A nurse is monitoring a client who is receiving warfarin and has an INR of 4 (0.8 to 1.1). Which of the following medications should the nurse plan to administer?

Choice A rationale

Laryngeal edema is a severe manifestation of an immediate hypersensitivity (Type I anaphylactic) reaction to penicillin. It involves swelling of the larynx, leading to airway obstruction, stridor, and difficulty breathing. This life-threatening condition requires immediate medical intervention, including epinephrine and airway management, making it the priority to monitor.

Choice B rationale

Urticaria, or hives, is a common cutaneous manifestation of a hypersensitivity reaction to penicillin. It involves transient, itchy wheals on the skin due to histamine release. While uncomfortable and requiring attention, it is typically not life-threatening unless accompanied by systemic symptoms like laryngeal edema or bronchospasm.

Choice C rationale

Epigastric distress, such as stomach upset or pain, is a common gastrointestinal adverse effect of oral penicillin V, often due to direct irritation of the gastric mucosa or altered gut flora. While it can cause discomfort, it is generally not a life-threatening condition and can often be managed with food or dose adjustment.

Choice D rationale

Maculopapular rash is a delayed hypersensitivity reaction to penicillin, usually appearing several days after initiation of therapy. It presents as flat, red areas with small raised bumps. While it indicates a drug allergy, it is generally not immediately life-threatening compared to acute airway compromise and resolves upon discontinuation of the medication.

Choice A rationale

Tuberculosis is a bacterial infection primarily affecting the lungs, caused by *Mycobacterium tuberculosis*. Didanosine is an antiretroviral medication, specifically a nucleoside reverse transcriptase inhibitor (NRTI), and as such, it does not possess antimicrobial activity against bacterial pathogens like *Mycobacterium tuberculosis*. Therefore, it is not indicated for treating tuberculosis.

Choice B rationale

Human immunodeficiency virus (HIV) is a retrovirus that attacks the body's immune system. Didanosine is an antiretroviral drug that inhibits the replication of HIV by interfering with the reverse transcriptase enzyme, which is crucial for the virus to convert its RNA into DNA. This mechanism of action effectively reduces the viral load and improves immune function in individuals with HIV infection.

Choice C rationale

Bacterial meningitis is an inflammation of the meninges, the membranes surrounding the brain and spinal cord, caused by various bacterial species. Didanosine is an antiviral agent specifically targeting retroviruses like HIV. It does not have any direct antibacterial properties or efficacy against the common bacterial pathogens responsible for meningitis, thus making it an inappropriate treatment.

Choice D rationale

Syphilis is a sexually transmitted infection caused by the bacterium *Treponema pallidum*. The primary treatment for syphilis is antibiotics, particularly penicillin. Didanosine, being an antiretroviral medication, does not exhibit any treponemicidal activity and is ineffective against *Treponema pallidum*. Therefore, it is not used in the treatment of syphilis.