Medication monitoring protocols

Medication monitoring protocols

Medication monitoring protocols

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TDM Fundamentals - The "Just Right" Dose

  • Goal: Maintain drug plasma concentration within the therapeutic window to maximize efficacy and minimize toxicity.
  • Indicated for: Drugs with a Narrow Therapeutic Index (NTI) where effect is related to concentration.
  • Key Metrics:
    • Trough ($C_{min}$): Lowest level, drawn just before the next dose. Monitors for toxicity.
    • Peak ($C_{max}$): Highest level, drawn after administration. Assesses efficacy.

⭐ For most NTI drugs like Vancomycin and Aminoglycosides, trough concentration is the primary monitoring parameter to prevent dose-dependent toxicity.

Drug concentration over time: therapeutic range and MIC

*A quick reference for high-risk medication monitoring.

Drug Class / AgentKey Monitoring Parameter(s) & Critical Thresholds
Anticoagulants
- WarfarinINR (Target: 2.0-3.0 for most indications)
- UFHaPTT (Target: 1.5-2.5x baseline)
Antiarrhythmics
- AmiodaroneTFTs, LFTs, PFTs (Baseline, then q6 months)
- DigoxinSerum Level (Therapeutic: 0.5-0.9 ng/mL), Serum K+, Renal function
Psychotropics
- LithiumSerum Level (Therapeutic: 0.6-1.2 mEq/L), TFTs, RFTs
- Clozapine⚠️ ANC weekly for 6 months, bi-weekly for 6 months, then monthly.
Other High-Risk
- MethotrexateCBC, LFTs, Creatinine (Baseline & periodic)
- StatinsLFTs (Baseline), CK (only if myalgia develops)

Warfarin & Digoxin - Heart-Watch Protocols

  • Warfarin (Oral Anticoagulant)

    • Monitor: Prothrombin Time (PT) / International Normalized Ratio (INR).
    • Target INR: 2.0-3.0 (standard); 2.5-3.5 (mechanical valves).
    • Antidote: Vitamin K, Fresh Frozen Plasma (FFP), Prothrombin Complex Concentrate (PCC).
    • 📌 Mnemonic: WEPTWarfarin, Extrinsic pathway, PT.
  • Digoxin (Cardiac Glycoside)

    • Monitor: Serum digoxin levels (trough levels).
    • Therapeutic Range: 0.8-2.0 ng/mL.
    • Toxicity Risk: ↑ with hypokalemia, renal failure.
    • Antidote: Digoxin Immune Fab (DigiFab).

⭐ Amiodarone significantly increases levels of both Warfarin (↑INR) and Digoxin; dose reduction is crucial.

Lithium & Antiepileptics - Brain-Balancer Surveillance

  • Lithium:

    • Baseline: TFT, RFT, ECG.
    • Therapeutic Level: 0.6-1.2 mEq/L. Check 12h post-dose, 5 days after start, then every 3-6 months.
    • Toxicity >1.5 mEq/L. Monitor TFT/RFT annually.
    • 📌 Mnemonic "LITH": Leukocytosis, Insipidus, Tremor, Hypothyroidism.
  • Key Antiepileptics:

    • Valproate: Monitor LFTs (hepatotoxicity) & CBC.
    • Carbamazepine: Monitor CBC (agranulocytosis). Screen Asians for HLA-B*1502 (SJS risk).
    • Phenytoin: Watch for nystagmus & ataxia (toxicity).

⭐ In Asian populations, screening for the HLA-B*1502 allele is crucial before starting Carbamazepine to prevent Stevens-Johnson syndrome (SJS).

Therapeutic Drug Monitoring Cycle

High‑Yield Points - ⚡ Biggest Takeaways

  • Lithium requires regular monitoring of thyroid (TSH) and renal function tests (RFTs).
  • Clozapine mandates strict Absolute Neutrophil Count (ANC) monitoring due to high agranulocytosis risk.
  • For Valproate, periodically check liver function tests (LFTs) and complete blood count (CBC).
  • Amiodarone necessitates baseline and periodic TFTs, LFTs, and chest X-rays/PFTs.
  • Warfarin/Acenocoumarol therapy is closely guided by PT/INR to prevent bleeding or thrombosis.
  • Methotrexate requires routine checks of CBC, LFTs, and RFTs.

Practice Questions: Medication monitoring protocols

Test your understanding with these related questions

A 22-year-old male with a history of difficult-to-treat bipolar disorder with psychotic features is undergoing a medication adjustment under the guidance of his psychiatrist. The patient was previously treated with lithium and is transitioning to clozapine. Which of the following tests will the patient need routinely?

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