Mayo Test Catalog, (Sorted By Test Name) - Mayo Medical ...

TIAG
82524
mcg/dL) -Normal TBG of 20.1 mcg/dL (normal=12-26 mcg/mL) The thyroxine-binding protein
electrophoresis assay identified that of the saturating dose of (125)I-T4: -52% was bound to albumin
(normal 12%-34%) -36% was bound to thyroxine-binding prealbumin (normal 49%-70%) -13% was
bound to TBG (normal 10%-25%)
Reference Values:
THYROXINE-BINDING PROTEIN ELECTROPHORESIS
10.3-24.9 mcg T4/dL bound to TBG
11.5-34.1 mcg T4/dL bound to albumin
48.8-70.4 mcg T4/dL bound to prealbumin
Other protein binders: normally not present
Thyroxine-binding globulin values may be elevated in females taking estrogens and by pregnancy.
THYROXINE, TOTAL
> or =12 months: 5.0-12.5 mcg/dL
Reference values have not been established for patients that are 95% absorbed, with oral bioavailability of about 90%. Tiagabine pharmacokinetics are linear over the
typical dose range of 2 to 24 mg. Steady-state is achieved within 2 days. Tiagabine is 96% bound to
human plasma proteins, mainly to serum albumin and alpha-1-acid glycoprotein. Co-administration with
valproate reduces protein binding to 94%, increasing the free fraction of tiagabine by 40%.(3,6) Based on
in vitro data, tiagabine is likely to be metabolized by the 3A isoform subfamily of hepatic cytochrome
P450 (CYP 3A), although contributions to the metabolism from CYP 1A2, CYP 2D06, or CYP 2C19
have not been excluded.(3)
Useful For: This test is used for monitoring tiagabine therapy. Because tiagabine has a wide
therapeutic index and dose-dependent toxicity, routine drug monitoring is not indicated in all patients.
Drug monitoring is indicated when initiating concomitant therapy with antiepileptic drug that induce
hepatic enzymes and when the patient does not respond to treatment to ascertain whether treatment failure
is due to noncompliance or nonresponse to the drug.
Interpretation: Trough tiagabine serum concentrations are in the range of 5 to 35 ng/mL in most
patients receiving therapeutic doses. Tiagabine serum concentration is proportional to dose.(2,8) A single
4-mg dose administered to a child produced peak serum concentration in the range of 52 to 108 ng/mL.(5)
At steady-state, an adult receiving 40 mg per day is expected to have peak serum concentration in the
range of 110 to 260 ng/mL, and an adult receiving 80 mg per day is expected to have peak serum
concentration in the range of 220 to 520 ng/mL. Serum concentrations >800 ng/mL indicates excessive
dosing associated with adverse effects such as asthenia, ataxia, difficulty concentrating, and depression. In
healthy adults administered tiagabine, steady-state peak serum concentrations within 1 hour of dosing are
typically in the following ranges:(2) -Peak serum concentration (4 mg q.i.d.): 36 to 92 ng/mL -Peak serum
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