Pharmacology drug treatment during pregnancy, breast feeding and the neonate Flashcards
What are the changes in drug absorption in pregnancy?
Gastric emptying delayed for oral preparations so can affect the drug absorption can delay onset of drug
What are the changes in drug distribution in pregnancy?
- 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
What are the changes in drug metabolism in pregnancy?
- Increased clearance of drugs which depend on liver enzyme activity e.g. phenytoin and theophylline
What are the changes in drug elimination in pregnancy?
- Increased renal plasma flow doubling the elimination of renally cleared drugs such as penicillins
What factors will influence placental transfer?
- Lipid solubility / water solubility
- Molecular size
- Protein binding
- Metabolism
(Small, lipid soluble, unbound uncharged cross more easily)
What drugs are most likely to affect blastocysts (day 0-16)?
cytotoxic drugs and alcohol
What drugs are most likely to affect organogenesis (day 17-60)?
Teratogens
What drugs are most likely to affect Cell and organ maturation stage (60 days-term)?
- Alcohol
- Nicotine
- Radio active iodine
- Corticosteroids
What are the seven A’s which are contraindicated in pregnancy?
- ACEi/ARB (ask about pregnancy before prescribe)
- Anticonvulsant
- Antibiotics
- Antipsychotics (lithium)
- Anti-thyroids
- Anticoagulants
- Abuse of (alcohol, cigs, opioids or bzds)
+ DMARDS
Antibiotics which can’t be used in pregnancy?
Tetracyclines
Trimethoprim
Metronidazole
What antithyroid can’t be used in pregnancy?
Iodine
Carbimazole
propylthiouracil
( can cause congenital hypothyroidism)
What anticoagulants can’t be used in pregnancy?
Warfarin
DOACs and NOACs (untested in pregnancy so are not used)
Which stage of pregnancy are foetuses at greatest risk?
First trimester
Do all drugs cross the placenta?
Yes just different amounts depending on drug
What is the safest way to prescribe during pregnancy?
Assume drug will cause harm and work from there
- assume pregnancy until proven otherwise
What are the rules for prescribing during pregnancy?
- There must always be sound reason for prescribing at all
- avoid prescribing during first trimester
- choose drug which has proven safety record if possible
What drugs can be prescribed for nausea and vomiting in pregnancy?
- 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
How is asthmas managed in pregnancy?
- maintain good inhaler use
- Prednisolone ok if needed
How is hypertension managed in pregnancy?
- older drugs
- Labetalol
- methyldopa
- nifedipine
How are UTIs managed in pregnancy?
- 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
What anticoagulants should be prescribed in pregnancy?
Heparin
How should anticonvulsants be managed in pregnancy?
- Seizures more risk than drugs than refer to specialist
Can drugs enter breast milk?
Yes most drugs detectable in breast milk though concentrations very low
What medications should not be taken when breast feeding?
- Diazepam
- Alcohol
- Lithium
- Iodine
- Opioide
- Tetracyclines
- Corticosteroids
What is neonate defined as?
first 6 months life
How does absorption change in neonates?
Skin - SA: body weight large so absorption greater of creams e.g. steroids
Intramuscular absorption impaired due to reduced mass
Rectal absorption relatively efficient
How does distribution change in neonates?
- 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
How does metabolism change in neonates?
- impaired oxidation increasing conc drugs like warfarin, diazepam and theophylline
- impaired glucuronidation increasing risk of toxicity to drugs which are metabolised by this mechanism
How does drug elimination change in neonates?
- 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
What inherited conditions make affect drug responses?
- oxidation/acetylation
- glucose-6-phosphate dehydrogenase deficiency can cause acute haemolytic
- pseudocholinesterase deficiency can cause prolonged apnoea after neuromuscular blockade if given anaesthetic
What are the rules for prescribing to neonates?
- 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
