Lecture 56: Drug Treatment in Pregnancy, Breast Feeding and Neonate

Question 1

describe drug absorption during pregnancy

Answer 1

gastric emptying is delayed for oral preparations so takes longer for drug to have effect

Question 2

describe drug distribution during pregnancy

Answer 2

• total body water and fat are increased resulting in lower concentrations of water soluble and lipid soluble drugs
• protein binding is reduced ^ free (active) drug conc

Question 3

describe drug metabolism during pregnancy

Answer 3

^ clearance of drugs which depend on liver enzyme activity; phenytoin, theophylline

Question 4

describe drug elimination during pregnancy

Answer 4

^ renal plasma flow doubling elimination of renal cleared drugs e.g. penicillins

Question 5

why might drug half lives decrease during pregnancy

Answer 5

despite absorption taking longer, metabolism and elimination are a lot faster

Question 6

what factors affect placental transfer of drugs

Answer 6

• lipid solubility/ water solubility
• molecular size
• protein binding
• metabolism

Question 7

what type of drug crosses placenta most easily

Answer 7

small, lipid soluble, unbound, uncharged molecule crosses most easily

Question 8

what are the common drugs you should avoid/show caution when prescribing to pregnant px

Answer 8

seven As + DMARDS

• ACEi/ARBs
• anticonvulsants
• antibiotics
• antipsychotics
• antithyroid
• anticoagulant
• (drug) abuse
• DMARDS/cytotoxics

Question 9

during what stage of pregnancy does administration of drugs pose the greatest risk

Answer 9

first trimester

Question 10

what are the main rules for prescribing in pregnancy

Answer 10

• must always be sound reasons fro prescribing a drug during pregnancy
• avoid prescribing during first trimester except during most exceptional circumstances
• if possible choose a drug within class which has proven safety record e.g. labetalol instead of ACEi when treating hypertension

Question 11

what drugs might be given for nausea/vomiting/morning sickness during pregnancy

Answer 11

• if mild: nothing, consider vit/electrolyte support
• 1st line: antihistamines (e.g. promethazine, cyclizine), prochlorperazine
• -> reassess 24hrs, if poor response switch class
• 2nd line: metoclopamide or ondansetron (<5dyas)
• methylprednisolone in severe cases

Question 12

what drugs might be given for asthma during pregnancy

Answer 12

• maintain good control w/ inhalers

- prednisolone ok if needed

Question 13

what drugs might be used for hypertension in pregnancy

Answer 13

older drugs e.g. labetalol, methyldopa, nifedipine

Question 14

what is the advice for antibiotic prescription for UTI during pregnancy

Answer 14

prescribe antibiotic to all women w/ suspected UTI in pregnancy

Question 15

what is the drug advice for anticoagulation during pregnancy

Answer 15

• heparin/LMWheparins are relatively safe
• warfarin should be avoided
• DOACs - manufactures advise avoid

Question 16

what is the drug advice for anticonvulsants during pregnancy

Answer 16

• seizure more risk than drug

- refer to specialist e.g. joint obstetric/neurology clinic (changing guidance)

Question 17

what should be considered when prescribing to a nursing mother

Answer 17

• most drugs detectable in breast milk though with very low conc
• consider timing, half life etc

Question 18

what drugs should be shown caution for nursing mother

Answer 18

• diazepam
• alcohol
• lithium
• iodine/propylthiouracil
• opioids
• tetracyclines
• corticosteroids

Question 19

describe drug absorption for neonates

Answer 19

skin:
- ^ SA per body weight so absorption of topical agents is increased e.g. steroids

intramuscular:
- absorption impaired due to reduced mass

rectal:
- absorption relatively efficient e.g. diazepam, theophyllines

Question 20

describe drug distribution in for neonates

Answer 20

• body water as % is greater than older children, so loading dose is greater for aminoglycosides, digoxin, aminophylline based on body weight
• albumin binding is decreased ^ free conc of highly bound drugs and ^ risk of drug/bilirubin interactions (newborn jaundice)

Question 21

describe drug metabolism in neonates

Answer 21

• ~50% of an adult
• impaired oxidation ^ conc of drugs such as warfarin, diazepam, and theophylline
• impaired glucuronidation ^ risk of toxicity to drugs metabolised by this mechanism e.g. chloramphenicol (grey baby syndrome)

Question 22

describe drug elimination in neonates

Answer 22

• glom filtration/tubular secretion and reabsorption all impaired, requiring dose reduction for renally cleared drugs based on body weight e.g. aminoglycosides, digoxin, penicillins
• by 6 months renal function is usually normal and standard doses based on body weight can be used

Question 23

what inherited conditions may affect drug response and how

Answer 23

• oxidation/acetylation
• -> slow - exaggerated or toxic responses
• -> fast - failure to respond to standard doses
• glucose-6-phospahte dehydrogenase deficiency
• -> develop acute haemolysis following treatment w/ number of drugs
• pseudocholinesterase deficiency
• -> prolonged apnoea after neuromuscular blockade

Question 24

what are the main rules for prescribing to neonates

Answer 24

• when possible base doses on estimated body SA
• use pediatric formulary
• special adjustments are necessary in neonates especially those who are premature
• avoid new drugs if possible
• remember that most drugs are not licensed for use in children and info is often poor
• adverse effects are often different from adults