Serum concentrations necessary to inhibit 50% of stimulated gastric acid secretion are estimated to be 36 to 94 ng/mL. Following a single oral dose of 150 mg, serum concentrations of ranitidine are in this range up to 12 hours. However, blood levels bear no consistent relationship to dose or degree of acid inhibition.
Ranitidine inhibits both daytime and nocturnal basal gastric acid secretions as well as gastric acid secretion stimulated by food, betazole, and pentagastrin, as shown in Table 2.
Time afterDose, h
% Inhibition of Gastric AcidOutput by Dose, mg
|Basal||Up to 4||99||95|
|Nocturnal||Up to 13||95||96||92|
|Betazole||Up to 3||97||99|
|Pentagastrin||Up to 5||58||72||72||80|
|Meal||Up to 3||73||79||95|
It appears that basal-, nocturnal-, and betazole-stimulated secretions are most sensitive to inhibition by ranitidine, responding almost completely to doses of 100 mg or less, while pentagastrin- and food-stimulated secretions are more difficult to suppress.
Ranitidine does not affect pepsin secretion. Total pepsin output is reduced in proportion to the decrease in volume of gastric juice.
Ranitidine has no significant effect on pentagastrin-stimulated intrinsic factor secretion.
Ranitidine has little or no effect on fasting or postprandial serum gastrin.
a. Gastric bacterial flora – increase in nitrate-reducing organisms, significance not known.
b. Prolactin levels – no effect in recommended dosage.
c. Other pituitary hormones – no effect on serum gonadotropins, TSH, or GH. Possible impairment of vasopressin release.
d. No change in cortisol, aldosterone, androgen, or estrogen levels.
e. No antiandrogenic action.
f. No effect on count, motility, or morphology of sperm.
Oral doses of 6 to 10 mg/kg per day in two or three divided doses maintain gastric pH>4 throughout most of the dosing interval.
In a multicenter, double-blind, controlled, US study of endoscopically diagnosed duodenal ulcers, earlier healing was seen in the patients treated with ranitidine as shown in Table 3.
|Ranitidine *||Placebo *|
In these studies, patients treated with ranitidine reported a reduction in both daytime and nocturnal pain, and they also consumed less antacid than the placebo-treated patients.
|Ulcer Healed||Ulcer Not Healed|
Foreign studies have shown that patients heal equally well with 150 mg two times a day and 300 mg at bedtime (85% versus 84%, respectively) during a usual 4-week course of therapy. If patients require extended therapy of 8 weeks, the healing rate may be higher for 150 mg two times a day as compared to 300 mg at bedtime (92% versus 87%, respectively).
Studies have been limited to short-term treatment of acute duodenal ulcer. Patients whose ulcers healed during therapy had recurrences of ulcers at the usual rates.
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