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Timing of breastfeeds if taking medication

I keep getting emails/ Facebook messages that mothers have been advised to pump and dump their breastmilk for a period of time after taking medication in order to minimise / prevent exposure of the baby to the drug. This has often been undertaken when the drug is compatible with breastfeeding and resulted in the unnecessary exposure of the baby to formula milk.

For most drugs taken for more than 3 days the amount in milk is constant across 24 hours. So timing feeds with respect to breastfeeding or dumping of the breastmilk is pointless. The half life of a drug is very important but just one of the factors in determining the compatibility with normal breastfeeding. If you want to know more please consider buying “Breastfeeding and Medication”

pdf of information Timing of medication and breastfeeds

Timing of drugs with respect to medication does not help to minimise levels to which babies are exposed in chronic conditions. Although the time to maximum level is often quoted, drugs reach a steady state 3-5 days after therapy begins and the levels then remain constant across the 24-hour period. Just as it takes approximately 5 half- lives for a drug to leave the body totally, it takes 5 half-lives to reach steady state. Before this time the levels increase gradually with every dose until they reach this point. Trying to time feeds disrupts normal breastfeeding and may result in engorgement with no benefit in milk levels to which the baby will be exposed. See Fig  1 below

Fig 1 accumulation of drug until it reaches steady state after 5 half lives (here taken to be 24 hours)

The half-life of a drug defines how long it takes to reach steady state and also how long it takes for it to be totally cleared from the mother’s body and milk. Five half-lives are taken as the closest measure in both cases.

Fig 2 Percentage of drug left where half-life is 24 hours

If the half-life of the drug is more than 24 hours the level may begin to accumulate in the baby’s body and be more likely to produce adverse effects e.g. diazepam half-life 43 hours.   Drugs with short half lives are preferred during breastfeeding. In  general long acting / slow release formulations are better avoided if possible.

Fig 2 Percentage of drug left where half-life is 24 hours