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Tacrine is not an ideal probe drug for measuring CYP1A2 activity in vivo
J T Larsen1, L L Hansen, K Brosen
1Institute of Public Health, Clinical Pharmacology, University of Southern Denmark, Main Campus: Odense University, Denmark.
Aims:
The aim of the present study was to examine the CYP1A2 substrate tacrine as a possible alternative to caffeine for assessing CYP1A2 activity in vivo.
Methods:
Eighteen, healthy, nonsmoking men participated. Each volunteer was tested by caffeine (200 mg orally), and caffeine metabolic ratios were calculated. Subsequently, on two occasions, separated by at least 4 weeks, each volunteer was tested with tacrine (40 mg orally). The apparent oral clearance, partial clearances and different metabolic ratios of tacrine were determined.
Results:
The median oral clearances of tacrine in the two study periods were 1893 l h-1 (range: 736-3098) and 1890 l h-1 (range: 438-4175), respectively. The interindividual coefficient of variation was 42% and 49%, respectively. The intraindividual coefficients of variation ranged from 0.28% to 64% (median: 13%). In both study periods, the oral clearance of tacrine correlated with the caffeine urinary metabolic ratio. However, only modest magnitudes of correlation were observed (rs: 0.64-0.66, P<0. 01). No tacrine metabolic ratio correlating with the oral clearance of tacrine was found. Conclusion The applicability of tacrine as a probe drug for measuring CYP1A2 activity in vivo appears limited.
Insights
Tacrine shows limited applicability as a probe drug for assessing CYP1A2 activity in vivo. While tacrine
Area of Science:
- Pharmacology
- Drug Metabolism
- Biochemistry
Background:
- Cytochrome P450 1A2 (CYP1A2) is a key enzyme in drug metabolism.
- Caffeine is a commonly used probe drug for assessing CYP1A2 activity.
- Investigating alternative probe drugs can improve in vivo assessments.
Purpose of the Study:
- To evaluate tacrine, a CYP1A2 substrate, as a potential alternative to caffeine for measuring CYP1A2 activity in vivo.
- To compare the reliability and correlation of tacrine's metabolic parameters with CYP1A2 activity.
Main Methods:
- Eighteen healthy, non-smoking men were enrolled.
- Participants were administered caffeine (200 mg) and tacrine (40 mg) orally on separate occasions.
- Caffeine metabolic ratios and tacrine's oral clearance and metabolic ratios were determined.
Main Results:
- Tacrine exhibited moderate interindividual variability in oral clearance (42-49%).
- Tacrine's oral clearance showed a modest correlation with the caffeine urinary metabolic ratio (r=0.64-0.66).
- No tacrine metabolic ratio correlated significantly with its oral clearance.
Conclusions:
- Tacrine's utility as a probe drug for in vivo CYP1A2 activity assessment is limited.
- The modest correlation and lack of internal correlation suggest potential issues with tacrine's reliability.
- Further research may be needed to identify more suitable CYP1A2 probe drugs.