Innovative Strategies For Optimizing Thyroid Function - Free CE ...

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Page 6Innovative Strategies for Optimizing Thyroid Function© 2010 Pharmaceutical Education Consultants, Inc. unless otherwise noted. All rights reserved.Reproduction in whole or in part without permission is prohibited.CLINICAL PHARMACOLOGY OVERVIEWT3 & T4• Profound influence on every organ system in thebody including development of the centralnervous system.• Normal thyroid gland: 200 mcg of T4/gm of gland,15mcg of T3/gm.• In circulation, 80% of peripheral T3 derived frommonodeiodination of T4. rT3 (calorigenicallyinactive) also formed from this process.CLINICAL PHARMACOLOGY OVERVIEWT3 & T4• T3 levels low in fetus/newborn, old age, chronicstarvation, hepatic cirrhosis, renal failure, surgicalstress, chronic illness.• Only partial absorption of T4..in GI tract can belimited and is dependent on healthy intestinal flora,proper delivery vehicle (like albumin), andavoidance of foods/drugs/supplements that blockabsorption.• T3 is almost totally absorbed (95% in four hours)CLINICAL PHARMACOLOGY OVERVIEWT3 & T4• Over 99% of circulating hormones bound to TBg,TBPA, and TBa.• T4 has higher affinity for TBg and TBPA as comparedto T3• May explain higher serum levels and longer half lifefor T4.LEVOTHYROXINE (T4)• Eutirox, Tirosint, Levoxyl andSynthroid• 1/2 life approx: 6.7 days• ~100% bioavailable• Metabolized mainly in liver,kidney, brains and muscles• Prohormone-requiresconversion in cell to active T3• Takes up to 10 days to seechange in activity
Page 7Innovative Strategies for Optimizing Thyroid Function© 2010 Pharmaceutical Education Consultants, Inc. unless otherwise noted. All rights reserved.Reproduction in whole or in part without permission is prohibited.LEVOTHYROXINE (T4)Average doses:• Adults: 1-1 1/2 tablet (1.7microg/kg body weight )per day• Children: may requiremore (up to 4 microg/kgbody weight) per day• Adults over 50 oryounger patients with hxof cardiac disease: .025-.05mg qd, check after 6-8weeks.• Best administered on emptystomach, in morning, at least 2hours prior to meal.• Adverse interactions: e.g. iron,soy, bran, calcium, coffee,grapefruit juice, cholestyramine,aluminum or Mg containingantacids can slow absorptionsignificantly.LEVOTHYROXINE (T4)LEVOTHYROXINE (T4)Other drugs, esp. theanticonvulsants phenytoinand carbamazepine andthe antituberculous agentrifampin, may acceleratelevothyroxine metabolism,necessitating higherlevothyroxine doses.LEVOTHYROXINE (T4)• Lithium, TCA’s can causetoxicity.• Overdose symptoms(hyperthyroid…tachycardianervousness, excessivehunger, etc.) may notappear for 6 hours to 11days.
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