Commonly used antivirals and antivirals of concern are reviewed in this section.

For more detailed information and references on specific medications or medications that are not covered in this section, please refer to LactMed, e-lactancia, Infant Risk, or Mother to Baby.

Oseltamivir phosphate and its metabolites have low milk transfer. There is no absolute indication to pump and dump with the use of this medication at prescribed doses.

There is no published data on Rimantadine during lactation and safer alternatives are recommended. Rimantadine has been found to concentrate at amounts greater than maternal serum in the milk of rats. Safety and efficacy of rimantadine for infants less than 1 year of age have not been established.¹ Alternative medications are preferred due to the lack of safety data in infants under 1 year of age.

Zanamivir is poorly absorbed orally, it is not likely to reach the bloodstream of the infant in clinically important amounts. There is no absolute indication to pump and dump while taking this medication.

Tenofovir is excreted in breastmilk in insignificant amounts. It is also combined with emtricitabine in the prevention of HIV.  There is not an absolute indication to pump and dump.

Adefovir is a medication used to treat Hepatitis B. The pharmacokinetics of this medication make transfer to milk possible in amounts that could be significant. Its use during breastfeeding is not recommended as there are no studies regarding its use in lactation.² Alternative treatments include Interferon Alfa (IFN-α), Lamivudine (3TC), Peginterferon alfa, and Tenofovir (TAF / TDF). Alternative medications are preferred due to the lack of data, theoretical high milk transfer, and availability of alternatives with more favorable safety profiles during lactation.

Ribavirin has not been studied in mothers who have Hepatitis C. Given its large volume of distribution ,  the amount of the medication found in breastmilk is not thought to be significant. Because it is used in infants for the treatment of RSV, it is compatible with lactation for short-term use. Caution is advised for long-term use, in the immediate neonatal period, and with  premature infants due to increased intestinal permeability.²

These medications may be used in treating herpes viruses, including the viruses that cause shingles, chickenpox, cold sores, and genital herpes.

Oral acyclovir used in the management of herpes viruses has low milk transfer. Acyclovir is also used as an antiviral for infants. Topical acyclovir applied to small areas of the mother’s body away from the breast is safe for the infant. If needed, only water-miscible cream or gel products should be applied to the breast because ointments may expose the infant to high levels of mineral paraffins.³ There is no absolute indication to pump and dump while taking this medication at prescribed doses  as it is excreted in breastmilk in insignificant amounts.

Valacyclovir is a prodrug that is quickly converted to acyclovir by the body. This medication and its metabolites are excreted into breast milk in clinically insignificant amounts with no documented side-effects observed among breastfed infants from treated mothers. There is no absolute indication to pump and dump while taking this medication at prescribed doses.

Relevant published data on excretion into breast milk were not found on famciclovir. Its low molecular weight and low percentage of plasma protein binding makes it likely that significant amounts may pass into breast milk. Alternative medications with more favorable safety profiles are preferred due to the lack of data on this medication and theoretical high milk transfer.

There is no published data on the excretion in breastmilk, however, its high molecular weight and short half-life make transfer to milk in significant amounts unlikely. Alternative medications with more safety data may be preferable during the neonatal period and in case of prematurity. There is no absolute indication to pump and dump.

This section reviews antiviral medications used in the management of COVID-19 currently or in the past. For more information about COVID-19, please see the section on COVID-19 Vaccines and Medications.

Paxlovid is used in the treatment of acute COVID-19 in at risk patients. Because of the poor oral bioavailability of nirmatrelvir and small amounts of ritonavir in milk, this combination is unlikely to adversely affect the nursing infant.  Breastfeeding is not contraindicated during nirmatrelvir-ritonavir therapy in the US and Canada, but cessation of breastfeeding during its use is recommended in Europe. Until more data are available it should only be used with infant monitoring for adverse effects. Although there is no absolute indication to pump and dump, shared decision-making is recommended regarding this medication prior to initiating it due to there being limited data on it in lactation.

This medication is no longer recommended for management of COVID-19. Remdesivir has negligible excretion observed in mother’s milk and is minimally transferred to  infant plasma from ingested breast milk. There does not appear to be an indication to avoid breastfeeding while on this medication. While there is limited data on this medication in lactation, it has poor oral bioavailability so there is no absolute indication to pump and dump.

While the options above are most commonly associated with the infections in the section they are in, the antivirals in this section may be used with multiple infections or may be used with more rare infections such as management of CMV in immunocompromised patients.

No published data on excretion of ganciclovir into breast milk were found. The known pharmacokinetic data about ganciclovir does not allow a good prediction of excretion in breast milk. However, its low oral bioavailability hinders the passage from ingested milk towards the infant’s plasma, except in preterm babies and immediate neonatal period, which may show an increased intestinal permeability.⁴ While the manufacturer recommends avoiding breastfeeding during ganciclovir use because of the risk of infant toxicity, infants are directly treated with ganciclovir for neonatal CMV infections.  Due to the lack of data, alternatives are preferred particularly during the newborn period or with a preterm infant. Patients should be engaged in shared decision making regarding the use of this medication, but there is no absolute indication to pump and dump.

There is no published data on its excretion in breast milk. Its pharmacokinetic data makes it likely that significant amounts will pass into breast milk. It has very low oral bioavailability makes it difficult for it to pass to the infant plasma from ingested breast milk, except in premature infants and in the immediate neonatal period in which there may be greater intestinal permeability. Common side effects are kidney failure, which can be severe, and anemia. Due to the risk for high milk transfer with greater absorption in preterm and newborn infants, alternative medications are preferred and infants should be closely monitored for side effects if breastfeeding is continued while on this medication.

This is a monoclonal antibody used in the management of respiratory syncytial virus (RSV). Due to its high molecular weight, palivizumab is not thought to enter breastmilk in a significant amount. There is no absolute indication to pump and dump.

Systemic absorption is low and plasma levels after topical administration is low.⁵ Avoidance of extensive application is recommended and  washing of hands after application is encouraged. Application to the breast is not recommended as ingestion can result in systemic toxicity. While caution should be used if this is applied where an infant could ingest it (such as on the breast), there is no absolute indication to pump and dump.

Serum levels are low after topical application.⁶ To reduce the possibility of infant ingestion, it should not be placed near the breast or nipple. There is no absolute indication to pump and dump.

This section will discuss pre-exposure prophylaxis (PrEP) medications for individuals at high risk of exposure and post-exposure prophylaxis (PEP) medications given after a needle stick or other exposure.

Highly Active Antiretroviral Therapy (HAART) used to manage Human Immunodeficiency Virus (HIV) encompasses a large and frequently changing group of medications and is not reviewed in this section. Some HAART medications are discussed below and may be discussed in sections above if they are used in the management of other commonly occurring viral infections.

For further information on medications used in HAART, please see the resources linked in the introduction to the article. For more information on lactation and HIV, see the section on HIV.

Truvada (Emtricitabine/Tenofovir Disoproxil Fumarate) and Descovy (Emtricitabine/Tenofovir Alafenamide) are both oral medications approved for PrEP for use in the prevention of HIV in people who are at risk for exposure to HIV through sex or injection drug use. Emtricitabine has less than 0.5% RID and breastfed infants typically have undetectable levels. Tenofovir is excreted in breastmilk in insignificant amounts. There is no absolute indication to pump and dump with Truvada or Descovy.

Cabotegravir is an injectable option for PrEP. This medication may be present in the parent’s circulation for up to 12 months after injection and there is no data on lactating women/people. It has been detected in nursing rat pups after administration to their parent. Due to the lack of data, detection of these medications in plasma for up to 12 months after administration, and lack of data on exposure to the infant via human milk, alternatives are preferred for PrEP in lactating individuals and those that who are on PrEP and may desire to breastfeed in the near future.

This medication is compatible with lactation. There is no absolute indication to pump and dump.

This medication is compatible with lactation. There is no absolute indication to pump and dump.

This medication is found in low quantities in breastmilk, but it has not been found to have harmful effects in breastfeeding infants. There is no absolute indication to pump and dump

This medication has negligible transfer to breastmilk. There is no absolute indication to pump and dump while taking this medication.