1. Introduction

Drug-induced acute kidney injury (AKI) significantly complicates the management of critically ill patients. It necessitates dynamic pharmacotherapy regimens that prioritize nephrotoxicity-sparing agents and account for altered drug disposition. Pharmacists play a crucial role in integrating trends in renal function, pharmacokinetic (PK) and pharmacodynamic (PD) changes, and the impact of extracorporeal therapies into individualized treatment plans to optimize outcomes and minimize further renal damage.

2. Identification and Discontinuation of Nephrotoxins

The cornerstone of any escalation pharmacotherapy plan for drug-induced AKI is the prompt identification, withdrawal, or substitution of offending agents. A thorough medication review is paramount.

Common Nephrotoxins:

• Aminoglycosides (e.g., gentamicin, tobramycin)
• Vancomycin
• Cisplatin and other chemotherapeutic agents
• Nonsteroidal anti-inflammatory drugs (NSAIDs)
• Calcineurin inhibitors (e.g., cyclosporine, tacrolimus)
• Amphotericin B
• Contrast media

Risk–Benefit Assessment:

A careful risk–benefit assessment is crucial. The clinical team must weigh the necessity of continuing a potentially nephrotoxic drug (e.g., for life-threatening infection control or essential immunosuppression) against the severity and potential reversibility of the AKI.

Substitution Strategies:

• Replace aminoglycosides with extended-spectrum beta-lactams (e.g., piperacillin-tazobactam, cefepime) or fluoroquinolones when antimicrobial susceptibilities permit.
• Consider using echinocandins (e.g., caspofungin, micafungin) or linezolid in place of vancomycin for select Gram-positive infections, particularly if vancomycin-associated AKI is suspected.
• In transplant recipients, switching from calcineurin inhibitors to mTOR inhibitors (e.g., sirolimus, everolimus) may be considered, though this requires careful specialist consultation.

3. Renal Function–Guided Dose Adjustment Algorithms

Accurate estimation of renal clearance, especially in the non-steady-state conditions of AKI and during RRT, is essential for guiding appropriate loading and maintenance doses of medications.

Renal Function Assessment:

• Timed Urine Collections: When feasible, timed urine collections (e.g., 2-hour or 4-hour) for creatinine clearance provide a more accurate measure of glomerular filtration rate (GFR) in dynamic AKI than estimation equations.
• Limitations of Equations: Standard GFR estimation equations like Cockcroft-Gault and MDRD are unreliable during acute changes in renal function as they assume stable serum creatinine.
• RRT Considerations: For patients on continuous renal replacement therapy (CRRT), residual renal clearance can be estimated by measuring creatinine in the effluent fluid, in addition to any native kidney function.

Dose Modification Framework:

• Loading Doses: Generally, initial loading doses of most medications should not be reduced in AKI, particularly in critically ill patients with sepsis. The volume of distribution (Vd) is often expanded due to capillary leak and fluid resuscitation, necessitating full loading doses to achieve therapeutic concentrations rapidly.
• Maintenance Doses: Maintenance doses or dosing intervals frequently require adjustment. Reductions should be guided by the stage of AKI, the specific drug’s pharmacokinetic profile (e.g., extent of renal elimination), and the type/intensity of RRT.

Adjustments for Renal Replacement Therapy (RRT):

• Intermittent Hemodialysis (IHD): Anticipate significant removal of small, water-soluble, and low protein-bound drugs. Doses of such medications should typically be administered post-dialysis to avoid subtherapeutic levels.
• Continuous Renal Replacement Therapy (CRRT): CRRT provides continuous drug clearance, which can be substantial for many agents. This may necessitate higher or more frequent dosing compared to patients with severe AKI not on CRRT, or those on IHD. Drug-specific literature and pharmacist consultation are vital.

4. Pharmacokinetic/Pharmacodynamic Optimization

Critical illness profoundly alters drug pharmacokinetics (PK), including volume of distribution (Vd), protein binding, and clearance. Pharmacodynamic (PD) targets must be tailored to these changes to ensure efficacy and minimize toxicity.

Pharmacokinetic Alterations in Critical Illness and AKI:

• Increased Volume of Distribution (Vd): Capillary leak syndrome, aggressive fluid resuscitation, and third-spacing can significantly increase the Vd of hydrophilic drugs (e.g., beta-lactams, aminoglycosides), potentially leading to lower peak concentrations if standard doses are used.
• Altered Protein Binding: Hypoalbuminemia, common in critical illness, increases the free (active) fraction of highly protein-bound drugs (e.g., phenytoin, ceftriaxone). This can enhance both efficacy and toxicity if not accounted for. Acid-base disturbances also affect protein binding.

Pharmacodynamic Targets and Strategies:

• Time-Dependent Agents (e.g., Beta-Lactams): Efficacy correlates with the duration the drug concentration remains above the minimum inhibitory concentration (MIC) of the pathogen (%T>MIC).
  • Strategy: Utilize extended or continuous infusions to maximize %T>MIC, especially for less susceptible organisms or in patients with augmented renal clearance (early sepsis) or unpredictable clearance (AKI/CRRT).
• Concentration-Dependent Agents (e.g., Aminoglycosides, Fluoroquinolones): Efficacy correlates with the peak concentration (Cmax) to MIC ratio or the area under the curve (AUC) to MIC ratio.
  • Strategy: Employ high-peak, extended-interval dosing for aminoglycosides to maximize Cmax/MIC and minimize nephrotoxicity.
• Vancomycin: Efficacy and reduced nephrotoxicity correlate with an AUC/MIC ratio of ≥400–600.
  • Strategy: Transition from traditional trough-based monitoring to AUC-guided monitoring whenever possible. This often involves using Bayesian software programs with one or two appropriately timed serum concentrations.

5. Comprehensive Pharmacotherapy Profiles

A detailed understanding of agent-specific nephrotoxicity mechanisms, appropriate dosing strategies in AKI, essential monitoring parameters, and suitable lower-risk alternatives is critical for effective management.

5.6 Alternative Agents with Lower Nephrotoxicity

When feasible, selecting alternative medications with a more favorable renal safety profile is a key strategy:

• For Gram-negative infections, prefer hydrophilic beta-lactams (e.g., piperacillin-tazobactam, meropenem if extended-spectrum beta-lactamase producers are suspected) over aminoglycosides, especially if the patient has risk factors for AKI.
• For resistant Gram-positive infections (e.g., MRSA), consider linezolid or daptomycin (monitor CPK with daptomycin; not for pneumonia) as alternatives to vancomycin, particularly if vancomycin-induced AKI is a concern or AUC monitoring is not feasible. Echinocandins are generally well-tolerated for fungal infections.
• In transplant recipients, early conversion from calcineurin inhibitors to mTOR inhibitors or other agents may be considered in cases of significant CNI-induced nephrotoxicity, under specialist guidance.

6. Prevention Strategies

Proactive measures are crucial to avert the development or escalation of drug-induced AKI in critically ill patients.

• Hydration Protocols: Ensure adequate intravascular volume. For specific toxins like cisplatin or intravenous contrast, implement targeted hydration protocols (e.g., isotonic crystalloid administration before, during, and after exposure).
• Nephrotoxin Stewardship: Implement multidisciplinary “nephrotoxin stewardship” rounds. These involve pharmacists, physicians, and nurses collaboratively reviewing medication profiles to identify and discontinue or substitute high-risk drugs, and to ensure appropriate dosing of necessary nephrotoxins.
• Therapeutic Drug Monitoring (TDM): Optimize TDM for drugs with narrow therapeutic indices and significant nephrotoxic potential (e.g., vancomycin, aminoglycosides, calcineurin inhibitors). TDM schedules should be based on the agent’s PK/PD, patient’s renal function (including changes and RRT status), and specific institutional protocols.
• Avoidance of Nephrotoxin Combinations: Minimize concurrent administration of multiple nephrotoxic agents whenever clinically possible (e.g., vancomycin + piperacillin-tazobactam + aminoglycoside + NSAID is a high-risk combination).

7. Supportive Care and Renal Replacement Therapy Considerations

Effective management of drug-induced AKI involves integrating pharmacotherapy plans with hemodynamic support and, when necessary, renal replacement therapy (RRT).

Hemodynamic Optimization:

• Maintain adequate renal perfusion by targeting a mean arterial pressure (MAP) of ≥65 mm Hg in most critically ill patients. This may require judicious use of intravenous fluids and vasoactive agents.
• Titrate vasoactive agents (e.g., norepinephrine) carefully to achieve perfusion goals while avoiding excessive vasoconstriction that could further impair renal blood flow.

Indications for RRT in Drug-Induced AKI:

RRT may be indicated if AKI leads to complications refractory to medical management, such as:

• Severe, refractory hyperkalemia (e.g., K+ >6.5 mEq/L or with ECG changes)
• Severe metabolic acidosis (e.g., pH <7.1-7.2)
• Signs of uremia (e.g., encephalopathy, pericarditis, intractable nausea/vomiting)
• Refractory fluid overload causing respiratory compromise
• Certain drug toxicities/overdoses where the drug is dialyzable

Modality Selection for RRT:

• Intermittent Hemodialysis (IHD): Suitable for hemodynamically stable patients requiring rapid solute and fluid removal. Drug dosing often needs to be coordinated around IHD sessions.
• Continuous Renal Replacement Therapy (CRRT): Preferred for hemodynamically unstable patients as it allows for slower, more continuous removal of solutes and fluid, minimizing hemodynamic swings. CRRT also has implications for drug dosing due to continuous clearance.
• Sustained Low-Efficiency Dialysis (SLED): A hybrid modality that can be an option in some centers.

Coordination of Drug Dosing with RRT:

It is critical to coordinate drug administration schedules with RRT (especially IHD) to avoid subtherapeutic drug concentrations (if dosed before a session and significantly cleared) or accumulation and toxicity (if not adequately cleared). Pharmacist involvement is key for dose adjustments based on RRT modality, intensity, and drug characteristics.

8. Monitoring Plan

A comprehensive monitoring plan is essential to track the patient’s response to interventions, guide escalation or de-escalation of therapy, and detect further complications.

Key Monitoring Parameters:

• Serum Drug Concentrations:
  • Vancomycin: AUC (preferred) or trough levels.
  • Aminoglycosides: Peak and trough levels.
  • Calcineurin inhibitors: Trough levels.
  • Other drugs as indicated by TDM.
• Renal Function Markers:
  • Hourly urine output: A critical real-time indicator of renal perfusion and function.
  • Daily (or more frequent, if rapidly changing) serum creatinine (SCr) and blood urea nitrogen (BUN) to trend kidney function.
• Electrolytes and Acid-Base Status:
  • Regular monitoring of serum potassium, sodium, magnesium, phosphorus, and calcium.
  • Arterial or venous blood gases to assess acid-base balance (e.g., for metabolic acidosis).
• Novel Biomarkers (where available and clinically indicated):
  • Neutrophil Gelatinase-Associated Lipocalin (NGAL)
  • Kidney Injury Molecule-1 (KIM-1)
  • Tissue Inhibitor of Metalloproteinases-2 (TIMP-2) and Insulin-like Growth Factor-Binding Protein 7 (IGFBP7) – [TIMP-2]*[IGFBP7] (Nephrocheck®)
  • These may offer earlier detection of AKI or risk stratification but are not yet standard practice in all ICUs.
• Documentation:
  • Meticulously document all pharmacotherapeutic interventions, adjustments, rationale, and trends in renal function and other monitored parameters in the patient’s medical record. This is vital for continuity of care and quality improvement initiatives.

9. Pharmacoeconomic Considerations

Resource allocation and cost-effectiveness are important aspects of managing drug-induced AKI in critically ill patients. Decisions should balance clinical efficacy with economic impact.

• Therapeutic Drug Monitoring (TDM): Evaluate the cost of TDM (assays, personnel time) against the potential savings from preventing AKI progression, reducing the need for RRT, shortening ICU and hospital length of stay (LOS), and avoiding long-term complications like chronic kidney disease (CKD).
• Alternative Agents: Assess the budget impact of adopting newer, potentially more expensive, but less nephrotoxic alternative medications compared to older, more nephrotoxic agents. This includes acquisition costs and costs associated with managing potential adverse events.
• Infusion Strategies: Consider the costs associated with extended or continuous infusions (e.g., dedicated IV lines, pump availability, pharmacy compounding time) versus the benefits of optimized PK/PD and potentially improved outcomes.
• Renal Replacement Therapy (RRT) Utilization: The choice between intermittent (IHD) and continuous (CRRT) modalities has significant cost implications (equipment, consumables, nursing intensity). Decisions should be primarily clinical, but resource availability and cost can be factors, especially in prolonged RRT.
• Pharmacist Involvement: Investing in clinical pharmacy services, including participation in ICU rounds and nephrotoxin stewardship programs, can lead to substantial cost savings by optimizing drug therapy, preventing adverse drug events (including AKI), and reducing RRT utilization and LOS.

10. Clinical Decision Algorithm for Drug-Induced AKI

A structured approach facilitates timely and effective management of drug-induced AKI.

Key Pearls Summary