Prescribing in Pregnancy Flashcards by Arya Nedungadi

At what gestation age do most women do their first scan?

12 weeks

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Approach to treating pregnant women

Consider non drug alternatives

physio instead of NSAID
CBT instead of anti-depressant

Prescribe if benefit > risk

Most drugs are not licensed for use in pregnancy
- prescribe out with license

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What are the most commonly used drugs during pregnancy?

Painkillers ~12%
Antibiotics ~11%
Antacids ~8%
(Also folic acid and iron)

Remember self-medication

NSAID
St John’s wort - antidepressant
Other herbal preparations

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Which drugs cross placenta?

Most drugs cross placenta

Except large molecular weight
ex. Heparin

Small, lipid-soluble drugs
- Cross more quickly

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Absorption and Pregnancy

Affected by morning sickness

Oral drugs come straight back up

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Distribution and pregnancy

Increased plasma volume and fat stores
- Volume of distribution increases

Decreased protein binding
- Increased free drug

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Metabolism and pregnancy

Increased liver metabolis of some drugs ex. phenytoin

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Elimination and pregnancy

Increased in renally excreted drugs

- Increased GFR

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Drugs to be monitored during pregnancy

Lithium
Digoxin

check concentrations and alter dose during pregnancy and after delivery

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Pharmacodynmics and pregnancy

No significant changes

Pregnant women may be more sensitive to some drugs
hypotension with antihypertensives in 2nd trimester

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Prescribing during pre-conception

Any woman of childbearing age

Are they pregnant?
Are they planning a pregnancy?
Could they become pregnant?

Folic acid 400mcg daily for 3 months prior and first 3 months of pregnancy

Counselling re chronic conditions
- Epilepsy, diabetes, hypertension

Optimise therapy to choose safest drugs

Review whether drug therapy necessary

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Why should drugs be avoided at all cost during 1st trimester (unless maternal benefit > foetal risk)?

Risk of early miscarriage

Organogenesis of foetus

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Which period has the greatest teratogenic risk?

4th to 11th week

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List the teratogenic drugs

ACE inhibitors/ARB - Renal hypoplasia

Androgens- Virilisation of female foetus

Anti-epileptics - Cardiac, facial, limb, neural tube defects

Cytotoxics - Multiple defects, abortion

Lithium- Cardiovascular defects

Methotrexate - Skeletal defects

Retinoids - Ear, cardiovascular, skeletal defects

Warfarin- Limb and facial defects

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2nd + 3rd trimesters

Growth of foetus
Functional development
- Intellectual impairment
- Behavioural abnormalities
Toxic effects on foetal tissue

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Valproate and pregnancy

Contraindicated

Need to sign a document to declare they have been educated on the effects if they require this treatmet

Around term

Adverse effects on labour

Progress of labour
Adaptation of foetal circulation
- Premature closure of ductus arteriosus
Suppression of foetal systems
- Opiates – respiratory depression
Bleeding
- Warfarin

Adverse effects on baby after delivery

Withdrawal syndrome
- opiates, SSRI
Sedation

Chronic conditions and pregnancy

Need to discuss risk/benefit balance with patient
- Ideally pre-conception
Compliance with medication may be poor

Anti-epileptic treatment to avoid during pregnancy

Valproate

Phenytoin

Why do women need to continue anti-epileptic treatment during pregnancy?

Anti-epileptics increase risk of congenital malformations

20-30% risk if on 4 drugs
Monotherapy preferred

96% of babies born to women taking anti-epileptics will not have major congenital malformations

Benefits of treatment outweigh risks in most cases

Managing diabetic pregnant mothers

Insulin thought to be safe

Requirements change during pregnancy

Poor control increases risk of congenital malformations and intra-uterine death

Sulfonylureas not safe
- Convert to insulin

Managing BP during pregnancy

BP falls during 2nd trimester

If need to treat, use one of:

Labetalol
Methyldopa (avoid in mothres prone to depression)
(Nifedipine MR)

Avoid ACE inhibitors / ARB

Beta blockers may inhibit foetal growth in late pregnancy

Common acute problems and their management

Nausea and vomiting
- Cyclizine safest

UTI – follow local guidelines
Nitrofurantoin, cefalexin, (3rd trimester – trimethoprim)

Pain
- Paracetamol

Heartburn
- Antacids

Pregnant women are at increased risk for which CV condition?

10 fold risk of VTE
Leading cause of maternal death in pregnancy
All pregnant women should be assessed for risk

Prevention of VTE in pregnancy

Those with significant risk factors should receive thromboprophylaxis with LMWH - 2 or more risk factors eg obesity, age>35yrs, smoking, para >3, previous DVT, Caesarean delivery - at delivery and up to 7 days post-partum

Treatment of venous thromboembolism in pregnancy

Treat suspected or established DVT or PE with therapeutic dose LMWH - Avoid warfarin in early pregnancy - Teratogenic Avoid warfarin in late pregnancy - Risk of haemorrhage during delivery

Breastfeeding and medication

Most drugs enter breast milk, especially - Small molecules - Fat soluble (lipophilic) drugs Few enter in sufficient quantities to cause a problem Some drugs are actively concentrated in breast milk Eg phenobarbitone – suckling difficulties

What are the feeding patterns and how it affects the amount of drugs in breastmilk?

Foremilk – protein rich Hindmilk – higher fat content Longer feeds, higher amounts of fat soluble drugs in milk

Drugs contraindicated in breastfeeding

Amiodarone – neonatal hypothyroidism Cytotoxics – bone marrow suppression Benzodiazepines- drowsiness Bromocriptine – suppresses lactation

Guidelines for prescribing during pregnancy

1. BNF | 2. UK Drugs in Lactation Advisory Service (UKDILAS)

``` Case: Essential hypertension BP 164/102mmHg after lifestyle measures - No regular medication - Planning pregnancy in next year ``` Worried about whether she will have problems due to her BP if she gets pregnant How do you manage this pateint?

Counsel about risks and benefits of treating hypertension in pregnancy Encourage further lifestyle improvement Options: - No treatment but monitor BP closely in pregnancy especially after 2nd trimester - Start treatment with drug thought to be safe in pregnancy - Labetalol or methyldopa - (Nifedipine MR)

Which antibiotic given during pregnancy or in early childhood can cause staining of teeth?

Tetracycline

Which ‘drug’ taken in excess in early pregnancy could cause deformed facial features?

Alcohol - Fetal alcohol syndrome

Which antiepileptic drug is particularly associated with cleft palate?

Phenytoin

Which drug taken during pregnancy can cause vaginal carcinoma in female offspring?

Diethylstilbesterol

Which antiepileptic drug is particularly associated with spina bifida and anencephaly

Valproate

What is the danger of epilepsy during pregnancy?

Incidence of congenital malformations higher in untreated women with epilepsy than women without epilepsy

Why are there increased seizures in 10% of women during pregnancy?

Non-compliance Changes in plasma concentrations of drugs - Persistent vomiting - Increased clearance

What is the consequence of frequent seizures during pregnancy?

``` lower verbal IQ in child hypoxia bradycardia antenatal death maternal death ```