Intranasal Ketamine Absorption and Bioavailability
Intranasal ketamine is absorbed through both nasal mucosa and gastrointestinal tract, achieving an absolute bioavailability of approximately 50-54%, with peak plasma concentrations reached within 20 minutes.
Absorption Mechanism
Intranasal ketamine follows a dual absorption pathway 1:
- 54% of the dose is absorbed directly through the nasal cavity (nasal mucosa), bypassing first-pass hepatic metabolism entirely
- 46% is swallowed and undergoes intestinal absorption followed by first-pass metabolism
- Of the swallowed portion, only 18.6% reaches systemic circulation due to extensive hepatic metabolism
- The nasal fraction (54%) is completely absorbed (100% of this fraction)
Bioavailability Data
The absolute bioavailability ranges from 50-54% depending on dose and formulation 1, 2:
- 28 mg intranasal dose: 54% bioavailability
- 56 mg intranasal dose: 54% bioavailability
- 84 mg intranasal dose: 51% bioavailability
- Pediatric studies confirm 50% bioavailability at 3 mg/kg and 9 mg/kg doses 2
This is substantially higher than oral ketamine (which has low and erratic bioavailability due to extensive first-pass metabolism) and approaches intravenous bioavailability without requiring venous access 3.
Pharmacokinetic Profile
Peak plasma concentrations occur rapidly at 15-21 minutes post-administration 1, 2:
- Tmax: 0.25 hours (15 minutes) in most studies
- Volume of distribution at steady state: 752 L
- Clearance: 114 L/h (hepatic flow-limited)
- Elimination half-life: 1.5 hours
- The major metabolite noresketamine peaks at approximately 120 minutes
Clinical Implications
The intranasal route offers distinct advantages 3:
- Avoids first-pass metabolism for the nasally absorbed fraction
- No venous access required, making it suitable for outpatient settings
- Rapid onset comparable to IV administration
- Ability to repeat doses quickly for breakthrough symptoms
- More predictable absorption than oral or rectal routes
Important Caveat
High-dose intranasal administration (>3 mg/kg) results in unacceptable variability because the large volume required leads to excessive swallowing and unpredictable absorption 2. This limits the intranasal route primarily to low-dose applications for analgesia or depression treatment rather than anesthetic induction.
Population Variations
Asian subjects show altered pharmacokinetics 1:
- 64% decrease in elimination rate constant
- 19.4% decrease in noresketamine clearance
- Japanese subjects show 34% increase in nasal absorption fraction
- These changes result in up to 36% higher drug exposure
Elderly patients (>60 years) demonstrate 21.9 L/h decrease in hepatic blood flow per decade, leading to increased drug exposure 1.