Which antiepileptic drugs affect the metabolism of the Pill (oral contraception) and what are the implications of this? What drugs are safe to give with the Pill?

Phenobarbitone

carbamazepine

Phenytoin

Topiramate

These drugs interfere with the metabolism of oral contraceptives due to protein binding, enzyme induction and enzyme inhibition. Enzyme-inducing antiepileptic drugs interfere with the women using oral contraception and these drugs reduce the effectiveness of contraception and can also lead to increased risk of fetal abnormalities in an unborn baby. Enzymes commonly induced are usually the Cytochrome P450. Carbamazepine also induces its own metabolism and we call it auto-induction.

Remedies that are safe to use with the pill are:

Valproate

Lamotrigine

Gabapentin

Leviteracetam

How is the kinetics of these drugs affected by age (from neonates to the elderly)?

There is individual variation in the absorption and metabolism of these drugs. Most drugs undergo first-order metabolism in the liver and are then in other words unsaturated, which means that as the dose of the drug increases, so can the enzymes involved. With the exception of Phenytoin, which then undergoes saturated metabolism (“zero-order”) at higher doses. Neonates generally undergo slower metabolism. Babies and children undergo faster metabolism than adults, in other words it may seem that the dose for a child is higher than in adults but this is because the metabolism of these drugs takes place faster in infants and children. Elderly people should receive a lower dose because liver and kidney function are no longer optimal.

In which cases is plasma blood level monitoring indicated?

Because some of these drugs have a small therapeutic index, we need to be careful with interactions of other drugs.

Where protein binding occurs, it is essential to monitor these plasma levels. However, there are some drugs that have no effect on the plasma levels in the body (these drugs have a relatively low protein binding capacity) and these include:

Gabapentin

Topiramate

Ethosuximide

Patients who have conditions such as chronic kidney failure, liver disease, hypoalbuminemia, people with burns (due to a lot of plasma lost leading to reduced albumin), pregnancy, malnutrition (not consuming enough protein in diet), displacing drugs (displaced seats of drugs) and age can also affect the amount of plasma proteins