Twenty four hourintragastric acidity andplasma gastrin concentration inhealthy volunteers taking

SUMMARY Ninehealthy volunteers were studied on theseventh dayofdosing at2100h with nizatidine 150mg (N150), nizatidine 300mg (N300), ranitidine 300mg (R300), orplacebo, given in a predetermined randomorder. Thedouble-blind 24hourstudies, using theRoyalFreeHospital standard protocol, simultaneously measured intragastric acidity andplasma gastrin concentration. Comparedwithplacebo, subjects responded todosing witheachH2-antagonist bya significant decrease of24hourintragastric acidity (N150 - 45%;N 300- 49% R 300- 56%;p<001)anda significant rise ofplasma gastrin concentration (N150+20%; N300+27%; R300+58%; p<001). Allthree drugregimens caused similar significant decreases ofnocturnal acidity (N150 - 72%; N 300- 79%;R 300- 85%;p<001)andincreases ofnocturnal plasma gastrin concentration (N150+41%; N300+52%; R 300+80%;p<001). Dosing withranitidine 300mg at2100halso caused a simultaneous significant decrease ofmorning acidity (-32%;p<0O05) witha significant increase ofplasma gastrin concentration (+36%;p<005), buttheantisecretory effects ofnizatidine 150or300mg at2100hwereonlyobserved during thenight, with noeffect during themorning. No drugregimen hadanyeffect onacidity orplasma gastrin intheafternoon orearly evening. Nizatidine (EliLilly andCompany) isa newlydeveloped histamine H2-receptor antagonist,' which inhibits humangastric acidsecretion stimulated by shamfeeding, pentagastrin, orpeptone meal.2 The oral bioavailability ofnizatidine inmanexceeds 90% andthedrughasahalf-life inplasma of1-6hours.2 Nizatidine doesnotinterfere withdrugmetabolism bybinding withcytochrome P-450,4 nordoesit influence malehormone function orfertility.' Thepurpose ofthepresent double blind placebo controlled studywastocomparetheeffects ata steady state oforal doses ofeither nizatidine (150 or 300mg)orranitidine 300mg - takenduring the