Phenytoin Calcium carbonate

LM is a 65-year-old woman with AF, a seizure disorder, and latent tuberculosis infection. LM s medications include digoxin, rifampin, calcium carbonate, phenytoin, and warfarin. Which of the following drugs can interfere with the oral absorption of T4 ... 

Cholestyramine, calcium carbonate, sucralfate, aluminum hydroxide, ferrous sulfate, soybean formula, and dietary fiber supplements may impair the absorption of levothyroxine from the GI tract. Drugs that increase nondeiodinative T4 clearance include rifampin, carbamazepine, and possibly phenytoin. Amiodarone may block the conversion of T4 to T3. 

Calcium Acetate (PhosLo) [Calcium Supplement/ Anti arrhythmic/Mmeral/ Electrolyte] Uses ESRD-associated hyper-phos-phatemia Action Ca " supl w/o aluminum to X P04 absorption Dose 2-4 tabs PO w/ meals Caution [C, ] Contra t Ca Disp Gelcap SE Can t Ca, hypophosphatemia, constipation Interactions t Effects OF quinidine X effects W/ large intake of dietary fiber, spinach, rhubarb X effects OF atenolol, CCB, etidronate, tetracyclines, fluoroquinolones, phenytoin, Fe salts, thyroid hormones EMS Pts have reduced renal Fxn, monitor ECG for signs of electrolyte disturbances OD S/Sxs of hypercalcemia (confusion, weakness, GI upset, constipation, N, V, and cardiac arrhythmias) give IV fluid for diuresis symptomatic and supportive Calcium Carbonate (TumS/ Alka Mints) [Antacid/ Calcium Supplement/Mineral/ Electrolyte] [OTC] Uses Hyperacidity associated w/ peptic ulcer Dz, hiatal hernia, etc Action Neutralizes gastric acid Dose 500 mg—2 g PO PRN -1- in renal impair Caution [C, ] Disp Chew tabs, susp SE t -1- PO constipation Interactions X Effect OF tetracyclines, fluo-... 

Drugs that have been associated with elevations in quinidine concentrations include acetazolamide, the antacids magnesium hydroxide and calcium carbonate, and the H2-receptor antagonist cimetidine. Cimetidine inhibits the hepatic metabolism of quinidine. Phenytoin, rifampin, and barbiturates increase the hepatic metabolism of quinidine and reduce its plasma concentrations. 

Drug Interactions Various drugs can decrease T absorption. Drugs such as aluminum hydroxide, ferrous sulfate, sucralfate, and calcium carbonate should be separated from T administration by 1 to 2 hours. Bile acid sequestrants (cholestyramine and colestipol) must be separated from T by at least 4 hours and preferably 6 hours. CYP450 enzyme inducing drugs such as phenytoin, carba-mazepine, rifampin, and phenobarbital can increase T requirements. 

Patients with hypothyroidism who are taking levothyroxine may become hypothyroid if given drugs that decrease T4 absorption (cholestyramine, iron salts, calcium carbonate, aluminum hydroxide, sucralfate, raloxifene, omeprazole, dietary soy and fiber), increase its clearance (phenytoin, car-bamazepine, phenobarbital, rifampin), or decrease T4 to T3 conversion (amiodarone, glucocorticoids, propranolol). 

CARBONIC ANHYDRASE INHIBITORS ANTIEPILEPTICS- BARBITURATES, PHENYTOIN Risk of osteomalacia Barbiturates and phenytoin have a small risk of causing osteomalacia this may be t by acetazolamide-induced urinary excretion of calcium Be aware... 

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