How to renally dose a Z-pack (azithromycin) for a patient with impaired renal function, creatinine clearance (CrCl) of 1.73 and glomerular filtration rate (GFR) of 39?

Azithromycin (Z-pack) Dosing in Renal Impairment

No dose adjustment is required for azithromycin in patients with renal impairment, regardless of the severity of kidney dysfunction. 1, 2

Rationale for Standard Dosing

• Azithromycin has substantial nonrenal clearance mechanisms that remain unaffected by renal dysfunction, making dose adjustment unnecessary even in severe renal impairment 1

• Pharmacokinetic studies demonstrate that neither the area under the plasma concentration curve, distribution volume (16 L/kg body weight), nor maximal plasma concentration are significantly affected by renal insufficiency 2

• The dosage regimen in patients with renal impairment should be the same as in patients with normal renal function 2

Specific Dosing for Your Patient

For a patient with CrCl 1.73 mL/min and GFR 39 mL/min/1.73 m²:

• Administer the standard Z-pack regimen: 500 mg on day 1, then 250 mg daily on days 2-5 1, 2

• No reduction in dose or extension of dosing interval is needed 1

Important Clinical Considerations

• While the nonrenal clearance of azithromycin is not affected by renal insufficiency, the concentration of the drug in the tubular lumen (the "tubular load") may be increased in patients with kidney disease 2

• This contrasts sharply with other antibiotics like cefuroxime, where extending dosing intervals rather than reducing doses is the preferred strategy in renal impairment 1

Common Pitfall to Avoid

• Do not assume all antibiotics require dose adjustment in renal impairment - this is a dangerous misconception that could lead to underdosing of azithromycin and treatment failure 1

• Unlike renally-cleared antibiotics, azithromycin's pharmacokinetics remain stable across all levels of renal function 2