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Prescribing in Pregnancy
In pregnancy and breast feeding, all drugs (including OTC) must be considered potentally armful unless or untl
proven otherwise.
Prescribes drugs in pregnancy s ould be “tried and tested”
Always use lowest efectie dose
P armacokinetcs in Pregnancy
Absorpton
- Delayed/reduced appearance of PO drug in plasma
o Vomitng (due to B- C))
o Reduced )I motlity (due to progesterone)
o Slower gastric emptying (due to progesterone)
- Increased absorpton from IM drugs (e.g. pet idine)
o Vasodilaton causes increased tssue perfusion
Distributon
- Total body water increases by 7-8 litres
- Body fat increases by around 4kg
- Fall in plasma albumin by 10-15 gm/l.
- Increased free drug normally bound to albumin
- Increased store of lipid soluble drugs.
Metabolism
- Hepatc metabolism increases Increased eliminaton of liver-excreted drugs (e.g. p enytoin, t eop ylline)
Eliminaton
- Renal plasma fow doubles )FR & creatnine clearance increased Increased eliminaton of renally-excreted
drugs (e.g. amoxicillin, LMWH)
Non-p ysiological Factors Interfering wit Medicaton
Intentonal non-compliance by patent for fear of side efects
Incorrect non-prescripton by ealt care professional
Teratogenic Drugs
T roug out Vitamin A (isotretnoin, retnoids) Spontaneous aborton, Microta, CNS defects,
pregnancy Mental retardaton, Craniofacial dysmorp ism, Cardiac defects, Clef lip
Androgens Foetal masculinisaton (late), Labio-scrotal fusion (early), Cliteromegaly
(w eneier)
ACE inhibitors Skull abnormalites, Lung abnormalites, Renal tubular agenesis,
Oligo ydramnios, IU)R (worse in 2nd/3rd trimesters)
ARBs Oligo ydramnios, Hypotension, Renal failure, and IUFD
AEDs
- Valproate NTD and Facial defects (1 in 10), Deielopmental disorders (1 in 3)
- P enytoin Craniofacial abnormalites, Learning disability, Cardiac defects, Nail and
distal p alangeal ypoplasia, IU)R
- Carbamazepine NTD, Microcep aly, IU)R
Aminoglycoside ANBX (e.g. )entamycin) CN8 damage, Ototoxicity/ earing loss
Lithium
- Early - Congenital eart disease (Ebstein anomaly)
- Late – )oitre, Kidney and CNS abnormalites
Statns (C olesterol important in foetus) Vertebral, anal and cardiac abnormalites
Tetracycline Toot enamel ypoplasia and yellowing
Thalidomide Bilateral limb defciency, Microta, Cardiac and )I anomalies
Warfarin
- Early - ‘Warfarin embryopat y’ (nasal ypoplasia, stppled bone epip yses, s ort
p alanges, optc atrop y, mental retardaton, microencep aly)
- Late - IU)R, Deielopmental delay, placental abrupton, foetal aemorr age
Early pregnancy Methotrexate Folic acid antagonist NTD
Trimethoprim Folic acid antagonist NTD
- )iie nitrofurantoin for UTIs in 1st and 2nd trimester, or Cephalexin w eneier
Diethyl Stlbestrol (DES) Vaginal adenocarcinoma in adult life (< 9 weeks gestaton)
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