Doxylamine succinate shares the actions and uses of other antihistamines. Because of its sedative effect, doxylamine succinate is used as a nighttime sleep aid in the short-term management of insomnia. Although the safety and efficacy of doxylamine as a nighttime sleep aid have not been fully established, the US Food and Drug Administration (FDA) states that, pending further accumulation of data, doxylamine-containing nighttime sleep aids that have been approved for this use may continue to be marketed in the US. The drug is also used in combination with antitussives and decongestants for the temporary relief of cold and cough symptoms.
Dosage and Administration
Doxylamine succinate is administered orally.
As a nighttime sleep aid, the usual dosage of doxylamine succinate for self-medication in adults and children 12 years of age or older is 25 mg taken 30 minutes before retiring or as directed by a clinician. Because chronic insomnia may be indicative of a serious underlying physical, emotional, or psychological condition requiring professional medical attention, patients should be advised to consult a clinician if insomnia persists continuously for longer than 2 weeks.
As an antihistamine, the usual dosage of doxylamine succinate for self-medication in adults and children 12 years of age and older is 7.5-12.5 mg every 4-6 hours, not to exceed 75 mg in 24 hours. Alternatively, under the direction of a clinician, these adults and children may receive dosages up to 25 mg every 4-6 hours, or 2 mg/kg or 60 mg/m daily in divided doses, not to exceed 150 mg daily. For self-medication in children 6 to younger than 12 years of age, the usual antihistaminic dosage is 3.75-6.25 mg every 4-6 hours, not to exceed 37.5 mg in 24 hours. Alternatively, under the direction of a clinician, these children may receive dosages up to 12.5 mg every 4-6 hours, or 2 mg/kg or 60 mg/m daily in divided doses, not to exceed 75 mg daily. Under the direction of a clinician, children 2 to younger than 6 years of age may receive an antihistaminic dosage of 1.9-3.125 mg every 4-6 hours, not to exceed 18.75 mg in 24 hours.(See Cautions: Pediatric Precautions.)
Doxylamine shares the toxic potentials of other antihistamines, and the usual precautions of antihistamine therapy should be observed.
Like other antihistamines, doxylamine should not be used in premature or full-term neonates. and 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.
Overdosage and toxicity (including death) have been reported in children younger than 2 years of age receiving preparations containing antihistamines (including doxylamine), cough suppressants, expectorants, and nasal decongestants alone or in combination for relief of symptoms of upper respiratory tract infection. There is limited evidence of efficacy for these preparations in this age group, and appropriate dosages (i.e., approved by the US Food and Drug Administration [FDA]) for the symptomatic treatment of cold and cough have not been established. Therefore, FDA stated that nonprescription cough and cold preparations should not be used in children younger than 2 years of age; the agency continues to assess safety and efficacy of these preparations in older children. Meanwhile, because children 2-3 years of age also are at increased risk of overdosage and toxicity, some manufacturers of oral nonprescription cough and cold preparations agreed to voluntarily revise the product labeling to state that such preparations should not be used in children younger than 4 years of age. FDA recommends that parents and caregivers adhere to the dosage instructions and warnings on the product labeling that accompanies the preparation if administering to children and consult with their clinician about any concerns. Clinicians should ask caregivers about use of nonprescription cough and cold preparations to avoid overdosage. For additional information on precautions associated with the use of cough and cold preparations in pediatric patients,
Pregnancy and Lactation
There is considerable controversy regarding the teratogenic potential, if any, of doxylamine; however, after evaluating extensive data and information concerning the possible teratogenicity of the drug, the US Food and Drug Administration (FDA) concluded that it is unlikely that doxylamine is teratogenic. FDA recognizes, however, that despite the large number of pregnancies evaluated to date the possibility that doxylamine may be weakly teratogenic cannot be excluded. Doxylamine was commercially available in the US for the treatment of nausea and vomiting associated with pregnancy in combination with dicyclomine and pyridoxine until 1976, and then in combination with only pyridoxine until 1983 when the manufacturer voluntarily discontinued manufacturing and distributing the combination. Most epidemiologic studies (case-control and cohort) in which fixed combinations of doxylamine and pyridoxine with or without dicyclomine were used during pregnancy indicate that an association between use of these combinations and adverse fetal effects does not appear to exist, but the possibility that the drug is weakly teratogenic cannot be excluded. In a few studies, a weak association between use of the fixed combinations during pregnancy and specific fetal abnormalities (e.g., pyloric stenosis, cardiac defects, oral clefts) was reported, but a causal relationship with the drugs was not established and these findings have not been confirmed by many other studies. Women considering self-medication with doxylamine during pregnancy should consult a health professional for advice regarding the relative risks and benefits of such therapy.
Most reproduction studies in various animal species using doxylamine and pyridoxine alone or in fixed combination have not revealed evidence of harm to the fetus. Studies in rats and mice using doxylamine succinate dosages up to 125 times the maximum human dosage did not reveal evidence of observable congenital abnormalities, but wavy ribs and diaphragmatic hernias occurred in rats at dosages 125-375 times the maximum human dosage; an overall increase in fetal wastage, varying from zero to threefold, occurred in most rodents receiving dosages 125 or more times greater than the maximum human dosage. In a small study in monkeys receiving a fixed combination of doxylamine succinate and pyridoxine hydrochloride throughout fetal organogenesis at dosages 10-20 times the maximum human dosage, intraventricular septal defects were present in 4 of 7 fetuses delivered on day 100 of gestation (full-term gestation is about 160 days), while 2 fetuses aborted on the 46th and 56th day of gestation appeared to be developing normally and 3 other fetuses allowed to develop to term were normal. The importance of septal defects in these monkeys is not known, since an opening in the septum is usually present early during fetal development in monkeys. In other studies in monkeys receiving the fixed combination for shorter periods of time, there was no evidence of fetal toxicity.
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.
Following oral administration of a single 25-mg dose of doxylamine succinate in healthy adults, mean peak plasma concentrations of about 100 ng/mL occur within 2-3 hours after administration. Sedative effects occur approximately 30 minutes after oral administration. The drug has an elimination half-life of about 10 hours in healthy adults.