Pharmacology in Pregnancy and Breast Feeding

Question 1

What are some ways that pregnancy can affect the absorption of drugs?

Answer 1

Orally - morning sickness may reduce absorption, there is also a decrease in gastric emptying and gut motility

IM route - blood flow often increases during pregnancy,, which would increase IM absorption

Inhalation - increased CO and decreased tidal volume can cause increases in absorption of inhaled drugs

Question 2

How can pregnancy affect the distribution of a drug?

Answer 2

Increased plasma volume and fat causes increased volume of distribution

Greater dilution of plasma during pregnancy causes reduced plasma protein concentration and therefore higher concentration of free drug

Question 3

How does pregnancy affect the excretion of drugs?

Answer 3

GFR is increased in pregnancy by about 50% leading to increased excretion of many drugs

May cause need for increased dose

Question 4

What are some factors affecting the ability of a drug to cross the placenta?

Answer 4

Molecular weight - smaller drugs cross more easily

Polarity - unionised drugs cross more easily

Lipid solubility - lipid soluble drugs will cross

Question 5

What are some of the important principles of drug prescribing in pregnancy?

Answer 5

• Try non-pharmacological treatments first
• Always use the drug with safest track record
• Use the lowest effective dose & use drug for shortest possible time
• Avoid drugs within the first 10 weeks of pregnancy if possible

Question 6

When does the highest risk of teratogenicity occur during pregnancy?

Answer 6

During organogenesis (3-8 weeks)

Question 7

What is folate antagonism? What are the common mechanisms by which drugs antagonize folate? What defects occur as a result of folate antagonism?

Answer 7

Antagonism of the metabolism of folate - which is key for DNA formation and new cell production

• Block the conversion of folate to THF via irreversibly binding the enzyme
• Block other enzymes in the pathway

Results in neural tube, oro-facial or limb defects

Question 8

What are some examples of complications associated with neural crest cell disruption?

Answer 8

Aortic arch abnormalities

Ventricular septal defects

Craniofacial malformations

Oesophageal atresia

Pharyngeal gland abnormalities

Question 9

What is fetotoxicity? Examples of commonly implicated drugs?

Answer 9

Toxic effect on the fetus later in pregnancy

Can cause effects like growth retardation, structural malformations, fetal death, functional impairment

ACE-inhibitors, ARB’s

Question 10

What are some examples of drug classes that should be avoided during pregnancy?

Answer 10

• Anticonvulsants
• Anticoagulants
• Antihypertensive agents
• NSAIDs
• Alcohol
• Retinoids

Question 11

After the child has been born is there still risk of the child being exposed to drugs the mother is taking?

Answer 11

yes, through lactation

Almost all drugs the mother is taking will to an extent be present in her breast milk

Question 12

What are some steps that can be taken to reduce the exposure of the child to drugs from the mothers lactation?

Answer 12

• Take drugs immediately after feeding baby
• Avoid drugs with long half life or active metabolites
• Use drugs that are highly protein bound (will be less in lipid component of breastmilk)
• Caution if baby is ill or premature

Question 13

What are some drugs that need to be avoided during breastfeeding?

Answer 13

• Cytotoxics
• Immunosuppressants
• Anti-convulsants (mostly)
• Drugs of abuse (hard drugs?)
• Amiodarone
• Lithium
• Radio-iodine

Question 14

Which patients should pregnancy be kept in mind when prescribing?

Answer 14

Any woman of child bearing age