Pharmacology Flashcards
why might a woman be on medication during pregnancy, childbirth and lactation?
- hypertension
- migraine
- asthma
- mental health disorders
- epilepsy
- long term anticoagulant therapy
how can pregnancy affect pharmacokinetics of drugs
affects any of the four basic kinetic processes:
- absorption
- distribution
- metabolism and elimination
- excretion
What absorption changes occur via the oral route during pregnancy?
- May be more difficult “morning sickness” nausea/vomiting
- Increase in gastric emptying and gut motility
describe absorption changes during pregnancy
oral route: decrease in gastric emptying and gut motility
intramuscular route: blood flow increased = absorption increased
inhalation: increased cardiac output, decreased tidal volume = absorption increased
describe distribution changes during pregnancy
increased Vd: increase in plasma volume and fat
increased fraction of free drug: greater dilution of plasma will decrease relative amount of plasma proteins.
describe metabolism changes during pregnancy
oestrogen and progestogens can induce or inhibit liver P450 enzymes, increasing or reducing metabolism
eg phenytoin levels reduced due to induction of metabolism or theophylline levels increased due to inhibition of metabolism
describe excretion changes during pregnancy
GFR increased = increased excretion of many drugs
this can reduce the plasma concentration, and can necessitate an increase in dose of medicines cleared by the kidney
how can pregnancy affect pharmacodynamics
site of drug action: metabolites at sites of biological action (changes in blood flow)
receptor response to drugs : mechanism of action (changes in receptors)
describe the exchange of materials across the placenta
What does placental transfer depend on?
- molecular weight (smaller sizes will cross more easily)
- polarity (unionised molecules cross more readily)
- lipid solubility (lipid soluble drugs will cross)
how does foetal distribution differ from adults?
- circulation is different (e.g. Umbilical vein to liver)
- less protein binding than adults therefore more “free” drug available
- little fat, so distribution different
- relatively more blood flow to brain
how does foetal metabolism differ from adults?
- reduced enzyme activity, though increases with gestation
- different p450 isoenzymes to adults
how does foetal excretion differ from adults?
- excretion is into amniotic fluid – this is swallowed and can allow recirculation
- drugs and metabolites can accumulate in amniotic fluid
- placenta not functioning at delivery so can be issues with excretory function
what are some drug associated problems in pregnancy
- teratogenicity: 1st trimester (3-8 weeks organogenesis)
- fetotoxicity: 2nd & 3rd trimester
what problem is there with people who have chronic conditions?
They are often undertreated due to fear that the drugs will affect the pregnancy