Breastfeeding and drugs: a mother's guide

1. Nearly all drugs pass into human milk but dilution in the mother's body before this entry, and the relatively small volume of milk swallowed, will mean that whatever drug reaches the baby is insufficient to cause adverse effects.2. Almost all medications appear in very tiny amounts - usually less than one per cent of the maternal dose - and the majority of drugs are safe for the baby.3. Very few drugs are contraindicated for breastfeeding mothers and although there are a few drugs that may still cause problems for infants, even in tiny doses, this is not the case for the vast majority.

Key factors
The decision about continuing breastfeeding when the mother takes a drug is far more involved than whether the baby will get any in the milk - and the issue of which drugs are safe to take during lactation is quite complicated. Many factors have to be taken into consideration, such as:

• The route of administration: drugs can enter your system in several different ways. Orally (by being swallowed), intravenously (injected directly into the blood stream), intramuscularly (being injected into the muscles), topically (from creams applied to the skin), or through inhalation (having been breathed in). Medications taken topically or from inhalation reach the milk in lesser amounts and more slowly than other routes and are almost always safe. Oral medications take longer to get into the milk - because they have to go through the mother's metabolic processes before they enter her blood stream and then the milk supply - than intravenous or intramuscular routes.
• The amount taken: the higher the dosage, the more the drug transfers into the milk.
• How often the drug is taken: medications/drugs taken 30-60 minutes before breastfeeding are likely to be at peak levels when your baby feeds.
• Your baby's age and level of maturity: premature babies have immature organs, and may, therefore, have trouble processing and eliminating even small quantities of drugs that might not cause problems for larger, full-term babies. However, even a full-term baby's protective metabolic system is not fully developed for the first few weeks of life, so may not be able to handle chemicals in milk as well as a baby who is several months old.
• The frequency and volume of feeding: the baby who is feeding once or twice a day and is supplemented the rest of the time will obviously receive less of a drug than the baby who is totally breastfed and who may be feeding ten to 12 times a day.
• Duration of drug therapy: a medication taken for weeks or months may have a greater impact on breastfeeding than one taken for just a few days.
• Type of medication: the characteristics of the drug, including the elimination time (just how quickly the body's metabolism can remove the drug), the fat solubility (a property that governs just how easily a drug can enter the