Pharmacology in Pregnancy Flashcards
list some common conditions during pregnancy and then also other normal conditions prior to pregnancy that still need treated.
- hypertension
- pain
- nausea and vomiting
- gestational diabetes
- anticoagulant therapy
- herpes virus
- mental health disorders
- migraine
- asthma
- epilepsy
ADME properties and how they differ during pregnancy: Absorption
- oral route may not be an option for women suffering nausea and vomiting (consider buccal)
- decreased gastric emptying and gut motility - higher incidence of constipation, may not affect regular drug therapies but could impact one off treatments.
- increased absorption of intramuscular drugs due to increased blood flow.
- increased cardiac output and reduced tidal volume may cause increased absorption of inhaled drugs.
ADME properties and how they differ during pregnancy: Distribution
Increase in plasma volume and fat will change the distribution of drugs; increasing the volume of distribution.
Greater dilution of plasma will decrease the relative amount of plasma proteins, increasing the amount of free drug in circulation (less protein bound).
ADME properties and how they differ during pregnancy: Metabolism
- Altered enzyme actions due to oestrogen and progesterone levels.
- Liver P450 enzymes may be induced or inhibited which can lead to increased or reduced metabolism – drug dependent.
Examples: - Phenytoin levels are reduced in pregnancy due to metabolism being induced (sped up).
- Theophylline levels increase during pregnancy due to metabolism being inhibited resulting in more free drug in circulation for longer.
ADME properties and how they differ during pregnancy: Excretion
GFR is increased in pregnancy by 50% leading to an increased excretion of many drugs.
This can result in a reduction in plasma concentration and can require for higher medication doses being required for renally cleared drugs; eg. Gentamicin and Digoxin.
pharmacodynamics in pregnancy
Pharmacodynamics is defined as the response of the body to the drug. It refers to the relationship between drug concentration at the site of action and any resulting effects namely, the intensity and time course of the effect and adverse effects.
Much less studies in pregnancy
Pregnancy may affect the site of action and receptor response to drugs
Efficacy of medicine may be different
Adverse effects may also be different
fetal pharmacokinetics: distribution, metabolism and excretion
ADME profile different in fetus to newborn baby.
Distribution:
- circulation is different
- less protein binding than adults, more free drug
- little fat, so distribution different
- more blood flow to brain
Metabolism:
- less enzyme activity, this increases with gestation
Excretion:
- drug excretion is into amniotic fluid and then swallowed and recirculated
- drugs and metabolites can accumulate in amniotic fluid due to this
what is a teratogen?
- an agent or factor which can cause congenital malformation
- can prevent implantation of the embryo, cause abortion, produce intrauterine growth restriction or cause fetal death
drugs given after the first 2 months of pregnancy are more likely to cause…
general growth retardation, or interfere with functional development of organs.
examples of fetotoxic drugs and their effects
- warfarin may cause intracranial haemorrhage if given in 2nd and 3rd trimester
- NSAIDs taken in the 3rd trimester can cause premature closure of ductus arteriosus resulting in neonatal pulmonary hypertension
- beta blockers given in late pregnancy may result in neonatal hypoglycaemia
what are the prescribing principles for women of child-bearing age?
- Always consider the possibility of pregnancy (planned or not)
- Warn women of potential risks
- If planning a pregnancy, advice to discuss treatment options prior to stopping medication
- Always discuss contraception
- Pregnancy Prevention Programmes – legal requirement for some treatments, eg. Isotretinoin, valproate. MHRA guidance, confirmed with negative pregnancy test prior to prescribing
what are the principles for prescribing during pregnancy?
- consider non-pharmacological treatments
- avoid all drugs in the first trimester if possible
- Avoid drugs that are known to be harmful
- Use the medicine with the best safety profile (avoid new drugs unless deemed safe)
- Use the lowest effective dose for the shortest period of time
- Consider the need for dose changes and additional therapeutic monitoring for some drugs
- Don’t under treat a condition, this may be more harmful to mum and baby
