Optimizing bioavailability of oral administration of small peptides through pharmacokinetic and pharmacodynamic parameters: The effect of water and timing of meal intake on oral delivery of Salmon Calcitonin

Calcitonin is a natural peptide hormone produced by parafollicular cells (C-cells) in the thyroid gland [1, 2], which is secreted in response to excess calcium in the serum [3]. Calcitonin was discovered more than 40 years ago [4, 5], and possesses potent anti-resorptive effects. Calcitonin binds directly to the calcitonin receptor on osteoclasts which result in a transient reversible inhibition of bone resorption [6].

Calcitonin (CT) is approved for the treatment of osteoporosis and other diseases involving accelerated bone turnover [6, 7]. Calcitonin treatment has until now been limited to either subcutaneous or intranasal administration, that occasionally is hampered by administration difficulties and local irritation [6]. Some subjects are reluctant to administer drugs intranasal or parenteral limiting the potential treatment population. An oral form of calcitonin may improve subject acceptance and facilitate improved subject compliance by providing a more acceptable, alternative delivery route for peptide therapy [6]. Thus, an increasing number of investigations have focused on formulating calcitonin to provide a novel oral formulation that includes but not are limited to [6‐18].

Oral drug delivery of small peptides is hampered by an array of obstacles [19, 20], including but not limited to degradation by proteolytic enzymes in the digestive tract and secondary intestinal uptake [19‐21]. These difficulties are best illustrated by the complete lack of peptides in oral formulations approved by the FDA.

Due to the short half-life of calcitonin in serum several attempts have been applied to increase plasma concentrations. One very recent approach of oral calcitonin formulation is the use of the Eligen technology [6]. This carrier [7, 22] interacts with the drug molecule to create an insoluble entity at low pH which later dissolves and facilitates intestinal uptake, by enhancing peptide transport over the non-polar biological membrane [22]. This has been demonstrated to result in clinical efficacy [6, 7].

Even in the face of already documented clinical efficacy with this formulation [6, 7], plasma concentrations of sCT may be further optimized through pushing of gastric emptying that would result in rapid transit of calcitonin through the gastrointestinal tract [23]. This may partly circumvent calcitonin degradation by the vast array of endopeptidases and other enzymes in the gastric tract optimally functioning at low pH [19, 20, 23]. Several techniques have been applied which prolong or shorten the retention in the gastric tract, with more or less success [19, 20, 24, 25], in which the effect of water remains to be carefully investigated in particular with special emphasis on peptide uptake.

The primary objective of the current study was to investigate the effects of two volumes of water used to take a single SMC021 tablet and the effect of three different post-dose meal timings on the pharmacokinetic (PK) and pharmacodynamic (PD) profile of 0.8 mg sCT, as assessed by C_max and AUC_0–4 of sCT and bone resorption by CTX-I. Additionally the PK and PD profiles of intranasally administered sCT (Miacalcic^® 200 IU NS) were evaluated for comparison in a small number of subjects; this treatment was not blinded and therefore comparisons may be affected by blinding bias.

The demographic characteristics of age, height, weight, and BMI of the study participants are given in Table 2. The subjects were aged between 56 and 70 years. All subjects attended all 5 study periods.

The effect of water volume and time between dosing and a subsequent meal on the absorption of sCT is shown in Figure 1. The sCT appeared rapidly in plasma reaching maximum concentrations approximately 15 minutes after drug intake with minimal if any effect of water and meal time on T_max (Table 3). However, the level of the maximum concentration, C_max, and the AUC of plasma sCT in the period between dosing and 4 hours post-dose, was dependent on the amount of water intake and timing of meal. A two- to three fold higher absorption was attained with the smaller amount of water of 50 ml as compared with 200 ml (Figure 2) and Table 3, e.g. in the women who fasted for 1 hour subsequent to dosing, the AUC_{0–4 hrs} of sCT was 74.4 (pg/ml × hrs) when SMC021 was taken with 50 ml of water and 33.6 (pg/ml × hrs) when taken with 200 ml of water. The effect of water volume was statistically highly significant irrespective of post-meal timing (10, 30 and 60 minutes post-meal time: p < 0.001). The AUC_{0–4 hrs} of nasal calcitonin was 16.4 pg/ml × hrs, lower than those observed with administration of 0.8 mg of oral sCT, although the comparison is based on a smaller number of observations There was increased absorption with delayed intake of meal, especially for the groups with intake of 50 ml of water, but the effect of timing of meal was far less pronounced than that of water. The delayed intake of water significantly increased sCT when comparing 10 and 60 minutes, and was borderline significant at 30 minutes compared to that of 10 minutes. Following the absorption phase, sCT was rapidly eliminated from the circulation with an elimination half-life T_1/2 between 11 and 20 minutes comparable between all groups (data not shown).

In accordance with the absorption of sCT, the water volume and time of meal post-dosing revealed a similar pharmacodynamic effect on bone resorption, measured by concentration of serum CTX-I over the 6 hours post-dose (Figure 3 and 4). Overall, dosing with SMC021 resulted in a significant suppression of serum CTX virtually reaching the same level of nadir 3 to 4 hours post-dose irrespective of water volume and time of meal post-dosing (Figure 3). However, the remission to baseline started earlier in subjects who took the medication with 200 ml of water as compared to that with 50 ml. In similar context, return to baseline values occurs earlier in subjects who had intake of meal 10 minutes after dosing as compared to those having meal 30 and 60 minutes after dosing. Taken together, and as presented in Figure 4, the largest treatment effect measured as the AUC of change in relative values of serum CTX-I during the 6 hours post-dose was achieved for the oral dose of 0.8 mg taken with 50 ml of water, 30 or 60 minutes before meal intake. The placebo-adjusted treatment effect of the dose given 60 minutes prior to meal was -171 (% × hrs) and -202 (% × hrs) for 0.8 mg SMC021 taken with 200 ml and 50 ml of water, respectively, and -114 (% × hrs) in the subjects receiving nasal calcitonin.

Oral drug delivery of small peptides is hampered by an array of obstacles that are best illustrated by the complete lack of peptides in oral formulations approved by the FDA. We have investigated the effect of water and meal time on the absorption of a single tablet of 0.8 mg of salmon calcitonin given orally by pharmacokinetic and pharmacodynamic parameters and compared them to that of the nasal spray of calcitonin given in a dose of 200 IU. These data are the first to demonstrate oral delivery of a small peptide in which optimization of drug intake parameters including amount of water intake can augment bioavailability and subsequently improve PD effect over 6 hours. The currently presented results are especially important in determining the optimal oral delivery of calcitonin, and they may be of use in development of other peptides to be formulated for oral administration.

An array of attempts have been made to formulate calcitonin for oral administration [9, 10, 12‐16, 19, 20, 23, 25, 28]. 5-CNAC is a novel compound, that already has been proven to be useful clinically [6, 7]. Even in the face of already proven clinical pharmacodynamic effects [6, 7], administration of this novel formulation may possibly be optimized further to enhance uptake and thereby improve clinical effect.

The current study clearly suggests that drug uptake of SMC021 is influenced by the amount of water given with the tablet. A water volume of 50 ml resulted in a two- to three-fold higher absorption of sCT in comparison with a volume of 200 ml of water. This doubling of absorption was seen irrespective of the timing of meal after dosing, i.e. meal given 10, 30, and 60 minutes post dosing, suggesting an impact of water intake on digestion and absorption. Secondarily, this resulted in improved efficacy, measured by the biochemical marker of bone resorption, serum CTX-I. These data are the first to demonstrate that water intake has an important effect on oral peptide uptake with the Eligen technology, improving bioavailability as much as 400%, and even more if placebo corrected. This finding may be extended to other formulations.

Previous studies have indicated that the bioavailability of some drug substances is heavily influenced by meal time [29‐31] compared to that of fasting state [32‐34]. The effect of meal timing on the oral delivery of small proteins/peptides has been investigated less than that of small molecules. The present study investigated the effect of two water volumes (50 mL and 200 mL) and meal intake (10, 30, and 60 minutes) after drug dosing to determine optimal dosing conditions. Dosing 60 minutes prior to meal time with 50 ml of water was significantly better compared to 10 minutes. This was borderline significant for 30 minutes. The results of the study are in alignment with previous studies, documenting the strong suppression of drug uptake when food is taken concomitantly [35, 36]. However these interactions are highly drug-specific, which hampers the general conclusions drawn, as lipophilic, hydrophilic and proteins all have different characteristics.

Biochemical markers of bone resorption such as serum CTX-I have on previous occasions been demonstrated to be independent predictors of fracture risk and predictive of drug efficacy [27, 37]. Serum CTX-I, which is an osteoclast specific generated collagen type I fragment [38], was significantly inhibited by oral sCT treatment to a greater extent than by the nasal formulation over 6 hours. This may be interpreted as a potential better efficacy. Thus, these data suggest the possibility of efficacy superior to that of the nasal spray observed in previously clinical trials [39].

Bone resorption exhibits marked diurnal variation [35, 40], most of which is linked to a post-prandial decrease [27, 36]. In the current study, this effect was clearly observed after the placebo treatment when the decrease in CTX-I started at meal time.

In conclusion, these data suggest that SMC021 given with 50 ml of water prior to meal time results in greater sCT bioavailability than when given with 200 ml of water, and that timing the dose 60 minutes pre-meal results in greater sCT bioavailability than 10 minutes pre-meal. Also, the sCT bioavailability and CTX-I pharmacodynamic effect appear to be greater compared to that of nasal calcitonin. Further clinical studies are needed to evaluate the safety and efficacy of SMC021 for the treatment of osteoporosis.