Navigating medication use while breastfeeding can be a source of anxiety for many parents. While the default advice in the past was often to stop breastfeeding, modern guidelines emphasize assessing the individual risks and benefits, recognizing that many common medications are safe for use. Most drugs enter breast milk via passive diffusion from the mother's plasma, but the amount can be influenced by a complex interplay of drug, maternal, and infant factors.
Factors That Influence Drug Excretion into Breast Milk
The amount of a drug that makes its way into breast milk and subsequently affects the infant is determined by several key pharmacological and physiological characteristics.
Drug Properties
- Molecular Weight: Drugs with a low molecular weight ($<500$ daltons) cross into breast milk more easily than those with high molecular weight ($>1,000$ daltons). Insulin and heparin, for example, have high molecular weights and are therefore minimally excreted into milk.
- Lipid Solubility: Highly lipid-soluble (fat-soluble) drugs can easily pass through the mammary gland cells and reach higher concentrations in breast milk, which has a higher fat content than plasma. Central nervous system (CNS) active drugs often have high lipid solubility.
- Protein Binding: The degree to which a drug binds to proteins in the mother's blood, primarily albumin, affects its transfer into milk. Only the 'free' (unbound) fraction of a drug can diffuse into milk, so drugs with high protein binding (e.g., ibuprofen, warfarin) appear in lower concentrations in milk.
- Ionization (pKa): The pH of breast milk (around 7.2) is slightly lower than maternal plasma (around 7.4), which can cause a phenomenon known as 'ion trapping'. Weakly basic drugs (e.g., codeine, opioids) can become ionized in the more acidic milk, trapping them and leading to a higher milk concentration.
- Half-life: The time it takes for half of the drug to be eliminated from the mother's body is important. Shorter-acting drugs are often safer as they are cleared quickly, minimizing infant exposure.
- Oral Bioavailability: Even if a drug is present in breast milk, its effect on the infant depends on whether the infant's gastrointestinal tract can absorb it. Many drugs are poorly absorbed or destroyed in the infant's stomach acid, which reduces their impact.
Maternal and Infant Factors
- Maternal Plasma Level: The concentration of the drug in the mother's blood is the most critical determinant of transfer. Milk levels generally mirror plasma levels. High maternal doses can increase the amount transferred to the infant.
- Postpartum Stage: In the first few days after birth, there are larger gaps between the mammary alveolar cells, which allows for greater passage of many substances into the colostrum. This effect is mitigated by the small volume of colostrum ingested, and the gaps close as mature milk production begins.
- Infant's Health and Age: Premature newborns and those with compromised health are more vulnerable to medication exposure due to immature metabolic and clearance functions. An older, healthy infant is at a much lower risk.
Which drugs are excreted through breast milk? Common Examples
Consulting up-to-date, reliable resources like the LactMed database or the InfantRisk Center is crucial for making informed decisions. The following examples are for informational purposes only.
Medications Generally Considered Safe
- Pain Relievers: Acetaminophen and ibuprofen are commonly recommended. Ibuprofen's high protein binding also minimizes transfer.
- Antidepressants: Many Selective Serotonin Reuptake Inhibitors (SSRIs) are safe, with Sertraline and Paroxetine often preferred due to low milk concentrations.
- Antibiotics: Most penicillins and cephalosporins are compatible, though infant allergies or gut flora changes are possible.
- Chronic Conditions: Medications for asthma (inhaled steroids), diabetes (insulin, metformin), and some hypertension drugs are generally safe.
Medications to Use with Caution
- Oral Decongestants: Pseudoephedrine can decrease milk supply, especially if lactation is not well-established.
- Certain Antidepressants: Fluoxetine has a long half-life, meaning it can accumulate. Infants should be monitored for irritability or poor feeding.
- Long-Acting NSAIDs: Naproxen has a long half-life and may accumulate with prolonged use. Ibuprofen is preferred.
- Some Beta-Blockers: Atenolol and Nadolol are excreted in higher amounts than metoprolol or propranolol.
- Benzodiazepines: Can cause infant sedation and drowsiness, especially with long-acting versions or prolonged use.
Medications to Avoid (Contraindicated)
- Illicit Drugs: All illicit substances, including cannabis, cocaine, and amphetamines, are dangerous for the infant.
- Chemotherapy Drugs: Antineoplastic agents like methotrexate can cause serious side effects and are contraindicated.
- Oral Retinoids: Isotretinoin and other oral retinoids are associated with serious risks.
- Codeine and Tramadol: The FDA warns against their use due to potential for rapid metabolization in the mother, leading to high levels of morphine in breast milk and infant respiratory depression.
- Aspirin: Can cause Reye's syndrome in infants and should be avoided.
- Lithium: Concentrates in breast milk and requires rigorous monitoring if used.
- Radiopharmaceuticals: Used in diagnostic procedures, they require temporary cessation of breastfeeding.
Strategies to Minimize Infant Exposure
For medications that are necessary but carry some risk, simple strategies can reduce the amount the baby receives:
- Timing Doses: Take medication immediately after a feeding or before the baby's longest sleep period. This allows time for the maternal plasma level to decrease before the next feeding.
- Choose Safer Alternatives: When possible, select medications with a shorter half-life, lower lipid solubility, and higher protein binding.
- Use Non-Oral Routes: Topical or inhaled medications are often preferred as they result in minimal systemic absorption.
- Consult a Professional: Always discuss any medication plan with a healthcare provider who can evaluate the risks based on your specific circumstances.
- Pump and Discard: For some medications requiring short-term use, temporarily pumping and discarding milk may be an option to maintain supply.
Comparison of Drug Properties Influencing Milk Transfer
| Drug Property | Impact on Milk Transfer | Examples |
|---|---|---|
| Molecular Weight | Low molecular weight drugs pass more easily. | Low: Alcohol, many antidepressants. High: Insulin, Heparin (less transfer). |
| Lipid Solubility | Highly lipid-soluble drugs transfer more readily. | High: CNS-active drugs like benzodiazepines. Low: Many antibiotics (less transfer). |
| Protein Binding | Highly protein-bound drugs transfer less freely. | High: Warfarin, Ibuprofen. Low: Lithium, Codeine (more transfer). |
| Half-life | Shorter half-life minimizes infant exposure. | Short: Ibuprofen, Acetaminophen. Long: Fluoxetine, Naproxen. |
| pKa | Weak bases can become 'ion-trapped' in milk. | Weak Base: Codeine, Opioids. Weak Acid: Penicillin (less trapping). |
Conclusion
While almost any drug has the potential to be excreted through breast milk, the amount and clinical significance for the infant vary widely. The decision to use a medication while breastfeeding requires careful consideration of the drug's properties, the mother's health needs, and the infant's age and clinical status. With a large number of medications proving compatible with breastfeeding, it is often possible to continue nursing safely with proper guidance. Always consult with a healthcare provider or a lactation specialist and use authoritative resources to ensure the best outcome for both mother and child.
For more information, the LactMed database is a reliable, comprehensive, and up-to-date resource on drugs and lactation: https://www.ncbi.nlm.nih.gov/books/NBK501922/.
