Pharmacology drug treatment during pregnancy, breast feeding and the neonate

Question 1

What are the changes in drug absorption in pregnancy?

Answer 1

Gastric emptying delayed for oral preparations so can affect the drug absorption can delay onset of drug

Question 2

What are the changes in drug distribution in pregnancy?

Answer 2

• Total body water and fat increased so lower concentrations of water soluble and lipid soluble drugs
• Protein binding is reduced, increasing free drug (active) concentrations

Question 3

What are the changes in drug metabolism in pregnancy?

Answer 3

• Increased clearance of drugs which depend on liver enzyme activity e.g. phenytoin and theophylline

Question 4

What are the changes in drug elimination in pregnancy?

Answer 4

• Increased renal plasma flow doubling the elimination of renally cleared drugs such as penicillins

Question 5

What factors will influence placental transfer?

Answer 5

• Lipid solubility / water solubility
• Molecular size
• Protein binding
• Metabolism
  (Small, lipid soluble, unbound uncharged cross more easily)

Question 6

What drugs are most likely to affect blastocysts (day 0-16)?

Answer 6

cytotoxic drugs and alcohol

Question 7

What drugs are most likely to affect organogenesis (day 17-60)?

Answer 7

Teratogens

Question 8

What drugs are most likely to affect Cell and organ maturation stage (60 days-term)?

Answer 8

• Alcohol
• Nicotine
• Radio active iodine
• Corticosteroids

Question 9

What are the seven A’s which are contraindicated in pregnancy?

Answer 9

• ACEi/ARB (ask about pregnancy before prescribe)
• Anticonvulsant
• Antibiotics
• Antipsychotics (lithium)
• Anti-thyroids
• Anticoagulants
• Abuse of (alcohol, cigs, opioids or bzds)
  + DMARDS

Question 10

Antibiotics which can’t be used in pregnancy?

Answer 10

Tetracyclines
Trimethoprim
Metronidazole

Question 11

What antithyroid can’t be used in pregnancy?

Answer 11

Iodine
Carbimazole
propylthiouracil
( can cause congenital hypothyroidism)

Question 12

What anticoagulants can’t be used in pregnancy?

Answer 12

Warfarin

DOACs and NOACs (untested in pregnancy so are not used)

Question 13

Which stage of pregnancy are foetuses at greatest risk?

Answer 13

First trimester

Question 14

Do all drugs cross the placenta?

Answer 14

Yes just different amounts depending on drug

Question 15

What is the safest way to prescribe during pregnancy?

Answer 15

Assume drug will cause harm and work from there

- assume pregnancy until proven otherwise

Question 16

What are the rules for prescribing during pregnancy?

Answer 16

• There must always be sound reason for prescribing at all
• avoid prescribing during first trimester
• choose drug which has proven safety record if possible

Question 17

What drugs can be prescribed for nausea and vomiting in pregnancy?

Answer 17

• mild don’t prescribe anything can give vitamin or electrolyte support
• 1st line promethazine, cyclizine or prochlorperazine
• 2nd line metoclopamide or ondansetron
• Methylprednisolone in severe cases

Question 18

How is asthmas managed in pregnancy?

Answer 18

• maintain good inhaler use

- Prednisolone ok if needed

Question 19

How is hypertension managed in pregnancy?

Answer 19

• older drugs
• Labetalol
• methyldopa
• nifedipine

Question 20

How are UTIs managed in pregnancy?

Answer 20

• Prescribe antibiotic to anyone with a suspected UTI still take urine sample and culture
• 1st line Nitrofurantoin
• 2nd line if no improvement then amoxicillin or cefalexin

Question 21

What anticoagulants should be prescribed in pregnancy?

Answer 21

Heparin

Question 22

How should anticonvulsants be managed in pregnancy?

Answer 22

• Seizures more risk than drugs than refer to specialist

Question 23

Can drugs enter breast milk?

Answer 23

Yes most drugs detectable in breast milk though concentrations very low

Question 24

What medications should not be taken when breast feeding?

Answer 24

• Diazepam
• Alcohol
• Lithium
• Iodine
• Opioide
• Tetracyclines
• Corticosteroids

Question 25

What is neonate defined as?

Answer 25

first 6 months life

Question 26

How does absorption change in neonates?

Answer 26

Skin - SA: body weight large so absorption greater of creams e.g. steroids
Intramuscular absorption impaired due to reduced mass
Rectal absorption relatively efficient

Question 27

How does distribution change in neonates?

Answer 27

• Body water greater so loading dose greater based on body weight
• albumin binding decreased so more free concentrations of highly bound drugs increasing risk of drug/bilirubin interactions

Question 28

How does metabolism change in neonates?

Answer 28

• impaired oxidation increasing conc drugs like warfarin, diazepam and theophylline
• impaired glucuronidation increasing risk of toxicity to drugs which are metabolised by this mechanism

Question 29

How does drug elimination change in neonates?

Answer 29

• GFR and reabsorption impaired so require lower dose for renally cleared drugs
• by 6 mon renal function normal and standard dose based on body weight can be used

Question 30

What inherited conditions make affect drug responses?

Answer 30

• oxidation/acetylation
• glucose-6-phosphate dehydrogenase deficiency can cause acute haemolytic
• pseudocholinesterase deficiency can cause prolonged apnoea after neuromuscular blockade if given anaesthetic

Question 31

What are the rules for prescribing to neonates?

Answer 31

• Base on estimated body surface when possible
• use paediatric formulary
• special adjustments needed especially if premature
• avoid new drugs most drugs not licensed for children
• adverse effects often very different than in adults