Prescribing in Pregnancy Flashcards
common drugs taken in pregnancy?
painkillers antibiotics antacids folic acid and iron supplements remember self medication - NSAIDs - st johns wort - herbal
how is the placenta involved in prescribing?
most drugs cross the placenta into foetal circulation
- except large molecular weight drugs such as heparin
small lipid soluble drugs cross more quickly
how does pregnancy affect pharmakokinetics?
absorption may be affected by morning sickness
increased volume of distribution due to increased plasma volume and fat stores
increased free drug levels due to decreased protein binding
increased liver metabolism of some drugs (phenytoin)
renal elimination of drugs is generally increased due to increased GFR
how does pregnancy affect pharmacodynamics?
no significant changes
pregnant women may be more sensitive to certain drugs
- e.g antihypertensives can cause hypotension in 2nd trimester
pre-conception considerations in prescribing?
are they/could they be pregnant?
are they planning a pregnancy?
should prescribe 400mcg folic acid daily for 3 months prior to and first 3 months of pregnancy
should give counselling about management of chronic conditions (epilepsy, diabetes etc)
optimise therapy to choose safest drugs
review whether drug therapy is neccessary
what trimester is the greatest risk?
1st
risk of early miscarriage
period of greatest teratogenic risk (4th - 11th week)
therefore avoid drugs if at all possible unless maternal benefit outweighs risk to foetus
what drugs are teratogenic in 1st trimester and what do they cause?
ACEi/ARBs = renal hypoplasia androgens = virilisation of female foetus antiepileptics = cardiac, facial, limb, neural tube defects cytotoxics = multiple defects, abortion lithium = cardio defects methotrexate = skeletal defects retinoids = ear, cardio, skeletal defects warfarin = limb and facial defects
effects of drugs in 2nd and 3rd trimester?
time of foetal growth and functional development
- can cause intellectual and behavioural abnormalities
- can also have toxic effect on foetal tissue
adverse effects of drugs at around term?
progress of labour
adaptation of foetal circulation (premaure closure of ductus arteriosus etc)
suppression of foetal systems (opiates can cuse resp depression)
bleeding (e.g if on warfarin)
effects on baby
- withdrawal syndrome (opiates, SSRI)
- sedation
epilepsy in pregnancy?
can cause more congenital malformations if untreated
increases rate of seizures (can be due to them stopping medications or changes in plasma conc of drugs - vomiting, increased clearence)
what can frequent maternal seizures cause in the baby?
lower verbal IQ hypoxia bradycardia antenatal death maternal death
effects of epilepsy treatment on baby?
congenital malformations
- 20-30% risk if on 4 drugs, so prefer monotherapy
how is epilepsy managed in pregnancy?
avoid valproate
folic acid 5mg daily
96% of babies born to women taking anti epileptics have no congenital malformations
(benefits of treatment outweigh risks)
how is diabetes managed in pregnancy?
insulin thought to be safe
requirements change in pregnancy
poor diabetic control increases risk of congenital malformation and intra-uterine death
sulfonylureas not safe (convert to insulin)
how is hypertension managed in pregnancy?
if need to treat use
- labetalol (first line)
- methyldopa
- nifedipine MR
avoid ACE inhibitors/ARBs
beta blockers may inhibit foetal growth in late pregnancy
be aware that BP generally falls in 2nd trimester
