Plasma antipyrine half-life can be determined from urine data

Area of Science:

• Pharmacokinetics
• Drug Metabolism
• Analytical Chemistry

Background:

• Accurate determination of drug half-life is crucial for effective therapeutic drug monitoring and understanding drug disposition.
• Non-invasive methods for assessing drug half-life are desirable for patient convenience and frequent sampling.
• Antipyrine is a model drug frequently used to assess drug-metabolizing enzyme activity.

Purpose of the Study:

• To evaluate the reliability of antipyrine half-life determination using spontaneously voided urine specimens.
• To compare antipyrine half-life estimates derived from urine with those from plasma and saliva.
• To assess the influence of urine output on the accuracy of urinary antipyrine half-life measurements.

Main Methods:

• Antipyrine concentrations were measured in urine, plasma, and saliva from eleven healthy subjects across forty-seven study occasions.
• Subjects received no interfering drugs, interferon, or ketoconazole during the baseline studies.
• Intrasubject correlation coefficients were calculated to assess the agreement between different biological matrices.

Main Results:

• Urine antipyrine half-life showed good intrasubject correlation with plasma (median r=0.85) and saliva (median r=0.75) half-lives.
• Correlation between plasma and urine half-lives was robust when total urine output was at least 1.1 L/day.
• A slight bias towards shorter urinary half-life estimates was observed (0.75 h for plasma-urine, 0.192 h for saliva-urine).

Conclusions:

• Urine antipyrine concentration measurements provide a reliable method for estimating drug half-life, correlating well with plasma and saliva.
• Adequate urine output is important for accurate pharmacokinetic assessments using urinary drug concentrations.
• This non-invasive approach offers a viable alternative for pharmacokinetic studies, particularly when frequent sampling is required.