A pharmacokinetic assessment of optimal dosing, preparation, and chronotherapy of aspirin in pregnancy

Am J Obstet Gynecol. 2019 Sep;221(3):255.e1-255.e9. doi: 10.1016/j.ajog.2019.04.027. Epub 2019 Apr 30.


Background: The benefit of aspirin in preventing preeclampsia is well established; however, studies over the years have demonstrated variability in outcomes with its use. Potential contributing factors to this variation in efficacy include dosing, time of dosing, and preparation of aspirin.

Objective: We aimed to compare the difference in pharmacokinetics of aspirin, through its major active metabolite, salicylic acid, in pregnant women and nonpregnant women, and to examine the effect of dose (100 mg vs 150 mg), preparation (enteric coated vs non-enteric-coated), and chronotherapy of aspirin (morning vs evening) between the 2 groups.

Materials and methods: Twelve high-risk pregnant women and 3 nonpregnant women were enrolled in this study. Pregnant women were in 1 of 4 groups (100 mg enteric coated, 100 mg non-enteric-coated, 150 mg non-enteric-coated morning dosing, and 150 mg non-enteric-coated evening dosing), whereas nonpregnant women undertook each of the 4 dosing schedules with at least a 30-day washout period. Blood samples were collected at baseline (before ingestion) and at 1, 2, 4, 6, 12, and 24 hours after ingestion of aspirin. Plasma obtained was analyzed for salicylic acid levels by means of liquid chromatography-mass spectrometry. Pharmacokinetic values of area under the curve from time point 0 to 24 hours point of maximum concentration, time of maximum concentration, volume of distribution, clearance, and elimination half-life were analyzed for statistical significance with SPSS v25 software.

Results: Pregnant women had a 40% ± 4% reduction in area under the curve from time point 0 to 24 hours (P < .01) and 29% ± 3% reduction in point of maximum concentration (P < .01) with a 44% ± 8% increase in clearance (P < .01) in comparison to that in nonpregnant women when 100 mg aspirin was administered. The reduction in the area under the curve from time point 0 to 24 hours, however, was minimized with the use of 150 mg aspirin in pregnant women, with which the area under the curve from time point 0 to 24 hours was closer to that achieved with the use of 100 mg aspirin in nonpregnant women. There was a 4-hour delay (P < .01) in the time of maximum concentration, a 47% ± 3% reduction in point of maximum concentration (P < .01) and a 48% ± 1% increase in volume of distribution (P < .01) with the use of 100 mg enteric-coated aspirin compared to non-enteric-coated aspirin, with no difference in the overall area under the curve. There was no difference in the pharmacokinetics of aspirin between morning and evening dosing.

Conclusion: There is a reduction in the total drug metabolite concentration of aspirin in pregnancy, and therefore a dose adjustment is potentially required in pregnant women. This is likely due to the altered pharmacokinetics of aspirin in pregnancy, with an increase in clearance. There was no difference in the total drug metabolite concentration of aspirin between enteric-coated and non-enteric-coated aspirin and between morning and evening dosing of aspirin. Further pharmacodynamic and clinical studies are required to examine the clinical relevance of these pharmacokinetic findings.

Keywords: aspirin; dose; pharmacokinetics; preeclampsia; pregnancy.

Publication types

  • Clinical Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Area Under Curve
  • Aspirin / administration & dosage
  • Aspirin / pharmacokinetics*
  • Aspirin / therapeutic use
  • Case-Control Studies
  • Dose-Response Relationship, Drug
  • Drug Chronotherapy*
  • Female
  • Humans
  • Platelet Aggregation Inhibitors / administration & dosage
  • Platelet Aggregation Inhibitors / pharmacokinetics*
  • Platelet Aggregation Inhibitors / therapeutic use
  • Pre-Eclampsia / prevention & control
  • Pregnancy / physiology*
  • Tablets, Enteric-Coated


  • Platelet Aggregation Inhibitors
  • Tablets, Enteric-Coated
  • Aspirin