SL22108-Prescribing in Pregnancy

CHALLENGES IN PREGNANCY

Consider mum ad fetus

entity as one

Pregnancy= childbearing potential

prescribing questions

Is the drug safe?

Is the drug necessary?

Are there alternatives that are as effective/ safer?

Effect of pregnancy on drugs and drugs on pregnancy

Assess need for extra monitoring of mum and baby

OFFER PRE - PREGNANCY COUNSELLING

pregnancy prescribing website

UKTIS

contains drug monographs

pregnancy trimesters

Pregnancy is divided into three trimesters

1st is up to 13 weeks

2nd is 13-28 weeks

3rd is after 28 weeks

1st trimester

1^st trimester increase in blood volume but reduction in protein binding due to pregnancy steroids, therefore alteration of medications are required eg levothyroxine increase usually 25%.

teratogenic defects

vomiting in pregnancy

Risk of vomiting in pregnancy: slow transit time reduced or increased absorbtion, therefore repeat doses required.

Metabolism: activation of cytochrome p450 enzyme pathway: eg lamotrigine

which drugs should be avoided

uMETHOTREXATE

uRADIOACTIVE IODINE

u(LITHIUM)

uISORETINONIN

uSODIUM VALPROATE

uWARFARIN

which medicines and which trimester do they affect

Within 20 days after fertilisation

All-or-nothing effect (death or no effect)

Highly resistant to birth defects

3-8 weeks after fertilization

Possibly no effect

Miscarriage

Obvious birth defect

Permanent but subtle effect only evident in later life

Organ development, particularly vulnerable to birth defects

2^nd and 3^rd trimesters

Changes in growth and function of normally formed organs and tissue

Unlikely to cause obvious birth defect

Unknown long-term effects

Organ development complete

pre pregnancy

uOnly switch drugs in pregnancy if meds unsafe and suitable alternative

uDifferent drugs at varying gestations

recreational drugs

Nicotine

Alcohol

Drugs of addiction

pregnancy pharmacokinetics

Plasma levels change, reduced absorption, dilution, excretion

Increase drug concentrations

Hyperemesis

morning sickness

caused by

uCyclizine

uMetoclopromide

uprochlorperazine

uOndansetron

uSteroids

teratogenesis

1-2% of babies born with a congenital abnormality

If a teratogenic agent is taken during the period of embryogenesis (up to 8 weeks) the result will be an anatomical malformation

Later in pregnancy function will be affected

seizure control in pregnancy

carbamazepine is contraindicated in pregnancy

it is teratogenic

patient must be counselled before medication switch as it can be difficult to make a switch when patient has good seizure control

also may need to delay pregnancy

recommended to take 5mg folic acid as anti-epileptics are weak folate antagonists

describe the consequences of antiepileptic drugs on fetus

Neural tube defects

ulow-set ears

u  broad nasal bridge

u  irregular teeth

u  hypoplastic nails and digits

gabapentin and pregabalin

•Newer anti-epileptics eg lamotrigene, gabapentin do not appear to be so risky but not entirely risk free

patient must have pre-natal screening

Asthma in pregnancy

Risk of uncontrolled asthma far outweighs small risk of harm to fetus.

Sometimes a short course of oral steroids, prednisolone may be prescribed in exacerbations

Pregnancy & Asthma: Risks

Fetal growth restriction, preterm birth, neonatal hypoxia, increased perinatal mortality, pre-eclampsia, and complicated labor.

Pregnancy & Asthma: Management

Use inhalers as normal, including short- and long-acting beta-2 agonists and corticosteroids. Oral corticosteroids should be used for exacerbations if needed.

Pregnancy & Diabetes: Primary treatment

Insulin remains the primary drug for Type 1, Type 2, and uncontrolled gestational diabetes.

Pregnancy & Diabetes: Risks of hyperglycemia

Structural abnormalities (CVS: 37%, CNS: 20%, GUS: 14%), spontaneous miscarriage, stillbirth, macrosomia, neonatal hypoglycemia, and childhood obesity.

Pregnancy & Hypertension: Treatment threshold

Blood pressure ≥140/90 mmHg (target: <135/85 mmHg).

Pregnancy & Hypertension: Safe antihypertensives

Methyldopa, nifedipine, labetalol, and hydralazine.

labetalol first line

but be aware in asthmatics, vasoconstriction

beta blocker

in most severe cases where hypertension can’t be controlled labour may be induced at an appropriate gestational age

Pregnancy & Hypertension: Contraindicated antihypertensives

ACE inhibitors, diuretics, and ATII receptor blockers.

Pregnancy & Analgesia: Preferred pain management

Paracetamol is the safest option. NSAIDs should be avoided, especially in the third trimester after 20 weeks

Pregnancy & Analgesia: Risks of opioid use

Neonatal withdrawal syndrome and potential fetal harm.

if taken prolonged

preclampsia

Medical emergency

organ damage

Pregnancy & Mental Health: Considerations before prescribing

Risks vs. benefits, teratogenic potential, and whether the medication can be safely switched or discontinued.

Pregnancy & Mental Health: Contraindicated psychiatric drugs

Lithium, sodium valproate, and some antipsychotics due to risks of congenital abnormalities.