Safety, Pharmacokinetic, and Pharmacodynamic Study of a Sublingual Formula for the Treatment of Vasovagal Syncope

Healthy, non-smoking adult subjects aged 18–50 years were recruited through postings in the medical center complex. Subjects were contacted by the study coordinators for an initial screening for eligibility. Eligibility screening occurred after obtaining written informed consent. During the in-person screening visit a physical examination, 12-lead ECG, blood samples for blood chemistries, CBC with differential and platelet count, and a urine sample for drug and pregnancy testing were obtained. Women able to bear children were required to practice at least two forms of contraception during and for 7 days after the treatment day and were required to have a negative pregnancy test on the morning of treatment. Subjects were also required to refrain from taking any of the components of the investigational product in their diet for 12 h before and 24 h after the study dose. A clinically unremarkable 12-lead ECG and laboratory panel was required in screening prior to the study date, and systolic (SBP) and diastolic blood pressure (DBP) at screening were required to be ≤ 130 mmHg and ≤ 80 mmHg, respectively. Subjects were allowed to continue taking concurrent medications that did not conflict with the eligibility requirements of the study. Concurrent medications taken within 48 h of the study doses were recorded.

The investigational drug product was a proprietary combination of capsaicin, PE, and caffeine in a gel base. The mixture was developed and qualified by the Zeeh Pharmaceutical Research Station located at the University of Wisconsin–Madison School of Pharmacy.

Of the three active components of CPC, the PE dose was the most uncertain and was thus the focus of dose escalation. The amount of capsaicin and caffeine in each 1 mL dose was held constant at 1 mg and 200 mg, respectively. The amount of PE was increased in a modified Fibonacci escalation to identify the dose that yielded an increase in SBP of at least 40 mmHg above baseline, yet did not exceed a SBP of 190 mmHg or greater. An initial sequence of PE doses of 0, 0.6, 1.2, and 1.8 mg was administered. Given minimal change in blood pressure (BP), a second series of escalating PE was approved and administered. A summary of the escalating PE doses is provided in Table 1.

A dose-limiting toxicity (DLT) was defined as a National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE)-defined adverse event (AE) Grade 4 [5], serious AE (SAE), or SBP > 190 mmHg. Dose escalation was based on the two-step model of the phase I dose escalation schemes evaluated by Storer [6]. This dose escalation scheme did not escalate dose within an individual. Instead, a single subject was exposed to the first dose level. If the subject did not experience a DLT, the next subject was exposed to the next, higher dose. The use of a single subject per dose level continued until the highest dose level of PE within the dosing cohort was reached (1.8 mg, then 30 mg), or until a DLT was experienced. If a subject developed a DLT after the first dose but before the second dose, the second dose was not administered. The maximum tolerated dose (MTD) was defined as the PE dose (in combination with 1 mg capsaicin and 200 mg caffeine) that caused a DLT in fewer than 33% of the subjects treated at that dose level (viz 0–1 subjects with DLT in six subjects treated at the MTD).

There was one dosing visit for this study. Within 15 days of the in-person screening visit, subjects were admitted to the UWHealth Hospital Clinical Research Unit (CRU) where standard admission procedures occurred. Assessment of the time of the last intake of capsaicin, PE, or caffeine was documented. Subjects were asked to be fasting within 2 h of the drug dosing and for 1 h after the second dose of CPC. For the remainder of the hospital stay, a caffeine and capsaicin restricted general diet was provided.

Frozen plasma samples were transported to PPD, Inc., Middleton, WI, USA, for analysis under current Good Laboratory Practices (cGLP), reflecting the May 2018 FDA Guidance for Industry—Bioanalytical Method Validation. All methods were performed using liquid chromatography–tandem mass spectrometry (LC-MS/MS). A summary of the qualification of the three assays is presented in Table 2. Stability testing demonstrated the sufficiency of sample processing and storage.

Plasma concentrations of capsaicin, PE, and caffeine were processed using non-compartmental methods using the PKNCA package (0.94) in R (4.0.4) within RStudio (1.4.1106) on a Dell 7410 computer operating on Windows 10. AUC was determined using the trapezoidal (linear up/logarithmic down) method.

No SAEs were noted. Non-serious AEs were observed and included mainly oral and gastric discomfort, which were most likely related to and expected from capsaicin. Of note, oral discomfort is a desired effect for the drug as we believe it to be the trigger for increased sympathetic activity and capsaicin-induced BP elevation. Despite the reported discomfort, none of the 17 volunteers refused to hold CPC sublingually for 1 min, swallow the drug, or take the second dose. Refusal to do any of these three things was used as a marker of intolerance of the drug.

In addition to the oral and gastric discomfort, vasovagal events thought to be the result of the frequent blood draws and intravenous catheter placement occurred in two subjects. The first subject belonged to the 1.8 mg PE group and experienced lightheadedness, hypotension, and nausea during blood draws around 5 min after receiving the first dose. The event was consistent with a vasovagal reaction and the decision was made to stop the study given the concerns that continued blood draws were likely to exacerbate the subject’s symptoms. The second subject experienced a vasovagal reaction at the sight of blood following intravenous catheter placement with no loss of consciousness. Within 5 min, the subject was back to normal and received both study doses (20 mg PE) with no further AEs. A summary of the AEs is provided in Table 4.

As noted earlier, nine and eight subjects received the lower and higher dose ranges of PE, respectively. In the nine subjects who received the lower PE doses (0–1.8 mg), the target increase in systolic BP was not reached and PE blood levels were consistently below 0.1 μg/L. Accordingly, higher doses of 10, 20, and 30 mg PE were prepared and administered to an additional eight subjects with no change in the doses of caffeine and capsaicin. A significant increase in SBP was noted in all subjects in the higher PE dose cohort but still did not reach the target of 40 mmHg. PE doses higher than 30 mg were not investigated given the magnitude of increased BP and good safety outcome.

Six subjects received CPC with the highest dose of PE (capsaicin 1 mg, PE 30 mg, caffeine 200 mg). The median age of the cohort was 34 years and included four women. The peak increase in SBP was at 2 min, with an average increase of 21 mmHg (range 15–33 mmHg). The increase in BP was statistically significant for at least 15 min with a gradual decline over 2 h. There was an initial increase in HR followed by a decrease to below baseline over the 2-h period (Fig. 5).

Following the first dose, the pain score (scale of 1–10) was highest at 2 min (mean 5, range 3–8) with a gradual decline over 15 min. The mean pain scores were 3, 2, and 1 at 5, 10, and 15 min, respectively. The pain score was 0 at 30 min in all subjects except for one who had a score of 1. The same trend, except with lower numbers, was noted with the second dose, with the highest pain score noted at 2 min (mean 4, range 1–6) followed by a gradual decline to 3, 1, and 1 at 5, 10, and 15 min respectively. As with the first dose, the pain score returned to 0 by 30 min in all subjects except for one who reported a score of 1.

The highest detected capsaicin blood level in our study following a 1 mg oral dose was 79 pg/mL or 79 ng/L, corresponding to 0.26 nmole/L. The only other clinical report of capsaicin concentrations was that of Chaiyasit et al. [7], who administered oral doses of 26.6 mg capsaicin and measured peak capsaicin concentrations of 2.5 μg/L or 2500 ng/L, which translates into 94 ng/L per milligram administered. This concentration is similar to our findings of 79 ng/L after the administration of 1 mg of capsaicin.

The half maximal effective concentration (EC₅₀) value for capsaicin on its VR1 receptor is in the micromolar range (10^-6 mole/L) [8, 9]. Therefore, the ratio of the highest blood level detected to EC₅₀ is 0.26  ×  10⁻³. The capsaicin blood levels detected in this study were therefore considered to be too low to cause any effect through the systemic circulation. We hypothesize that the hemodynamic effects were due to local irritation and reflex increase in sympathetic activity. Indeed, the peak increase in SBP coincided with the highest pain score at 2 min and the decline in SBP at 15 min coincided with a mean pain score of 1, consistent with resolution of the oral discomfort.

The median PE maximum concentration (C_max) after 30 mg oral doses in the current study was 1750 ng/L (10.5 nM), which is somewhat lower than the average of 4492 ng/L reported by Gelotte and Zimmerman [10]. There is no obvious reason why the concentration would be lower than expected, unless the coadministration with caffeine and capsaicin decreased the rate or extent of absorption.

A PE blood concentration of 20 nM corresponding to 3000 ng/L is associated with a mean increase of 3 mmHg in SBP [11]. We speculate that the contribution of PE to SBP elevation was around 1–2 mmHg. Furthermore, we believe the effect was limited to the time period of 15–120 min when the blood levels started to exceed 1000 ng/L.

The first caffeine dose of 200 mg resulted in a median C_max of 4.74 mg/L. This is in agreement with the 1.5 mg/L concentration reported by Perera et al. after a 100 mg oral dose [12]. A single dose of 200–250 mg of caffeine is associated with an increase in SBP of 3–14 mmHg within 30 min with a maximal increase at 60–120 min [13]. At a concentration of 3.7 mg/L, SBP increased from 132 ± 12 to 133 ± 10 mmHg (p < 0.05) at 18 min post caffeine ingestion (3 mg/kg) [14]. In the current study, the caffeine dose was 200 mg and the blood levels were 2–6 μg/mL or mg/L. We speculate that the maximum contribution of caffeine to SBP elevation was approximately 1–2 mmHg. Similar to PE, we believe the effect was limited to the time period of 15–120 min when the blood levels started to exceed 2 mg/L.

Despite the absence of significant blood levels of PE and caffeine in the first 15 min post drug administration, we believe all three drug components should continue to be part of the product for the following reasons:

With caffeine, the effects on BP are likely to be minimal in the absence of syncope; however, we hypothesize that its effects are greater at the time of pending syncope due to the endogenous release of adenosine [15] and caffeine’s ability to block adenosine receptors. Indeed, the caffeine blood levels after 15 min are high enough to counteract the cardiovascular effects of endogenous adenosine release at the time of VVS. The affinity of caffeine for A1 and A2 adenosine receptors are 10 and 9 µM, respectively [16], corresponding to 1.9 mg/L. The observed blood levels in our study of 2–6 mg/L 15–120 min post drug intake were at least twice that amount.

2. Effects of PE and caffeine on fatigue after a syncopal event: Up to 94% of patients experience fatigue following VVS [17] , with some stating “I slept for hours as if I had run a marathon”. We believe that PE and caffeine will mitigate these symptoms.

Two additional studies are planned to assess the effects of CPC on VVS. In the first study, we will be testing the hypothesis that a single administration of sublingual CPC preparation during the prodromal phase aborts tilt-induced syncope or near syncope with SBP ≤ 70 mmHg in patients with a history of VVS (phase IIa trial). In the second study, we will be testing the hypothesis that a single administration of sublingual CPC preparation prevents tilt-induced hypotensive syncope or near syncope with SBP ≤ 70 mmHg in patients with a history of VVS (phase IIb trial). Once completed, a large multicenter trial will be conducted to demonstrate the drug efficacy and safety in patients with spontaneous VVS (phase III trial).

Additional potential use of the drug include the treatment and prevention of hemodialysis-induced hypotension. There are approximately 300,000 patients receiving chronic hemodialysis in the US, with approximately 45 million sessions per year. Hypotension during hemodialysis occurs in 6–27% of patients with a 20% incidence being most cited [18]. Suggested contributors include autonomic dysfunction, particularly in diabetics [19], release of adenosine during organ ischemia [20], increased synthesis of endogenous vasodilators such as nitric oxide [21], and insufficient increase in vasoconstrictors such as vasopressin [22]. We hypothesize that administration of CPC in patients with hemodialysis-induced hypotension reduces the magnitude of BP drop and thus premature termination of hemodialysis.

Lastly, CPC may be helpful in the treatment of orthostatic hypotension. The prevalence of orthostatic hypotension is 5–30% depending on age and type of population studied [23, 24]. While many conditions could lead to orthostatic hypotension, up to 40% of patients have no definite cause [25]. We hypothesize that CPC administration reduces the orthostatic drop in BP and thus risk of syncope and falls in patients with symptomatic orthostatic hypotension.