Drug interactions & teratogenic meds

Question 1

What always needs to be specifically asked about when taking drug hx

Answer 1

prescription drugs
non prescription drugs
recreational drugs
herbal preparations
dietary supplements

Question 2

What methods can be used for people on enzyme inducers
What about EC

Answer 2

DMPA injection
LNG-IUS
Cu-IUD
Condoms

EC - copper coil, or double does LNG-EC

Question 3

Topiramate - any action needed

Answer 3

An AED - has enzyme inducing activity at higher but not at lowr doses. Topiramate is a teratogen so it is suggested to err on side of caution and use methods not affected by enzyme inducers.

Question 4

Effect on thyroid function?

Answer 4

HRT and combined oral contraception can increase requirement for thyroxine. It is suggested that TFTs are checked after 6w of commencing.

Question 5

Good practice points for those on lamotrigine

Answer 5

• Oestrogen REDUCES serum levels of lamotrigine which could = reduced seizure control. Conversely there could be risk of lamotrigine toxicity during any HFI!
• Desogestrel may INCREASE exposure to lamotrigine in some individuals
• Lamotrigine reduces exposure to progestogens

1. So if use of CHC is unavoidable - may need to increase lamotrigine and monitor serum levels. Do not use HFI.
2. Those on prog only contraceptions should be vigilant for signs of lamotrigine toxicity (dizziness, ataxia, diplopia). Consider monitoring serum levels when prog stopped.
3. When starting or stopping hormones, do it with a neurologist / psychiatrist or GP so dose adjustments canbe made

Depot, IUD/IUS not expected to be affected.

Question 6

What drugs can effect EC-UPA

Answer 6

small risk that drugs such as omeprazole that increase gastric ph can reduce exposure of EC-UPA

If cant avoid taking PPI then advise cu-IUD > LNG > UPA

Question 7

Which drugs induce enzyme hepatic activity?

Answer 7

Carbamazepine
Eslicarbazepine acetate
Nevirapine
Oxcarbazepine
Phenytoin
Phenobarbital
Primidone
Ritonavir
St John’s Wort
Topiramate
RIFABUTIN [abx]
RIFAMPICIN [abx]
griseofulvin

Question 8

Advice for women on CHC patches, rings, or tablets who need enzyme inducers should be advised:

Answer 8

switch to:
- depo provera or norethisterone depo or
- IUS, cu-IUD

or if that is unacceptable:
- can increase dose of ethinylestradiol to 50mcg and encourage tricycling of packs with short 4d break, can increase to 70mcg. Cant use patches or rings.

if short course of enzyme inducer could continue contracep and use condoms

NB this does not apply to rifabutin or rifampicin as they are such potent enzyme inducers. Alternative methods should always be suggested

–> Continue use of alternative method for 4 weeks after stopping enzyme inducer

Question 9

Interactions progestogen-only contraceptives

Answer 9

ORAL: interact like combined orals - use alternative
PARENTERAL: IM norethisterone and SC medroxyprogesterone acetate = not affected and they may be continued as normal
Implant - may have interactions - use alternative methods

Question 10

Name 5 teratogenic drugs

Answer 10

Benzos e.g alprazolam, loraz
BBs e.g. atenolol
Statins e.g atorvastatin
Antipsychotics / AEDs e.g. carbamazepine, valproate
ARVs eg efavirenz
ACEis & ARBS eg enalapril / losartan
Antifungals eg fluconazole (can use topical or pessaries)
Psych: Lithium, paroxetine
Methotrexate
Warfarin
Tetracyclines eg doxycycline
Spiro