R06AA59 - Doxylamine, Combinations

Probably not porphyrinogenic

Rationale

Doxylamine: No evidence of CYP3A4 or CYP2C9 induction in humans. Substrate for CYP2D6, CYP1A2, and CYP2C9. No CYP-related drug-drug interactions noted. Pyridoxine (vitamin B6) - vitamin.

Chemical description

Doxylamine is an ethanolamine antihistamine (DrugBank). Pyridoxine is the 4-methanol form of vitamin B6 (DrugBank).

Therapeutic characteristics

Doxylamine is used to treat insomnia and allergy symptoms but is also used in combination with pyridoxine in the treatment of nausea and vomiting in pregnancy (DrugBank). It is taken orally (DrugDex, SmPC). Pyridoxine is indicated for the treatment of vitamin B6 deficiency and for the prophylaxis of isoniazid-induced peripheral neuropathy. It is also used in combination with doxylamine in the treatment of nausea and vomiting in pregnancy. It may be administered orally, or by intravenous or intramuscular injection (DrugBank, DrugDex).

Metabolism and pharmacokinetics

Doxylamine is biotransformed in the liver primarily by the cytochrome P450 enzymes CYP2D6, CYP1A2, and CYP2C9, to its principal metabolites N-desmethyl-doxylamine and N,N-didesmethyldoxylamine (SmPC). Doxylamine has showed a marked induction of CYP2B enzymes and a modest induction of CYP3A and CYP2A in mice (Bookstaff 1996) However, there is no evidence that doxylamine is an enzyme inducer of either CYP2C9 or CYP3A4 in humans (IARC 2001). No CYP-related drug interactions are noted in the interactions databases for doxylamin or pyridoxine.

Published experience

No case reports found.

Similar drugs

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References

#	Citation details	PubMed ID
1.	Effects of doxylamine succinate on thyroid hormone balance and enzyme induction in mice. Bookstaff RC, Murphy VA, Skare JA, Minnema D, Sanzgiri U, Parkinson A. Toxicol Appl Pharmacol. 1996; 141(2): 584-94. doi:10.1006/taap.1996.0325	8975784
Drug reference publications
2.	DrugBank Doxylamine. https://go.drugbank.com/ Access Date: 2025-August-25
3.	DrugBank {Pyridoxine} Access Date: 2025-October-07
4.	Micromedex® 2.0 (online). {pyridoxine}. Access date: {26.08.2025}. Ann Arbor, Michigan, USA: Merative. Available from: https://www.micromedexsolutions.com/
Drug interaction databases
5.	Micromedex® 2.0 (online). Merative™ Micromedex® Drug Interaction Checking (electronic version). Ann Arbor, Michigan, USA: Merative. Available from: https://www.micromedexsolutions.com/ Access Date: 2025-August-26
6.	Stockley’s Interaction Checker Preston, C.L. (ed). London: Pharmaceutical Press. Available from: https://www.medicinescomplete.com/#/interactions/stockley (Accessed: 26 August 2025). Access Date: 2025-August-26
Summary of Product Characteristics
7.	SPC {Xonvea}. Exeltis UK Ltd. Date of revision of text: 26 February 2024. Available from: https://www.medicines.org.uk/emc/
Other sources
8.	International Agency for Research on Cancer (IARC) Summary & Evaluation. Doxylamine Succinate. 2001; 79: 145. Available from: https://www.inchem.org/documents/iarc/vol79/79-05.html (Accessed 27 August 2025).