Failure to Perform/Communicate Therapeutic Drug Monitoring (Acute Care)

Service: Risk Management
Subject: Care
Setting: Medications

Sector: Acute Care

Therapeutic drug monitoring (TDM) provides important information for tailoring the dosage of prescribed medication(s) to an individual patient. TDM uses blood serum concentrations of medications to optimize drug dosing to minimize toxicity and maximize treatment benefit. Not all medications require TDM since most drugs have a wide therapeutic range or “window” and can be prescribed based upon pre-established dosing schedules. When medications have a narrow therapeutic range (e.g. antiarrhythmic, anticoagulant, anticonvulsant); there is a very small margin between effective therapy and under or overdosing. TDM is required to maintain the right concentration of those medications in the blood system. Failure to perform and/or communicate and act on therapeutic drug monitoring results can result in significant harm to the patient.

Common Claim Themes

  • Cumbersome, impractical and/or conflicting TDM protocols/guidelines.
  • Lack of clarity as to who is responsible for obtaining serum levels, interpreting results and communicating results to the most responsible practitioner.
  • Critical and/or toxic serum levels not communicated to the most responsible practitioner and/or the patient.
  • Systems not in place to advice practitioners of the availability of testing.
  • Assumption that another practitioner will be monitoring therapeutic drug levels.
  • Poor understanding/compliance with TDM protocols/guidelines.
  • Poor documentation practices (e.g. signs/symptoms of toxicology; communication of test results to the most responsible practitioner; patient education/training, etc.); particularly with charting by exception.
  • Poor patient education and instructions regarding signs/symptoms of toxicity and requirements for blood work.
  • Healthcare practitioners with little to no experience in TDM.
  • Communication gaps between nursing, lab and clinical pharmacists related to the relay of/acting on TDM results during hospital stay and prior to discharge.
  • Communication gaps with community providers related to the provision of results received after the patient has left the hospital.

Case Study 1

A patient with diabetes was admitted to hospital to undergo aggressive therapy for osteomyelitis of the foot, the result of a previous foot injury weeks earlier. Discharged on antibiotic therapy, community nurses monitored the patient’s progress. Approximately five weeks later the patient was diagnosed with ototoxicity and vestibular dysfunction which are recognized complications of gentamicin toxicity. Expert opinion revealed that based on culture results taken while in hospital, there was no indication for using gentamicin for such a prolonged period and once culture results were available it should have been discontinued in three to five days to avoid toxicity especially given the patient’s diabetic condition. Combined with serum monitoring not having been performed outside of the hospital, the claim was considered indefensible.

Case Study 2

A patient was receiving warfarin anticoagulant therapy after having undergone hip surgery. No official policy or guideline regarding the monitoring of prothrombin time was in place at the time, but it was practice at the hospital to monitor the international normalized ratio (INR) of patients starting anticoagulant therapy twice weekly until stable and then once weekly. The patient’s blood level was not monitored for two weeks after warfarin was started. Although the patient was closely followed, none of the healthcare practitioners realized that the INR had not been tested. Ultimately, the patient began to show signs consistent with bleeding. The patient’s INR was finally tested and the result came back as critically high.


Mitigation Strategies

Note: The Mitigation Strategies are general risk management strategies, not a mandatory checklist. Please also refer to the Medication Adverse Events Risk Reference Sheet.

Reliable Care Processes

  • Work with an interdisciplinary team to develop protocols/algorithms to guide decision making surrounding medications requiring TDM (e.g. anticoagulants, aminoglycoside antibiotics, theophylline, phenytoin, cyclosporine, digoxin, lithium) that consider:
    • Therapeutic and toxic drug levels/ranges;
    • Individual responsible for obtaining levels;
    • Timing of blood samples;
    • Escalation steps and time thresholds if the levels are not available at the time of next dose;
    • Escalation steps and time thresholds if the levels are abnormal/critical/toxic;
    • The need to ask if the patient is experiencing the side effects that could be early indicators of toxicity.
  • Leverage technology and innovation to help assist with prevention efforts (e.g. decrease omission errors) from a system level. Consider, when purchasing or updating electronic systems, clinical decision supports/embedded algorithms to order lab tests and instruct users on how to promptly respond to/act on critical levels.
  • Adopt a standardized nomogram for monitoring TDM levels where possible. Adopt best practices for the communication of critical test results to the most responsible/ordering practitioner, including alternative contacts for critical results.
  • Adopt a standardized process to ensure TDM requirements are included in discharge orders including therapeutic and toxic levels and the need for stringent compliance with obtaining and communicating TDM levels to the most responsible practitioner).


  • Ensure complete and timely documentation (including date/time):
    • When blood is drawn;
    • Upon delivery and receipt of TDM levels;
    • When communicating results to the most responsible practitioner including the name of the practitioner contacted and any resulting actions taken with respect to the information provided;
    • If lab results are pending and how these will be relayed to the MRP in the community;
    • Of education/training provided to patient/family (e.g. the need for strict adherence/compliance with administration/testing/monitoring schedule, possibility of repeat testing, signs/symptoms of toxicology, the need to report changes or untoward symptoms immediately to the most responsible practitioner.


  • Provide regular in-services/training to all nursing administering and/or monitoring patients with TDM requirements including therapeutic and toxic levels, signs/symptoms of toxicity, risk factors impacting metabolism and clearance of medications (e.g. age, disease, drug interactions, impaired renal failure) and the need for stringent compliance with obtaining and communicating TDM levels to the most responsible practitioner.

Post-Incident Management

  • Ensure timely notification, documentation, disclosure and investigation of significant TDM patient safety incidents.

Measurement and Monitoring

  • Ensure laboratory services have a formal quality assurance process regarding adherence to drawing of blood samples; and communication of critical/toxic levels to the most responsible practitioner.
  • Track and review incidents involving medications with a narrow therapeutic index.
  • Implement formal strategies to help ensure consistent adherence to TDM policies/practices (e.g. periodic chart/e-record audits, analysis of reported incident/events, learning from medico-legal matters).