Prescribing In Pregnancy Flashcards
What drugs are proven to have benefit in pregnancy?
- Folic acid (500 micrograms or 4mg OD) for prevention of neural tube defects
- Acyclovir for prevention of vertical herpes infection transmission
- Iron supplementation
- Anaesthetic agents in labour
- Zidovudine for prevention of vertical transmission of HIV
What foods and household products might a woman worry about eating/using during pregnancy?
- Caffeine
- Hairspray
- Cigarette smoke
- Alcohol
- Illicit drugs
Is caffeine teratogenic?
No, and there is only a very weak association with miscarriage.
Is hairspray teratogenic?
Nope
What common and basic drugs might a pregnant woman be worried about taking during pregnancy?
Are these teratogenic?
- Antiemetics
- Aspirin
- Paracetamol
- Antihistamines
- Oral contraceptives
None of these are considered teratogenic.
Which classes of drugs are teratogenic?
- Anti-epileptics
- Androgens
- Retinoids
- ACE Inhibitors
- Anti-thyroid drugs
- Warfarin
- Folic acid antagonists
- Some antibiotics
- Cyclophosphomide
- Vitamin A
Which antibiotics have a teratogenic effect?
- Tetracyclines
- Streptomycin
- Trimethoprim
- Aminoglycosides
- Quinolones
Other than during pregnancy, when is pregnancy important to consider in prescribing?
In a woman of childbearing age, especially one who wishes to conceive.
In men trying to father a child.
Which period of pregnancy is most at risk of congenital malformations?
The first trimester (up to end of week eleven)
Which period of pregnancy is most at risk of growth restriction or functional development issues?
Second and third trimesters.
What principles should be used when prescribing in pregnancy?
- Only use if benefit to mother outweighs risk to foetus
- Avoid all in first trimester
- Use drugs with evidence of no effect in pregnancy where possible
- Smallest effective doe used
If a potentially teratogenic drug is prescribed for a woman of child-bearing age, what should be prescribed alongside it?
Contraception as well as written advice about effects on pregnancy.
If a pt with pre-eclampsia also has asthma, what do we prescribe instead of labetalol?
Nifedipine
Which drug has in recent history caused lots of problems when prescribed in pregnancy?
Thalidomide
Which drugs cross the placenta?
All o them pretty much, apart from those with a high molecular weight e.g. insulin and heparin.
Why do drugs with a narrow therapeutic index need monitoring and adjusting in pregnancy?
Volume of distribution changes during pregnancy
Will a drug that has caused harm in one pregnancy cause the same effect in a subsequent pregnancy?
No, not necessarily.
Why might an OCP become less effective when the pt is carbamazepine?
Carbemazepine is an enzyme-inducer which causes oestrogens and progestogens from contraceptives to be metabolised faster and reduce efficacy of OCP.
If a woman is on an enzyme-inducer e.g. carbamazepine, what contraceptives should be used for best efficacy?
-Progestogen-only impant
If tablet is preferred:
-OCP containing at least 50 micrograms of ethinylestradiol (continuous or tri-cycling regimen).
What does the teratogenicity of a drug depend upon?
- Dose
- Polypharmacy
- Stage of pregnancy/timing of exposure
What are the 2 main outcomes from drug exposure during the embryonic phase of pregnancy i.e. first 17 days?
Cellular damage leading to either:
- Spontaneous abortion
- Replacement of damaged cells -> normal pregnancy
How does gut motility change in pregnancy?
It decreases
How does lung function change in pregnancy?
It increases
How do plasma volume and body water change in pregnancy?
They both increase
How does glomerular filtration change in pregnancy?
It increases
How does plasma protein levels change in pregnancy?
They decrease.
Where can information about prescribing in pregnancy be found?
- BNF
- Local /Regional NHS medicines information centre
- UK teratology Information Service
- Manufacturer
- Electronic Medicines Compendium
What kind of paracetamol use is safe in pregnancy?
Occasional use and short courses.
How does the folic acid dose change for n/low risk mothers compared to high risk mothers?
500 micrograms for low risk
4 mg for high risk
Take throughout first trimester for both.
Do enzyme inducing drugs such as carbamazepine have an effect on hormonal emergency contraception?
Yes
What should a woman on an enzyme inducer such as carbamazepine take for emergency contraception?
- Preferably non-hormonal i.e. copper coil
- If this is not an option, a double dose of levonorgestrel (i.e 3mg) should be given.
A woman is on the following drugs. Which should be discontinued during pregnancy?
Gliclazide Metformin Ramipril Simvastatin Lithium
Gliclazide - discontinue Metformin - continue Ramipril - discontinue Simvastatin - discontinue Lithium - ideally discontinue but practically the risk to the mother will often outweigh benefits of stopping.
What drug is used forgestational hypertension?
Labetalol
If labetalol and nifedipine are both contraindicated, what drug can be used to treat hypertension in pregnancy?
What is the caveat to this?
Methyldopa BUT MUST STOP within 2 days of birth as the side effects include postnatal depression and sedation.
How do thyroxine requirements change in early pregnancy?
They increase by 30-50% in early pregnancy!
Why do thyroxine requirements increase in pregnancy?
The placental enzymes increase metabolism of thyroxine, plasma volume increases, and maternal thyroid hormone is transferred to the developing foetus.
How should euthyroidism be maintained in pregnancy?
- Check TFTs as soon as pregnancy confirmed
- Maintain trimester specific TSH and free T4 levels.
- Endocrinologist involvement for dosing and monitoring requirements
- Review again after birth and once breastfeeding as stopped.
