Lecture 56: Drug Treatment in Pregnancy, Breast Feeding and Neonate Flashcards
describe drug absorption during pregnancy
gastric emptying is delayed for oral preparations so takes longer for drug to have effect
describe drug distribution during pregnancy
- 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
describe drug metabolism during pregnancy
^ clearance of drugs which depend on liver enzyme activity; phenytoin, theophylline
describe drug elimination during pregnancy
^ renal plasma flow doubling elimination of renal cleared drugs e.g. penicillins
why might drug half lives decrease during pregnancy
despite absorption taking longer, metabolism and elimination are a lot faster
what factors affect placental transfer of drugs
- lipid solubility/ water solubility
- molecular size
- protein binding
- metabolism
what type of drug crosses placenta most easily
small, lipid soluble, unbound, uncharged molecule crosses most easily
what are the common drugs you should avoid/show caution when prescribing to pregnant px
seven As + DMARDS
- ACEi/ARBs
- anticonvulsants
- antibiotics
- antipsychotics
- antithyroid
- anticoagulant
- (drug) abuse
- DMARDS/cytotoxics
during what stage of pregnancy does administration of drugs pose the greatest risk
first trimester
what are the main rules for prescribing in pregnancy
- 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
what drugs might be given for nausea/vomiting/morning sickness during pregnancy
- 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
what drugs might be given for asthma during pregnancy
- maintain good control w/ inhalers
- prednisolone ok if needed
what drugs might be used for hypertension in pregnancy
older drugs e.g. labetalol, methyldopa, nifedipine
what is the advice for antibiotic prescription for UTI during pregnancy
prescribe antibiotic to all women w/ suspected UTI in pregnancy
what is the drug advice for anticoagulation during pregnancy
- heparin/LMWheparins are relatively safe
- warfarin should be avoided
- DOACs - manufactures advise avoid
what is the drug advice for anticonvulsants during pregnancy
- seizure more risk than drug
- refer to specialist e.g. joint obstetric/neurology clinic (changing guidance)
what should be considered when prescribing to a nursing mother
- most drugs detectable in breast milk though with very low conc
- consider timing, half life etc
what drugs should be shown caution for nursing mother
- diazepam
- alcohol
- lithium
- iodine/propylthiouracil
- opioids
- tetracyclines
- corticosteroids
describe drug absorption for neonates
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
describe drug distribution in for neonates
- 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)
describe drug metabolism in neonates
- ~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)
describe drug elimination in neonates
- 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
what inherited conditions may affect drug response and how
- 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
what are the main rules for prescribing to neonates
- 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
