Why is zidovudine (AZT) preferred during pregnancy?

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Last updated: March 27, 2025 • View editorial policy

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From the Guidelines

Zidovudine (AZT) is preferred during pregnancy because it effectively prevents mother-to-child transmission of HIV. The standard regimen includes zidovudine 300 mg twice daily as part of combination antiretroviral therapy throughout pregnancy, with intravenous zidovudine during labor (2 mg/kg loading dose followed by 1 mg/kg/hour until delivery) and oral zidovudine syrup for the newborn (4 mg/kg twice daily for 4-6 weeks) 1.

Key Points

  • Zidovudine has been extensively studied in pregnancy since the landmark PACTG 076 trial, which demonstrated a reduction in transmission rates from 25% to 8% 1.
  • It has excellent placental transfer, creating protective drug levels in the fetus, and has a well-established safety profile with decades of pregnancy data showing minimal risk of birth defects 1.
  • While newer antiretrovirals are also used in pregnancy, zidovudine remains a cornerstone therapy due to its proven efficacy, particularly during labor and delivery when transmission risk is highest 1.
  • For pregnant women with high viral loads or who present late in pregnancy, adding zidovudine to their regimen is especially important to maximize protection for the newborn 1.

Recommendations

  • Zidovudine should be included as a component of antenatal therapy whenever possible 1.
  • Intravenous intrapartum zidovudine and the standard 6-week course of zidovudine for the infant is recommended, regardless of the antepartum antiretroviral regimen 1.
  • If a woman has not received zidovudine as a component of her antenatal therapeutic antiretroviral regimen, intravenous zidovudine should still be administered to the pregnant woman during the intrapartum period, when feasible 1.

From the FDA Drug Label

Zidovudine treatment during pregnancy reduced the rate of maternal-fetal HIV-1 transmission from 24.9% for infants born to placebo-treated mothers to 7.8% for infants born to mothers treated with zidovudine. The recommended dosage regimen for administration to pregnant women (greater than 14 weeks of pregnancy) and their neonates is: Maternal Dosing 100 mg orally 5 times per day until the start of labor. During labor and delivery, intravenous zidovudine should be administered at 2 mg per kg (total body weight) over 1 hour followed by a continuous intravenous infusion of 1 mg per kg per hour (total body weight) until clamping of the umbilical cord.

Zidovudine is preferred during pregnancy because it reduces the rate of maternal-fetal HIV-1 transmission. The recommended dosage regimen for pregnant women and their neonates aims to minimize this risk. Key points include:

  • Maternal dosing: 100 mg orally 5 times per day until the start of labor
  • Intrapartum dosing: intravenous zidovudine administered at 2 mg per kg over 1 hour, followed by a continuous infusion of 1 mg per kg per hour until clamping of the umbilical cord
  • Neonatal dosing: started within 12 hours after birth and continued through 6 weeks of age 2 2

From the Research

Zidovudine (AZT) During Pregnancy

  • Zidovudine (AZT) is preferred during pregnancy due to its ability to prevent mother-to-child transmission of HIV-1 infection 3, 4, 5, 6.
  • Studies have shown that AZT administration during pregnancy can reduce the risk of mother-to-child transmission by two thirds 4 and by approximately half 4.
  • The drug has been found to cause only limited toxicity among infants, with mild side effects such as anemia and macrocytosis, which resolve by the second month of life 3.

Effectiveness of Zidovudine

  • Zidovudine monotherapy has been shown to significantly reduce the risk of mother-to-child transmission of HIV infection (Peto odds ratio 0.46,95% confidence interval 0.35 to 0.60) 5, 6.
  • The risk of transmission using a 'short-short' course of zidovudine is higher than the risk using a 'long-long' course 5, 6.
  • Zidovudine also appears to decrease the risk of infant death within the first year of birth and the risk of maternal death 5, 6.

Pharmacokinetics of Zidovudine

  • A study on maternal and fetal zidovudine pharmacokinetics during pregnancy and labor found that fetal exposures resulting from maternal oral administration and infusion were estimated and compared with therapeutic exposures 7.
  • The study suggested that maternal infusion rates could be reduced to 1 mg/kg/h during 1 h followed by 0.5 mg/kg/h, or the mother could only take oral ZDV every 5 h from start of labor until delivery with her neonate having their first ZDV dose as soon as possible after birth 7.

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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