Synonyms |
|
Sodium
valproate, Valproic acid, Epilim
|
Clinical
Indications |
|
Sodium
valproate is the drug of choice for treatment of myoclonic
seizures and generalised absence seizures.
|
|
Drug Kinetics |
|
Valproate
has a complex pharmacokinetic profile. It is strongly protein
bound to plasma proteins and this binding is concentration
dependent so that the free fraction rises (and hence the
apparent clearance) at higher concentrations (~ >50 mgl/L).
Free fatty acids displace valproate from binding sites and
clearance is different in fed and fasting states. This helps
explain the wide circadian variation and marked variations in
serum concentration (up to 100%) that can occur across the
dosage interval.
|
|
Request
Form |
|
Combined Pathology Blood form
(Yellow/Black or Blue for GP's).
Please state dosage on request form.
|
Availability |
|
Analysed by referral
laboratory if specific criteria met.
|
Specific
Criteria |
|
Most
evidence shows that serum monitoring is unnecessary in the
majority of patients on valproate therapy and is potentially
misleading. Occasionally, levels may be necessary
(requested by Consultant Psychiatrists) in establishing
whether dose can be increased in patients already receiving
high doses (>1500 mg/day). Also, in children under 20 kg
where dosage needs to be increased above 20 mg/kg. Requests
addressing compliance must be discussed with Consultant
Biochemist.
|
Patient
Preparation |
|
Patient
should be fasting and samples should be collected before next dose (trough)
|
Turnaround
Time |
|
2
weeks
|
Specimen |
|
Serum
|
Volume |
|
2 ml
|
Container |
|
Red
or pink top (plain) tube preferred. Yellow top (SST) tube
acceptable if sample separated within 12 hours.
|
Lab.
Handling |
|
Aliquot and store at 4C.
Samples
should not be used if left on gel for over 12 hours.
(SVAL & send; VAL & save)
|
Causes
for Rejection |
|
Unlabelled sample
|
Target
Range |
|
Target
ranges are difficult to define but a suggested range is 50 -
100 mg/L
|
Toxicity |
|
Symptoms
of neurotoxicity (nausea, vomiting, drowsiness) are
increasingly frequent as levels exceed 100 mg/L (700 umol/L)
|