generally 2.0–2.5 hours in a patient with normal creatinine clearance. Excretion: The primary route of excretion is the urine. In addition, about 30% of the orally administered dose is collected in the urine as unabsorbed drug in 24 hours. Elderly In the elderly population, the plasma half-life of ranitidine is prolonged to 3–4 hours secondary to decreased kidney function causing decreased clearance. Children In general, studies of pediatric patients (aged one month to 16 years) have shown no significant differences in pharmacokinetic parameter values in comparison to healthy adults, when correction is made for body weight. History Ranitidine was first prepared in England as AH19065 by John Bradshaw in the summer of 1977 in the Ware research laboratories of Allen and Hanburys, part of the larger Glaxo organisation. Its development was a response to the first in class histamine H2 receptor antagonist, cimetidine, developed by Sir James Black at Smith, Kline and French, and launched in the United Kingdom as Tagamet''' in November 1976. Both companies eventually merged as GlaxoSmithKline (GSK), following a sequence of mergers and acquisitions, starting with the integration of Allen and Hanbury's Ltd and Glaxo to form Glaxo Group Research in 1979, and ultimately with the merger of Glaxo Wellcome and SmithKline Beecham in 2000. Ranitidine was the result of a rational drug-design process using what was by then a fairly refined model of the histamine H2 receptor and quantitative structure-activity relationships. Glaxo refined the model further, by replacing the imidazole ring of cimetidine with a furan ring with a nitrogen-containing substituent, and in doing so developed ranitidine. Ranitidine was found to have a far-improved tolerability profile (i.e. fewer adverse drug reactions), longer-lasting action, and 10 times the activity of cimetidine. Ranitidine has 10% of the affinity that cimetidine has to CYP450, so it causes fewer side effects, but other H2 blockers famotidine and nizatidine have no CYP450 significant interactions. Ranitidine was introduced in 1981, and was the world's biggest-selling prescription drug by 1987. Subsequently, it was largely superseded by the more effective proton-pump inhibitor (PPI) class of drugs, with omeprazole becoming the biggest-selling drug for many years. When omeprazole and ranitidine were compared in a study of 144 people with severe inflammation and erosions or ulcers of the oesophagus, 85% of those treated with omeprazole healed within eight weeks, compared with 50% of those given ranitidine. In addition, the omeprazole group reported earlier relief of