Pharmacology of pregnancy

Question 1

How is the absorption of a drug orally affected during prengnacy

Answer 1

Oral route may not be an option -> N&V
Decreased gastric emptying & gut motility

Question 2

How is absorption of a drug intramuscuarly affected

Answer 2

Increased absortion of IM drugs (increased blood flow)

Question 3

How is absoprtion of an inhaled drug affected?

Answer 3

Increased cardiac output & reduced tidal volume -> increased absoprtion of inhaled drugs

Question 4

How is the distribution of a drug effected during pregnancy

Answer 4

Increase in plasma volume & fat -> increased volume of distribution

Greater dilution of plasma -> decreases relative amount of plasma proteins -> increase in amount of free drug in circulaiton

Question 5

How is the metabolism of a drug affected in pregnancy?

Answer 5

Altered enzyme action due to oestrogen & progesterone
Liver P450 enzyme may be induced or inhibited, either increasing or reducing metabolism of a drug.

Question 6

Describe the effects of pregnancy on phenytoin levels

Answer 6

Phenytoin levels are reduced in pregnancy due to metabolism being induced

Question 7

Describe the effects of pregnancy on theopylline levels

Answer 7

Theophylline levels increase during pregnancy due to the inhibition of metabolism -> results in more free drug in circulation

Question 8

Describe the effect of pregnancy on excretion of drugs

Answer 8

• GFR is increased in pregnancy by 50% -> increase in excretion of many drugs
• Can result in reduction in plasma concentration and may require higher medication doses for renally cleared drugs e.g. gentamicin & digoxin.

Question 9

What is pharmacodynamics & how does pregnancy affect this>

Answer 9

• response of the body to a drug
• Prenancy may affect the site of action & receptor response of a drug
• Efficacy and adverse effects of a drug may be different

Question 10

What is the function of the placenta?

Answer 10

• Exchange of materials
• Mother provides oxygen, glucose, fat, vitamins and antibodies
• Baby transfers urea, CO2 & other waste products back to the mother

Question 11

List some factors which affect placenta transfer of medicine

Answer 11

• Drug type (lipid soluble cross more readily than polar drugs)
• Length of exposure
• Stage of pregnancy

Question 12

Distribution of drugs in fetal circulation compared to adults

Answer 12

• Less protein binding & so more free drug
• Little fat which effects distribution, resulting in more blood flow to the brain

Question 13

Excretion of drugs in fetal circulation compared to adults

Answer 13

• Drug excretion is into amniotic fluid, it is then swallowed and re-circulated
• Drugs & metabolites can accumulate in the amniotic fluid due to this

Question 14

metabolism of drugs in fetal circulation compared to adults

Answer 14

Less enzyme activity in fetal circulation
This increases with gesgation

Question 15

What is a teratogen?

Answer 15

Agent or factor which can cause congenital malformations

• It can prevent implantation of the conceptus (embryo), cause abortion, produce intrauterine growth restriction or cause fetal death.

Question 16

When is the biggest risk of exposure from teratogenic drugs?

Answer 16

Biggest risk of exposure is during the organogenesis period (between 3-10 weeks)

Question 17

What does fetotoxicity mean?

Answer 17

-> toxic effects to the fetus
Drugs given after the first 2 months of pregnancy are more likely to cause general growth retardation, or interfere with functional development of organs.

Question 18

List 3 drugs which may cause fetotoxicity

Answer 18

• Warfarin
• NSAIDs
• B blockers

Question 19

Effects of Warfarin on the fetus

Answer 19

• May cause intracranial haemorrhage if given in 2nd & 3rd trimester

Question 20

Effects of NSAIDs on the fetus

Answer 20

When taken in the 3rd trimester, can cause premature closure of ductus arteriosus, resulitng in **neonatal pulmonary hypertension **

Question 21

Effects of B blockers on the fetus

Answer 21

If given late in pregnancy, may result in neonatal hypoglycamia

Question 22

What are pregnancy prevention programmes?

Answer 22

Legal requirement for some treatments, eg. Isotretinoin, valproate. MHRA guidance, confirmed with negative pregnancy test prior to prescribing

Question 23

1st line medication for UTI in 1st and 2nd trimester of prengnacy

Answer 23

Nitrofurantoin oral 100mg m/r 12 hourly

2nd line = cefalexin (1st tri)/ trimethoprim (2nd tri)

Question 24

1st line medication for UTI in 3rd trimester

Answer 24

Trimethoprim oral 200mg 12 hourly

2nd line- cefalexin oral 500mg 12 hourly