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Protease Inhibitors Increase Small-For-Gestational-Age But Not Other Pregnancy Risks

Pregnant women with HIV can be reassured that protease inhibitors are safer than previously thought in terms of risk to the foetus, according to research from the National Perinatal Epidemiology Unit (NPEU) at Oxford Population Health, a research institute based at the University of Oxford.

Antiretroviral therapy (ART) is recommended for all pregnant women living with HIV, and plays a crucial role both in improving maternal health and in reducing transmission of HIV from mother to child. However, there has been a critical lack of evidence about the effects of ART on the risk of adverse pregnancy outcomes, with particular concern about protease inhibitors.

Current guidelines recommend that protease inhibitor-based therapies should be used in pregnancy only if first-line treatments (such as integrase and reverse-transcriptase based treatments) are either unsuitable or unavailable. These guidelines also often advise against the use of a specific protease inhibitor, lopinavir/ritonavir, citing an increased risk of preterm birth. However, such advice may restrict treatment options for pregnant women with HIV on the basis of limited evidence.

Largest Review To-Date

The NPEU researchers, therefore, conducted the largest systematic review to date of adverse perinatal outcomes after a range of antiretroviral therapies. It included 34 cohort studies published between 1980 and 2020 and involving over 57,000 pregnant women with HIV in 22 different countries. The review, published in eClinicalMedicine, looked for evidence of 11 perinatal outcomes:

  • Preterm birth, very preterm birth and spontaneous preterm birth
  • Low birth weight, very low birth weight, term low birth weight and preterm low birth weight
  • Small for gestational age and very small for gestational age
  • Stillbirth, and neonatal death

Using pairwise random-effects meta-analyses, researchers compared protease inhibitor versus non-protease inhibitor-based ART, as well as specifically looking at the comparative risks associated with different protease inhibitor regimens.

They found that protease inhibitor-based ART significantly increased the risk of small or very small for gestational age babies, with relative risks of 1.24 (95% CI 1.08 to 1.43; I2=66.7%) and 1.40 (95% CI1.09 to 1.81; I2=0.0%), respectively. However there were no significant differences in other adverse pregnancy outcomes for protease inhibitors compared with other therapies.

In addition, researchers found no significant differences in perinatal outcomes between ART regimens containing lopinavir/ritonavir, atazanavir/ritonavir, or darunavir/ritonavir, which are the most frequently used protease inhibitors.

No Increased Risk of Preterm Birth

Senior author Dr Joris Hemelaar, senior clinical research fellow at the NPEU and honorary consultant in obstetrics at the John Radcliffe Hospital in Oxford, said: "Antiretroviral therapy in pregnancy has clear benefits for maternal health and prevention of HIV transmission to the child, but our study has shown for the first time that protease inhibitors are associated with babies being small or very small for their gestational age.

"However, there was no increased risk of preterm birth, or any other adverse pregnancy outcomes. This means protease inhibitors remain an important option for pregnant women living with HIV if other treatments are unsuitable, for example due to drug resistance, or unavailable. The evidence presented here indicates that the commonly used protease inhibitors atazanavir, lopinavir, and darunavir are comparable with regard to perinatal outcomes, which should inform international treatment guidelines."

Over 70% of the studies assessed were conducted in high-income countries, and Dr Hemelaar added that there is an urgent need for more research on pregnancy outcomes after different ART in low- to middle-income countries, where the burden of HIV is highest.

Professor Yvonne Gilleece, a spokesperson for the British HIV Association (BHIVA) and immediate past chair of the BHIVA guidelines on the management of HIV in pregnancy and the post-partum period commented: "Pregnancy is a unique life situation in which we must consider the safety of both the birthing parent and the baby. Due to ongoing under-representation of all women in clinical trials, but particularly pregnant women, we do not have enough evidence on which to base all our management decisions. This systematic review includes large numbers of pregnant women living with HIV and can, therefore, improve an informed discussion regarding the safety of the use of protease inhibitors during pregnancy."

Dr Hemelaar told Medscape UK: "Many international treatment guidelines cite adverse pregnancy outcomes, in particular preterm birth, associated with protease inhibitor (PI)-drugs as a reason for caution for their use in pregnancy. However, PI drugs are not associated with preterm birth in our analysis. This suggests that PI drugs may not be as detrimental as previously thought (and we found no differences between different PI drugs used) and, hence, these drugs may have a more favourable profile for use in pregnancy.

"However, many other aspects of treatment, including the extent to which the virus can be suppressed, adverse drug effects, adherence to drug prescriptions, antiretroviral drug resistance, drug interactions, drug cost and availability, should also be taken into account by clinicians and guideline development committees."

Lead Image Credit: Getty Images/Photo Researchers RM