Breastfeeding and Medicines

Question 1

what is the first important information about breastfeeding and medicines?

Answer 1

If a mother is taking chronic medication check the information of safety in breastfeeding during the antenatal period.

Question 2

what is pharmacokinetics?

Answer 2

How the drug is absorbed, transported, metabolised and excreted

Question 3

what happens once the drug is absorbed?

Answer 3

• Once the drug is absorbed, how does it move into the blood and subsequently into the milk It is important to remember once the baby has consumed the milk, they will also have to absorb, metabolise it before it has an effect

Question 4

what is important to remember about once babies have consumed milk after mums have taken certain medications?

Answer 4

they will have also absorb, metabolised it before it has an effect.
- The dose will be significantly lower that is secreted through breastmilk than if they were going to get it as a therapeutic dose.

Question 5

what is a drugs half life?

Answer 5

half life is the time taken for 50% of the drug to leave the system

Question 6

what happens after 5 half lifes?

Answer 6

After 5 half-lives the amount of drug left in the system is so small that it can be said to have left the system. Therefore, it will have minimal effect to no effect on mum and no effect on baby via breastfeeding.

Question 7

if a mum is not breastfeeding during the half life time for drugs to leave her system what is important to do?

Answer 7

It is important that if a mum is withholding milk while the drug half lives as in leave the system, that you support the mother with maintaining her milk supply to avoid mastitis.

Question 8

what is the problem with chronic medication exposure?

Answer 8

The problem comes when a drug is taken every day and the half-life is more than 24 hours, in particular if the baby is under 6 weeks as their liver and kidneys function have not matured.

Question 9

what is the significance of pethidine?

Answer 9

• A drug you need to be aware of in particular is pethidine.
  
  • These drugs begin to accumulatedue to the amount of drug left in the system when the next dose is taken. This can lead to toxicity.
  • Babies exposed to pethidine in the neonatal period may become sleepier and feeding can be affected.

Question 10

what is the important message 2 about breastfeeding and medicines?

Answer 10

• Try to avoid drugs with long half lives under 24 hours
  
  • Use drugs with high protein binding, ideally >90% (found in hale)
  • Choose medications with a milk-plasma ratio <1
  • High molecular weight = less passage into milk and less oral bioavailability
    Drugs licensed for use in children are ideal and will reach concentrations way below that of treatment dose.

Question 11

what is steady state concentration?

Answer 11

timing does in relation to feeding. This only works with acute medications e.g. blood pressure meds, pain meds.
- Once a drug has been taken for 5 half-lives it has reached steady state concentration. This means the level of drug is constant across 24 hours.
Therefore, it is not possible to avoid/reduce exposure with long term medication

Question 12

how does medications transfer into milk?

Answer 12

• In the first few days after birth, drugs can pass freely in to the milk
  
  • This is due to the intracellular gaps being wide open to allow the free transport of immunoglobulins to the baby via the milk.
    the intracellular gaps close around day 3 and at this point the drug must pass through the cell membrane which is much more difficult.

Question 13

what is the rule for therapeutic range?

Answer 13

• As a rule, if it is licensed for use in children, it will be safe in breastfeeding.
  Sometimes mother and baby will be taking the same medications e.g., paracetamol. The amount passed to the baby through the milk is low and does not affect the dose the child is taking. Baby can also have paracetamol and ibuprofen when the mum has during breastfeeding also.

Question 14

what is the importance of the size of the molecule?

Answer 14

• The larger the molecule the less ability to pass into the milk.
  Large molecules tend to have low or no oral bioavailability

Question 15

what is milk-plasma ratio?

Answer 15

• This refers to the concentration of the protein free fraction in the milk and plasma.
  
  • Any ratio over 1 would indicate the drug may have the ability to concentrate in the milk. Other pharmacokinetic factors should be considered in this instance.

Question 16

what does protein binding mean in relation to breastfeeding?

Answer 16

• Once absorbed, drugs either bind to proteins or remain free. It is only the free portion that can enter the milk.
  
  • The more drug is bound to proteins, the less will enter the milk
  • Highly bound drugs e.g., penicillin cannot penetrate the milk.
  • Highly bound drugs are the choice for administration to breastfeeding mothers
    Some drugs will compete for binding sites that are normally occupied by bilirubin in the 1st week postpartum. This bilirubin can be displaced by certain drugs and there is a theoretical risk of kernicterus and brain damage in the infant

Question 17

what is bioavailability in relation to breastfeeding?

Answer 17

• The ability of the drug to reach the systemic circulation following oral administration
  
  • Drugs with poor oral bioavailability tend to be larger molecules. These are unable to pass through the cell membrane easily and need to be administered parenterally. It is therefore unlikely they will enter the milk.
  • As a rule, drugs that are metabolised by the liver are deemed safer.
  • If a drug cannot be absorbed from the gut. No matter how much drug is in the milk, it will not be absorbed via the child’s gut.
    If drug needs to get given IV then it is not been able to taken orally. If the molecule cannot be absorbed by the gut then it will pass through the child’s gut and remain unchanged and secreted unchanged via urine etc.