Week 5: Pharmacotherapy for Endocrine Disorders, Chapters 48-49
HYPOTHYROIDISM
Radioactive iodine adverse effects
The effect of treatment is delayed, taking several months to reach its
maximum.
Treatment is associated with a significant incidence of delayed
hypothyroidism. Hypothyroidism results from excessive dosage and occurs in
up to 90% of patients within the first year after exposure.
Adverse Effects: hypothyroidism, radiation sickness, bone marrow
suppression, sore throat/sialadenitis, fetal harm (destroys fetal thyroid)
Methimazole indication and MOA
Suppresses synthesis of thyroid hormones
INDICATIONS: First-line drug for hyperthyroidism.
Graves’ disease- used as sole form of therapy.
Adjunct to radiation therapy until the effects of radiation become
manifest.
Suppresses thyroid hormone synthesis in preparation for thyroid
gland surgery (subtotal thyroidectomy)
Patients with thyrotoxic crisis
MOA: Blocking synthesis of thyroid hormones. Two mechanisms are
involved.
1) Prevents the oxidation of iodide, thereby inhibiting
incorporation of iodine into tyrosine.
2) Prevents iodinated tyrosines from coupling.
*Both effects result from inhibiting peroxidase, the enzyme that
catalyzes both reactions.
Levothyroxine – T4
EDUCATION: Taken on an empty stomach in the morning at least 30-60
minutes before breakfast. Separate reactive drugs by 4 hours.
POPULATION CONSIDERATIONS:
Caution in patients with cardiovascular disease- start with lower
doses in older adult patients.
MONITORING:
, DRUG INTERACTIONS: Absorption of Levo can be reduced by
histamine H2 receptor blockers, PPIs, Sucralfate/Carafate,
Cholestyramine/Questran, Colestipol/Colestid, aluminum-containing
antacids (Maalox/Mylanta), calcium supplements (Tums), Iron
supplements, magnesium salts, or orlistat.
Absorption can be accelerated by coadministration with levothyroxine,
phenytoin, carbamazepine (Tegretol, Carbatrol), rifampin (Rifadin),
sertraline (Zoloft), and phenobarbital.
Warfarin: accelerates the degradation of vitamin K-dependent clotting
factors.
Catecholamines: Thyroid hormones increase cardiac responsiveness to
catecholamines, thereby increasing the risk for catecholamine-induced
dysrhythmias.
Insulin/digoxin: when converting patients from a hypothyroid to an
euthyroid state, dosages of insulin/digoxin may need to be increased.
DOSING: Levothyroxine is always administered by mouth. IV
administration is used for myxedema coma and for patients who
cannot take Levo PO for an extended time.
ADJUSTMENTS: Based on TSH levels
TSH high- increase dose, TSH low-decrease dose
Hyperthyroidism treatment considerations
Pioglitazone contraindications
Gemfibrozil drug interactions
Long-acting insulins
Insulin glargine (u-100)- Lantus- Onset 70 minutes, no peak, duration 18-24
hrs.
Insulin detemir- Levemir- Onset 60-120 minutes, peak 12-24 hrs., duration
varies
Insulin glargine administration
HYPOTHYROIDISM
Radioactive iodine adverse effects
The effect of treatment is delayed, taking several months to reach its
maximum.
Treatment is associated with a significant incidence of delayed
hypothyroidism. Hypothyroidism results from excessive dosage and occurs in
up to 90% of patients within the first year after exposure.
Adverse Effects: hypothyroidism, radiation sickness, bone marrow
suppression, sore throat/sialadenitis, fetal harm (destroys fetal thyroid)
Methimazole indication and MOA
Suppresses synthesis of thyroid hormones
INDICATIONS: First-line drug for hyperthyroidism.
Graves’ disease- used as sole form of therapy.
Adjunct to radiation therapy until the effects of radiation become
manifest.
Suppresses thyroid hormone synthesis in preparation for thyroid
gland surgery (subtotal thyroidectomy)
Patients with thyrotoxic crisis
MOA: Blocking synthesis of thyroid hormones. Two mechanisms are
involved.
1) Prevents the oxidation of iodide, thereby inhibiting
incorporation of iodine into tyrosine.
2) Prevents iodinated tyrosines from coupling.
*Both effects result from inhibiting peroxidase, the enzyme that
catalyzes both reactions.
Levothyroxine – T4
EDUCATION: Taken on an empty stomach in the morning at least 30-60
minutes before breakfast. Separate reactive drugs by 4 hours.
POPULATION CONSIDERATIONS:
Caution in patients with cardiovascular disease- start with lower
doses in older adult patients.
MONITORING:
, DRUG INTERACTIONS: Absorption of Levo can be reduced by
histamine H2 receptor blockers, PPIs, Sucralfate/Carafate,
Cholestyramine/Questran, Colestipol/Colestid, aluminum-containing
antacids (Maalox/Mylanta), calcium supplements (Tums), Iron
supplements, magnesium salts, or orlistat.
Absorption can be accelerated by coadministration with levothyroxine,
phenytoin, carbamazepine (Tegretol, Carbatrol), rifampin (Rifadin),
sertraline (Zoloft), and phenobarbital.
Warfarin: accelerates the degradation of vitamin K-dependent clotting
factors.
Catecholamines: Thyroid hormones increase cardiac responsiveness to
catecholamines, thereby increasing the risk for catecholamine-induced
dysrhythmias.
Insulin/digoxin: when converting patients from a hypothyroid to an
euthyroid state, dosages of insulin/digoxin may need to be increased.
DOSING: Levothyroxine is always administered by mouth. IV
administration is used for myxedema coma and for patients who
cannot take Levo PO for an extended time.
ADJUSTMENTS: Based on TSH levels
TSH high- increase dose, TSH low-decrease dose
Hyperthyroidism treatment considerations
Pioglitazone contraindications
Gemfibrozil drug interactions
Long-acting insulins
Insulin glargine (u-100)- Lantus- Onset 70 minutes, no peak, duration 18-24
hrs.
Insulin detemir- Levemir- Onset 60-120 minutes, peak 12-24 hrs., duration
varies
Insulin glargine administration
