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Prevalence of debrisoquine oxidation phenotypes in glaucoma patients
L Salminen1, R Lindberg, H R Toivari
1Department of Ophthalmology, University of Turku, Finland.
Abstract:
The oxidation of debrisoquine, a sympatholytic antihypertensive agent, exhibits genetic polymorphism. The debrisoquine/4-OH-debrisoquine metabolic ratio (MR) separates the population to poor (PM, MR greater than 12.6) and extensive (EM, MR less than 12.6) metabolizers. 5-10% of the caucasians belong to the PM phenotype. The oxidation of many other drugs, like timolol, correlates with the debrisoquine phenotype. We determined the debrisoquine phenotype in 102 glaucoma patients. The majority of the patients was treated with ophthalmic timolol. Five patients were classified as PMs. However, two of them were on quinidine, a well known inhibitor of debrisoquine oxidation. The prevalence of debrisoquine PM phenotype in glaucoma patients was 2.9% (excluding patients on quinidine) or 4.9% (with patients on quinidine). The figures are slightly lower than the mean value reported for the normal Finnish population. However, both figures lay within the 95% confidence limits of the prevalence of PM phenotype in the normal Finnish population. The beta-blocking activity of oral timolol is increased in PMs. The significance of timolol oxidation phenotype during ocular timolol therapy warrants further investigation.
Insights
The prevalence of poor debrisoquine metabolizers (PMs) in glaucoma patients treated with timolol is within normal Finnish population limits. Further research is needed to understand the impact of timolol oxidation phenotype on ocular therapy.
Area of Science:
- Pharmacogenetics
- Ophthalmology
- Clinical Pharmacology
Background:
- Debrisoquine oxidation exhibits genetic polymorphism, classifying individuals into poor metabolizers (PMs) and extensive metabolizers (EMs) based on the metabolic ratio (MR).
- This genetic variation influences the metabolism of various drugs, including timolol, a beta-blocker commonly used in glaucoma treatment.
- Understanding the prevalence of PMs in specific patient populations is crucial for optimizing drug therapy.
Purpose of the Study:
- To determine the prevalence of the debrisoquine phenotype in glaucoma patients undergoing treatment with ophthalmic timolol.
- To assess potential correlations between the debrisoquine phenotype and timolol therapy in this patient group.
Main Methods:
- Phenotyping of debrisoquine oxidation in 102 glaucoma patients using the debrisoquine/4-OH-debrisoquine metabolic ratio (MR).
- Classification of patients into poor metabolizers (MR > 12.6) and extensive metabolizers (MR < 12.6).
- Consideration of confounding factors, such as concurrent quinidine use, a known inhibitor of debrisoquine oxidation.
Main Results:
- Five patients (4.9%) were initially classified as PMs; however, two were on quinidine.
- Excluding quinidine users, the prevalence of PMs in glaucoma patients was 2.9%, which falls within the 95% confidence limits of the normal Finnish population.
- The beta-blocking activity of oral timolol is known to be increased in PMs.
Conclusions:
- The prevalence of the debrisoquine poor metabolizer phenotype in glaucoma patients treated with timolol is comparable to the general Finnish population.
- The clinical significance of the timolol oxidation phenotype during ocular timolol therapy requires further investigation.