H1 Receptor

Absorption, Distribution and Excretion
Readily absorbed via the gastrointestinal tract.
H1 antagonists are eliminated more rapidly by children than by adults and more slowly in those with severe liver disease. /H1 Receptor Antagonists/
The H1 antagonists are well absorbed from the gastrointestinal tract. Following oral administration, peak plasma concentrations are achieved in 2 to 3 hours ... . /H1 Receptor Antagonists/
Elimination and metabolic profiles of the glucuronide products of doxylamine and its N-demethylated metabolites were determined after the oral admin of (14)C-doxylamine succinate (13.3 and 133 mg/kg doses) to male and female Fischer 344 rats. The cumulative urinary and fecal eliminations of these conjugated doxylamine metaboites at the 13.3 mg/kg dose were 44.4 + or - 4.2% and 47.3 + or - 8.1% of the total recoverd dose for male and female rats, respectively. The cumulative urinary and fecal eliminations of conjugated doxylamine metabolites at the 133 mg/kg dose were 55.2 + or - 2.6% and 47.9 + or - 2.5% of the total recovered dose for male and female rats, respectively. The conjugated doxylamine metabolites that were isolated, quantitiated, and identified are doxylamine O-glucuronide, N-desmethyl-doxylamine O-glucuronide, and N,N-didesmethyldoxylamine O-glucuronide.
The elimination of doxylamine and metabolites was determined after iv admin of (14)C-doxylamine succinate at 0.7 and 13.3 mg/kg to the adult female rhesus monkey. Although the total recovery of radioactivity was the same for the low- and high-dose studies (90.2%), the rate of plasma elimination of doxylamine and its demethylated metabolite (desmethyldoxylamine) was slower for the high dose group. The 24 hr urinary excretion of doxylamine metabolites, desmethyl- and didesmethyldoxylamine, was significantly incr and the polar doxylamine metabolites were significantly decr as the iv doxylamine succinate dose was incr. The plasma elimination of GC-detected doxylamine was determined after po admin of Bendectin (doxylamine succinate and pyridoxine hydrochloride) /also contains dicyclomine hydrochloride/ at 7, 13.3, and 27 mg/kg to adult female rhesus monkeys. As the dose incr, the clearance of doxylamine decr. A statistically evaluated fit of the po data to a single-compartment, parallel first-order elimination model and a single-compartment, parallel first- and second-order (Michaelis-Menten) elimination model indicated that the more complex model containing the second-order process was most consistent with the observed elimination data. /Doxylamine succinate/

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Metabolism / Metabolites
Hepatic.
The conjugated doxylamine metabolites that were isolated, quantitiated, and identified are doxylamine O-glucuronide, N-desmethyl-doxylamine O-glucuronide, and N,N-didesmethyldoxylamine O-glucuronide.
Analysis of doxylamine N-oxide and pyrilamine N-oxide as synthetic standards and biologically derived metabolites by thermospray mass spectrometry (TSP/MS) provided (M + H) + ions for each metabolite. ... In addition, TSP/MS and TSP/MS/MS analysis of ring-hydroxylated N-desmethyldoxylamine ... is also reported.
Hepatic.
Half Life: 10 hours

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Biological Half-Life
10 hours
The drug has an elimination half-life of about 10 hours in healthy adults.

Toxicity Summary
Like other antihistamines, doxylamine acts by competitively inhibiting histamine at H1 receptors. It also has substantial sedative and anticholinergic effects.

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Hepatotoxicity
Despite widespread use over many decades, doxylamine has not been linked to liver test abnormalities or to clinically apparent liver injury. The reason for its safety may relate its short half-life and limited duration of use.
Likelihood score: E (unlikely to be a cause of clinically apparent liver injury).
References on the safety and potential hepatotoxicity of antihistamines are given together after the Overview section on Antihistamines.
Drug Class: Antihistamines

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Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
Small occasional doses of doxylamine would not be expected to cause any adverse effects in breastfed infants. Larger doses or more prolonged use may cause drowsiness and other effects in the infant or decrease the milk supply, particularly in combination with a sympathomimetic such as pseudoephedrine or before lactation is well established.
◉ Effects in Breastfed Infants
Relevant published information on doxylamine was not found as of the revision date. In one telephone follow-up study, mothers reported irritability and colicky symptoms 10% of infants exposed to various antihistamines and drowsiness was reported in 1.6% of infants. None of the reactions required medical attention.
◉ Effects on Lactation and Breastmilk
Antihistamines in relatively high doses given by injection can decrease basal serum prolactin in nonlactating women and in early postpartum women. However, suckling-induced prolactin secretion is not affected by antihistamine pretreatment of postpartum mothers. Whether lower oral doses of antihistamines have the same effect on serum prolactin or whether the effects on prolactin have any consequences on breastfeeding success have not been studied. The prolactin level in a mother with established lactation may not affect her ability to breastfeed.

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Interactions
Concurrent use may potentiate the CNS depressant effects of either these medications /alcohol or other CNS depression-producing medications/ or antihistamines; also, concurrent use of maprotiline or tricyclic antidepressants may potentiate the anticholinergic effects of either antihistamines or these medications. /Antihistamines/
Anticholinergic effects may be potentiated when these medications /anticholinergics or other medications with anticholinergic activity/ are used concurrently with antihistamines; patients should be advised to report occurrence of gastrointestinal problems promptly since paralytic ileus may occur with concurrent therapy. /Antihistamines/
Concurrent use of monoamine oxidase (MAO) inhibitors with antihistamines may prolong the intensify the anticholinergic and CNS depressant effects of antihistamines; concurrent use is not recommended. /Antihistamines/
Concurrent use /of ototoxic medications/ with antihistamines may mask the symptoms of ototoxicity such as tinnitus, dizziness, or vertigo. /Antihistamines/
For more Interactions (Complete) data for DOXYLAMINE (7 total), please visit the HSDB record page.

[1]. Sjöqvist F, Lasagna L. The hypnotic efficacy of doxylamine. Clin Pharmacol Ther. 1967;8(1):48-54.

[2]. Subcutaneous infiltration of doxylamine on cutaneous analgesia in rats. Pharmacol Rep. 2018;70(3):565-569.

[3]. Jackson CD, Blackwell BN. Subchronic studies of doxylamine in B6C3F1 mice. Fundam Appl Toxicol. 1988;10(2):254-261.

Doxylamine is a clear colorless liquid. (NTP, 1992)
Doxylamine is a member of pyridines and a tertiary amine. It has a role as a histamine antagonist, a cholinergic antagonist, a sedative, an antiemetic, a H1-receptor antagonist, an anti-allergic agent and an antitussive.
Histamine H1 antagonist with pronounced sedative properties. It is used in allergies and as an antitussive, antiemetic, and hypnotic. Doxylamine has also been administered in veterinary applications and was formerly used in parkinsonism.
Doxylamine is an Antihistamine. The mechanism of action of doxylamine is as a Histamine Receptor Antagonist.
Doxylamine is a first generation antihistamine that is used for symptoms of allergic rhinitis and the common cold and as a short acting sedative. Doxylamine has not been linked to instances of clinically apparent acute liver injury.
Doxylamine is a first generation ethanolamine with antiinflammatory, sedative and antihistamine properties. Doxylamine competitively inhibits the histamine 1 (H1) receptor, thereby preventing the action of endogenous histamine as well as the subsequent release of pro-inflammatory mediators from basophils and mast cells. This agent acts as an inverse agonist that combines with, and stabilizes the inactive form of the H1-receptor, shifting the H1 receptor equilibrium toward the inactive state. This results in downregulation of nuclear factor-kappaB (NF-kappaB) and NF-kappaB dependent antigen presentation, chemotaxis, as well as expression of cell-adhesion molecules and pro-inflammatory cytokines.
Histamine H1 antagonist with pronounced sedative properties. It is used in allergies and as an antitussive, antiemetic, and hypnotic. Doxylamine has also been administered in veterinary applications and was formerly used in parkinsonism. [PubChem]
Histamine H1 antagonist with pronounced sedative properties. It is used in allergies and as an antitussive, antiemetic, and hypnotic. Doxylamine has also been administered in veterinary applications and was formerly used in PARKINSONISM.
See also: Doxylamine Succinate (has salt form).

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Drug Indication
Used alone as a short-term sleep aid, in combination with other drugs as a night-time cold and allergy relief drug. Also used in combination with Vitamin B6 (pyridoxine) to prevent morning sickness in pregnant women.

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Mechanism of Action
Like other antihistamines, doxylamine acts by competitively inhibiting histamine at H1 receptors. It also has substantial sedative and anticholinergic effects.

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Therapeutic Uses
Anti-Allergic Agents; Antiemetics; Antitussive Agents; Histamine H1 Antagonists; Sedatives, Nonbarbiturate
ANTIHISTAMINIC AGENT PROBABLY EFFECTIVE FOR SYMPTOMATIC TREATMENT OF... ALLERGIC RHINITIS, VASOMOTOR RHINITIS, ALLERGIC CONJUNCTIVITIS DUE TO INHALANT ALLERGENS & FOODS, MILD, UNCOMPLICATED ALLERGIC SKIN MANIFESTATIONS OF URTICARIA & ANGIOEDEMA, AMELIORATION & PREVENTION OF...REACTIONS TO BLOOD OR PLASMA... /SUCCINATE/
VET USE: AS ARE OTHER ANTIHISTAMINES IN STOMATITIS, LAMINITIS, URTICARIA, RESPIRATORY DISORDERS, BLOAT, & INDIGESTION IN CATTLE; IN URTICARIA & LAMINITIS IN HORSES; IN DERMATITIS, URTICARIA, MOTION SICKNESS, & IN PREVENTION OF DEPIGMENTATION IN BLUE NOSED DOGS. /SUCCINATE/
Antihistamines are indicated in the prophylactic and symptomatic treatment of perennial and seasonal allergic rhinitis, vasomotor rhinitis, and allergic conjunctivitis due to inhalant allergens and foods. /Antihistamines; Included in US product labeling/
For more Therapeutic Uses (Complete) data for DOXYLAMINE (9 total), please visit the HSDB record page.

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Drug Warnings
PERSONS TAKING ANTIHISTAMINES SHOULD BE ALERTED TO THEIR SEDATIVE EFFECTS & SHOULD BE CAUTIONED NOT TO DRIVE AUTOMOBILE, FLY AIRPLANE, OR OPERATE HAZARDOUS MACHINERY... /ANTIHISTAMINES/
VET: USE OF ANTIHISTAMINES IN STOMATITIS, GANGRENOUS MASTITIS, METRITIS, & TOXIC ENGORGEMENTS HAVE BEEN QUESTIONED. /SUCCINATE/
Like other antihistamines, doxylamine should not be used in premature or full-term neonates. Safety and efficacy of doxylamine as a nighttime sleep aid in children younger than 12 years of age have not been established. In addition, children may be more prone than adults to paradoxically experience CNS stimulation rather than sedation when antihistamines are used as nighttime sleep aids. Because doxylamine may cause marked drowsiness that may be potentiated by other CNS depressants (e.g., sedatives, tranquilizers), the antihistamine should be used in children receiving one of these drugs only under the direction of a physician. As an antihistamine, doxylamine should be used in children 2 to younger than 6 years of age only under the direction of a physician; use of the drug in children younger than 2 years of age is not recommended.
Because of the potential for serious adverse reactions to antihistamines in nursing infants, a decision should be made whether to discontinue nursing or doxylamine, taking into account the importance of the drug to the woman.
For more Drug Warnings (Complete) data for DOXYLAMINE (11 total), please visit the HSDB record page.

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Pharmacodynamics
Doxylamine is an antihistamine commonly used as a sleep aid. This drug is also used to relieve symptoms of hay fever (allergic rhinitis), hives (rash or itching), and other allergic reactions. Doxylamine is a member of the ethanolamine class of antihistamines and has anti-allergy power far superior to virtually every other antihistamine on the market, with the exception of diphenhydramine (Benadryl). It is also the most powerful over-the-counter sedative available in the United States, and more sedating than many prescription hypnotics. In a study, it was found to be superior to even the barbiturate, phenobarbital for use as a sedative. Doxylamine is also a potent anticholinergic.

C17H22N2O

270.3695

270.173

469-21-6

Doxylamine succinate;562-10-7;Doxylamine-d5 succinate;1216840-94-6

3162

LIQ

1.043 g/cm3

364.9ºC at 760 mmHg

25°C

174.5ºC

1.5486 (estimate)

2.923

0

3

6

20

276

0

CC(C1=CC=CC=C1)(C2=CC=CC=N2)OCCN(C)C

HCFDWZZGGLSKEP-UHFFFAOYSA-N

InChI=1S/C17H22N2O/c1-17(20-14-13-19(2)3,15-9-5-4-6-10-15)16-11-7-8-12-18-16/h4-12H,13-14H2,1-3H3

N,N-dimethyl-2-(1-phenyl-1-pyridin-2-ylethoxy)ethanamine

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)