Citric Acid in Drug Formulations Causes Pain by Potentiating Acid-Sensing Ion Channel 1

Towards more tolerable subcutaneous administration: Review of contributing factors for improving combination product design

Subcutaneous (SC) injections can be associated with local pain and discomfort that is subjective and may affect treatment adherence and overall patient experience. With innovations increasingly focused on finding ways to deliver higher doses and volumes (≥2 mL), there is a need to better understand the multiple intertwined factors that influence pain upon SC injection. As a priority for the SC Drug Development & Delivery Consortium, this manuscript provides a comprehensive review of known attributes from published literature that contribute to pain/discomfort upon SC injection from three perspectives: (1) device and delivery factors that cause physical pain, (2) formulation factors that trigger pain responses, and (3) human factors impacting pain perception. Leveraging the Consortium's collective expertise, we provide an assessment of the comparative and interdependent factors likely to impact SC injection pain. In addition, we offer expert insights and future perspectives to fill identified gaps in knowledge to help advance the development of patient-centric and well tolerated high-dose/high-volume SC drug delivery solutions.

Satisfaction with the Injection Experience of a New, Citrate-Free Formulation of Ixekizumab

INTRODUCTION

A new, citrate-free ixekizumab formulation, which is bioequivalent to the original formulation, was associated with significant reduction in injection site pain. This study evaluates patient satisfaction with the first injection experience of citrate-free ixekizumab in a real-world setting.

METHODS

A non-interventional, observational, web-based survey of adults (≥ 18 years) with psoriasis, psoriatic arthritis, or axial spondyloarthritis was conducted between August 2022 and March 2023. Patients enrolled in the Taltz US Customer Support Program were identified as receiving either the original ixekizumab or initiating citrate-free ixekizumab. Patients receiving original ixekizumab completed one survey at baseline to assess satisfaction with the formulation and one survey after switching to assess satisfaction, willingness to continue using and recommending citrate-free ixekizumab, and formulation preference. Participants previously exposed to ixekizumab completed one survey to assess their satisfaction and willingness to continue using and recommending citrate-free ixekizumab. Descriptive and comparative statistics are reported for patients that switched from original to citrate-free ixekizumab (n = 361); and descriptive statistics are reported for patients not previously exposed to ixekizumab (n = 90).

RESULTS

A total of 451 patients were included in the analysis. Significantly more patients were satisfied with their first injection with citrate-free ixekizumab compared to original ixekizumab (83.9% vs. 71.7% respectively; p = 0.0001). Almost all patients who switched from original ixekizumab were definitely or mostly willing to continue using and recommending citrate-free ixekizumab (93.9% and 93.4%, respectively). Additionally, 94.2% of patients who switched from original to citrate-free ixekizumab preferred citrate-free ixekizumab or had no preference. Three-fourths of patients not previously exposed to ixekizumab were satisfied with their first injection with citrate-free ixekizumab and 94.5% were definitely or mostly willing to continue using citrate-free ixekizumab.

CONCLUSION

The citrate-free ixekizumab formulation was preferred and well accepted by most patients who switched from the original ixekizumab formulation. Similar findings were seen for those newly initiating citrate-free ixekizumab.

TAT peptide at treatment-level concentrations crossed brain endothelial cell monolayer independent of receptor-mediated endocytosis or peptide-inflicted barrier disruption

The peptide domain extending from residues 49 to 57 of the HIV-1 Tat protein (TAT) has been widely shown to facilitate cell entry of and blood-brain barrier (BBB) permeability to covalently bound macromolecules; therefore, TAT-linked therapeutic peptides trafficked through peripheral routes have been used to treat brain diseases in preclinical and clinical studies. Although the mechanisms underlying cell entry by similar peptides have been established to be temperature-dependent and cell-type specific and to involve receptor-mediated endocytosis, how these peptides cross the BBB remains unclear. Here, using an in vitro model, we studied the permeability of TAT, which was covalently bound to the fluorescent probe fluorescein isothiocyanate (FITC), and evaluated whether it crossed the "in vitro BBB", a monolayer of brain endothelial cells, and whether the mechanisms were similar to those involved in TAT entry into cells. Our results show that although TAT crossed the monolayer of brain endothelial cells in a temperature-dependent manner, in contrast to the reported mechanism of cell entry, it did not require receptor-mediated endocytosis. Furthermore, we revisited the hypothesis that TAT facilitates brain delivery of covalently bound macromolecules by causing BBB disruption. Our results demonstrated that the dose of TAT commonly used in preclinical and clinical studies did not exert an effect on BBB permeability in vitro or in vivo; however, an extremely high TAT concentration caused BBB disruption in vitro. In conclusion, the BBB permeability to TAT is temperature-dependent, but at treatment-level concentrations, it does not involve receptor-mediated endocytosis or BBB disruption.

Ion Channel Genes in Painful Neuropathies

Neuropathic pain (NP) is a typical symptom of peripheral nerve disorders, including painful neuropathy. The biological mechanisms that control ion channels are important for many cell activities and are also therapeutic targets. Disruption of the cellular mechanisms that govern ion channel activity can contribute to pain pathophysiology. The voltage-gated sodium channel (VGSC) is the most researched ion channel in terms of NP; however, VGSC impairment is detected in only <20% of painful neuropathy patients. Here, we discuss the potential role of the other peripheral ion channels involved in sensory signaling (transient receptor potential cation channels), neuronal excitation regulation (potassium channels), involuntary action potential generation (hyperpolarization-activated cyclic nucleotide-gated channels), thermal pain (anoctamins), pH modulation (acid sensing ion channels), and neurotransmitter release (calcium channels) related to pain and their prospective role as therapeutic targets for painful neuropathy.

Risk Factors of Ixekizumab-Induced Injection Site Reactions in Patients with Psoriatic Diseases: Report from a Single Medical Center

Ixekizumab (Taltz^®) is a humanized anti-IL-17A monoclonal antibody approved for the treatment of various inflammatory diseases including psoriasis and psoriatic arthritis. Despite the favorable efficacy and safety, ixekizumab is also known for its high incidence of injection site reactions (ISRs), ranging from 6% to 55% in different studies according to different definitions and studied population. However, specific risk factors for ixekizumab-induced injection site reactions in patients with psoriatic diseases had not been well studied. In this retrospective study, we found that overweight or obesity might be a protective predictor for the occurrence of ixekizumab-induced ISRs in patients with psoriatic disease. Meanwhile, having a positive family history of psoriasis might be a potential risk factor. Last but not least, patients with diarrhea following ixekizumab injection were associated with a higher risk of developing ISRs. Future high-quality studies with larger samples are warranted to verify the relationship.

A Systematic Literature Review of Injection Site Pain Perception in Adult Patients Treated with Citrate-Free and Citrate-Containing Biologic Agents

OBJECTIVE

To investigate injection site pain (ISP) and other injection site outcomes caused by biologics administered alongside citrate-free (CF) and citrate-containing (CC) formulations.

METHODS

Electronic literature databases (Medline, Embase, and Cochrane Library) were systematically searched for clinical trials and observational studies reporting on injection site outcomes after subcutaneous administration of biologics. Studies with unknown excipient formulations were excluded. The primary outcome was ISP, and secondary outcomes included any other reported injection site reactions (ISRs). Meta-analysis approaches were used to aggregate evidence identified via the conducted systematic literature review.

RESULTS

A total of two observational studies, two cross-over/sequential trials, and three head-tohead comparison trials directly comparing CF with CC biologics were identified, as well as seven placebo-controlled trials. Evidence from five of the seven direct comparison studies suggested reduced pain perception at the injection site when CF formulations were applied. Findings for other ISRs were balanced between both formulations, with slightly favorable results for preparations without citrate. A meta-analysis of placebo-controlled trials found no significant difference between arms with CF formulations and placebo regarding the proportion of patients experiencing ISP (OR 0.62, 95% CI 0.30-1.28).

CONCLUSION

Excipient formulations are rarely specified in studies assessing pain and other ISRs of subcutaneously administered biologics. The available data indicate that subcutaneous administration of biologic agents without citrate may be associated with lower pain perception outcomes compared with treatment using CC formulations. Importantly, ISP is influenced by many factors which may have affected the results. More research is needed to assess how formulation excipients influence ISRs.

A 10-mg dose of amiloride increases time to failure during blood-flow-restricted plantar flexion in healthy adults without influencing blood pressure

Amiloride has been shown to inhibit acid-sensing ion channels (ASICs), which contribute to ischemia-related muscle pain during exercise. The purpose of this study was to determine if a single oral dose of amiloride would improve exercise tolerance and attenuate blood pressure during blood-flow-restricted (BFR) exercise in healthy adults. Ten subjects (4 females) performed isometric plantar flexion exercise with BFR (30% maximal voluntary contraction) after ingesting either a 10-mg dose of amiloride or a volume-matched placebo (random order). Time to failure, time-tension index (TTI), and perceived pain (visual analog scale) were compared between the amiloride and placebo trials. Mean blood pressure, heart rate, blood pressure index (BPI), and BPI normalized to TTI (BPInorm) were also compared between trials using both time-matched (TM50 and TM100) and effort-matched (T50 and T100) comparisons. Time to failure (+69.4 ± 63.2 s, P < 0.01) and TTI (+1,441 ± 633 kg·s, P = 0.02) were both significantly increased in the amiloride trial compared with placebo, despite no increase in pain (+0.4 ± 1.7 cm, P = 0.46). In contrast, amiloride had no significant influence on the mean blood pressure or heart rate responses, nor were there any significant differences in BPI or BPInorm between trials when matched for time (all P ≥ 0.13). When matched for effort, BPI was significantly greater in the amiloride trial (+5,300 ± 1,798 mmHg·s, P = 0.01), likely owing to an increase in total exercise duration. In conclusion, a 10-mg oral dose of amiloride appears to significantly improve the tolerance to BFR exercise in healthy adults without influencing blood pressure responses.

An Investigation Into Local Infusion Site Pain After Infusion of Ultra Rapid Lispro Excipients Across Sites and Depths

BACKGROUND

This phase 1, randomized, one-day, five-period crossover study in adults with type 1 diabetes on continuous subcutaneous insulin infusion investigated local infusion site pain following infusion of the excipients of ultra rapid lispro (URLi; without insulin) across infusion sites and depths.

METHODS

Forty participants (mean age, 40.5 years; body mass index [BMI], 27.5) were randomized to one of five infusion site sequences consisting of the arm, thigh, buttock (6 mm cannula depth), and abdomen (6 and 9 mm depth). Basal infusion of sodium citrate and treprostinil in diluent with magnesium chloride was initiated (10 μL/h) and at three, six, and nine hours after basal initiation, 15 unit-equivalent boluses (150 μL) were given. Participants rated their pain on a 0 to 100 mm validated visual analog scale (VAS) at 5 minutes pre-bolus and 1 and 15 minutes post-bolus.

RESULTS

At one minute post-bolus, increased VAS scores were occasionally reported. Most one minute post-bolus scores were ≤10 mm (little to no discomfort) while 7 of 577 were >45 mm (generally considered clinically meaningful pain). Painful infusions were reported more frequently for the arm, and mean VAS scores were higher for the arm compared with the thigh and abdomen. The VAS score distributions were similar between cannula depths. By 15 minutes post-bolus, VAS scores returned to pre-bolus levels.

CONCLUSIONS

Local infusion site discomfort after infusion of URLi excipients was reported by a small subset of participants; it was transient, tolerable, and dependent on infusion site but not infusion depth. Given differences within individuals, patients may consider using a different infusion site if they experience discomfort.

CLINICALTRIAL.GOV IDENTIFIER

NCT05067270.

Citric Acid: A Multifunctional Pharmaceutical Excipient

Citric acid, a tricarboxylic acid, has found wide application in the chemical and pharmaceutical industry due to its biocompatibility, versatility, and green, environmentally friendly chemistry. This review emphasizes the pharmaceutical uses of citric acid as a strategic ingredient in drug formulation while focusing on the impact of its physicochemical properties. The functionality of citric acid is due to its three carboxylic groups and one hydroxyl group. These allow it to be used in many ways, including its ability to be used as a crosslinker to form biodegradable polymers and as a co-former in co-amorphous and co-crystal applications. This paper also analyzes the effect of citric acid in physiological processes and how this effect can be used to enhance the attributes of pharmaceutical preparations, as well as providing a critical discussion on the issues that may arise out of the presence of citric acid in formulations.

New insight into the importance of formulation variables on parenteral growth hormone preparations: potential effect on the injection-site pain

Reducing injection-site pain (ISP) in patients with chronic conditions such as growth hormone deficiency is a valuable strategy to improve patient compliance and therapeutic efficiency. Thus understanding different aspects of pain induction following subcutaneous injection of biotherapeutics and identifying the responsible factors are vital. Here we have discussed the effects of formulation's viscosity, concentration, osmolality, buffering agents, pH, and temperature as well as injection volume, dosing frequency, and different excipients on ISP following subcutaneous injection of commercially available recombinant human growth hormone products. Our literature review found limited available data on the effects of different components of parenteral rhGH products on ISP. This may be due to high cost associated with conducting various clinical trials to assess each excipient in the formulation or to determine the complex interactions of different components and its impact on ISP. Recently, conducting molecular dynamics simulation studies before formulation design has been recommended as an alternative and less-expensive approach. On the other hand, the observed inconsistencies in the available data is mainly due to different pain measurement approaches used in each study. Moreover, it is difficult to translate data obtained from animal studies to human subjects. Despite all these limitations, our investigation showed that components of parenteral rhGH products can significantly contribute to ISP. We suggest further investigation is required for development of long acting, buffer-free, preservative-free formulations. Besides, various excipients are currently being investigated for reducing ISP which can be used as alternatives for common buffers, surfactants or preservatives in designing future rhGH formulations.

Acid-sensing ion channels as potential therapeutic targets

Tissue acidification is associated with a variety of disease states, and acid-sensing ion channels (ASICs) that can sense changes in pH have gained traction as possible pharmaceutical targets. An array of modulators, ranging from small molecules to large biopharmaceuticals, are known to inhibit ASICs. Here, we summarize recent insights from animal studies to assess the therapeutic potential of ASICs in disorders such as ischemic stroke, various pain-related processes, anxiety, and cardiac pathologies. We also review the factors that present a challenge in the pharmacological targeting of ASICs, and which need to be taken into careful consideration when developing potent and selective modulators in the future.