Drug use in pregnancy

What are the stages if pregnancy? and how long do they last?

1st trimester 1-12 weeks

2nd trimester 13-27 weeks

3rd trimester 28-40 weeks

What are the stages of development in pregnancy? and how long do they last?

Pre-embryonic 0-17 days, implantation of fertilised ovum

Embryonic 18-56 days, major organ systems development

Foetal 8-38 weeks, maturation and development and growth

What are some issues with drug use in pregnancy?

Women may take medicines unaware that they’re pregnant

Want to be pregnant but require essential treatment for chronic Medical conditions

How does absorption change in pregnancy?

Reduced gut motility

Increased skin blood circulation

Increased lung function

How does distribution change during pregancy?

Increase plasma volume

Increased fat disposition

Increase body water

Reduced plasma proteins

How does metabolism change during pregnancy?

Enzyme induction increased

Affects on drugs difficult to predict

Methadone may need higher maintenance doses

Theophylline may need lower doses

Monitor drugs with narrow therapeutic range

How does elimination change during pregnancy?

Increased glomerular filtration

Increased penicillin and digoxin elimination

What are teartogens?

An agent that directly or indirectly causes structural or functional abnormalities in the foetus or child after birth

What are the principles of teratogenisis?

Timing of exposure, differences in susceptibility, dose-response relationships

How does timing of exposure in each stage of pregnancy affect?

Pre-embryonic: all or nothing principle

Embryonic phase: Greatest risk of major birth defects

Foetal phase: Less susceptible to toxic effects but some structural/functional abnormalities and growth retardation

What are the dose response relationoships in teratogenisis?

Teratogenic effects are dose dependent

dose response curve is steep

cumulative exposure of drug to foetus is important

What is placental drug transfer?

Most drugs cross the placenta except high molecular weight drugs

Lipid soluble, unionized drugs cross the placenta more easily than polar, ionized, hydrophilic drugs

Pharmacological effects can be both direct and indirect

What are drugs for foetal disorders?

Drugs may be administered to pregnant women to treat their foetal disorders

What drugs taken by men can cause adverse effects?

Finastride

Griseofulvin

What issues can arise from maternal drug use during latter stages of pregnancy?

Allergic drug reactions - sensitized in uterus

Reduced capacity for drug accumulation

Withdrawal effects - morphine oral solutions used to wear babies off methadone

What are the key principles for drug use in pregnancy?

Consider non drug treatment

Only use drugs when necessary

Do not use teratogens

Know what questions to ask

Avoid new drugs

Avoid poly pharmacy

Use lowest effective dose for minimum time

What pre conception advice could be given?

Avoid all drugs, alcohol, smoking, VITAMIN A products

Use folic acid

What questions to ask to pregnant woman?

What drug?

Indication?

Frequency?

Route?

Duration?

Stage of pregnancy?

Previous pregnancy?

Family history?