In a patient about to undergo cisplatin chemotherapy, should a mannitol bolus or PNSS (Peripheral Nutrition Support Solution) IV (Intravenous) with KCl (Potassium Chloride) be given first?

Pre-Cisplatin Hydration Protocol: Sequence of Administration

Administer normal saline (PNSS) with potassium chloride supplementation FIRST to achieve adequate hydration and electrolyte balance, followed by mannitol as part of the cisplatin infusion solution or as forced diuresis during administration.

Rationale for Sequencing

Initial Hydration with PNSS + KCl

The FDA-approved cisplatin label explicitly states that "pretreatment hydration with 1 to 2 liters of fluid infused for 8 to 12 hours prior to a cisplatin dose is recommended," with the drug then diluted in 2 liters of 5% Dextrose in 1/2 or 1/3 normal saline containing 37.5 g of mannitol 1. This clearly establishes that baseline hydration precedes mannitol administration.

• Pre-hydration must establish euvolemia and saline diuresis (urine NaCl concentration ~1%) of at least 100 mL/hour before cisplatin administration 2
• Potassium supplementation should be included in the initial hydration because cisplatin causes potassium-wasting nephropathy through tubular epithelial cell damage, and prophylactic replacement prevents severe hypokalemia 3
• The NCCN guidelines emphasize that "adequate amounts of IV fluids need to be administered in order to prevent renal toxicity" both before and after cisplatin, with patients often requiring outpatient IV fluids for 5-7 days post-chemotherapy 4, 5

Mannitol Administration Timing

Mannitol should be administered AFTER adequate pre-hydration is established, either:

1. Mixed into the cisplatin infusion solution (37.5 g in 2 liters over 6-8 hours per FDA label) 1, OR
2. As forced diuresis during/after cisplatin administration

• Mannitol without adequate pre-hydration can worsen renal injury by causing osmotic diuresis in a hypovolemic state
• Evidence shows mannitol combined with hydration significantly reduces nephrotoxicity, particularly in patients receiving cisplatin >80 mg/m² or those with hypertension 6, 7
• Mannitol should be "considered for high-dose cisplatin and/or patients with preexisting hypertension" as forced diuresis 8

Practical Algorithm

Step 1: Pre-Hydration Phase (8-12 hours before cisplatin)

• Infuse 1-2 liters of normal saline (0.9% NaCl or 0.45% NaCl) 1
• Add KCl 10-20 mEq per liter to prevent hypokalemia 3
• Target urine output ≥100 mL/hour (3 mL/kg/hour in children <10 kg) 4, 5
• Loop diuretics may be added if urine output inadequate (except in obstructive uropathy or hypovolemia) 4

Step 2: Cisplatin Administration Phase (6-8 hours)

• Dilute cisplatin in 2 liters of 5% Dextrose in 1/2 or 1/3 normal saline 1
• Add 37.5 g mannitol to the cisplatin infusion solution 1
• Do NOT dilute cisplatin in 5% Dextrose alone 1
• Infuse over 6-8 hours 1

Step 3: Post-Hydration Phase (24 hours after cisplatin)

• Continue IV hydration to maintain urine output ≥100 mL/hour 4, 5
• Continue KCl supplementation as needed based on electrolyte monitoring 3
• Patients often require outpatient IV fluids for 5-7 days 4, 5

Critical Monitoring and Caveats

High-Risk Patients Requiring Enhanced Mannitol Use

• Cisplatin dose ≥100 mg/m²: 11-fold increased nephrotoxicity risk 6
• Hypertension: 3-fold increased nephrotoxicity risk 6
• Baseline creatinine ≥100 μmol/L: 8-fold increased risk 9
• Concomitant radiation therapy: significantly increased benefit from mannitol 7

Electrolyte Monitoring

• Monitor electrolytes every 6 hours for first 24 hours in high-risk patients 3
• Hypomagnesemia exacerbates potassium wasting and must be aggressively corrected 3
• Continue daily monitoring until electrolyte levels stabilize 3

Contraindications to Consider

• Relative contraindications to aggressive saline hydration: congestive heart failure, significant urinary obstruction 4
• Aluminum-containing equipment: causes cisplatin precipitation and loss of potency 1

Common Pitfall to Avoid

Never administer mannitol as a bolus before establishing adequate hydration status. Mannitol causes osmotic diuresis, and if given to a hypovolemic patient, it will worsen renal perfusion and increase nephrotoxicity risk. The sequence must always be: hydration first → then mannitol with cisplatin 1, 8, 7.