Inclusion Criteria

INCLUSION CRITERIA:

1. Subject has signed the informed consent document;

2. Subject is greater than or equal to 18 years of age;

3. Subjects diagnosed with thyroid cancer participating in protocol 77DK0096;

4. Subjects receiving THST with levothyroxine;

5. Serum TSH less than 0.4 mIU/L while on THST, and more than 20 mIU/L while off THST.

EXCLUSION CRITERIA:

Subject is pregnant, currently breast-feeding, practicing birth control with hormonal
contraceptives, or is on hormone replacement therapy (HRT).

Subject is a smoker.

Subject has a confounding medical illness (es) that in the judgement of the investigators
would pose an added risk for the subject (e.g. severe respiratory disease).

Subject has a history of substance abuse within the past 5 years or drug or alcohol use,
that may affect enzyme levels and function.

Caffeine or caffeine-containing beverages and chocolate bars consumption within 48 hours
of scheduled caffeine administration for CYP1A2 phenotyping; scheduled omeprazole
administration during or within 14 days of the study; scheduled dextromethorphan
administration during or within 30 days of study; scheduled fexofenadine administration
during or within 7 days of the study.

AST or ALT greater than or equal to 2 times the upper normal reference limit.

Concurrent administration of known CYP and/or P-gp inducers (barbiturates, phenytoin,
carbamazepine, rifampicin) and inhibitors (amiodarone, atorvastatin, chloroquine,
cimetidine, co-trimoxazole, cyclosporine, diltazem, erythromycin, fluoxetine fluvoxamine,
isoniazid, itrakonazole, ketokonazole, metronidazole, mexiletine, nefazadone, norfloxacin,
verapamil) or use of any alternative/complementary therapies for at least 30 days prior to
study or during the study. Non-herbal vitamin and mineral preparations will be allowed.

Inability to obtain venous access for sample collection, or basal hemoglobin of equal or
less than 10 g/dl.

Patients receiving scheduled therapy with alprazolam, triazolam, clonazepam, diazepam,
lorazepam, oxazepam, temazepam or chlorodiazepoxide, during or within 30 days of study.

Patients consuming grapefruit products (juice or the fresh fruit), apple and orange juice
during or within 72 hrs of study.

History of intolerance to caffiene, omeprazole, dextromethorphan, midazolam or
fexofenadine.

The presence of persistent diarrhea or malabsorption syndromes that would interfere with
the patient's ability to adequately absorb drugs; and/or

Patients receiving monoamine oxidase inhibitors (MAOIs) such as phenelzine,
tranylcypromine, and isocarboxazid.

Patients with a history of cheloids formation.