IBCLC Pharmacology and Toxicology 2 — Questions and Answers
Question 1: Which resource is considered the gold standard for evaluating medication safety during lactation?
- The drug manufacturer's package insert
- LactMed database and Hale's Medications and Mothers' Milk (Correct answer)
- General drug interaction databases
- Internet search results
Correct answer: LactMed database and Hale's Medications and Mothers' Milk
LactMed and Hale's are the most authoritative, evidence-based resources for evaluating drug safety during lactation.
LactMed (NIH) is freely available online and regularly updated. Hale's provides a Lactation Risk Category system. Drug package inserts often advise against breastfeeding as a liability precaution without evidence of actual risk.
Question 2: A breastfeeding mother needs a diagnostic procedure using gadolinium-based contrast for an MRI. What is the recommendation?
- Stop breastfeeding permanently
- Pump and dump for 48 hours
- Breastfeeding can continue without interruption as less than 0.04% of gadolinium is excreted in breast milk (Correct answer)
- Stop breastfeeding for 1 week
Correct answer: Breastfeeding can continue without interruption as less than 0.04% of gadolinium is excreted in breast milk
The amount of gadolinium excreted into breast milk is extremely small, making it safe to continue breastfeeding.
Less than 0.04% of the maternal dose appears in milk, and less than 1% of that would be absorbed from the infant's GI tract. Both the American College of Radiology and the ABM state that breastfeeding can continue without interruption.
Question 3: Which class of antidepressants is generally considered most compatible with breastfeeding?
- Monoamine oxidase inhibitors (MAOIs)
- Selective serotonin reuptake inhibitors (SSRIs), particularly sertraline and paroxetine (Correct answer)
- Tricyclic antidepressants
- Benzodiazepines
Correct answer: Selective serotonin reuptake inhibitors (SSRIs), particularly sertraline and paroxetine
SSRIs, particularly sertraline and paroxetine, have the most extensive safety data during breastfeeding.
Sertraline is often the preferred first-line choice with a very low relative infant dose (RID) of approximately 0.5-3%, and infant serum levels are typically undetectable. Both LactMed and Hale rate sertraline as L2 (safer).
Question 4: A mother who is a regular cannabis user asks about the safety of breastfeeding. What should the IBCLC advise?
- Cannabis is safe during breastfeeding
- THC is lipophilic, concentrates in breast milk, is stored in infant fat tissue, and may affect neurodevelopment; abstaining is recommended (Correct answer)
- Cannabis only affects breastfeeding if smoked, not if ingested
- There are no studies on cannabis and breastfeeding
Correct answer: THC is lipophilic, concentrates in breast milk, is stored in infant fat tissue, and may affect neurodevelopment; abstaining is recommended
THC is highly lipophilic, concentrates in breast milk at levels up to 8 times maternal plasma, and may affect neurodevelopment.
THC concentrates in breast milk with ratios up to 8:1. It is stored in the infant's fat tissue and brain with a long half-life, meaning cumulative exposure increases over time. The ABM recommends abstaining from cannabis use during breastfeeding.
Question 5: What is the relative infant dose (RID) and what threshold is generally considered acceptable?
- RID is the actual dose the infant receives; any amount is concerning
- RID is the percentage of the maternal weight-adjusted dose received by the infant through breast milk; less than 10% is generally acceptable (Correct answer)
- RID is the ratio of drug in milk to drug in maternal blood
- RID measures how quickly a drug is eliminated from breast milk
Correct answer: RID is the percentage of the maternal weight-adjusted dose received by the infant through breast milk; less than 10% is generally acceptable
The RID expresses the infant's dose as a percentage of the mother's weight-adjusted dose, with less than 10% generally considered acceptable.
RID is calculated as: (infant dose via milk in mg/kg/day) divided by (maternal dose in mg/kg/day) times 100%. Most commonly used medications have RIDs well below 10%. Premature infants may be more vulnerable due to immature hepatic and renal function.
Question 6: A breastfeeding mother is prescribed radioactive iodine (I-131) for thyroid ablation. What is the correct advice?
- Breastfeeding can continue with no interruption
- Breastfeeding must be permanently discontinued for this infant as I-131 concentrates in breast milk and the thyroid of the breastfed infant (Correct answer)
- Pump and dump for 24 hours then resume
- Wait one week then resume breastfeeding
Correct answer: Breastfeeding must be permanently discontinued for this infant as I-131 concentrates in breast milk and the thyroid of the breastfed infant
Radioactive I-131 concentrates in breast milk and in the infant's thyroid gland, posing serious radiation risk.
I-131 is actively concentrated in breast milk by the sodium-iodide symporter. The breastfed infant would receive a significant radiation dose to their thyroid gland. I-131 has a half-life of 8 days and can persist in breast tissue for weeks. If therapy is elective, it should be delayed until after weaning.
