Pregnancy & Breast Feeding
PREGNANCY
TERM DEFINITION
↑ Blood Volume By 30-50% a ecting distribution of drugs
Dilution of albumin = more free drug in
circulation
↑ Cardiac Output Leads to increased elimination of drugs cleared
& Renal Blood Flow by the kidney
Physiological
↓ GI Motility Delayed absorption (Mainly PO meds)
Changes
Hormonal Changes Can alter drug metabolism
Placental Transfer Drugs can cross the placenta e.g. LMWH,
leading to foetal exposure
PHYSIOLOGICAL IMPACT OF PREGNANCY VIA SYSTEM
▪ Increased eGFR Increases elimination of water soluble
drugs (e.g. beta-lactam abx)
Renal
▪ Reduced renal threshold Lower capacity to excrete drugs = higher
serum concentrations of drugs
▪ Increased Cardiac Output May a ect anti-hypertensives or beta
blockers
Cardiovascular
▪ Vascular resistance Impacts pharmacodynamics of beta
blockers
▪ Delayed Gastric Emptying Slower GI tract = ↑ absorption time
impacting drugs with rapid onset time (e.g.
GI NSAIDs)
▪ Increased pH A ect absorption of PH sensitive drugs
(e.g. antiretrovirals)
TERATOGENICITY
Potential of a substance to cause developmental
Teratogenicity abnormalities/birth defects in a foetus when mother is exposed to
it during pregnancy
▪ First trimester (0-12 weeks)
The most sensitive period for teratogenicity due to the formation of organs
Drugs taken during this period can cause major structural defects
Critical period of risk ▪ Second and third trimesters
Can a ect the growth and functional development (e.g. brain and lung develop.)
and lead to neurodevelopment issues
Common Teratogenic ▪ Thalidomide ▪ Sodium Valproate ▪ Isotretinoin
Drugs ▪ Warfarin ▪ ACE Inhibitors
Prescribing ▪ Low bar for referral ▪ Risk Vs. Benefit (mother + foetus)
considerations in ▪ Avoid drugs in the first trimester ▪ Avoid newer drugs
Pregnancy ▪ Patient-centred SDM is essential ▪ Avoid polypharmacy
▪ Use the lowest but e ective dose for the shortest duration
Prescribing ▪ Is she pregnant? ▪ Is she using contraception?
considerations in ▪ Is she at risk of unplanned pregnancy?
fertile women ▪ Is she trying to become pregnant?
Interactions with ▪ Carbamazepine ▪ Primidone ▪ Phenytoin
contraception ▪ Rifampicin ▪ St Johns Wort
PREGNANCY
TERM DEFINITION
↑ Blood Volume By 30-50% a ecting distribution of drugs
Dilution of albumin = more free drug in
circulation
↑ Cardiac Output Leads to increased elimination of drugs cleared
& Renal Blood Flow by the kidney
Physiological
↓ GI Motility Delayed absorption (Mainly PO meds)
Changes
Hormonal Changes Can alter drug metabolism
Placental Transfer Drugs can cross the placenta e.g. LMWH,
leading to foetal exposure
PHYSIOLOGICAL IMPACT OF PREGNANCY VIA SYSTEM
▪ Increased eGFR Increases elimination of water soluble
drugs (e.g. beta-lactam abx)
Renal
▪ Reduced renal threshold Lower capacity to excrete drugs = higher
serum concentrations of drugs
▪ Increased Cardiac Output May a ect anti-hypertensives or beta
blockers
Cardiovascular
▪ Vascular resistance Impacts pharmacodynamics of beta
blockers
▪ Delayed Gastric Emptying Slower GI tract = ↑ absorption time
impacting drugs with rapid onset time (e.g.
GI NSAIDs)
▪ Increased pH A ect absorption of PH sensitive drugs
(e.g. antiretrovirals)
TERATOGENICITY
Potential of a substance to cause developmental
Teratogenicity abnormalities/birth defects in a foetus when mother is exposed to
it during pregnancy
▪ First trimester (0-12 weeks)
The most sensitive period for teratogenicity due to the formation of organs
Drugs taken during this period can cause major structural defects
Critical period of risk ▪ Second and third trimesters
Can a ect the growth and functional development (e.g. brain and lung develop.)
and lead to neurodevelopment issues
Common Teratogenic ▪ Thalidomide ▪ Sodium Valproate ▪ Isotretinoin
Drugs ▪ Warfarin ▪ ACE Inhibitors
Prescribing ▪ Low bar for referral ▪ Risk Vs. Benefit (mother + foetus)
considerations in ▪ Avoid drugs in the first trimester ▪ Avoid newer drugs
Pregnancy ▪ Patient-centred SDM is essential ▪ Avoid polypharmacy
▪ Use the lowest but e ective dose for the shortest duration
Prescribing ▪ Is she pregnant? ▪ Is she using contraception?
considerations in ▪ Is she at risk of unplanned pregnancy?
fertile women ▪ Is she trying to become pregnant?
Interactions with ▪ Carbamazepine ▪ Primidone ▪ Phenytoin
contraception ▪ Rifampicin ▪ St Johns Wort
