Toxicity serum digoxin levels

Digoxin at high levels can cause confusion and sedation in the elderly but Mrs GG does not present with confusion. Also digoxin toxicity can cause arrhythmias or bradycardia which can result in a drop in cardiac output leading to a fall. Again she does not presently exhibit any symptoms of digoxin toxicity so this is unlikely. A digoxin serum level may be useful to confirm this. 

High serum potassium levels decrease cardiac effects Associated with potentiated digoxin toxicity (possibly due to low intracellular potassium levels caused by hypomagnesemia)... 

An 86-year-old man taking fiirosemide, digoxin, domperidone and sustained-release theophylline developed signs of theophylline toxicity when amiodarone 600 mg daily was given. After 9 days his serum theophylline levels had doubled, from about 16.8 to 35 mg/L. The toxicity disappeared when the theophylline was stopped. The reason for this adverse reaction is not understood but it has been suggested that amiodarone may reduce the metabolism of the theophylline by the liver. This is an isolated case and its general importance is uncertain. More study is needed. 

A man with major depression responded well to desipramine 175 mg daily with serum desipramine levels in the range of 500 to 1000 nanomol/L. When he was treated for paroxysmal atrial fibrillation with digoxin 250 micrograms daily and propafenone 150 mg twice daily and 300 mg at night he developed markedly elevated serum desipramine levels (2092 nanomol/L) and toxicity (dry mouth, sedation, shakiness) while taking desipramine 150 mg daily. The adverse effects resolved when the desipramine was stopped for 5 days, but when it was restarted at 75 mg daily his serum desipramine levels were still raised (1130 nanomol/L). 

Raja Rao MP, Panduranga P, Sulaiman K, Al-JufaiH M. Digoxin toxicity with normal digoxin and serum potassium levels beware of magnesium, the hidden malefactor. J Emerg Med 2013 45(2) e31-4. 

RED FLAG Hypokalemia may result in digoxin toxicity. Monitor serum digoxin and potassium levels closely at the start of therapy and until maintenance doses are determined. 

Buspirone causes less additive CNS depression than do the other antianxiety drugs. However, it is recommended that concurrent use with a CNS depressant be avoided. Buspirone may increase serum digoxin levels, which increases the risk of digitalis toxicity. 

The effects of buspirone are decreased when the drug is administered with fluoxetine Increased serum levels of buspirone occur if the drug is taken with erythromycin or itraconazole Should any of these combinations be required, the dosage of buspirone is decreased to 2.5 mg BID, and the patient is monitored closely. Venlafaxine blood levels increase with a risk of toxicity when administered witii MAOIs or cimetidine There is an increased risk of toxicity when trazodone is administered with the phenothiazines and decreased effectiveness of trazodone when it is administered with carbamazepine Increased serum digoxin levels have occurred when digoxin is administered with trazodone There is a risk for increased phenytoin levels when phenytoin is administered witii trazodone... 

Which of Hie following serum digoxin levels would be most indicative that a patient taking digoxin may be experiencing toxicity ... 

Electrical cardioversion It may be desirable to reduce the dose of digoxin for 1 to 2 days prior to electrical cardioversion of atrial fibrillation to avoid the induction of ventricular arrhythmias, but physicians must consider the consequences of increasing the ventricular response if digoxin is withdrawn. If digitalis toxicity is suspected, delay elective cardioversion. If it is not prudent to delay cardioversion, select the lowest possible energy level to avoid provoking ventricular arrhythmias. Lab test abnormalities Periodically assess serum electrolytes and renal function (serum creatinine concentrations) the frequency of assessments will depend on the clinical setting. 

Serum digoxin levels when compliance, effectiveness, or systemic availability is questioned or toxicity suspected... 

Mordel A, Halkin H, Zulty L, et al. Quinidine enhancers digitalis toxicity at therapeutic serum digoxin levels. Clin Pharmacol Ther 1993 53 457 -62. 

Duhme DW, Greenblatt DJ, Koch-Weser J. Reduction of digoxin toxicity associated with measurement of serum levels. Ann Intern Med 1974 80 516-9... 

Digoxin 0.125 mg q.o.dy q.d. (daily or every other day) 0.25 mg/day 25% 100% 100% 100% In ESRD and total body clearance decreased decrease loading dose by 50% serum level 12 hr after dose is best guide to clearance use digoxin-immune antibodies to treat severe toxicity Radioimmunoassay may overestimate serum levels in uremia clearance decreased by amiodarone, spironolactone, quinidine, and verapamil hypokalemia and hvDomaanesemia enhance toxicitv NC NC Dose for GFR 10-50 ml/min... 

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