- Among the antibiotics listed, Penicillin V requires dose adjustment in patients with severe renal impairment (GFR below 30 mL/min).

- Penicillin V is primarily excreted unchanged by the kidneys. Therefore, in patients with significantly reduced renal function, drug accumulation can occur, increasing the risk of toxicity. Dose adjustment is essential to prevent adverse effects.

- Azithromycin is predominantly eliminated via the liver and biliary route. Its pharmacokinetics are not significantly affected by renal impairment, so dose modification is generally not required in patients with low GFR.

- Ceftriaxone has a unique elimination pathway; it is excreted both renally and via the biliary system. Due to its dual clearance route, dose adjustment is typically not necessary even in severe renal impairment.

- Clindamycin is metabolized mainly in the liver and excreted in bile and urine. Renal impairment does not substantially affect its clearance, so dose adjustment is usually not needed.

Key points to remember:
- Penicillin V: Renal excretion → dose adjustment required in GFR
- Azithromycin: Hepatic elimination → no dose adjustment needed.
- Ceftriaxone: Dual elimination (renal and biliary) → usually no adjustment in renal failure.
- Clindamycin: Hepatic metabolism → no dose adjustment needed.

Reference: Katzung BG, Trevor AJ. *Basic & Clinical Pharmacology*, 15th Edition, Chapter 45: Antibacterial Drugs / Page 720-725.