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Drug Safety in Pregnancy

Drug Safety in Pregnancy. Mother Child. Adverse Drug Reactions.

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Drug Safety in Pregnancy

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  1. Drug Safety in Pregnancy • Mother • Child

  2. Adverse Drug Reactions An appreciably harmful or unpleasant reaction, resulting from an intervention related to the use of a medicinal product, which predicts hazard from future administration and warrants prevention or specific treatment, or alteration of the dosage regimen, or withdrawal of the product

  3. Adverse Drug Reactions • Common • 6.2% of all hospital admissions • >100,000 deaths in the US p.a. • Occupy 7 800-bed hospitals in the UK

  4. Drug Safety in Pregnancy • Pre-existing disorders, e.g. epilepsy • Infections, e.g. urinary tract infections • Disorders of pregnancy • Treatment of foetus

  5. Physiological changes in Pregnancy Absorption Decrease in intestinal motility Decreased gastric emptying Emesis/reflux - decreased absorption

  6. Physiological changes in Pregnancy Distribution Increased plasma volume by 45% (32 wks) Total body fat increased Protein concentration decreased Uterine blood flow increased (<1% to 16-25%)

  7. Physiological changes in Pregnancy • 50% Increase in glomerular filtration rate by mid pregnancy • Increased excretion of drugs, increased dose requirements Excretion

  8. Bacteriuria in pregnancy • 6% of normal pregnant women have asymptomatic bacteriuria • 23-40% of these will develop acute pyelonephritis • Screening at initial visit • E. coli commonest

  9. Bacteriuria in pregnancy Treatment • Asymptomatic Trial of single dose therapy If fails, 7-day course • Safe: Penicillins and nitrofurantoin • Contraindicated: Quinolones, tetracycline and trimethoprim

  10. Bacteriuria in pregnancy • Symptomatic UTI: 1-2% of pregnant women • Prevent complication to mother and foetus • Prevent recurrence • Ampicillin 10-14 day course Treatment

  11. Adverse Effects of Penicillins • Nausea • Pregnancy can cause nausea • UTI may cause nausea • Drug can cause nausea

  12. Adverse Effects of Penicillins • Diarrhoea • Vary in severity • Mild to fulminant colitis Pseudomembranous Colitis – Clostridium difficile

  13. Adverse Effects of Penicillins:Rash

  14. Causality • Pregnancy-related? • Disease-related? • Drug-related?

  15. Causality • Temporal relationship • Rechallenge • Exclusion of other causes • Previous reports • ALWAYS CONSIDER DRUGS IN DIFFERENTIAL DIAGNOSIS OF NEW SYMPTOMS

  16. Placental Circulation Maternal Foetal

  17. Placental transfer • Molecular weight of drug <500 daltons • Lipid solubility • Degree of ionisation of drug • Extent of plasma protein binding

  18. Placental transfer • Type I - equal concentrations complete transfer profile • Type II - higher foetal than maternal plasma concentrations • Type III - higher maternal concentrations; incomplete transfer profile

  19. Teratogenicity • Regard every drug as being potentially teratogenic • 1-5% of all congenital anomalies are caused by drugs • Thalidomide disaster • Yellow card adverse drug reaction reporting scheme

  20. YELLOW CARDS • Introduced in 1964 • 500,000 reports • ~ 20,000 reports per year

  21. Teratogenicity Screening for teratogenicity • Animals used as models for man • 2 species (rat or mouse and rabbit) • 3 dose levels • Period of organogenesis • Males tested for effect on fertility • Females administered drug in 3rd trimester to assess effects on foetal growth

  22. Teratogenicity • Period of organogenesis • Late stages may lead to fetal growth retardation and/or mental retardation Stage of pregnancy

  23. Teratogenicity • Alcohol • Anticonvulsants • Thalidomide • Corticosteroids • Vitamin A and derivatives

  24. Sources of Information

  25. Sources of information • Dug Information Centres • National Teratology Information Centre, The Regional Drug and Therapeutic Centre, Wolfson Unit, Claremont Place, Newcastle-upon-Tyne. Tel No. 0191 232 1525

  26. Prescribing in pregnancy • Disease pre-pregnancy - does drug therapy need to be continued? - does it need to be altered? • Try non-drug treatment first • Avoid multiple drugs • Select the safest and most efficacious drug • Dose changes may be necessary

  27. Adverse drug reaction in pregnancy • Consider stopping drug • Treat mother • If harm to the foetus suspected, get specialist advice • Communication with mother • Report the adverse reaction

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