Prescribing in special groups 1

  • Created by: z
  • Created on: 22-02-16 08:31


  • Definition: a substance, physical agents or deficiency state capable of induicing abnormal structure of function such as:
    • gross structural abnormalities
    • functional deficiencies
    • IUGR
    • behavioural aberrations
    • demise
  • drugs cause 2-3% of all congenital malformations (0.15% of all pregnancies)
  • susceptibilty depends on genotype of mother/baby and on developmental stage of foetus
  • 1st trimester
    • drugs can cause congenital malformations
    • 3rd to 8th week is period of highest risk as organ systems are formed
    • pre-embryonic phase (0-14 days post-conception) is "all or nothing" i.e. completely healthy or spontabneois abortion
  • 2nd and 3rd trimester
    • drugs can cause IUGR or functional development or have toxic effects on tissues
    • a/e on neonate if given shortly before or during labour e.g. diazepam or pethidine
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FDA pharmaceutical pregnancy categories

  • Pregnancy category A
    • adequate and well controlled studies have failed to demonstrate risk to foetus in 1st T.
  • Pregnancy category B
    • animal reproduction studies failed to show risk if no adequate studies in pregnant women OR animal studies show adverse effect but adequate, well controlled human studies do not
  • Pregnanacy category C
    • animal reproduction studies have shown adverse effect and there are no adequate, well controlloed human studies but potential benefits may warrant use
  • Pregnancy category D
    • positive evidence of human foetal risk based on adverse reaction dta from investigational or marketing experience or human studies but potential benefits may warrant use
  • Pregnancy category E
    • studies in humans or animals have dmeonstrated foetal abnormalities and/or there is positive evidence of human foetal risk and the risks involved clearly outweigh any potential benefits
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Drugs to avoid in pregnancy

  • ACE inhibitors: impaired neonatal BP control and renal function
  • Aminoglycosides: eighth nerve damage
  • Androgens: virilisation, multiple congenital defects
  • Opiates: perinatal respiratory depression
  • Quinolone antibiotics: skeletal abnormalities
  • Sodium valproate: neural tube defects
  • Tetracyclines: yelolow discolouration of teeth, inhibtis bone growth
  • Warfarin: multiple congential defects
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Prescribing in pregnancy

  • assume all drugs will cross the placenta unless they have high molecular weight
  • avoid drugs in 1st trimester if possible
  • only prescribe if benefit to mother outweighs risk to foetus
  • check all drugs in BNF
  • check UK Teratology Informatrion Service

NB on dosing:

  • maternal drug concentration is often lower than in non-preganant women (incr vol of distribution)
  • renal elimination may incr thus higher dose needed (enoxaparin)
  • lamotrigine metabolism enhanced so need higher dose (antiepileptic)
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Prescribing in breastfeeding

  • avoiding breatsfeeding to take drugs is NOT a no harm option
  • most drugs are passed in small qunatities so are not a concern
  • neonates and prem babies are at greater risk due to poor excretion and thus accumulation
  • risk depends on:
    • passage of drug to milk
      • reduced passage= good
        • HMW (e.g. insulin, heparins)
        • high protein binding (e.g. warfarin, NSAIDS)
        • low lipid solubility (e.g. loratidine)
        • lower pH (e.g. amoxacillin) because pH of breat milk lower than plasma (6.9 vs 7.4)
    • amount of active drug delivered to infant
    • infant pharmacokinetics
      • absorption, distributioni, elimination
    • adverse reaction profile
    • infant age
    • infant co-morbidities
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Drugs to avoid in breastfeeding

  • Amiodarone
    • present in milk in significant amounts
    • risk from release of iodine
  • Antithyroid drugs
    • neonatal goitre and hypothyroidism
  • Benzodiazepines
    • presentin breast milk
  • Lithium salts
    • present in milk and risk of toxicity
  • Radioactive iodine
    • breastfeeding contraindicated
  • Statins
    • high conc in breast milk
  • Sulphonamides
    • risk of kemicterus (bilirubin-induced brain dysfunction) in jaundiced infants
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Drug effects on lactation

  • drugs which affect dopamine activity will cause changes in lactation b/c dopamine inhibits release of prolactin from ant pituitary
    • dopamine agonists (e.g. cabergoline) reduce milk production
    • dopamine antagonists (e.g. domperidone) promote lactation
  • early postpartum use of oestrogen reduces milk volume
    • therefore use POP as contraception postpartum
  • some drugs (e.g. phenobarbital) inhibit the infant's suckling reflex
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