A client with a respiratory infection has been receiving an antibiotic and an antipyretic for five days. Which current result is the best indication that the antibiotic has been effective? Reference range: White Blood Cell (WBC) [5,000 to 10,000/mm³ (5 to 10 × 10⁹/L)]

Choice A reason: A WBC count of 12,000/mm³ is elevated above the normal range, indicating ongoing infection or inflammation. Stability at this level does not confirm resolution of infection, so it is not the best indicator of antibiotic effectiveness. Choice B reason: Being afebrile for forty-eight hours suggests improvement, but fever reduction can result from antipyretic use rather than antibiotic effectiveness. Therefore, it is not a definitive measure of infection resolution. Choice C reason: A therapeutic antibiotic level confirms appropriate dosing but does not guarantee eradication of the infection. The drug may be present in effective concentrations, yet the infection may persist. Choice D reason: A sputum culture showing no growth is the most direct and reliable indicator that the antibiotic has eradicated the infectious organism. This result confirms that the treatment has been effective in eliminating the pathogen.