Parenteral Administration
In
hospitalized patients with pathological hypersecretory conditions or intractable
ulcers, or in patients who are unable to take oral medication, cimetidine
may be administered parenterally.
Intermittent
Intravenous Infusion: 300 mg every 6 to 8 hours, infused over 15
to 20 minutes. In some patients it may be necessary to increase dosage. When
this is necessary, the increases should be made by more frequent administration
of a 300 mg dose, but should not exceed 2400 mg per day.
Continuous Intravenous Infusion: 37.5 mg/hour (900
mg/day). For patients requiring a more rapid elevation of gastric pH, continuous
infusion may be preceded by a 150 mg loading dose administered by I.V. infusion
as described above. Note: A volumetric pump is recommended if the volume for
24-hour infusion is less than 250 mL. In one study in patients with pathological
hypersecretory states, the mean infused dose of cimetidine was 160 mg/hour
with a range of 40 to 600 mg/hour.
These doses maintained
the intragastric acid secretory rate at 10 mEq/hour or less. The infusion
rate should be adjusted to individual patient requirements.
NOTE: The products accompanying this insert are for I.V.
infusion only. Much of the following relates to the use of oral cimetidine
and is for informational purposes only. See Parenteral Administration (above)
for specific dosing recommendations.
Duodenal Ulcer
Active
Duodenal Ulcer: Clinical studies have indicated that suppression
of nocturnal acid is the most important factor in duodenal ulcer healing (see CLINICAL PHARMACOLOGY − Acid Secretion).
This is supported by recent clinical trials (see Clinical
Trials−Active DuodenalUlcer). Therefore, there is no apparent rationale,
except for familiarity with use, for treating with anything other than a once-daily
at bedtime oral dosage regimen (h.s.).
In a U.S. oral
dose-ranging study of 400 mg h.s., 800 mg h.s. and 1600 mg h.s., a continuous
dose response relationship for ulcer healing was demonstrated.
However,
800 mg h.s. is the dose of choice for most patients, as it provides a high
healing rate (the difference between 800 mg h.s. and 1600 mg h.s. being small),
maximal pain relief, a decreased potential for drug interactions (see PRECAUTIONS − Drug Interactions) and maximal
patient convenience. Patients unhealed at four weeks, or those with persistent
symptoms, have been shown to benefit from two to four weeks of continued therapy.
It
has been shown that patients who both have an endoscopically demonstrated
ulcer larger than 1 cm and are also heavy smokers (i.e., smoke one pack of
cigarettes or more per day) are more difficult to heal. There is some evidence
which suggests that more rapid healing can be achieved in this subpopulation
with cimetidine 1600 mg at bedtime. While early pain relief with either 800
mg h.s. or 1600 mg h.s. is equivalent in all patients, 1600 mg h.s. provides
an appropriate alternative when it is important to ensure healing within four
weeks for this subpopulation. Alternatively, approximately 94% of all patients
will also heal in eight weeks with cimetidine 800 mg h.s.
Other
cimetidine oral regimens in the U.S. which have been shown to be effective
are: 300 mg four times daily, with meals at bedtime, the original regimen
with which U.S. physicians have the most experience, and 400 mg twice daily,
in the morning and at bedtime (see Clinical Trials−Active Duodenal Ulcer).
Concomitant
antacids should be given as needed for relief of pain. However, simultaneous
administration of oral cimetidine and antacids is not recommended, since antacids
have been reported to interfere with the absorption of oral cimetidine.
While healing with cimetidine
often occurs during the first week or two, treatment should be continued for
4 to 6 weeks unless healing has been demonstrated by endoscopic examination.
Maintenance Therapy for Duodenal Ulcer: In those
patients requiring maintenance therapy, the recommended adult oral dose is
400 mg at bedtime.
Active
Benign Gastric Ulcer
The recommended adult
oral dosage for short-term treatment of active benign gastric ulcer is 800 mg
h.s., or 300 mg four times a day with meals and at bedtime. Controlled clinical
studies were limited to six weeks of treatment (see Clinical
Trials). 800 mg h.s. is the preferred regimen for most patients
based upon convenience and reduced potential for drug interactions. Symptomatic
response to cimetidine does not preclude the presence of a gastric malignancy.
It is important to follow gastric ulcer patients to assure rapid progress
to complete healing.
Prevention
of Upper Gastrointestinal Bleeding
The recommended
adult dosing regimen is continuous I.V. infusion of 50 mg/hour. Patients with
creatinine clearance less than 30 cc/min. should receive half the recommended
dose. Treatment beyond 7 days has not been studied.
Pathological Hypersecretory Conditions (such as
Zollinger−Ellison Syndrome)
Recommended adult
oral dosage: 300 mg four times a day with meals and at bedtime. In some patients
it may be necessary to administer higher doses more frequently. Doses should
be adjusted to individual patient needs, but should not usually exceed 2400
mg per day and should continue as long as clinically indicated.
Dosage Adjustment for Patients with Impaired Renal Function
Patients with severely impaired renal function
have been treated with cimetidine. However, such usage has been very limited.
On the basis of this experience the recommended dosage is 300 mg every 12
hours orally or by intravenous injection. Should the patient's condition require,
the frequency of dosing may be increased to every 8 hours or even further
with caution. In severe renal failure, accumulation may occur and the lowest
frequency of dosing compatible with an adequate patient response should be
used. When liver impairment is also present, further reductions in dosage
may be necessary. Hemodialysis reduces the level of circulating cimetidine.
Ideally, the dosage schedule should be adjusted so that the timing of a scheduled
dose coincides with the end of hemodialysis.
Patients
with creatinine clearance less than 30 cc/min. who are being treated for prevention
of upper gastrointestinal bleeding should receive half the recommended dose.
Do not add other drugs to premixed Cimetidine in 0.9% Sodium
Chloride Injection, USP in plastic containers.
All
parenteral drug products should be inspected visually for particulate matter
and discoloration prior to administration.