Prescribing drugs during pregnancy

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Prescribing drugs during pregnancy

• Khalid A. Yarouf

www.4MedStudents.com
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Introduction

• Pregnancy poses important problems. Most drugs
  will diffuse passively across placenta, and some
  are transported actively, so the potential
  benefit of a drug to mother has to be considered
  in relation to the potential risk to the fetus.
  As a general rule, all drugs should be avoided in
  pregnancy unless theres a compelling reason for
  their use. Some drugs have been definitely linked
  to fetal abnormalities (Table.1).

3
Cont

• The safety of most drugs in pregnancy has not
  been firmly established as the effects may not be
  apparent for many years after birth. The past
  use of stilboesterol in pregnant women with
  threatened abortion has resulted in development
  of adenocarcinoma of vagina in female children in
  their teens and early 20s.
• Theres a possibility that the use of other drugs
  in pregnancy predisposes to more conditions e.g.
  DM or HTN. Such associations would not be easily
  recognized.

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Effects on fertilization implantation

• The principal mode of contraceptive action of
  progestogens is to prevent implantation, which
  normally occurs 2-3 weeks after fertilization.
  IUCD have similar effect. Damage to the embryo
  before implantation results in failure of
  implantation and is therefore unlikely to cause
  fetal abnormalities.

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Effects on fetal development

• The intra-uterine period between 2 weeks 3
  months is when the most serious abnormalities of
  fetal development can be caused by drugs. Its
  during this period that the major organs are
  being formed. In animal studies, even one dose
  of a drug administered at the critical time has
  been shown to have a major effect. The
  mechanisms of damage are not yet known, but the
  molecular basis of differentiation of embryonic
  cells is an intense area of basic research and is
  likely to provide new insights in the near
  future.
• Ampicillin and Cephalosporins are considered one
  of the safest drugs which can be used during
  pregnancy.

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Toxicity to the formed fetus

• During T2 T3 of pregnancy, adverse effects on
  fetus of drugs administered to the mother are
  generally an exaggeration of the effects seen in
  the adult. Exceptions to this rule are the
  damage to tissues which are still developing e.g.
  teeth bones by Tetracycline, and the impairment
  of brain development by Coumarin anticoagulant.
• Particular care must be taken with drugs given
  shortly before delivery. Analgesics, e.g.
  Meperidine (Pethidine), and tranquillizers e.g.
  (Benzodiazepines) may severely impair neonatal
  respiration. In addition, the newborn lacks many
  enzymes necessary for the efficient metabolism of
  drugs.

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Breastfeeding

• Although most drugs can be detected in breast
  milk, the dose administered to the infant is
  generally low. This is because, unless theres
  concentration of drug by breast tissue, the
  concentration of milk tends to be similar to that
  of the maternal plasma. Clearly in this case the
  final concentration in the infants plasma is
  likely to be much less than that in the mothers.
• Examples of safe drugs during breastfeeding
  include Penicillins, Aminoglycosides, and
  Cephalosporins.

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Cont

• Some drugs which cause problems via
  breastfeeding Carbimazole (may affect infant
  thyroid function) and Tetracyclines (also
  excreted in milk).
• As with pregnancy, its important to avoid all
  drugs in nursing mother unless theres a
  compelling need. A list of drugs excreted in
  breast milk and known to have problems is given
  in an appendix to the British National Formulary
  (BNF).
• Examples include Chloramphenicol (BM
  suppression), Sulfonamides (hemolysis with G6PD
  deficiency), Nitrofurantoin (hemolysis with G6PD
  deficiency), Tetracycline (stains teeth bones),
  Lithium, anti-neoplastic and immunosuppressants,
  and psychotropic agents.

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MCQs

• What may Diazepam cause if taken late in
  pregnancy?
• Hypotension.
• Hyper-ventilation.
• Bradycardia.
• Hypoglycemia.
• Which of the following drugs does not cross
  placenta?
• Succinyl-choline.
• N2O.
• Morphine.
• Meperidine (Pethidine).
• Diazepam.

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Matching

• Match the following medications effect during
  pregnancy with the appropriate medication.
• Tetracycline.
• Nitrofurantoin.
• Sulfas.
• Streptomycins.
• Chloramphenicol.
• Is excreted after binding, utilizing glucuronyl
  transferase.
• May cause aplastic anemia.
• Ototoxic.
• Discolors decidual teeth.