Epileptic Patients - The Need for Blood Tests

Today many forms of epilepsy in our pets can be successfully controlled by the use of anticonvulsant drugs. These are often needed for long periods of time, usually for life and can have side effects. Therefore it is prudent to monitor the pet carefully while on the medication. This helps to ensure:

• the drug is effective and
• there are no problems being caused by long term use of the drugs

What do these tests involve?

Monitoring involves a series of simple blood tests to measure the level of the anticonvulsive medication in the body. If the dose has to be changed for any reason follow up tests will be carried out to see if any further adjustment of dosage is needed. The aim of the tests is to achieve and maintain dose levels that fall between carefully specified levels called the therapeutic range. Experience has shown that if drug levels can be kept within this range, then the expectation is that maximal long term control of seizures will be achieved with minimal side effects.

Does this involve a lot of tests?

In the newly diagnosed patient frequent blood testing may be needed initially to ensure the dose is correct. Once this has been established and if the animal is stable and not fitting, testing usually is done every 3-6 months. The longer the pet is on the medication without complications the fewer tests will be needed. In many patients on long term anticonvulsant therapy annual testing may be all that is required.

How long does stabilisation on anticonvulsants take?

During the initial period of medication the blood levels of the anticonvulsant drug or drugs will gradually rise eventually reaching the so-called steady state (state of equilibrium). Stabilisation time varies with the individual animal and also the drug being used. In some cases this may take up to four months during which period more frequent tests may have to be performed. 

Are there any other blood tests required apart from those establishing the pet's drug levels?

Some anticonvulsants do have side effects. These can affect the liver and sometimes the bone marrow. As a result periodic blood testing is recommended to assess the effects of medication on the rest of the body. This usually involves a complete blood count (CBC) and biochemistry profile. Please see relevant handouts or contact us if you would like to discuss this.

Are any special preparations necessary prior to blood sampling?

It is important to follow our instructions closely regarding the timing of the doses. Medication should be regular and consistent. 

• This will ensure that the value reported on the blood tests is as accurate as possible.
• Some anticonvulsants, e.g. phenobarbitone, require sampling a specific time after administration of the medication. Therefore it is important that we know precisely when you are giving the tablets so that we can book the appointment accordingly.
• The general rules regarding blood testing apply. Ensure that your pet is as stress free as possible and it is a good idea to avoid any food for about four hours before the blood sample is collected.

While on anticonvulsant medication are there any signs I should note?

• It is most important to report any reactions, however mild, while on medication. This may indicate that the dose is not correct or that the frequency needs to be adjusted
• Signs of slight drowsiness or restlessness may occur initially as the pet adjusts to the effect of the medication.  
• Heavy drowsiness as well as staggering, lethargy or lack of energy, also vomiting or lack of appetite should be reported to us without delay. These are signs to indicate the level of medication is too high and further blood tests may be necessary.