Doxylamine Succinate and Pyridoxine Hydrochloride Dailymed

Initially, take two doxylamine succinate and pyridoxine hydrochloride delayed-release tablets orally at bedtime (Day 1). If this dose adequately controls symptoms the next day, continue taking two tablets daily at bedtime. However, if symptoms persist into the afternoon of Day 2, take the usual dose of two tablets at bedtime that night then take three tablets starting on Day 3 (one tablet in the morning and two tablets at bedtime). If these three tablets adequately control symptoms on Day 4, continue taking three tablets daily. Otherwise take four tablets starting on Day 4 (one tablet in the morning, one tablet mid-afternoon and two tablets at bedtime). The maximum recommended dose is four tablets (one in the morning, one in the mid-afternoon and two at bedtime) daily. Take on an empty stomach with a glass of water [see Clinical Pharmacology (12.3)]. Swallow tablets whole. Do not crush, chew, or split doxylamine succinate and pyridoxine hydrochloride delayed-release tablets.   Take as a daily prescription and not on an as needed basis. Reassess the woman for continued need for doxylamine succinate and pyridoxine hydrochloride delayed-release tablets as her pregnancy progresses.

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice. The safety and efficacy of doxylamine succinate and pyridoxine hydrochloride were compared to placebo in a double-blind, randomized, multi-center trial in 261 women with nausea and vomiting of pregnancy. The mean gestational age at enrollment was 9.3 weeks, range 7 to 14 weeks gestation [see Clinical Studies (14)]. Adverse reactions for doxylamine succinate and pyridoxine hydrochloride that occurred at an incidence ≥5 percent and exceeded the incidence for placebo are summarized in Table 1. Table 1: Number (Percent) of Subjects with ≥ 5 Percent Adverse Reactions in a 15-Day Placebo-Controlled Study of Doxylamine Succinate and Pyridoxine Hydrochloride (Only Those Adverse Reactions Occurring at an Incidence ≥ 5 Percent and at a Higher Incidence with Doxylamine Succinate and Pyridoxine Hydrochloride than Placebo are Shown) Doxylamine Succinate and Pyridoxine Hydrochloride (N = 133) Placebo (n = 128) Somnolence 19 (14.3%) 15 (11.7%)



Risk Summary Doxylamine succinate and pyridoxine hydrochloride is intended for the treatment of nausea and vomiting of pregnancy in women who do not respond to conservative management. Maternal risks are discussed throughout the labeling. No increased risk for congenital malformations has been reported in epidemiologic studies in pregnant women. In the U.S. general population, the estimated background risks for major birth defects and miscarriage in clinically recognized pregnancies are 2-4% and 15-20%, respectively. Data Human Data The combination of doxylamine succinate and pyridoxine hydrochloride has been the subject of many epidemiological studies (cohort, case control and meta-analyses) designed to detect possible teratogenicity. A meta-analysis of 16 cohort and 11 case-control studies published between 1963 and 1991 reported no increased risk for malformations from first trimester exposures to doxylamine succinate and pyridoxine hydrochloride, with or without dicyclomine hydrochloride. A second meta-analysis of 12 cohort and 5 case-control studies published between 1963 and 1985 reported no statistically significant relationships between fetal abnormalities and the first trimester use of the combination doxylamine succinate and pyridoxine hydrochloride with or without dicyclomine hydrochloride.

The pharmacokinetics of doxylamine succinate and pyridoxine hydrochloride has been characterized in healthy non-pregnant adult women. Pharmacokinetic results for doxylamine and pyridoxine, including its vitamin B6 metabolites, pyridoxal, pyridoxal 5’-phosphate, pyridoxamine and pyridoxamine 5’-phosphate, are summarized in Tables 2 to 5.  

The pharmacokinetics of doxylamine succinate and pyridoxine hydrochloride has been characterized in healthy non-pregnant adult women. Pharmacokinetic results for doxylamine and pyridoxine, including its vitamin B6 metabolites, pyridoxal, pyridoxal 5’-phosphate, pyridoxamine and pyridoxamine 5’-phosphate, are summarized in Tables 2 to 5.   Absorption A single-dose (two tablets) and multiple-dose (four tablets daily), open-label study was conducted to assess the safety and pharmacokinetic profile of doxylamine succinate and pyridoxine hydrochloride administered in healthy non-pregnant adult women. Single-doses (two tablets at bedtime) were administered on Days 1 and 2. Multiple-doses (one tablet in the morning, one tablet in the afternoon and two tablets at bedtime) were administered on Days 3-18. Blood samples for pharmacokinetic analysis were collected pre-and post-dose on Days 2 and 18 as well as pre-dose prior to bedtime dose only (trough) on Days 9, 10, 11, 16, 17, and 18. Doxylamine and pyridoxine are absorbed in the gastrointestinal tract, mainly in the jejunum. The Cmax of doxylamine and pyridoxine are achieved within 7.5 and 5.5 hours, respectively (see Table 2). Table 2 – Single-Dose and Multiple-Dose Pharmacokinetics of Doxylamine Succinate and Pyridoxine Hydrochloride in Healthy Non-Pregnant Adult Women Single Dose Multiple Dose AUC0-inf (ng•h/mL) Cmax (ng/mL) Tmax (h) AUC0-inf (ng•h/mL) Cmax (ng/mL) Tmax (h) Doxylamine 1,280.9 ± 369.3 83.3 ± 20.6 7.2 ± 1.9 3,721.5 ± 1,318.5 168.6 ± 38.5 7.8 ± 1.6 Pyridoxine 43.4 ± 16.5 32.6 ± 15.0 5.7 ± 1.5 64.5 ± 36.4 46.1 ± 28.3 5.6 ± 1.3 Pyridoxal 211.6 ± 46.1 74.3 ± 21.8 6.5 ± 1.4 1,587.2 ± 550.0 210.0 ± 54.4 6.8 ± 1.2 Pyridoxal 5’Phosphate 1,536.4 ± 721.5 30.0 ± 10.0 11.7 ± 5.3 6,099.7 ± 1,383.7 84.9 ± 16.9 6.3 ± 6.6 Pyridoxamine 4.1 ± 2.7 0.5 ± 0.7 5.9 ± 2.1 2.6 ± 0.8 0.5 ± 0.2 6.6 ± 1.4 Pyridoxamine 5’-phosphate 5.2 ± 3.8 0.7 ± 0.5 14.8 ± 6.6 94.5 ± 58.0 2.3 ± 1.7 12.4 ± 11.2 Multiple-dose administration of doxylamine succinate and pyridoxine hydrochloride results in increased concentrations of doxylamine as well as increases in doxylamine Cmax and AUC0-last of absorption. The time to reach the maximum concentration is not affected by multiple doses. The mean accumulation index is more than 1.0 suggesting that doxylamine accumulates following multiple dosing (see Table 3).   Although no accumulation was observed for pyridoxine, the mean accumulation index for each metabolite (pyridoxal, pyridoxal 5’-phosphate, and pyridoxamine 5’-phosphate) is more than 1.0 following multiple-dose administration of doxylamine succinate and pyridoxine hydrochloride. The time to reach the maximum concentration is not affected by multiple doses (see Table 2). Table 3 – Pharmacokinetics of Doxylamine and Pyridoxine Following Single Dose and Multiple Dose Administration of Doxylamine Succinate and Pyridoxine Hydrochloride to Healthy Non-Pregnant Adult Women AUC0-last (ng•h/mL) AUC0-inf (ng•h/mL) Cmax (ng/mL) Tmax (h) T½el (h) Doxylamine Mean±SD N=18 Single 911.4 ± 205.6 1,280.9 ± 369.3 83.3 ± 20.6 7.2 ± 1.9 10.1 ± 2.1 Multiple 3,661.3 ± 1,279.2 3,721.5 ± 1,318.5 168.6 ± 38.5 7.8 ± 1.6 11.9 ± 3.3 Pyridoxine Mean±SD N=18 Single 39.3 ± 16.5 43.4 ± 16.5 32.6 ± 15.0 5.7 ± 1.5 0.5 ± 0.2 Multiple 59.3 ± 33.9 64.5 ± 36.4 46.1 ± 28.3 5.6 ± 1.3 0.5 ± 0.1 Food Effect The administration of food delays the absorption of both doxylamine and pyridoxine. This delay is associated with a lower peak concentration of doxylamine, but the extent of absorption is not affected (see Table 4). The effect of food on the peak concentration and the extent of absorption of the pyridoxine component is more complex because the pyridoxal, pyridoxamine, pyridoxal 5’-phosphate and pyridoxamine 5’-phosphate metabolites also contribute to the biological activity. Food significantly reduces the bioavailability of pyridoxine, lowering its Cmax and AUC by approximately 50% compared to fasting conditions. Similarly, food significantly reduces pyridoxal AUC and reduces its Cmax by 50% compared to fasting conditions. In contrast, food slightly increases pyridoxal 5’-phosphate Cmax and extent of absorption. As for pyridoxamine and pyridoxamine 5’-phosphate, the rate and extent of absorption seem to decrease under fed conditions. Table 4 – Pharmacokinetics of Doxylamine and Pyridoxine Following Administration of Doxylamine Succinate and Pyridoxine Hydrochloride Under Fed and Fasted Conditions in Healthy Non-Pregnant Adult Women AUC0-t (ng•h/mL) AUC0-inf (ng•h/mL) Cmax (ng/mL) Tmax (h) T½el (h) Doxylamine Mean±SD N=42 Fasted 1,407.2 ± 336.9 1,447.9 ± 332.2 94.9 ± 18.4 5.1 ± 3.4 12.6 ± 3.4 Fed 1,488.0 ± 463.2 1,579.0 ± 422.7a 75.7 ± 16.6 14.9 ± 7.4 12.5 ± 2.9a Pyridoxine Mean±SD N=42 Fasted 33.8 ± 13.7 39.5 ± 12.9c 35.5 ± 21.4 2.5 ± 0.9 0.4 ± 0.2c Fed 18.3 ± 14.5 24.2 ±14.0b 13.7 ± 10.8 9.3 ± 4.0 0.5 ± 0.2b aN=37; bN=18; cN=31 Distribution Pyridoxine is highly protein bound, primarily to albumin. Its main active metabolite, pyridoxal 5’-phosphate (PLP) accounts for at least 60% of circulating vitamin B6 concentrations. Metabolism Doxylamine is biotransformed in the liver by N-dealkylation to its principle metabolites N-desmethyl-doxylamine and N, N-didesmethyldoxylamine. Pyridoxine is a prodrug primarily metabolized in the liver. Excretion The principle 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 12.5 hours and 0.5 hours, respectively (see Table 5). Table 5 – Terminal Elimination Half-Life (T1/2el) for Doxylamine Succinate and Pyridoxine Hydrochloride Administered as a Single Dose of Two Tablets under Fasting Conditions in Healthy Non-Pregnant Adult Women T½el (h) Doxylamine 12.6 ± 3.4 Pyridoxine 0.4 ± 0.2 Pyridoxal 2.1 ± 2.2 Pyridoxal 5’-Phosphate 81.6 ± 42.2 Pyridoxamine 3.1 ± 2.5 Pyridoxamine 5’-Phosphate 66.5 ± 51.3 Use in Specific Populations Race: No pharmacokinetic studies have been conducted related to race. Hepatic Impairment: No pharmacokinetic studies have been conducted in hepatic impaired patients. Renal Impairment: No pharmacokinetic studies have been conducted in renal impaired patients.