Digoxin

Digoxin is used in the treatment of cardiac diseases such as atrial fibrillation, atrial flutter and heart failure.

Due to its narrow therapeutic window, generally between 0.5 and 2.0 ng/mL, and the risk of toxicity, monitoring is essential in clinical practice, particularly in the elderly, patients with renal impairment or those with fluctuating renal function.

Levels above this range increase the risk of toxicity, while lower levels may be ineffective. Symptoms of digoxin toxicity may include nausea, vomiting, dizziness, confusion, visual disturbances (such as yellow or green vision) and cardiac arrhythmias. As these symptoms may be non-specific or severe, it is essential to measure digoxin levels to confirm toxicity.

If digoxin toxicity is suspected, rapid digoxin testing is essential to diagnose the condition and initiate appropriate treatment, such as the administration of digoxin-specific antibody fragments (anti-digoxin immunoglobulins).

Lithium is a mood stabilizer widely used to treat manic and depressive episodes and to prevent their recurrence. However, it has a narrow therapeutic window, meaning that the difference between a therapeutic dose and a toxic dose is small.

Lithium levels need to be within a specific range to be effective. For most patients, the therapeutic range is between 0.6 and 1.2 mmol/L (milliequivalents per litre). Monitoring ensures that the dose is sufficient to manage symptoms without causing toxicity.

The appropriate dose of lithium can vary between individuals due to factors like age, kidney function, and body weight. Regular blood tests help guide dose adjustments to maintain lithium levels within the therapeutic range.

Symptoms of lithium toxicity include nausea, vomiting, diarrhea, tremors, confusion, and in severe cases, seizures, coma, or death.

Early detection of elevated lithium levels allows for timely intervention, such as dose reduction or cessation of the drug, before serious toxicity develops.
Interpretation of Lithium Levels:

• Therapeutic Range: The generally accepted therapeutic range for lithium in the blood is 0.6 to 1.2 mmol/L, though this can vary slightly depending on the clinical situation.
• Toxic Levels: Levels above 1.5 mmol/L are considered potentially toxic, with levels above 2.0 mmol/L requiring urgent medical attention.
• Timing of Blood Tests: Lithium levels should be measured 12 hours after the last dose (known as a "trough" level) to ensure an accurate assessment of the steady-state concentration.