Btx-A is a neurotoxin that acts as a neuromuscular blocking agent by blocking the release of
acetylcholine from presynaptic nerve terminals, thereby interfering with vascular smooth muscle contraction and enhancing local circulation [66].
The SEDUCE study group recently evaluated the effects of sildenafil on ischemic digital ulcer healing in SSc in a randomized placebo-controlled trial [51]. Eighty-three patients with a total of 192 digital ulcers were included in the intention-to-treat analysis (89 in the sildenafil group, 103 in the placebo group), however the primary endpoint was not reached. In order to expand therapeutic options for the treatment of SSc-related RP attacks, tadalafil was studied in a prospective double-blind placebo-controlled crossover study. Patients were randomized to receive a fixed dose of tadalafil at 20 mg daily or placebo for a 4 week period, and the RP condition score, frequency of RP episodes, and duration of RP episodes between treatment groups was compared. While tadalafil was well-tolerated, there was no significant difference in treatment response between the tadalafil arm and the placebo arm [52].
However, a subsequent study examined the benefits of tadalafil as an add-on therapy for the healing and prevention of digital ulcers. This double-blind, randomized, cross-over trial evaluated the efficacy of tadalafil as add-on therapy in patients with treatment-resistant RP. Patients with SSc and MCTD who were on vasodilators, but still having 4 or more episodes of RP attacks per week were included and randomized to receive either tadalafil 20 mg per day or placebo. Significant improvements from baseline were observed in several outcome measures during tadalafil therapy compared to placebo, including mean daily frequency of RP episodes, mean daily duration of RP, and mean daily RP condition score. In the tadalafil group, all 24 digital lesions healed compared to only 3 of 13 in the placebo group, and only one new ulcer was reported during tadalafil therapy compared to 13 in patients on placebo therapy [53]. In a recent double-blind, RCT, Btx-A was administered (50 units in 2.5 ml sterile saline) in one randomly selected hand and sterile saline (2.5 ml) in the opposite hand [67].
Follow-up at 1 and 4 months post-injection included laser Doppler imaging of hands, patient-reported outcomes, and physical examination. At 1-month follow-up, a significantly greater reduction in average blood flow was observed in Btx-A-treated hands compared to placebo-treated hands (p = 0.024).
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Change in blood flow at a 4-month follow-up was not significantly different between groups.
A systematic review and meta-analysis recently examined the effects of local topical nitrates in primary and secondary RP with respect to parameters of digital blood flow, and clinical severity was recently completed [65]. Seven placebo-controlled trials were included (346 patients) in the meta-analysis, with 4 trials involving nitroglycerin ointments, 2 involving the nitroglycerin gel vehicle MQX-503, and 1 involving a compounded nitrite. The results of the meta-analysis demonstrated a moderate-to-large treatment effect in RP (standardized mean difference [SMD] = 0.70; 95% CI, 0.35–1.05; P < .0001). Subgroup analyses showed a large treatment effect in secondary RP (SMD = 0.95; 95% CI, 0.25–1.65; P = .008) and moderate effect in primary RP (SMD = 0.45; 95% CI, 0.05–0.85; P = .03) [65]. A relatively novel therapy that shows promise in RP involves the local injection of botulinum toxin type A (Btx-A) in the hands of patients with SSc. Ultimately, the investigators concluded that there may be a role of Btx-A in treating a subset of patients with
RP, and that further studies defining the patients who are most likely to benefit from this intervention are warranted.
A phase 3 study is currently recruiting in France to assess whether or not a single injection schedule of BTX-A in both hands improves RP secondary to SSc better than a placebo at 4, 12, and 24 weeks after the treatment.
Collectively, these data suggest that phosphodiesterase-inhibitors play an important role in the healing and prevention of digital ulcers in SSc-related RP. Prostacyclins and prostaglandins continue to serve as key therapies used to treat challenging cases of RP in the context of SSc. Iloprost, for example, serves as a standard treatment of existing digital ulcers [54–56]. It is currently indicated for patients with severe disabling Raynaud’s unresponsive to other therapies for the prevention of ischemic pain, peripheral ulcers, and necrosis of the digits to prevent amputation. It may be administered by one of three schedules: (a) 3-day schedule as an inpatient for RP/SSc; (b) 5-day schedule as an outpatient for RP/SSc; or (c) continuous infusion for the treatment of patient with active or extensive digital ulcers, severe digital ischemia, or for patients who cannot tolerate higher rates of the infusion.
Details of the complex infusion protocols can be found here [57]. Treprostanil, a synthetic analog of prostacyclin (PGI2), has also been studied as a therapy for patients with SSc-associated Raynaud’s and/or digital ulcers, in both oral and topical formulations. Oral treprostanil initially showed promise in patients with SSc and digital ischemia in a phase 1 study, where effective absorption and temporal associations with improved cutaneous perfusion and temperature were noted [58]. The recurrence of digital ulcers in patients with SSc after discontinuation of oral treprostanil was also noted in a multicentered retrospective study, also suggesting some benefit [59]. However, the association between vascular biomarkers and digital ulcerations in SSc was recently evaluated using the DISTOL-1 randomized controlled trial cohort, and a lack of strong response to any vascular, angiogenic, or inflammatory markers suggested that these patways are not primary drivers in the development of digital ulcer clinical outcomes in an SSc population [60]. Riociguat, a stimulator of soluble guanylate cyclase which has downstream effects stimulating vasodilation, was recently studied to determine its efficacy and safety in SSc-associated digital ulcers [68].
The purpose of subsequent RAPIDS-2 trial is to evaluate the effects of bosentan compared to placebo on ulcer prevention and healing over a 24-week treatment period. Patients received bosentan 62.5 mg twice daily for 4 weeks and then 125 mg twice daily for 20 weeks or the equivalent placebo, and time to complete healing of the cardinal ulcer and the total number of new digital ulcers per patient over 24 weeks was assessed [63]. The investigators found that bosentan treatment was associated with a 30% reduction in the number of new ulcers compared with placebo (mean ± standard error: 1.9 ± 0.2 vs 2.7 ± 0.3 new ulcers; p = 0.04), and that the effect was greater in patients who entered the trial with more ulcers. There was no significant difference between treatments in healing rate of the cardinal ulcer [63]. This data suggests that bosentan may play an important role in digital ulcer prevention in SSc, but its role in digital ulcer healing is unclear.
As bosentan demonstrated success in its positive effects on digital ulcer preventions, an international group of investigators evaluated the efficacy of a newer dual endothelin receptor antagonist, macitentan, in reducing sildenafil citrate 100 mg the number of new digital ulcers in SSc patients. Two double-blind placebo-controlled trials were conducted and enrolled patients with SSc and active digital ulcers, and patients were randomized to receive oral doses of 3 mg macitentan, 10 mg of macitentan, or placebo once daily and stratified according to the number of digital ulcers at baseline. In both trials, patients on placebo had a lower mean number of new digital ulcers and had fewer adverse events than patients in both treatment groups. As a result, the investigators recommended against using macitentan for the prevention of digital ulcers in this patient population [64] (NCT01474109; NCT01474122). The data supporting the efficacy of a variety of topical agents in the management of RP have been variable. In this multi-center randomized, double-blind, placebo-controlled pilot study, SSc patients with at least one visible active or painful digital ulcer were enrolled and
The effects of topical treprostanil have also been a focus of recent work. Treprostanil iontophoresis in patients with SSc was also studied to determine its ability to improve digital blood flow during local (hand) cooling [61]. It showed promised as digital treprostanil iontophoresis shifted skin blood flow upward during local cooling on the hand and during the initial rewarming 20mg sildenafil phase in patients with SSc. The safety profile of treprostinil hydrogel iontophoresis was also recently examined in a 2-stage randomized, placebo-controlled single ascending-dose study among healthy volunteers and patients with SSc-related digital ulcers and was found to be fairly well-tolerated, with 2 minimal local adverse effects reported among 5 SSc patients with digital ulcers [62]. A phase 2 multi-center, double-blind, RCT is currently examining the effects of intravenous iloprost on RP in patients with SSc.
Forty-one patients were enrolled and randomized to receive either intravenous iloprost or placebo infusion, and the primary endpoint is the change in weekly frequency of symptomatic RP attacks at 21 days. Results of this study are pending (NCT03867097), and the phase 3 trial is enrolling (NCT04040322). Endothelin-1 is a well-recognized promoter of vasculopathy in SSc. Prior studies have demonstrated that bosentan, a dual endothelin receptor antagonist, successfully prevents RP-related digital ulcers in SSc. In an earlier clinical trial, RAPIDS-1, which enrolled SSc patients with or without digital ulcers at baseline, bosentan significantly reduced the number of new digital ulcers compared to placebo. randomized (1:1 placebo or riociguat maximum of 2.5 mg three times daily) for an 8-week titration period, followed by an 8-week stable dosing period.
| Property | Description | Value | Notes |
|---|---|---|---|
| Active ingredient | Sildenafil citrate | - | Main component |
| Mechanism of action | PDE5 inhibitor | - | Enhances blood flow |
| Half-life | Approximately 4 hours | 3-5 hours | Duration of effect |
| Absorption | Rapid, peaks in 30-120 minutes | - | After oral intake |