Penetration of roxatidine into the cerebrospinal fluid

A mathematical model for prediction of drug molecule diffusion across the blood-brain barrier

BACKGROUND

Predicting the ability of drugs to enter the brain is a longstanding problem in neuropharmacology. The first step in creating a much-needed computational algorithm for predicting whether a drug will enter brain is to devise a rigorous mathematical model.

METHODS

Employing two experimental measures of blood-brain barrier (BBB) penetrability (brain/plasma ratio and the brain-uptake index) and 14 theoretically derived biophysical predictors, a mathematical model was developed to quantitatively correlate molecular structure with ability to traverse the BBB.

RESULTS

This mathematical model employs Stein's hydrogen bonding number and Randic's topological descriptors to correlate structure with ability to cross the BBB. The final model accurately predicts the ability of test molecules to cross the BBB.

CONCLUSIONS

A mathematical method to predict blood-brain barrier penetrability of drug molecules has been successfully devised. As a result of bioinformatics, chemoinformatics and other informatics-based technologies, the number of small molecules being developed as potential therapeutics is increasing exponentially. A biophysically rigorous method to predict BBB penetrability will be a much-needed tool for the evaluation of these molecules.

Comparative effects of H2-receptor antagonists on subjective and objective assessments of sleep

BACKGROUND

Clinically, it is common for patients to experience drowsiness in association with consumption of H1-receptor antagonists. Reported side-effects with H2-receptor antagonists include insomnia and somnolence. The present study was designed to assess and compare the effects of three H2-receptor antagonists (cimetidine, famotidine, and ranitidine) on nocturnal and daytime sleepiness.

METHODS

This is a double-blind crossover study on 12 normal volunteers. Subjects were studied under conditions of placebo, cimetidine (400 mg b.d.), famotidine (20 mg b.d.), and ranitidine (150 mg b.d.) for one week. Sleep was assessed at the end of each one-week interval via polysomnographic evaluation conducted on nights 6 and 7 of drug administration. On the day between the two nights in the sleep laboratory, a multiple sleep latency test was conducted.

RESULTS

The results revealed a significant reduction in the sleep onset latency with famotidine administration, but since there were no effects of any of the medications in the multiple sleep latency test, this finding is of dubious clinical significance. Cimetidine revealed a small increase in subjective estimates of sleepiness. No effects on sleep-related respiratory parameters were noted.

CONCLUSIONS

This study demonstrates the lack of effect of peripheral administration of H2-receptor antagonists on sleep stages, while subjective or objective assessment of daytime alertness revealed small effects of famotidine and cimetidine.

Roxatidine acetate. A review of its pharmacodynamic and pharmacokinetic properties, and its therapeutic potential in peptic ulcer disease and related disorders

Roxatidine acetate is a histamine H2-receptor antagonist which, after almost complete oral absorption (greater than 95%), is rapidly converted to its active metabolite, roxatidine, by esterases in the small intestine, plasma and liver. Roxatidine is a potent inhibitor of basal and stimulated gastric acid secretion in animals and humans and, like most other H2-receptor antagonists, has no anti-androgenic effects and does not interfere with the hepatic metabolism of other drugs. Large-scale trials have shown that roxatidine acetate 150mg per day is as effective as standard doses of cimetidine and ranitidine in the treatment of patients with duodenal or gastric ulcer, and that roxatidine acetate 75mg in the evening is likely to become a 'standard' regimen for the prevention of peptic ulcer recurrence. Preliminary data also suggest that roxatidine acetate may be useful in the treatment of reflux oesophagitis and stomal ulcer, and in the prevention of pulmonary acid aspiration. Roxatidine acetate is an H2-receptor antagonist which has been well tolerated in clinical trials. However, broader experience is required before definitive statements about tolerability relative to other H2-receptor antagonists can be made, and before the role of roxatidine acetate in the treatment of reflux oesophagitis and stomal ulcer, and the prophylaxis of acid aspiration pneumonitis, can be clearly defined.