Fallacious results from measuring salivary carbamazepine concentrations

Area of Science:

• Pharmacokinetics
• Clinical Chemistry

Background:

• Salivary drug monitoring offers a non-invasive alternative to plasma sampling.
• Accurate interpretation of salivary drug concentrations relies on understanding drug disposition in saliva.

Purpose of the Study:

• To investigate the potential for oral retention of carbamazepine (CBZ) to affect salivary drug concentrations.
• To determine the duration and elimination kinetics of salivary CBZ following oral administration.

Main Methods:

• Carbamazepine (tablets or syrup) was briefly held in the mouth (5 seconds) and then expectorated, followed by rinsing.
• Salivary and plasma concentrations of CBZ were measured over time.
• Salivary elimination half-life of CBZ was calculated.

Main Results:

• Measurable salivary CBZ concentrations persisted for at least 2 hours after administration, despite brief oral retention and rinsing.
• Salivary CBZ demonstrated an apparent mean half-life of 21.0 ± 4.8 minutes.
• Disproportionately high salivary CBZ levels were observed relative to plasma levels in the initial hours post-dose.

Conclusions:

• Oral retention of carbamazepine can significantly impact salivary concentrations.
• Salivary CBZ measurements within 2 hours of dosing may lead to invalid therapeutic drug monitoring results.
• Careful consideration of oral drug retention is crucial for accurate salivary pharmacokinetic studies.