95% CI 0.21-0.84) and higher infarct volume (adjusted β value 22.11, 95% CI 0.55-43.67). A predominant intimal ICAC subtype, linked to underlying atherosclerosis, correlated with larger infarct volume and poorer 90-day functional outcomes in EVT-treated AIS patients. Intracranial atherosclerosis appears to be a relevant factor hampering clinical benefits post-EVT.

Comparative Preclinical Pharmacokinetics and Disposition of Favipiravir Following Pulmonary and Oral Administration as Potential Adjunct Therapy Against Airborne RNA Viruses.

Favipiravir is administered orally, even against airborne RNA viruses, in a loading-dose/maintenance dose regimen. We investigated whether-(a) pulmonary delivery of favipiravir would generate high concentrations in the luminal side of the respiratory tract; and (b) avoiding first-pass metabolism by the liver by inhaled drug would generate comparable pharmacokinetics (PK) with doses significantly smaller than the oral maintenance dose. A dry powder inhalation (DPI) of favipiravir formulated by mixing with Inhalac 400® was prepared and characterized. Inhalations of ~ 120µg dose strength, with or without a prior oral loading dose were administered to mice. Comparator mice received human-equivalent oral doses (3mg). Three mice per sampling time point were sacrificed and favipiravir concentrations in the blood plasma, bronchio-alveolar lavage fluid (BALF) and lung tissue homogenate determined by HPLC. One-compartment PK modeling of concentration-time data indicated that the area under the curve (AUC0-24h) generated in the BALF recovered from mice receiving inhalations of ~ 1/25th of the oral dose subsequent to an oral loading dose was 86.72 ± 4.48µg⋅mL-1⋅h. This was consistently higher than the AUC observed in the BALF of orally-dosed mice (56.71 ± 53.89µgmL-1⋅h). In blood serum, the respective values of AUC were 321.55 ± 124.91 and 354.71 ± 99.60µg⋅mL-1⋅h. Pulmonary delivery of significantly smaller doses of favipiravir generates meaningful drug disposition and pharmacokinetics at the site of respiratory viral infections. We provide the rationale for designing a self-administered, non-invasive, low-cost, targeted drug delivery system against airborne RNA virus infection.

Sublingual Fast-Dissolving Thin Films of Loratadine: Characterization, In Vitro and Ex Vivo Evaluation.

Loratadine (LOR) is a second-generation antihistamine that exhibits a low and variable oral bioavailability (10-40%) and delayed onset owing to poor solubility and an extensive first-pass effect. Therefore, in light of the clinical need, the main goal of the present study was to develop sublingual fast-dissolving thin films of LOR-citric acid co-amorphous systems (LOR-CAs) with the aim of eliciting a faster onset and improving the bioavailability. We formulated sublingual fast-dissolving thin films of LOR by a film-casting technique using hydrophilic polymers like hydroxypropyl methylcellulose (HPMC E15), polyvinyl pyrrolidone K30 (PVP K30), and hydroxypropyl cellulose EL (HPC-EF) and citric acid as a pH modulator, while glycerin served as a plasticizer. The sublingual fast-dissolving thin films were characterized by FTIR, SEM, DSC, and XRD and evaluated for in vitro dissolution and ex vivo mucoadhesion. The best formulation (F1) developed using HPMC E15 as a polymer, glycerin as a plasticizer, and citric acid as a pH modulator was found to be the optimized formulation as it was smooth, clear, flexible, and displayed good mucoadhesion (11.27 ± 0.418 gm/cm2) and uniform thickness (0.25 ± 0.02 mm). The formulation F1 was found to display a significantly shorter DT (30.30 ± 0.6 s) and rapid release of LOR (92.10 ± 2.3% in 60 min) compared to other formulations (ANOVA, p < 0.001). The results indicated that the prepared sublingual films are likely to elicit a faster therapeutic effect, avoid first-pass metabolism, and improve the bioavailability.

To Explore Nasal-Brain Lymphatic System for Brain-Targeted Drug Delivery and to Treat Neurodegenerative Diseases.

Brain-related Neurodegenerative Disorders (NDD) are the leading cause of low life expectancy globally. Brain-targeted drug delivery is required for treating most the NDD via bypassing the blood-brain barrier, and hepatic first-pass metabolism. The nasal-brain drug delivery route has the advantage of locally enhancing drug delivery to the brain, mainly through the olfactory route rather than systemic circulation. To overcome the limitations of nasal-brain drug delivery, a nanocarrier approach and mucoadhesive polymers are needed. Notwithstanding these constraints, various nanotechnology techniques have been created, including polymeric micelles, liposomes, polymeric nanoparticles, solid lipid nanoparticles, & nano-emulsions. This review aims to explore the intranasal pathway for drug delivery through the nasal-brain lymphatic systems, considering brain anatomy and physiology along with a drug formulation design approach.

Advances in Mucoadhesive drug Delivery System: Enhancing Efficacy and Patient Compliance

The goal of mucoadhesive drug delivery systems (MDDS) is to improve drug delivery effectiveness by adhering to the body's mucosal tissues. The material used in this approach adheres to mucosal surfaces, including those in the mouth, gastrointestinal system, nasal passages, and vaginal walls. The most important goal is to extend the medication's residence duration at the absorption site in order to improve drug absorption and provide a more regulated and prolonged release. Mucoadhesion refers to the adhesion between two materials, one of which is biological, through interfacial forces over an extended period. This characteristic provides an effective solution to challenges in traditional drug delivery systems, such as avoiding first-pass metabolism and facilitating localized delivery of biomolecules, including proteins, peptides, and oligonucleotides. It holds significant promise for delivering compounds via routes like ocular, nasal, vaginal, and buccal administration This study addresses the introduction, benefits, drawbacks, mechanisms, and theories of mucoadhesion in addition to polymer categorization, mucoadhesive dosage forms, assessment, and factors affecting mucoadhesion and several kinds of mucoadhesive dosage forms. Keywords: Mucoadhesion, Theories, Mucoadhesive Dosage Form, bio adhesion

The Vecta 46 intermediate catheter for mechanical thrombectomy of distal medium vessel occlusions: A single-center experience.

With emerging evidence supporting the clinical efficacy and safety of mechanical thrombectomy (MT) for distal medium vessel occlusions (DMVOs), MT devices specifically designed to navigate through smaller caliber and more delicate tortuous distal cerebrovasculature are required. This study describes our single-center experience using the AXS Vecta 46 intermediate catheter for first-line thromboaspiration of DMVOs. We identified all patients who underwent MT using the Vecta 46 for first-line thromboaspiration for primary or secondary DMVOs. We collected baseline clinical data, angiographic and clinical outcomes, as well as procedural complications. The primary outcome in question was the rate of successful recanalization, which was defined as a modified Thrombolysis in Cerebral Infarction score of ≥2b. We identified 43 patients who underwent MT using the Vecta 46 catheter for thromboaspiration of 54 DMVOs. Intervened vessels included the M2 (23/54), M3 (19/54), and M4 (6/54) branches of the middle cerebral artery, A2 (1/54), A3 (1/54), and A4 (1/54) branches of the anterior cerebral artery, and P1 (1/54), P2 (1/54), and P4 (1/54) branches of the posterior cerebral artery. The median number of passes for primary DMVOs was 2 (IQR: 1-3) and 1 (IQR: 1-1.25) for secondary DMVOs. The rate of successful recanalization was 100% (18/18) for primary DMVOs and 80.6% (29/36) for secondary DMVOs. First-pass effect (FPE) was noted in 55.6% (30/54) of all primary and secondary DMVO cases. Improved short-term clinical outcomes were observed in both the primary (National Institute of Health Stroke Scale [NIHSS] shift: -5 [IQR: -14.25 to -0.25]) and secondary (NIHSS shift: -5 [IQR: -10 to -2]) DMVO groups. A total of six patients died during their hospitalization, though none were deemed procedural-related. Our study demonstrates the safety and efficacy of the Vecta 46 intermediate catheter for thromboaspiration of both primary and secondary DMVOs, achieving high rates of successful recanalization and FPE.

Impact of D-dimer on the outcomes of endovascular thrombectomy for acute ischemic stroke: A systematic review and meta-analysis.

There has been growing data about the association between D-dimer levels and thrombectomy outcomes in acute ischemic stroke patients (AIS) with no cumulative evidence. This systematic review and meta-analysis aim to discuss and analyze the findings of the current studies to provide more robust evidence in this regard. A systematic search was conducted through PubMed, Web of Science, Embase, and Scopus to retrieve all relevant investigations. A meta-analysis was conducted, and the results were presented in odds ratio (ORs) for binary variables and ratio of means (ROM) for continuous variables, each accompanied by its respective 95% confidence intervals (CIs). After searching and screening, 14 studies were included. The analysis showed that the low D-dimer group had significantly higher rates of favorable functional outcome (OR: 4.40; 95%CI: 2.65-7.30; p < 0.001, n = 3) and recanalization (OR: 4.13; 95%CI: 1.57-10.84; p = 0.004, n = 3) than the high one. The association between D-dimer levels and first-pass effect and re-occlusion risk was also demonstrated. Eventually, two studies also demonstrated a significant association between high D-dimer levels and deep venous thrombosis and symptomatic intracranial hemorrhage as post-thrombectomy complications. Current evidence indicates a significant association between D-dimer levels and post-thrombectomy outcomes in AIS patients. However, current data are remarkably heterogeneous, and additional comparative investigations are needed.

Transdermal Drug Delivery Systems: Different Generations and Dermatokinetic Assessment of Drug Concentration in Skin.

Transdermal drug delivery systems (TDDS) are a highly appealing and innovative method of administering drugs through the skin, as it enables the drugs to achieve systemic effects. A TDDS offers patient convenience, avoids first-pass hepatic metabolism, enables local targeting, and reduces the toxic effect of drug. This review details several generations of TDDS and the advancements made in their development to address the constraints associated with skin delivery systems. Transdermal delivery methods of the first generation have been consistently growing in their clinical application for administering small, lipophilic, low-dose drugs. Second-generation TDDS, utilizing chemical enhancers and iontophoresis, have led to the development of clinical products. Third-generation delivery systems employ microneedles, thermal ablation, and electroporation to specifically target the stratum corneum, which is the skin's barrier layer. Dermatokinetics is the study of the movement of drugs and formulations applied to the skin over a period of time. It provides important information regarding the rate and extent to which drugs penetrate skin layers. Several dermatokinetic techniques, including tape stripping, microdialysis, and laser scanning microscopy, have been used to study the intricate barrier properties and clearance mechanisms of the skin. This understanding is essential for developing and improving effective TDDS.

Formulation, Optimization, and Evaluation of Solid-lipid Formulation for Bioavailability Enhancement Utilizing Diltiazem Hydrochloride

Background: Cardiac arrhythmia is a health concern, requiring effective medication for proper treatment. Diltiazem hydrochloride (DTZ.HCL), a class IV anti-arrhythmic calcium channel blocker, was used as a model drug due to its ability to block Ca++ channels in the SA and AV nodes, reducing calcium entry into cardiac cells and subsequently decreasing the force of contraction and oxygen consumption by the heart. Despite its good oral absorption, DTZ.HCL bioavailability is reduced to approximately 40% due to extensive first-pass metabolism. A nano-enabled drug delivery system has the advantage of incorporating both lipophilic and hydrophilic drugs with improved physical stability and enhanced bioavailability. Objective: The objective of this study was to develop a solid-lipid formulation utilizing diltiazem hydrochloride and evaluate it for its bioavailability enhancement. Method: In the experimental study, SLNs were prepared using the microemulsion technique. A blend ratio (1:1) of lipid (stearic acid: compritol 888 ATO), span 80, PEG 200, and water was selected based on the microemulsion region obtained from the Triplot (4.1) ternary phase diagram. The hydrophilic drug diltiazem hydrochloride was incorporated into the lipid blend, and a preheated Smix was maintained at 80°C to obtain a transparent microemulsion, which then crystallized to form SLNs upon subsequent dispersion in cold water (1:25). Critical process parameters, including magnetic stirring speed, homogenizer speed, and probe sonication cycle, were optimized using Design Expert 10 software to achieve the desired particle size diameter, PDI, and entrapment efficiency. Results: The results revealed that the particle size and PDI were significantly influenced by the span 80 and PEG 200. An increase in the concentration of the lipid blend resulted in large particle sizes. The optimized formulation showed a particle size of 415.4±0.2 nm, PDI of 0.184±0.01, and zeta potential of -24.19±0.12 mV. These results were corroborated by DSC thermograms, which indicated reduced enthalpy associated with the reduced particle size of SLNs. Given that diltiazem hydrochloride is a hydrophilic drug with high water solubility, the entrapment efficiency was relatively 30.6% ±0.45. In vitro release studies demonstrated an initial burst release, followed by a sustained release of 85% over 24 hours. The optimized SLNs followed the Higuchi matrix model, with a coefficient of correlation (R²) value of 0.9369. Conclusion: Results concluded successful development of SLNs with improved bioavailability when compared by way of in-vitro method with marketed preparations.

Development and in vitro Evaluation of Cannabidiol Mucoadhesive Buccal Film Formulations Using Hot-Melt Extrusion Technology

Introduction: Cannabidiol (CBD) has sparked considerable interest because of its wide range of pharmacological uses and the fact that it does not induce psychoactive effects. CBD formulation development presents significant challenges due to its limited water solubility and susceptibility to first-pass metabolism, both of which restrict its overall bioavailability. The current research aimed to use hot-melt extrusion (HME) technology to develop mucoadhesive buccal films to improve CBD solubility and reduce first-pass metabolism. Methods: Five formulations containing 10% w/w CBD were extruded using a counter-rotating twin-screw extruder (Haake Minilab II, Thermo Fisher Scientific). Different characterization studies were conducted on the developed formulations. Results: Differential scanning calorimetry (DSC) revealed that the CBD endothermic peak disappeared in some of the developed films, indicating that CBD was converted from crystalline to amorphous form. A bio-adhesion study showed that the formulations containing Carbopol® (BF2, BF3, BF4, and BF5) had higher adhesiveness properties. In vitro release and solubility studies showed an increase in CBD release and water solubility in the developed formulations when compared to pure CBD. Stability studies revealed that CBD content and release in the lead formulation (BF2) was stable over 15 months. Conclusion: The current study demonstrates that HME was successfully used as an approach to develop CBD mucoadhesive buccal films and CBD solubility was enhanced.

A Comprehensive Review of Self-Nanoemulsifying Systems in the Delivery of Herbal Drugs.

Self-nanoemulsifying drug delivery systems (SNEDDS) are an isotropic mixture of oils, co-surfactants, and surfactants and can form fine O/W Nanoemulsions in aqueous media. These components are advantageous in terms of improved solubility and bioavailability. Limited permeability, solubility, and bioavailability remain a significant challenge in developing herbal drugs. This review explores the potential of self-nanoemulsifying drug delivery systems (SNEDDS) as a promising strategy to overcome this problem. The SNEDDS is considered a novel technique for the delivery of low water-soluble drugs. It can bypass the first-pass metabolism, resulting in steady and sustained drug levels in the systemic circulation. The present article provides a comprehensive overview of the SNEDDS formulation of herbal drugs. It includes their composition, characterization, in vitro and in vivo studies conducted in various disease conditions, and pharmacokinetic studies.

Can the clot meniscus and claw signs predict thrombectomy and clinical outcomes in patients with stroke? A systematic review and meta-analysis

BackgroundThe angiographic shape of an occlusion, like the clot meniscus sign and the claw sign, has been reported to potentially impact the recanalization rate and clinical outcome in patients undergoing...

Simvastatin and Captopril Combined Transdermal Delivery System for Controlling Blood Pressure and Fat: Design, Characterization, and In Vivo Pharmacokinetic Evaluation

We developed a sustained-release transdermal drug delivery system (TDDS) containing simvastatin (SIM) and captopril (CAP) to treat hypertension and hyperlipidemia and overcome treatment drawbacks, including significant liver first-pass effects, low bioavailability, and the short half-life of SIM and CAP oral tablets. We used a transdermal diffusion meter to preselect the formula of the SIM-CAP TDDS. Based on in vitro permeation experiments, we optimized the formula of the SIM-CAP TDDS to include 24% SIM, 24% CAP, 34% polyvinyl alcohol (PVA), 16% oleic acid (OA)–azone, and 2% polyacrylic acid resin II. We evaluated the optimized SIM-CAP TDDS formula by its appearance, stability, stickiness, drug content, in vivo pharmacokinetics, and skin irritation tests. The results indicated that the patch had good stability and stickiness. The SIM and CAP contents were 5.02 ± 0.41 mg/cm2 in the 1 cm2 SIM-CAP TDDS. The pharmacokinetic results indicated that the system continuously released SIM and CAP for 24 h and significantly enhanced their bioavailability, with a higher area under the curve. The SIM-CAP TDDS exhibits a sustained-release effect with good characteristics and pharmacokinetics. And it is safe and has no irritating effects on the skin; therefore, it is an ideal formulation.

Rosuvastatin Flexible Chitosomes: Development, In Vitro Evaluation and Enhancement of Anticancer Efficacy Against HepG2 and MCF7 Cell Lines.

Rosuvastatin (ROS), a statin drug with promising anticancer properties has a low bioavailability of approximately 20% due to lipophilicity and first-pass metabolism. This study aimed to enhance ROS anticancer efficacy through loading into flexible chitosomes. The chitosomes were prepared starting from negatively charged liposomes through electrostatic interactions with chitosan. The conversion of zeta potential from negative to positive confirmed the successful formation of chitosomes. The chitosan coating increased the particle size and zeta potential, which ranged from 202.0 ± 1.7nm to 504.7 ± 25.0nm and from - 44.9 ± 3.0 mV to 50.1 ± 2.6 mV, respectively. Chitosan and drug concentrations had an important influence on the chitosome properties. The optimum chitosome formulation was used to prepare ROS-loaded flexible chitosomes using different concentrations of four edge activators. The type and concentration of edge activator influenced the particle size, drug entrapment efficiency, and drug release rate of the flexible chitosomes. Flexible chitosomes significantly increased drug permeation through rat abdominal skin compared to control transferosomes and drug solution. The optimal ROS flexible chitosomes containing sodium deoxycholate as an edge activator had a 2.23-fold increase in ROS cytotoxic efficacy against MCF7 cells and a 1.84-fold increase against HepG2 cells. These results underscore the potential of flexible chitosomes for enhancing ROS anticancer efficacy.

9224 Evaluation of Safety and Efficacy of Administration of Estradiol by Subcutaneous Injection in Transgender Women

Abstract Disclosure: H. Perkins: None. H. Moreau: None. J. LaBudde: None. W. Craig: None. D.I. Spratt: None. Background: Off-label use of subcutaneous (SC) estradiol (E2) by transgender women for gender-affirming hormone therapy is becoming increasingly widespread, despite a lack of published data regarding its efficacy and safety. Methods: This retrospective cohort study used manual data extraction from electronic medical records for patients ages 18-79 years, currently or previously receiving oral (PO) 17-beta E2 or SC E2 valerate therapy at Maine Medical Center Reproductive Endocrinology and Infertility and Gender Clinics between 5/30/14-5/30/23, who completed E2 dose adjustments aimed at obtaining a serum E2 of 75-250 pg/mL. SC E2 was administered weekly and PO E2 daily. Serum testosterone (T), estrone (E1), and sex hormone binding globulin (SHBG) levels were recorded if drawn within 90 days of E2 measurement on an optimized dose. In a subset of patients receiving SC E2, serum E2 levels were drawn 1-2 days post- and pre-injection. All patient-reported local or systemic reactions were recorded. Data are expressed as median (full range) or mean ± standard deviation (full range). Results: 45 patients were included with no significant differences in demographics between PO (n=20) and SC (n=25) groups. Both groups achieved therapeutic E2 levels after dose adjustment without statistical difference in mean serum E2 (pg/mL) between SC and PO groups: 148.7 ± 41.0 (78-226) vs. 151.6 ± 31.7 (97-208); p=0.79 by t-test. In patients without orchiectomy, both SC and PO groups had T (ng/dL) suppressed to normal adult female range (10-55) in 11/12 SC patients and in 17/17 PO patients; median T was 14.0 (7.7-86) for SC vs. 20.6 (3.4-42) for PO; p=0.98 by Mann-Whitney U test. Median E2 dose (mg/week) in the SC group was 3.0 (1.4-6.0) and in the PO group was 42.0 (28-84). Median serum E1 (pg/mL) was lower in the SC group than the PO group: 73.5 (29-115), n=12 vs. 907 (596-1601), n=5, p&amp;lt;0.001 by Mann-Whitney U test. E1/E2 ratio was lower in the SC group than the PO group: 0.4 ± 0.1 vs. 8.0 ± 2.9; p&amp;lt;0.001 by t-test. There was no significant difference in median serum SHBG (nmol/L) between SC and PO groups: 71.7 (19.3-146.7), n=15 vs. 73.4 (51.0-187.4), n=14; p=0.20 by Mann-Whitney U test. Mean post- and pre-dose serum E2 levels in 5 patients were 138.0 ± 24.0 and 88.0 ± 57.6, respectively. There was one transient local reaction and no systemic allergic or inflammatory reactions in the SC group with no systemic reactions in the PO group. Conclusion: These results demonstrate that SC E2 at doses of 1.4-6 mg/week can be administered safely to achieve therapeutic serum E2 levels and suppress serum T levels to within the normal female range. Our preliminary data reveal lower serum E1 levels in the SC group than in the PO group suggesting reduced hepatic first-pass metabolism with SC administration; this pattern was not seen with serum SHBG levels. Post- and pre-dose serum E2 levels revealed only a mild decline in E2 levels between injections. Presentation: 6/3/2024

6961 Evaluation of Safety and Efficacy of Administration of Estradiol by Subcutaneous Injection in Transgender Women

Abstract Disclosure: H. Perkins: None. H. Moreau: None. J. LaBudde: None. W. Craig: None. D.I. Spratt: None. Background: Off-label use of subcutaneous (SC) estradiol (E2) by transgender women for gender-affirming hormone therapy is becoming increasingly widespread, despite a lack of published data regarding its efficacy and safety. Methods: This retrospective cohort study used manual data extraction from electronic medical records for patients ages 18-79 years, currently or previously receiving oral (PO) 17-beta E2 or SC E2 valerate therapy at Maine Medical Center Reproductive Endocrinology and Infertility and Gender Clinics between 5/30/14-5/30/23, who completed E2 dose adjustments aimed at obtaining a serum E2 of 75-250 pg/mL. SC E2 was administered weekly and PO E2 daily. Serum testosterone (T), estrone (E1), and sex hormone binding globulin (SHBG) levels were recorded if drawn within 90 days of E2 measurement on an optimized dose. In a subset of patients receiving SC E2, serum E2 levels were drawn 1-2 days post- and pre-injection. All patient-reported local or systemic reactions were recorded. Data are expressed as median (full range) or mean ± standard deviation (full range). Results: 45 patients were included with no significant differences in demographics between PO (n=20) and SC (n=25) groups. Both groups achieved therapeutic E2 levels after dose adjustment without statistical difference in mean serum E2 (pg/mL) between SC and PO groups: 148.7 ± 41.0 (78-226) vs. 151.6 ± 31.7 (97-208); p=0.79 by t-test. In patients without orchiectomy, both SC and PO groups had T (ng/dL) suppressed to normal adult female range (10-55) in 11/12 SC patients and in 17/17 PO patients; median T was 14.0 (7.7-86) for SC vs. 20.6 (3.4-42) for PO; p=0.98 by Mann-Whitney U test. Median E2 dose (mg/week) in the SC group was 3.0 (1.4-6.0) and in the PO group was 42.0 (28-84). Median serum E1 (pg/mL) was lower in the SC group than the PO group: 73.5 (29-115), n=12 vs. 907 (596-1601), n=5, p&amp;lt;0.001 by Mann-Whitney U test. E1/E2 ratio was lower in the SC group than the PO group: 0.4 ± 0.1 vs. 8.0 ± 2.9; p&amp;lt;0.001 by t-test. There was no significant difference in median serum SHBG (nmol/L) between SC and PO groups: 71.7 (19.3-146.7), n=15 vs. 73.4 (51.0-187.4), n=14; p=0.20 by Mann-Whitney U test. Mean post- and pre-dose serum E2 levels in 5 patients were 138.0 ± 24.0 and 88.0 ± 57.6, respectively. There was one transient local reaction and no systemic allergic or inflammatory reactions in the SC group with no systemic reactions in the PO group. Conclusion: These results demonstrate that SC E2 at doses of 1.4-6 mg/week can be administered safely to achieve therapeutic serum E2 levels and suppress serum T levels to within the normal female range. Our preliminary data reveal lower serum E1 levels in the SC group than in the PO group suggesting reduced hepatic first-pass metabolism with SC administration; this pattern was not seen with serum SHBG levels. Post- and pre-dose serum E2 levels revealed only a mild decline in E2 levels between injections. Presentation: 6/3/2024