Rectal bioavailability of lidocaine from a suppository and a slow release preparation in man
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In a previous investigation it was shown that the systemic availability of lidocaine in humans following rectal administration of an aqueous solution was about twofold higher than after oral administration. Most likely this was due to a partial avoidance of hepatic ‘first-pass’ metabolism.
In the present study the systemic availability of two different rectal dosage forms of lidocaine was examined. Six healthy volunteers received in a balanced cross-over design a rectal capsule with slow release granules and a suppository, both containing 300 mg lidocaine as lidocaine. HCl. Plasma concentrations were measured for 8 h after drug administration by capillary gas chromatography. The mean rectal systemic availability of the two preparations was not significantly different: 49% (suppository) and 54% (capsule), when compared to the results obtained in a previous investigation after intraveneous administration. Early defaecation occasionally caused a loss of still unabsorbed drug. Mean bioavailability of the rectal aqueous solution was 70%. As expected, the absorption from the suppository was more rapid than from the capsule: the mean peak times were 122 min and 195 min respectively (p < 0.05). The mean maximum plasma concentrations were comparable: 0.70Μg/ml (suppository) and 0.69Μg/ml (capsule) respectively. These results confirm the previous findings that rectal administration of lidocaine results in a higher systemic availability than oral administration, but they are at the same time rather variable with the dosage forms studied.
KeywordsLidocaine Systemic Availability Rhein Rectal Administration Pharmaceutisch Weekblad Scientific Edition
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