Doxylamine and Pyridoxine
Pronunciation
(dox IL a meen & peer i DOX een)
Synonyms
Doxylamine Succinate and Pyridoxine Hydrochloride; Pyridoxine and Doxylamine
Canadian Brand Names
Diclectin®
Use
Treatment of pregnancy-associated nausea and vomiting
Restrictions
Not available in U.S.
Pregnancy Risk Factor
A
Pregnancy Implications
Doxylamine has been approved for use in pregnancy-associated nausea and vomiting.
Lactation
Excretion in breast milk unknown
Contraindications
Hypersensitivity to doxylamine, pyridoxine, or any component of the formulation
Warnings/Precautions
May cause drowsiness; patient should avoid tasks requiring alertness (eg, driving, operating machinery) until effects are known. Sedative effects of CNS depressants or ethanol are potentiated. Use with caution in patients with angle-closure glaucoma, pyloroduodenal obstruction (including stenotic peptic ulcer), urinary tract obstruction (including bladder neck obstruction and symptomatic prostatic hyperplasia), hyperthyroidism, increased intraocular pressure, and cardiovascular disease (including hypertension and tachycardia).
Adverse Reactions
Frequency not defined.
Cardiovascular: Palpitations, tachycardia
Central nervous system: Dizziness, disorientation, drowsiness, headache, paradoxical CNS stimulation, vertigo
Gastrointestinal: Anorexia, dry mucous membranes, diarrhea, constipation, epigastric pain, xerostomia
Genitourinary: Dysuria, urinary retention
Ocular: Blurred vision, diplopia
Drug Interactions
Anticholinergic agents: Central and/or peripheral anticholinergic syndrome can occur when administered with narcotic analgesics, phenothiazines and other antipsychotics (especially with high anticholinergic activity), tricyclic antidepressants, quinidine and some other antiarrhythmics, and antihistamines.
Cholinergic agents: Drugs with high anticholinergic activity may antagonize the therapeutic effect of cholinergic agents; includes donepezil, rivastigmine, and tacrine.
CNS depressants: Sedative effects may be additive with CNS depressants; includes ethanol, benzodiazepines, barbiturates, narcotic analgesics, and other sedative agents; monitor for increased effect.
Ethanol/Nutrition/Herb Interactions
Ethanol: Avoid ethanol (may increase CNS depression).
Herb/Nutraceutical: Avoid valerian, St John's wort, kava kava, gotu kola (may increase CNS depression).
Mechanism of Action
Doxylamine competes with histamine for H1-receptor sites on effector cells; blocks chemoreceptor trigger zone, diminishes vestibular stimulation, and depresses labyrinthine function through its central anticholinergic activity. Pyridoxine is a vitamin which may have modest antiemetic effects.
Pharmacodynamics/Kinetics
Absorption: Well absorbed
Distribution: Vd: 2.5 L/kg
Metabolism: Via multiple metabolic pathways including N-demethylation, oxidation, hydroxylation, N-acetylation to metabolites including nordoxylamine, dinordoxylamine
Half-life elimination: 10-12 hours
Excretion: Urine (primarily as metabolites)
Dosage
Oral: Adults: Two delayed release tablets (a total of doxylamine 20 mg and pyridoxine 20 mg) at bedtime; in severe cases or in cases with nausea/vomiting during the day, dosage may be increased by 1 tablet in the morning and/or afternoon
Dosage adjustment in renal impairment: No dosage adjustment required
Administration
Main dose should be taken at bedtime to provide relief in the early morning hours.
Patient Education
Inform prescriber of all other prescriptions, OTC medications, or herbal products you are taking and any allergies you have. Take exactly as directed; do not take more than recommended. May cause drowsiness, headache, disorientation, or double vision (use caution when driving or engaged is tasks requiring alertness until response to drug is known); mouth sores, gastrointestinal upset, lack of appetite (small frequent meals, frequent mouth care, or sucking lozenges may help). Report rapid heart beat, palpitations; change in urinary pattern (urinary retention); unusual CNS changes; or other persistent adverse reactions.
Dosage Forms
Tablet, delayed release: Doxylamine succinate 10 mg and pyridoxine hydrochloride 10 mg
International Brand Names
Diclectin® (CA)