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2.1.2: Employ various techniques to calculate drug concentrations, ratio strengths, and/or extent of ionization

GT is a 26-year-old patient with a diagnosis of bipolar disorder. He is currently not receiving any medication for treatment and presents to the emergency room via ambulance in an acute manic phase. The psychiatry fellow evaluates the patient and orders lithium for treatment of bipolar disorder. The provider wants to order 8 mEq three times per day. What is the correct dose of lithium to dispense?

(A) 300 mg every 24 hours

(B) 300 mg every 12 hours

(C) 300 mg every 8 hours

(D) 450 mg every 8 hours

The correct answer is (C).

Lithium is prescribed as a carbonate salt, which contains 8.12 mEq of lithium per 300 mg tablet or capsule (C). Be careful not to confuse mEq (milliequivalent) with mg (milligram). The dosage should be written in mg to avoid confusion. Check prescriptions for unusually high volumes of the syrup formulation for dosing errors.

300 mg every 24 hours would be 8 mEq every 24 hours (A). 300 mg every 12 hours would be 8 mEq every 12 hours (B). 450 mg every 8 hours would be 12 mEq every 12 hours (D).

Which of the following are differences between calcium gluconate and calcium chloride parenteral preparations?

(A) The mechanism of action of calcium chloride is superior in calcium channel blocker poisoning.

(B) The mechanism of action of calcium gluconate is superior in calcium channel blocker poisoning.

(C) Calcium chloride provides three times more cation compared to calcium gluconate on an equal volume basis.

(D) Calcium gluconate is more irritating when given intravenously than calcium chloride.

(E) Both c and d.

The correct answer is (C).

Calcium chloride contains 13.6 mEq of calcium per gram compared to calcium gluconate which provides 4.65 mEq of calcium per gram. Both products are commercially available as 10% solutions, making calcium chloride three times more potent per equivalent volume of calcium gluconate.

Choice (A) is incorrect. Administration of either of the calcium salts in appropriate dose provides the body with increased cation levels to attempt to overcome competitive blockade imposed by calcium channel blockers.

Choice (B) is incorrect. See explanation above.

Choice (D) is incorrect. Calcium chloride is significantly more irritating when given intravenously compared to calcium gluconate.

Choice (E) is incorrect.

How much aspirin equivalent is contained in 5 mL of ...

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