In-vitro and In-vivo Relationship of Gabapentin from Floating and Immediate Release Tablets

Gabapentin is effective against post-traumatic spinal injury-induced neuropathic pain. It requires high dosage and frequency in the management of neuropathic pain. The present research work was an attempt to formulate and evaluate gabapentin gastro-retentive tablets to prolong gastric residence and increase drug absorption and further increase bioavailability. The floating tablets of gabapentin were prepared in two doses (300 and 600 mg) by using two polymers (hydroxyl propyl methyl cellulose and hydroxyl propyl cellulose). Immediate release tablets of gabapentin containing the same doses were prepared and used as reference formulations. The physicochemical characteristics of the prepared tablets were determined (drug content, weight variation, friability, hardness, thickness and diameter). Drug release from the prepared tablets was followed and found that by increasing drug concentration in the tablets release rate increases. Floating tablets showed prolonged drug release (over 96%) to more than 15 hrs. Immediate release tablets showed over 97% drug release within 48 min. In-vivo results showed that plasma exposure to gabapentin in animals receiving the drug does not dose proportional and therefore may not reach therapeutically useful levels. AUC0-24 and Cmax in case of 300 mg tablets are more than those in case of 600 mg tablets. The in-vivo release of gabapentin does not correlate with the in-vitro release of the drug.