NAPLEX Question of the Week: To Fill or Not to Fill?

A patient presents a prescription to fill at your pharmacy. Should you fill it?
NAPLEX Question of the Week: To Fill or Not to Fill?

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LW is a 29-year-old non-pregnant female who presents to her community pharmacy with a new prescription for Lithobid. She has complained of significant mood and behavior swings in the last few months, prompting her recent visit to her primary care physician. She was referred to a psychiatrist who prescribed Lithobid 300mg PO TID as she previously failed other therapies.  In addition to her prescription medications, LW also admits to taking Tylenol for occasional headaches.

Past Medical History: GERD, Hyperlipidemia, Hypertension

Medication List:

Amlodipine 5 mg QD

Microzide 25 mg QD

Lipitor 40mg HS

Protonix 40 mg BID

What is the most appropriate next line of action for the pharmacist on duty?

A. Fill the prescription as is, but educate the patient that Tylenol is contraindicated with Lithobid and should not be taken simultaneously.

B. Do not fill the prescription due to Lithobid being contraindicated with Lipitor due to enhanced musculoskeletal toxicity.

C. Contact the prescriber to discuss due to a possible drug interaction with Microzide.

D. Contact the prescriber to discuss due to a possible drug interaction with Protonix.

E. Fill the prescription as is, educate the patient on possible side effects such as polyuria, polydipsia, and weight loss. 


Bipolar Disorder is characterized by recurrent fluctuations in mood, energy, and behavior. Lithobid has an FDA indication for bipolar maintenance and acute mania. Lithium in general is not a first-line therapy for these conditions due to its side effect profile and potential for drug interactions, especially involving fluid fluctuations. However there are some patients that lithium is required to control their symptoms.  Therefore anytime a pharmacist is presented with a lithium prescription, a careful review of any potential drug interactions is necessary to promote safe and effective therapy. 

Answer A is incorrect. Tylenol is considered a safe pain management option for those taking Lithobid, and no significant interaction exists between the two.

Answer B is incorrect. There is no known drug interaction between statins and lithium. 

Answer C is correct. Microzide is a diuretic commonly used to treat hypertension. Co-administration of Lithobid and Microzide can reduce lithium excretion leading to elevated, and potentially toxic, lithium concentrations. Lithium toxicities can be life-threatening in severe cases and there are two different prescribers involved. Ensuring the psychiatrist is aware of Microzide would be important as this is Lithobid regimen is on high end of normal for initiation. 

Answer D is incorrect. Protonix is a proton pump inhibitor (PPI), and there is not a significant drug interaction present between Protonix and Lithobid. PPIs can decrease absorption of certain drugs that require an acidic environment for absorption, such as iron or ketoconazole. 

Answer E is incorrect. While adherence and regular lab monitoring are important things to consider with Lithobid, there is a drug interaction present and dispensing this medication could cause harm to the patient. Especially with two different prescribers involved, ensuring the lithium should still be prescribed is important. In addition, lithium can cause weight gain, not typically loss so this would make this incorrect. 

Therefore the correct answer is C.

Brand/Generics covered: Amlodipine (Norvasc), Hydrochlorothiazide (Microzide), Atorvastatin (Lipitor), Pantoprazole (Protonix), Acetaminophen (Tylenol), Lithium (Lithobid)

NAPLEX Competencies covered:

1.4 - From medical records: treatment adherence, or medication-taking behavior; chief complaint, medication history, medical history, family history, social history, lifestyle habits, socioeconomic background

2.2 - Commercial availability; prescription or non-prescription status; brand, generic, or biosimilar names; physical descriptions; or how supplied

2.4 - Pregnancy or lactation

3.3 - Medication reconciliation; indication or therapeutic uses; lack of indication; inappropriate indication; duplication of therapy; omissions

3.7 - Adverse drug effects, toxicology, or overdose

3.8 - Drug interactions

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