3) Prescribing in breastfeeding Flashcards
Why is breastfeeding recommended?
Breast milk is the best form of nutrition for infants. Exclusive breastfeeding is recommended for the first six months, with continued breastfeeding alongside solid foods beyond six months.
What characteristics facilitate drug excretion into breast milk?
- Lack of ionization
- Small molecular weight
- Low volume of distribution
- Low maternal serum protein binding
- High lipid solubility
How does milk composition change after birth?
- Colostrum: Thick, yellowish milk secreted in the first days.
- Transitional milk: Produced between approximately 4-10 days.
- Mature milk: Produced from 10 days onwards.
How do drugs transfer from maternal plasma to breast milk?
By passive diffusion, distributing within the aqueous, protein, and lipid phases of milk.
How does milk composition change over time?
Milk composition evolves in lactose, fat, and protein content over the first 28 days postpartum, with lactose levels increasing and protein levels decreasing.
How does milk composition change during a single feeding?
Milk composition changes from the start to the end of a feed, with fat content increasing towards the end.
What are some risks associated with medication use in breastfeeding?
- Drug exposure to infant
- Potential safety concerns for infant
- Feeding disruption
- Medication adherence issues
- Lack of awareness regarding risks
Why is the timing of maternal medication not always reliable?
Mothers are often advised to take medication immediately after feeding to avoid peak milk concentrations, but this is not always practical or effective due to drug pharmacokinetics.
What pharmacokinetic factors affect drug distribution into breast milk?
- Acid-base characteristics
- Relative protein binding in plasma and milk
- Lipid solubility
- Milk composition
How does volume of distribution affect drug transfer into milk?
Drugs with a high volume of distribution have only a small proportion in plasma, reducing availability for milk transfer.
What factors influence an infant’s steady-state plasma drug concentration?
- Dose rate
- Oral bioavailability
- First-pass metabolism (e.g., morphine)
- Infant clearance
What is the Milk:Plasma (M:P) ratio?
A measure of drug transfer into milk, but concentrations in milk and plasma do not always rise and fall in parallel.
What is the Exposure Index?
A calculation incorporating M:P ratio and infant clearance:
Exposure Index = A × (M/P ratio) / CLi (where A = 0.1 mL/kg/min).
What is the Relative Infant Dose (RID)?
The percentage of maternal dose received by the infant through breast milk:
RID = (Dose in infant via milk / Dose in mother) × 100.
RIDs <10% are generally safe but require consideration of drug toxicity.
Which drugs affect lactation?
- Dopamine agonists (e.g., bromocriptine, cabergoline) reduce prolactin and milk production.
- Dopamine antagonists (e.g., metoclopramide) increase prolactin.
- Hormonal agents and pseudoephedrine decrease milk production.
- Diuretics reduce maternal blood volume.
- Phenobarbital inhibits infant suckling reflex.
What are the key prescribing principles for breastfeeding mothers?
- Simplify medication regimen.
- Consider alternatives.
- Prefer drugs with short half-lives, high protein binding, low oral bioavailability, and high molecular weight.
- Avoid medicines known for serious toxicity.
- Monitor infant for adverse effects.
What drug factors should be considered in prescribing?
- Maternal plasma concentration
- Molecular weight
- Lipid solubility
- Half-life
- Protein binding
- pH
- Oral bioavailability
- Drug side-effects
- Relative Infant Dose (RID)
- Milk:Plasma ratio
What infant factors should be considered in prescribing?
- Age and maturity
- Drug safety in infants
What maternal factors should be considered in prescribing?
- Severity of the condition
- Risk of non-treatment
- Short-term vs long-term medication use
- Stage of breastfeeding
What is a case example of drug toxicity in breastfeeding?
A 12-day-old infant died after developing lethargy due to high morphine levels from maternal codeine use.
The mother had an ultra-rapid CYP2D6 metabolism, leading to excessive morphine production.
Why is stopping breastfeeding when taking medication not always a ‘no-risk’ option?
Breastfeeding has significant benefits, and stopping it due to medication concerns can be unnecessary if a safer alternative exists.
What is the pharmacist’s role in medication safety for breastfeeding?
Pharmacists assess risks, provide advice, and help breastfeeding mothers find safe medication options.
What are reliable information sources on medicine use in breastfeeding?
- UK Drugs in Lactation Advisory Service (UKDILAS)
- NICE Clinical Knowledge Summaries
- British National Formulary (BNF)
- Electronic Medicines Compendium
What is the main takeaway about drug safety in breastfeeding?
While evidence is limited, safety is inferred from pharmacokinetics, pharmacodynamics, and historical clinical experience. Prefer drugs with a safe profile and monitor infants.
