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High-Risk Medicines Parameters

A concise checklist designed to form the basis of a clinical check or patient counselling intervention for three commonly encountered high-risk medicines.

1. Lithium Therapy

Lithium has a narrow therapeutic index (0.4 - 1.0 mmol/L). Toxicity is severe and often irreversible (renal/neurological).

Required Monitoring

  • Lithium levels: Every 3-6 months. Must be taken 12 hours post-dose.
  • Renal function (U&Es): Every 6 months. Lithium is strictly renally cleared; declining eGFR increases toxicity risk.
  • Thyroid function (TFTs): Every 6 months. Lithium frequently induces hypothyroidism.

Counselling Checklist

  • Maintain consistent fluid and sodium intake. Avoid dehydration (hot weather, D&V).
  • OTC interactions: Strictly avoid NSAIDs (Ibuprofen, Naproxen) as they reduce renal clearance of lithium, precipitating toxicity.
  • Toxicity signs: Coarse tremor, severe nausea/diarrhoea, ataxia, confusion.

2. Oral Methotrexate (Non-Oncology)

Used for Rheumatoid Arthritis and severe psoriasis. The single most common fatal error is prescribing or dispensing this daily instead of weekly.

Required Monitoring

  • FBC, U&Es, LFTs: Every 1-2 weeks until therapy stabilised, then every 2-3 months.
  • Risk of severe myelosuppression and hepatotoxicity.

Counselling Checklist

  • Frequency: Take ONCE WEEKLY, ideally on the same day.
  • Folic Acid: Ensure Folic acid is prescribed (usually 5mg once weekly) but taken on a different day to Methotrexate.
  • Warn about signs of blood dyscrasias (unexplained bruising, severe sore throat, infection).

3. Direct Oral Anticoagulants (DOACs)

Apixaban, Rivaroxaban, Edoxaban, Dabigatran. Underdosing increases stroke risk; overdosing causes fatal bleeds.

Required Monitoring

  • Creatinine Clearance (CrCl): Must be calculated via Cockcroft-Gault, not eGFR. Use our calculator.
  • Frequency: CrCl should be recalculated at least annually, or every 6 months if baseline CrCl < 60 mL/min or frail.
  • Weight: Required for accurate CrCl calculation and sometimes direct dosing (Apixaban).

Counselling Checklist

  • Rivaroxaban 15mg and 20mg must be taken with food to ensure adequate absorption.
  • Do not stop taking unless explicitly instructed by a clinician.
  • Carry an anticoagulant alert card.