XP13512 [(+/-)-1-([(alpha-isobutanoyloxyethoxy)carbonyl] aminomethyl)-1-cyclohexane acetic acid], a novel gabapentin prodrug: II. Improved oral bioavailability, dose proportionality, and colonic absorption compared with gabapentin in rats and monkeys.

The absorption of gabapentin (Neurontin) is dose-dependent and variable between patients. Rapid clearance of the drug necessitates dosing three or more times per day to maintain therapeutic levels. These deficiencies appear to result from the low capacity, limited intestinal distribution, and variable expression of the solute transporter responsible for gabapentin absorption. Saturation of this transporter at doses used clinically leads to unpredictable drug exposure and potentially ineffective therapy in some patients. XP13512 [(+/-)-1-([(alpha-isobutanoyloxyethoxy)carbonyl]aminomethyl)-1-cyclohexane acetic acid] is a novel prodrug of gabapentin designed to be absorbed by high-capacity nutrient transporters located throughout the intestine. XP13512 was efficiently absorbed and rapidly converted to gabapentin after oral dosing in rats and monkeys. Exposure to gabapentin was proportional to prodrug dose, whereas exposure to intact XP13512 was low. In rats, >95% of an oral dose of (14)C-XP13512 was excreted in urine in 24 h as gabapentin. In monkeys, oral bioavailability of gabapentin from XP13512 capsules was 84.2% compared with 25.4% after a similar oral Neurontin dose. Compared with intracolonic gabapentin, intracolonic XP13512 gave a 17-fold higher gabapentin exposure in rats and 34-fold higher in monkeys. XP13512 may therefore be incorporated into a sustained release formulation to provide extended gabapentin exposure. XP13512 demonstrated improved gabapentin bioavailability, increased dose proportionality, and enhanced colonic absorption. In clinical use, XP13512 may improve the treatment of neuropathic pain, epilepsy, and numerous other conditions by increasing efficacy, reducing interpatient variability, and decreasing frequency of dosing.

Determination of tranexamic acid (AMCA) and fibrin/fibrinogen degradation products in cerebrospinal fluid after aneurysmal subarachnoid haemorrhage.

Six patients with recently ruptured intracranial aneurysms were treated preoperatively with tranexamic acid (AMCA). Two patients received 6 g daily in i.v. infusion, two had 6 g daily by i.v. injection, and two patients were given AMCA 9 g daily by mouth during the first week after bleeding. Serial assays of AMCA and fibrin/fibrinogen degradation products (FDP) in cerebrospinal fluid (CSF) were performed during 6--13 days after the initial subarachnoid haemorrhage (SAH). Judged from the decline in CSF-FDP, an assumed therapeutic level of greater than or equal to 1 mg/l of AMCA in CSF was reached within 24--36 hours after the first dose when the drug was administered intravenously and within 48 hours when the drug was given orally.