Ranitidine Hydrochloride (Page 2 of 6)

Pharmacodynamics

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.

Antisecretory Activity

1. Effects on Acid Secretion

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.

Table 2. Effect of Oral Ranitidine on Gastric Acid Secretion

Time after

Dose, h

% Inhibition of Gastric Acid

Output by Dose, mg
75-80 100 150 200
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.

2. Effects on Other Gastrointestinal Secretions

Pepsin

Ranitidine does not affect pepsin secretion. Total pepsin output is reduced in proportion to the decrease in volume of gastric juice.

Intrinsic Factor

Ranitidine has no significant effect on pentagastrin-stimulated intrinsic factor secretion.

Serum Gastrin

Ranitidine has little or no effect on fasting or postprandial serum gastrin.

Other Pharmacologic Actions

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.

Pediatrics

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.

Clinical Trials

Active Duodenal Ulcer

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.

Table 3. Duodenal Ulcer Patient Healing Rates
*
All patients were permitted antacids as needed for relief of pain.
P <0.0001.
Ranitidine * Placebo *

Number

Entered

Healed/

Evaluable

Number

Entered

Healed/

Evaluable

Outpatients

69/182 31/164
(38%) (19%)
195 188
Week 4 137/187 76/168
(73%) (45%)

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.

Table 4. Mean Daily Doses of Antacid
Ulcer Healed Ulcer Not Healed
Ranitidine 0.06 0.71
Placebo 0.71 1.43

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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