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August 9th, 2017 
admin The pharmacology of levothyroxine and propylthiuracil is outlined in the table below
| Components of Drug Therapy | Hypothyroidismlevothyroxine (Synthroid) | Hyperthyroidismpropylthiuracil (PTU) |
| Drug Dosage | 1.7 mcg/kg/day. | 300mg initial dose100-150 maintenance dose |
| Action | Supplemental therapyInhibits TSH | Inhibits synthesis of thyroid hormones |
| Onset of Action | Immediately | Immediately |
| Peak of Action | Peak concentration occurs in 1 hour. | 1 hour. |
| Duration of Action | 24 hours | 6-15 hours |
| Serum Half Life | 6-7 days | 1 hour |
| Absorption | 40 – 80%. Absorption increased by fasting | Readily absorbed 50-80 % from GIT. |
| Metabolism | in the liver | In the liver. |
| Excretion | Kidneys and in feaces. | 35% excreted in urine |
| Contraindications | Myocardial infarction, thyrotoxicosis and adrenal insufficiency | hypersensitivity to the drug |
| Precautions | Careful dosage is important. | report any symptom of hepatic dysfunction |
| Adverse Effects | Dysphoria, raised appetite, palpitation,weight loss and fatigue | Liver injury, aplastic anaemia, kidney injury and bleeding |
| Drug to Drug Interactions. | Glucocorticoids. NP should reduce their dosage.Levothyroxine increases anticoagulation activity.
More antidiabetics requirement. Diabetics should be closely monitored. Concurrent use with ketamine may cause hypertension. Action of sympathomometics may be exercabated. |
Increases activity of anticoagulants. monitoring of INR is requiredBeta blocker agent. Reduce the dose of the beta blockers
Increases the serum digitalis. Reduce the amount of the digitalis. Decreases theophiline clearance hence the dose should be reduced.
|
| Drug to Food Interactions | Food reduces absorption of the drug e g cotton seed meal. | Food reduces absorption |
| Drug to Herb Interactions | Herbal drugs reduce the absorption of the drug | Herbal drugs reduces absorption of the drug |
| Patient Education | Correct dosing and side effect reporting. | Right dosing and adverse effect to report. |
| Monitoring of Therapy | Monitoring of blood pressure and sugar | Monitoring of blood pressure and blood sugar. |
References
Woo,T., &Wynne, A. (2012). Pharmacotherapeutics for the nurse practitioner prescribers.Philadelphia: F.A. Davis.
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