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Axid Oral Solution

Axid Oral Solution

CLINICAL PHARMACOLOGY

Clinical Pharmacology in Adults

Nizatidine is a competitive, reversible inhibitor of histamine at the histamine H2-receptors, particularly those in the gastric parietal cells.

Antisecretory Activity
Effects on Acid Secretion

Nizatidine significantly inhibited nocturnal gastric acid secretion for up to 12 hours. Nizatidine also significantly inhibited gastric acid secretion stimulated by food, caffeine, betazole, and pentagastrin (Table 1).

Table 1: Effect of Oral Nizatidine on Gastric Acid Secretion

  Time After Dose (h) % Inhibition of Gastric Acid Output by Dose (mg)
20-50 75 100 150 300
Nocturnal Up to 10 57 - 73 - 90
Betazole Up to 3 - 93 - 100 99
Pentagon Up to 6 - 25 - 64 67
Meal Up to 4 41 64 - 98 97
Caffeine Up to 3 - 73 - 85 96

Effects on Other Gastrointestinal Secretions—Pepsin

Oral administration of 75 to 300 mg of nizatidine did not affect pepsin activity in gastric secretions. Total pepsin output was reduced in proportion to the reduced volume of gastric secretions.

Intrinsic Factor: Oral administration of 75 to 300 mg of nizatidine increased betazolestimulated secretion of intrinsic factor.

Serum Gastrin Concentration: Nizatidine had no effect on basal serum gastrin concentration. No rebound of gastrin secretion was observed when food was ingested 12 hours after administration of nizatidine.

Other Pharmacologic Actions
  1. Hormones: Nizatidine was not shown to affect the serum concentrations of gonadotropins, prolactin, growth hormone, antidiuretic hormone, cortisol, triiodo-thyronine, thyroxin, testosterone, 5 a-dihydro-testosterone, androstenedione, or estradiol.
  2. Nizatidine had no demonstrable antiandrogenic action.
Pharmacokinetics

The absolute oral bioavailability of nizatidine exceeds 70%. Peak plasma concentrations (700 to 1,800 μg/L for a 150-mg dose and 1,400 to 3,600 μg/L for a 300-mg dose) occur from 0.5 to 3 hours following the dose. Plasma concentrations 12 hours after administration are less than 10 μg/L. The elimination halflife is 1 to 2 hours, plasma clearance is 40 to 60 L/h, and the volume of distribution is 0.8 to 1.5 L/kg. Because of the short half-life and rapid clearance of nizatidine, accumulation of the drug would not be expected in individuals with normal renal function who take either 300 mg once daily at bedtime or 150 mg twice daily. Nizatidine exhibits dose proportionality over the recommended dose range.

The oral bioavailability of nizatidine is unaffected by concomitant ingestion of the anticholinergic propantheline. Antacids consisting of aluminum and magnesium hydroxides with simethicone decrease the absorption of nizatidine by about 10%. With food, the AUC and Cmax increase by approximately 10%. In humans, less than 7% of an oral dose is metabolized as N2-monodesmethylnizatidine, an H2-receptor antagonist, which is the principal metabolite excreted in the urine. Other likely metabolites are the N2-oxide (less than 5% of the dose) and the S-oxide (less than 6% of the dose).

More than 90% of an orally administered dose of nizatidine is excreted in the urine within 12 hours. About 60% of an oral dose is excreted as unchanged drug. Renal clearance is about 500 mL/min, which indicates excretion by active tubular secretion. Less than 6% of an administered dose is eliminated in the feces.

Moderate to severe renal impairment significantly prolongs the half-life and decreases the clearance of nizatidine. In individuals who are functionally anephric, the half-life is 3.5 to 11 hours, and the plasma clearance is 7 to 14 L/h. To avoid accumulation of the drug in individuals with clinically significant renal impairment, the amount and/or frequency of doses of nizatidine should be reduced in proportion to the severity of dysfunction (see DOSAGE AND ADMINISTRATION).

Approximately 35% of nizatidine is bound to plasma protein, mainly to a1-acid glycoprotein. Warfarin, diazepam, acetaminophen, propantheline, phenobarbital, and propranolol did not affect plasma protein binding of nizatidine in vitro.

At a dose of 150 mg, the Axid® Oral Solution (15 mg/mL) is bioequivalent to nizatidine capsules.

Clinical Pharmacology in Pediatric Patients

Pharmacokinetics

Table 2 presents pharmacokinetic data of nizatidine administered orally to adolescents with gastroesophageal reflux (GER) and healthy adults. Pharmacokinetic parameters for adolescent patients ages 12 to 18 years are comparable to those obtained for adults.

Table 2: Pharmacokinetics of Oral Nizatidine

Age Range Formulation Dose Cmax (ng/mL) Tmax (h) AUC0-8 (ng?h/mL) CLF(L/h) VdF (L) T½ (h)
12-18 yr Adolescents with GER Capsule 150 mg SD 1422.9 1.3 3764.2 41.0 71.4 1.2
150 mg SS 1480.2 1.4 3776.1 41.1 74.2 1.3
Healthy Adults Capsule 150 mg SD 1367.6 1.0 3703.1 41.9 83.4 1.4
Oral Solution 150 mg SD 1340.6 0.8 3610.9 43.0 86.4 1.4
Apple Juice 150 mg SD 762.8 1.3 2694.1 57.5 142.3 1.7
SD=single dose
SS=steady state

Administration of nizatidine capsules in apple juice results in 27% reduction of nizatidine bioavailability.

Pharmacodynamics

Pharmacodynamics of nizatidine were evaluated in 48 pediatric patients. These data suggest that gastric acid suppression is similar to that observed in adult studies (Table 3).

Table 3: Pharmacodynamics of Oral Nizatidine

Age %Time
pH>3
%Time
pH>4
AUEC0-12h
(pH.h)
12-18 years 57 42 41.4
Adults 31 19 34.8

Clinical Trials (Adults)

1. Active Duodenal Ulcer: In multicenter, double-blind, placebo-controlled studies in the United States, endoscopically diagnosed duodenal ulcers healed more rapidly following administration of nizatidine, 300 mg h.s. or 150 mg b.i.d., than with placebo (Table 4). Lower doses, such as 100 mg h.s., had slightly lower effectiveness.

Table 4: Healing Response of Ulcers to Nizatidine

  Nizatidine Placebo
300 mg h.s. 150 mg bid
Number
Entered
Healed/
Evaluable
Number
Entered
Healed/
Evaluable
Number
Entered
Healed/
Evaluable
STUDY 1
Week 2     276 93/265 (35%) * 279 55/260 (21%)
Week 4       198/259 (76%)   95/243 (39%)
STUDY 2
Week 2 108 24/103 (23%)* 106 27/101 (27%)* 101 9/93 (10%)
Week 4   65/97 (67%)*   66/97 (68%)*   24/84 (29%)
STUDY 3
Week 2 92 22/90 (24%)†     98 13/92 (14%)
Week 4   52/85 (61%)*       29/88 (33%)
Week 8   68/83 (82%)*       39/79 (49%)

2. Maintenance of Healed Duodenal Ulcer: Treatment with a reduced dose of nizatidine has been shown to be effective as maintenance therapy following healing of active duodenal ulcers. In multi-center, double-blind, placebo-controlled studies conducted in the United States, 150 mg of nizatidine taken at bedtime resulted in a significantly lower incidence of duodenal ulcer recurrence in patients treated for up to 1 year (Table 5).

Table 5: Percentage of Ulcers Recurring by 3, 6, and 12 Months in Double-Blind Studies Conducted in the United States

Month Nizatidine. 150 mg h.s. Placebo
3 13% (28/208)* 40% (82/204)
6 24% (45/188)* 57% (106/187)
12 34% (57/166)* 64% (112/175)

3. Gastroesophageal Reflux Disease (GERD): In 2 multi-center, double-blind, placebo-controlled clinical trials performed in the United States and Canada, nizatidine was more effective than placebo in improving endoscopically diagnosed esophagitis and in healing erosive and ulcerative esophagitis. In patients with erosive or ulcerative esophagitis, 150 mg b.i.d. of nizatidine given to 88 patients compared with placebo in 98 patients in Study 1 yielded a higher healing rate at 3 weeks (16% vs 7%) and at 6 weeks (32% vs 16%, P < 0.05). Of 99 patients on nizatidine and 94 patients on placebo, Study 2 at the same dosage yielded similar results at 6 weeks (21% vs 11%, P < 0.05) and at 12 weeks (29% vs 13%, P < 0.01).

In addition, relief of associated heartburn was greater in patients treated with nizatidine. Patients treated with nizatidine consumed fewer antacids than did patients treated with placebo.

4. Active Benign Gastric Ulcer: In a multicenter, double-blind, placebo-controlled study conducted in the United States and Canada, endoscopically diagnosed benign gastric ulcers healed significantly more rapidly following administration of nizatidine than of placebo (Table 6).

Table 6

Week Treatment Healing Rate vs. Placebo p-value*
4 Nizatidine 300 mg h.s. 52/153 (34%) 0.342
Nizatidine 150 mg b.i.d 65/151 (43%) 0.022
Placebo 48/151 (32%)  
8 Nizatidine 300 mg h.s 99/153 (65%) 0.011
Nizatidine 150 mg b.i.d 105/151 (70%) < 0.001
Placebo 78/151 (52%)  
*P-values are one-sided, obtained by Chi-square test, and not adjusted for multiple comparisons.

In a multicenter, double-blind, comparator-controlled study in Europe, healing rates for patients receiving nizatidine (300 mg h.s. or 150 mg b.i.d.) were equivalent to rates for patients receiving a comparator drug, and statistically superior to historical placebo control rates.

Last reviewed on RxList: 8/24/2012
This monograph has been modified to include the generic and brand name in many instances.

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