Small Animal Clinical Pharmacology - CYF MEDICAL DISTRIBUTION

LAXATIVE THERAPY
● Erythromycin may increase serum concentrations of
theophylline and terfenadine. In humans, this effect
is particularly important because this combination
has been associated with the development of fatal
arrhythmias.
● The metabolism of methylprednisolone may be
inhibited and the clearance of theophylline may be
increased by concurrent erythromycin administration.
The significance of the former interaction is not
clear, whilst the interaction with theophylline may
lead to theophylline toxicity and close pharmacological
monitoring is recommended.
● Erythromycin may prolong prothrombin times and
lead to bleeding when given to a patient previously
stabilized on warfarin.
● Other reported human drug interactions of erythromycin
include ciclosporin, carbemazepine and triazolam.
However, the significance of such interactions
for veterinary species is less well established.
● Administration of erythromycin may falsely elevate
serum concentrations of ALT and AST if colorimetric
assays are used and urinary catecholamine measurements
may be altered in a similar manner.
LAXATIVES, ENEMAS AND
BOWEL CLEANSERS
These drugs are commonly used to evacuate the large
bowel and the main pathological indications are constipation
and obstipation.
LAXATIVE THERAPY
A number of groups of laxative drugs exist, including
bulk-forming laxatives, emollient laxatives, lubricant
laxatives, hyperosmotic laxatives and stimulant
laxatives.
Bulk-forming laxatives
Most of the available agents in this group are dietary
fiber supplements which contain poorly digestible polysaccharides
and celluloses. These are mainly derived
from cereal grains, wheat bran and psyllium. This group
of agents can either be given in a purpose-formulated
‘prescription’ diet or as a preparation added to the existing
diet. Examples include psyllium (Vetasyl®, Metamucil®,
Genifiber®, etc.) and sterculia (Peridale®). Dietary
fiber supplements are usually well tolerated, more effective
and more physiological than the other groups of
laxatives.
Psyllium
• DOGS: 5 mL (1 teaspoonful) to 30 mL (2 tablespoonfuls) PO
q.12–24 h
• CATS: 5–20 mL (1–4 teaspoonfuls) PO with each meal
Sterculia
DOGS and CATS
• 15 kg: 4 g PO q.12–24 h
Emollient laxatives
Emollient laxatives are anionic detergents that reduce
surface tension, thus increasing the miscibility of water
and lipid digesta. This thereby increases lipid absorption
and impairs the absorption of water. There is some evidence
that docusate sodium (dioctyl sodium sulfosuccinate),
the main agent used in this group, also increases
colonic mucosal cell cAMP concentration and thus
increases both ion secretion and fluid permeability.
Most of the effect of this drug is local, although some
drug is absorbed from the small intestine and then
excreted into bile.
Docusate is present as the sole agent in enemas (e.g.
Fletcher’s enemette, Dioctynate®, Enema-DSS®, Docusoft®,
Ther-evac®) and some oral preparations (tablets,
capsules and syrups of various strengths) or in combination
products with dantron, a fecal softener (e.g. ‘condanthrusate’,
Docusol®; 50 mg dantron and 60 mg
docusate/5 mL). The enema preparations are all veterinary-licensed
products, but the oral preparations are
not.
Clinical efficacy has not been established definitively.
Nevertheless, they are safe agents when used in healthy
well-hydrated individuals. However, these preparations
should be avoided in patients with pre-existing electrolyte
or fluid deficits. These drugs have few reported side
effects when used at recommended doses; cramping,
diarrhea and intestinal mucosal damage have been
reported, whilst liquid oral preparations can sometimes
cause pharyngeal irritation. Concurrent administration
of mineral oil is not recommended, because enhanced
absorption of the oil may occur. If overdose occurs, it
is advisable to monitor hydration and systemic electrolyte
status. If concurrent administration is essential, it
is advisable to stagger dosing by at least 2 h.
Docusate sodium (dioctyl sodium sulfosuccinate)
• DOGS: 50–300 mg PO q.12–24 h; 10–15 mL of a 5% solution
mixed with 100 mL of water and instilled per rectum
• CATS: 50 mg PO q.12–24 h; 2 mL of a 5% solution mixed with
50 mL of water and instilled per rectum
485