Pharmacology Flashcards

A patient with chronic hepatitis B is started on tenofovir. What is the mechanism of action of this antiviral?

Answer: Nucleotide reverse transcriptase inhibitor

Tenofovir is a nucleotide analogue reverse transcriptase inhibitor (NtRTI) that incorporates into viral DNA by HBV polymerase/reverse transcriptase, causing chain termination. It has a high barrier to resistance and is first-line for chronic hepatitis B alongside entecavir.

A patient develops QT prolongation on their medication. Which of the following drugs is most likely responsible?

Answer: Erythromycin

Erythromycin is well-known to cause QT prolongation by blocking the hERG potassium channel, increasing the risk of torsades de pointes and sudden cardiac death. It should be avoided in patients with pre-existing QT prolongation or those on other QT-prolonging drugs.

A patient with rheumatoid arthritis on methotrexate develops pancytopenia. What supplement should have been co-prescribed to prevent this complication?

Answer: Folic acid

Folic acid supplementation (5 mg weekly, taken on a different day from methotrexate) reduces the incidence of methotrexate side effects including pancytopenia, stomatitis, and GI upset. Methotrexate inhibits dihydrofolate reductase, causing folate depletion.

Which class of drugs is used for the acute management of anaphylaxis?

Answer: Adrenaline (epinephrine)

Adrenaline (epinephrine) IM injection (0.5 mg for adults, anterolateral thigh) is the first-line and most critical drug in anaphylaxis management. It acts on alpha-1 (vasoconstriction), beta-1 (chronotropy/inotropy), and beta-2 (bronchodilation) receptors. Delay in administration increases mortality.

A patient with depression is started on venlafaxine. At low doses it acts primarily on serotonin reuptake. What additional effect does it have at higher doses?

Answer: Noradrenaline reuptake inhibition

Venlafaxine is a serotonin-noradrenaline reuptake inhibitor (SNRI). At lower doses (75 mg), it primarily inhibits serotonin reuptake. At higher doses (≥150 mg), it additionally inhibits noradrenaline reuptake, providing a dual mechanism that may be more effective for severe depression.

A patient taking clopidogrel is prescribed omeprazole for dyspepsia. What is the clinical significance of this drug interaction?

Answer: Omeprazole inhibits CYP2C19, reducing clopidogrel activation

Clopidogrel is a prodrug that requires CYP2C19 for activation to its active metabolite. Omeprazole inhibits CYP2C19, potentially reducing clopidogrel's antiplatelet efficacy. Pantoprazole is the preferred PPI in patients on clopidogrel as it has less CYP2C19 inhibition.