Pharmacology In pregnancy and breast feeding Flashcards
What is pharmacokinetics?
It is the effect that the body has on drugs
What is pharmacodynamics?
Its the effect that the drug has on the body
How many % of women take a PRESCRIBED medicine during pregnancy?
60%
How many % of women take OTC medicine during pregnancy?
90%
How many women of child-bearing age take medication?
80%
What absorption changes occur in pregnancy?
Morning sickness might limit oral intake
Gastric emptying and gut motility decreases
Blood flow increases so subcutaneous and intramuscular routes might be absorbed quicker
Inhalation increases which can ^ inhaled drug absorption
When does morning sickness most occur in pregnancy?
First 3 months.
What happens to the fraction of free drugs in pregnancy?
They increase (because plasma is diluted and theres not as many plasma proteins)
What happens to the volume of distribution in pregnancy?
This increases due to the plasma volume and fat increasing.
What happens to the metabolism of drugs in pregnancy?
oestrogen and progesterone can induce or inhibit liver P450 enzymes - increasing or decreasing metabolism.
What happens to excretion in pregnancy?
it increases, GFR increases by 50%.
Doses might need to be increased progressively as the pregnancy progresses.
Which drugs can cross the placenta?
Most drugs can cross the placenta. You should assume that all drugs can.
What makes a drug more likely to cross the placenta?
molecular weight - smaller sizes will cross more easily
polarity - unionised crosses more easily
lipid solubility - lipid soluble drugs will cross more readily
Why is the drugs different in the foetus?
- circulation is different
- less protein - more free drugs
- more blood flow to brain, less developed blood brain barrier
How do the foetus metabolise the drug?
slower, theres less P450 enzymes but they increase with gestation.
How does the foetus excrete of the drug?
Into the amniotic fluid, but it can be re swallowed by the foetus, they can accumulate and cause toxicity.
What is most common in the first trimester of gestation?
teratogenicity
What is most common in the second and third trimester of gestation?
fetotoxicity
What are the principles of prescribing for women of the child bearing age?
- always consider pregnancy
- warm of possible risks
- tell a women to try and attend the doctor before they get pregnant when treating a condition
- discuss contraception if prescribing teratogenic medicines
- don’t prescribe certain drugs without contraception
How many foetal abnormalities are drugs a cause of?
2% of foetal abnormalities
When is the foetus at highest risk of teratogenicity?
during organogenesis (3-8 weeks)
how do drugs block the folate metabolism?
- They can bind to the enzyme (tetra hydrofolate reductase) to block the conversion of folate
- they can block other enzymes
What does folate antagonism lead to?
Oro-facial, neural tube or limb defects.
What do retinoid drugs cause for the foetus?
- aortic arch anomalies
- ventricular septal defects
- craniofacial malformations
- oesophageal atresia
- pharyngeal gland abnormalities
Which drugs cause enzyme-mediated teratogenesis?
NSAIDs - can cause orofacial clefts and cardiac septal defects
What effect does fetotoxicity have on the foetus?
- growth retardation
- structural malformations
- fetal death
- functional impairment
- carcinogenesis
Which drugs often cause fetotoxicity?
ACE inhibitors, ARBs.
Which drugs are teratogenic in the foetus?
Anticonvulsants - sodium valproate anticoagulants antihypertensives NSAIDs Alcohol Retinoids
Which antihypertensive agents aren’t teratogenic?
Methyl dopa, labetalol, nifedipine.
Which drugs are present in milk?
Any drug the mother takes is present in the milk.
When is the best time for a mother to take her medication?
As soon as she has fed her baby.
Are protein or lipid soluble drugs preferred in breastfeeding?
Protein soluble.
These are less likely to bind to the lipid component of breast milk.
Which drugs should be avoided in breast feeding?
immunosuppressants anti-convulsants amiodarone lithium radio-iodine
What are galactagogues?
Medications (can be OTC) which are used to induce, maintain and increase milk production.
What are two common galactagogues?
Fenugreek
Comfrey
When is trimethoprim teratogenic?
Usually just in the first trimester, apart from that it’s safe. But avoid use if possible.
