Differences in color vision impairment caused by digoxin, digitoxin, or pengitoxin

Area of Science:

• Pharmacology
• Ophthalmology
• Cardiology

Background:

• Digitalis glycosides are commonly prescribed for heart failure.
• Cardiac medications can have ocular side effects.
• Color vision is crucial for daily activities and requires precise neural processing.

Purpose of the Study:

• To investigate the effect of digoxin, digitoxin, and pengitoxin on color discrimination.
• To determine if digitalis glycoside plasma levels correlate with color vision impairment.
• To compare the ocular toxicity profiles of different digitalis glycosides.

Main Methods:

• Farnsworth's Munsell 100 hue test administered to 53 heart failure patients and 32 healthy volunteers.
• Radioimmunoassay used to measure glycoside plasma levels.
• Color vision tested after reaching steady-state plasma concentrations or after months of treatment.

Main Results:

• Increased total error scores (indicating poorer color discrimination) correlated with higher glycoside plasma levels.
• Therapeutic digoxin concentrations impaired color vision in 17 of 28 subjects.
• Toxic plasma levels of all tested glycosides, particularly digoxin, significantly impaired color discrimination.

Conclusions:

• Digoxin exhibits a greater tendency to impair color vision compared to digitoxin and pengitoxin at therapeutic and toxic levels.
• Retinal uptake or distribution differences may explain digoxin's higher ocular toxicity.
• Monitoring color vision may be advisable for patients on digitalis glycosides, especially digoxin.