Monograph: |
Carbachol
Incompatibility. Chlorocresol (0.025 to 0.1%) and chlorbu-
tol (0.5%) were both found to be incompatible with a solution
of carbachol (0.8%) and sodium chloride (0.69%), very slight
precipitates forming on heating and increasing on standing.'
Adverse Effects and Treatment
As described for choline esters under Acetylcholine Chloride.
Carbachol has substantial nicotinic activity which
may be unmasked by the use of atropine to counteract mus-
carinic effects. Carbachol also produces adverse effects simi-
lar to those of other miotics such as pilocarpine
when used in the eye but may produce more ciliary spasm
than pilocarpine.
Effects on the gastro-intestinal tract. A report of fatal
oesophageal rupture following subcutaneous injection of car-
bachol to relieve urinary retention.
Overdosage. A report of life-threatening attacks of profuse
sweating, intestinal cramps, explosive defaecation, hypother-
mia, hypotension, and bradycardia in a 36-year-old man fol-
lowing deliberate poisoning with 30 to 40 mg of carbachol.
The patient's 10-year-old son had died after poisoning with a
similar dose of carbachol.
Precautions
As described for choline esters under Acetylcholine Chloride.
For precautions when used as a miotic see under Pi-
Locarpine . Carbachol should not be given by the intra-
venous or intramuscular routes as very severe muscarinic
adverse effects are liable to occur, calling for emergency
treatment with atropine.
Interactions
NSAIDs. According to a manufacturer of acetylcholine
chloride ophthalmic preparations there have been reports of
acetylcholine and carbachol being ineffective when used in
patients treated with topical (ophthalmic) NSAIDs.
Uses and Administration
Carbachol, a choline ester, is a quaternary ammonium para-
sympathomimetic with the muscarinic and nicotinic actions
of acetylcholine . It is not inactivated by cholineste-
rases so that its actions are more prolonged than those of ace-
tylcholine.
Carbachol has a miotic action and eye drops containing 0.75
to 3% are sometimes used up to four times daily to lower in-
tra-ocular pressure in glaucoma usually in conjunction with
other miotics. Miosis occurs within 10 to 20 minutes of instil-
lation of carbachol eye drops and lasts for 4 to 8 hours; reduc-
tion in intra-ocular pressure lasts for 8 hours.
Carbachol is also administered intra-ocularly, up to 0.5 mL of
a 0.01% solution being instilled into the anterior chamber of
the eye (intracameral instillation), to produce miosis in ocular
surgery, and reduce postoperative rises in intra-ocular pres-
sure. The maximum degree of miosis is usually obtained
within 2 to 5 minutes of intra-ocular instillation and miosis
lasts for 24 to 48 hours.
Carbachol has been used as an alternative to catheterisation in
the treatment of urinary retention in a dose of 2 mg
given three times daily by mouth on a empty stomach, al-
though catheterisation is generally preferred. For the acute
symptoms of postoperative urinary retention doses of 250 ng
have been given subcutaneously repeated twice if necessary
at 30-minute intervals. For a warning to avoid intravenous or
intramuscular administration, see under Precautions, above.
Carbachol has also been used in some countries for the treat-
ment of decreased gastro-intestinal motility .
Dry mouth. Carbachol has been used as an alternative to
pilocarpine in the treatment of radiation-induced xerostomia.
Glaucoma and ocular hypertension. Carbachol is some-
times used as an alternative to pilocarpine in the management
of glaucoma when resistance or intolerance to pilo-
carpine develops. It is also instilled into the anterior chamber
of the eye (intracameral instillation) to minimise postopera-
live rises in intra-ocular pressure associated with ocular sur-
gery, and is considered by some to be more effective than
acetylcholine.
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