American Board of Internal Medicine (ABIM) Certification Practice Exam

Why is Nitrofurantoin not an adequate treatment for pyelonephritis?

1. It is ineffective against Gram-negative bacteria

2. It achieves active levels only in the urine, not in kidney parenchyma

3. It causes significant side effects

4. It is only effective in patients with normal kidney function

The correct answer is: It achieves active levels only in the urine, not in kidney parenchyma

Nitrofurantoin is not considered an adequate treatment for pyelonephritis primarily because it achieves therapeutic levels only in the urine, not in the kidney parenchyma where the infection occurs. Pyelonephritis, an infection of the kidney, requires systemic antibiotics that can penetrate kidney tissue effectively to eradicate the infection. Nitrofurantoin is specifically formulated to treat lower urinary tract infections by concentrating in the urine; it does not distribute well in tissues, including the kidneys, limiting its effectiveness in treating more severe infections that require higher drug concentrations in the kidney itself. In addition to this, while nitrofurantoin does possess activity against certain pathogens, it is not effective against all pathogens associated with pyelonephritis, particularly those that can cause severe kidney infections. This further substantiates why nitrofurantoin is not the appropriate choice for treating pyelonephritis. It is important to consider that systemic infections often require antibiotics that can achieve adequate concentrations in the body's various tissues, something that nitrofurantoin cannot adequately provide. Therefore, alternative antibiotics that can fulfill this requirement are preferred for the management of pyelonephritis.