A combination of Pyridoxine Hydrochloride and Doxylamine Succinate (P/D) is considered the first line for the symptomatic treatment of nausea and vomiting during pregnancy (NVP). NVP affects up to 85% of pregnant women and is one of the most common indications for hospital admission among pregnant women [1] . NVP is defined as the symptom of nausea and/or vomiting during pregnancy when the onset is prior to 16 weeks of gestation and where there is no other cause [1] [2] . A slow-release combination of P/D is licensed in some countries such as the UK, Australia, Canada and the United States for treatment of NVP as first-line treatment [1] - [4] . A delayed-release formulation containing P/D 10 mg/10 mg has been available in Canada since 1979 and since 2013 in the USA [5] . The combination P/D modified release was approved by the Food and Drug Administration (FDA) in November 2016 for the treatment of NVP when conservative management failed, and the modified formulation of P/D 20 mg/20 mg was introduced to the American market in April 2018 [6] .

In a controlled clinical trial conducted in healthy, premenopausal women under fasting conditions, a fixed-dose combination tablet of P/D 20 mg/20 mg tablets was bioequivalent to two combination tablets of P/D 10 mg/10 mg, based on the exposure (AUC) and peak concentration (C_max) of Doxylamine and baseline corrected pyridoxal 5'-phosphate [6] .

The effect of P/D 20 mg/20 mg modified release is based on two separate compounds. Pyridoxine Hydrochloride is a vitamin B6 analog. The chemical name for Pyridoxine Hydrochloride is 3,4-pyridinedimethanol, 5-hydroxy-6-methyl-, hydrochloride. The empirical formula is C 8H 11NO 3HCl and the molecular mass is 205.64 [6] [7] . The structural formula is ( Figure 1 ):

Pyridoxine Hydrochloride is the usual form of vitamin B6 included in pharmaceutical products. Vitamin B6 is a collective name for pyridoxine, pyridoxal, and pyridoxamine, which are related natural compounds with similar biological properties [8] . Pyridoxine is readily absorbed from the GI tract, mainly in the jejunum. The drug is primarily metabolized in the liver to its four active metabolites pyridoxal, pyridoxal-5-phosphate (PLP), this is the main metabolite with antiemetic activity, others metabolites as pyridoxamine, and pyridoxamine-5-phosphate also participate in biological effects [9] . Following phosphorylation, its main metabolite, PLP, is released into the circulation and is highly protein bound. PLP is a cofactor in over 160 enzyme activities involved in a number of metabolic processes of amino acids, nucleic acids, unsaturated fatty acids, carbohydrates, glycogen, neurotransmitters, and porphyrin. The major metabolite 4-pyridoxic acid is inactive, and is excreted by the kidney [6] [7] .

The chemical name for Doxylamine Succinate is ethanamine, N, N-dimethyl-2-[1-phenyl-1-(2-pyridinyl)ethoxy]-,butanedioate (1:1). The empirical formula is C 17H 22N 2OC 4H 6O 4and the molecular mass is 388.46 [6] . The structural formula is ( Figure 2 ):

Doxylamine Succinate is a first-generation antihistamine derivate, a member of the ethanolamine class. It strongly antagonizes histamine’s effects on histamine 1 (H1) receptor sites; as a result, it possesses sedative effects. As with other members of this group of drugs, Doxylamine possesses substantial antimuscarinic activity with a low incidence of gastrointestinal adverse effects [10] . As with any other H1 blocker, Doxylamine may exhibit anticholinergic effects if taken in large doses. Doxylamine is well absorbed from the GI tract, with peak plasma concentrations achieved within 2 - 4.5 h, and the therapeutic effects usually persist for 4 - 6 h. Doxylamine is biotransformed in the liver by N-dealkylation to its principal metabolites N-desmethyl and N, N-didesmethyl doxylamine, which are excreted by the kidney [6] [7] .

The pharmacokinetics (PK) of P/D 20 mg/20 mg, modified release tablets, have been studied in healthy non-pregnant adult women in a single-dose study (one tablet) and multiple-dose study (two tablets per day on days 1 - 11). PK parameters of P/D 20 mg/20 mg reported in clinical trials and summary of the product, Bonjesta® are: C_max (90.4 ± 13 - 98.7 ± 18) ng/mL, AUC_0-t ( 203.7 ± 51.7) h*ng/mL and AUC_0-inf (233.6 ± 55.9) h*ng/mL [11] [12] for Pyridoxine and C_max (90.4 ± 13 - 98.7 ± 18) ng/mL, AUC_0-t (1367 ± 356) h*ng/mL and AUC_0-inf (1425 ± 405) h*ng/mL for Doxylamine, in a single oral dose and fasting condition. The median peak plasma concentration of Pyridoxine was reached within 0.5 hours and Doxylamine within 4.5 hours, post a single dose in fasted condition [6] [7] .

After multiple doses, the concentration of Doxylamine was increased and C_max value was 1.8 times and the AUC value of absorption, increased by 2 times. Multiple-dose administration reduced the time to peak concentration from a mean of 20.0 hours (range, 2.00 - 23.0) to 3.50 hours (range, 1.00 - 20.0). The mean accumulation index was 1.99, suggesting that Doxylamine accumulates after multiple doses [6] - [10] . Although no accumulation of Pyridoxine was observed, the mean accumulation index of the main active metabolite, pyridoxal-5'-phosphate, after multiple doses was 2.61. Multiple dose administration slightly reduced the time to peak concentration: from a mean of 21.0 hours (range, 15.0 - 23.9) to 15.0 hours (range, 2.00 - 24.0). Administration of a high-fat and high-calorie meal slowed down the absorption of Doxylamine, Pyridoxine and pyridoxine metabolites. Food significantly reduced the bioavailability of Pyridoxine. The Cmax value decreased by approximately 67% and the AUC value by approximately 37% compared to the fasting state. Besides, the C_max and AUC values and the main active metabolite, pyridoxal-5'-phosphate, were not affected by food. The principal metabolites of Doxylamine, N-desmethyl-doxylamine and N, N-didesmethyldoxylamine, are excreted by the kidney. The terminal elimination half-life of Doxylamine and Pyridoxine are 11.9 hours and 0.4 hours, respectively [6] - [15] .

In the efficacy studies the combination of 10 mg/10 mg of P/D, was evaluated with Pyridoxine and Doxylamine separately, and comparable (90% CI 80 - 120) after administration of the same daily dose. Therefore these results of efficacy of 10mg/10mg tablets support the use of 20 mg/20 mg of P/D [6] - [15] . The efficacy and safety of the combination (P/D) were evaluated in clinical trials randomized, placebo controlled, involving adult women aged 18 years or older with the average gestational age at the time of study [1] [6] [7] . The maximum daily dose was 40mg/40mg of P/D, divided doses per day [1] [6] [13] . The primary efficacy endpoint was the change from baseline in the Pregnancy-Unique Quantification Emesis (PUQE) questionnaire score on day 15. The mean baseline PUQE score was 9.0 in the P/D group and 8.8 in the placebo group. On day 15, the PUQE score of the P/D group was reduced (nausea and vomiting symptoms were relieved) by an average of 0.9 points from baseline compared to placebo (95% CI 0.2 - 1.2; p-value 0.006) [1] [6] [13] .

A Cochrane review, systematic reviews and meta-analyses have reported on the safety and efficacy of many antiemetics for use in NVP, with no increased risk of teratogenesis or other adverse pregnancy outcomes [1] [13] . These drugs include: antihistamines (H1 receptor antagonists) such as P/D. Also that review reported safety and efficacy data for first line antiemetics such as P/D and concluded that this treatment should be prescribed initially when required for NVP and HG (Evidence Grade A-UK guidelines) [1] .

The purpose of our study was to assess and compare the PK profiles and safety of Bonjesta® (Exeltis, Exeltis Health Care S.L, España) as reference (R) formulation to Pyridoxine/Doxylamine (Laboratorios Leti, S.A.V., República Bolivariana de Venezuela) as test (T) formulation of Pyridoxine Hydrochloride/Doxylamine Succinate 20 mg/20 mg, in healthy female adults, non lactating, non pregnant, under fasting condition, randomized crossover study.

This study was conducted by a Clinical Research Operator (CRO), at Synergen Bio Private Limited, India. Pharmadesk Solutions Pvt. Ltd., was in charge of monitoring the study and was present during the conduct of the study.

NVP affects up to 85% of pregnant women and is one of the most common indications for hospital admission among pregnant women, with typical stays of between three and four days [22] . This condition can vary in a range of severity from mild nausea to the most severe form in these patients, impacting their quality of life and increasing the cost associated with the use of health resources and health services [22] .

Pyridoxine/Doxylamine (P/D) modified release, is a combination considered as first line treatment of NVP, was approved by the US Food and Drug Administration (FDA) and has been available in Canada and other countries [1] - [5] . The formulation of P/D 20mg/20mg oral tablets, has been only licensed for treatment of NVP in the UK [1] .

This study assessed the bioequivalence of P/D 20 mg/20 mg modified release tablets, in a healthy adult, non lactating, non pregnant female subjects, under fasting condition. It was a randomized crossover study, two treatments, two periods and one single dose. The 90% CIs for P/D was assessed by determined bioequivalence standards of 80% - 125% for C_max, AUC_0-t and AUC_0-inf [20] [21] . The study included 44 healthy female subjects, aged between 18 and 45 years. Only 41 completed the study and were included in PK evaluation and statistical analysis, it was a sufficient number of subjects to ensure statistical power to demonstrate the bioequivalence between both formulations.

The PK mean values of Pyridoxine for C_max, AUC_0-t and AUC_0-inf were 62.6940 ng/mL, 70.5483 h * ng/mL and 71.0220 h * ng/mL to R and 62.7046 ng/mL, 63.8400 h * ng/mL and 64.4915 h * ng/mL to T formulations respectively. The PK mean values of Doxylamine for C_max, AUC_0-t and AUC_0-inf was 106.5452 ng/mL, 2013.4618 h * ng/mL and 2123.5189 h * ng/mL to R formulation and 96.3638 ng/mL, 1884.0081 h * ng/mL and 1938.7458 h * ng/mL to T formulation, which are included into the range of BE acceptance (limit of 80% - 125%) ( Table 2 and Table 4 ). Other parameters evaluated were T_1/2 (0.27 ± 0.25 h and 0.49 ± 0.47 h) for Pyridoxine T and R formulations y and T_1/2 (16.02 ± 2.23 h and 15.91 ± 2.06 for Doxylamine R and T formulation, respectively ( Table 2 and Table 4 ). These PK parameters of P/D reported in this study are comparable to those PK data found in other clinical trials in a single oral dose and fasting condition [6] - [11] [13] - [15] .

The 90% CIs for GMRs ranged from Ln C_max was 96.84% with CIs (82.80 - 113.26), AUC_0-t was 88.94% with CIs (80.87 - 97.81) and AUC_0-inf was 89.53% with CIs (81.72 - 98.09) was determined for Pyridoxine and Ln C_max was 89.45% with CIs (84.54 - 94.64), AUC_0-t was 91.04% with CIs (86.63 - 95.68) and AUC_0-inf was 90.81% with CIs (86.30 - 95.56) for Doxylamine. These values are within the 90% CIs and acceptance criteria of 80 - 125% and this BE is based on (90% CI) of Pyridoxine and Doxylamine [20] .

Following the EMA BE guideline [20] [21] the evaluation of BE was based on measured concentrations of the parent compound [21] . The reason for this is that C_max of a parent compound is usually more sensitive to detect differences between formulations in absortion rate than C_max of a metabolite [6] [7] . The active metabolites of pyridoxine, pyridoxal 5'-phosphate and pyridoxal no were measured. An adequate washout period was used to avoid the carryover effect [7] .

The mean P/D plasma concentrations-time curves of T product vs R product, in arithmetic and logarithm scale were similar ( Figures 3-6 ). BE was demonstrated between the T and R formulations, in oral tablets, modified release at a dose of 20 mg/20 mg, in fasting condition. The mean plasma concentration profiles of Pyridoxine demonstrated high variability in both plasma concentration profiles per hour to T and R formulations ( Figure 3 and Figure 4 ).

NVP is a common condition that affects the health of a pregnant woman and her fetus [1] . It can diminish a woman’s quality of life and also significantly contributes to health care costs and time lost from work [22] . P/D as pharmacological treatment in the early stages may prevent more serious complications, including hospitalization, and result in a safe and effective available treatment. Evidence suggests that delayed release formulations of P/D are more effective than other antiemetics in the treatment of NVP [1] .

Royal College of Obstetricians and Gynaecologists of the UK, recommended in the NVP management guidelines 2025, P/D 20 mg/20 mg as a first-line treatment [1] .

Regulatory agencies in Latin America are demanding more attention in the process of conducting bioequivalence studies to make decisions ensuring greater access and adherence to these treatments [23] - [25] .

We did not evaluate the fed condition for supportive evidence of bioequivalence.

This study of a single oral dose of Pyridoxine/Doxylamine 20 mg/20 mg modified release tablets, demonstrated bioequivalence of the T formulation to R formulation, in healthy female subjects under fasting conditions. The PK profiles for both P/D products were similar and demonstrated by the 90% CIs of C_max, AUC_0-t and AUC_0-inf within the accepted BE criteria of 80% - 125%.

This study was conducted at the third party Pharmadesk Solutions Pvt., Ltd., and VerGo Pharma Research Pvt. Ltd, (Division-VerGo Clinicals). India.

EP, AI, AT, XS, and JGC performed the statistical analysis, interpretation, writing, revision, of the manuscript.

The authors certify that they have obtained all appropriate patient consent.

This study was funded by Laboratorios Leti S.A.V.

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.