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G
1)
GABAPENTIN
a)
Classification
i)
An anticonvulsant drug
b)
General Information
i)
An oral prescription medication capable of helping reduce
neuropathic and other chronic pain states
(1)
Although its mechanism is unknown, it has been shown to affect
central sensitization
c)
Advantages/Recommended use
i)
Chronic pain management
ii)
Generally free from adverse effects or drug interaction
d)
Cautionary Information
i)
May cause a transient drowsiness usually lasting no more than a few
days
ii)
Excreted unchanged in the urine
(1)
Reduce dose or discontinue in patients with renal dysfunction
iii)
Withdraw this drug gradually to avoid rebound pain
e)
Dosage Information
i)
Dogs
(1)
2.0 to 10 mg/kg (1.0 to 5.0 mg/lb) BID to QID PO
ii)
Cats
(1)
2.0 to 5.0 mg/kg (1.0 to 2.5 mg/lb) BID PO
iii)
May be able to gradually reduce to SID if doing well after extended
therapy
iv)
Available in 100 mg, 300 mg, 400 mg, 600 mg,
and 800 mg sizes
v)
Use of the liquid form of
gabapentin, which contains xylitol, is not recommended
f)
Cost
i) Branded product is expensive - generics are bringing
the price down to a moderate level
Chronic
Oral Gabapentin Reduces Elements of Central Sensitization in Human
Experimental Hyperalgesia. Gottrup H, Juhl G, Kristensen AD, Lai
R, Chizh BA, Brown J, Bach FW, Jensen TS: Anesthesiology.
Dec;101(6):1400-1408, 2004
2)
GLYCOPYRROLATE
a)
Classification
i)
Anticholinergic
b)
General Information
i)
Decreases salivary secretions
(1)
Can make them thicker, more ropey
(a)
Only reduces serous portion of salivary secretions leaving the
thicker mucoid portion
ii)
Does not cross blood brain-barrier or placenta
c)
Advantages/Recommended use
i)
Much longer duration of effect (2 to 3 hours) compared to atropine
ii)
When bradycardia is clinically significant
(1)
Partial dosing can be used for partial effect but it is not immune
to paradoxical bradycardic effect at lower doses
(2)
This is, perhaps, a gentler anticholinergic than atropine
iii)
Prior to procedure that stimulate strong vagal effect
(1)
Bronchoscopy
(a)
May need to postpone until after respiratory diagnostics have been
completed
iv)
Prior to dental procedures to decrease salivary secretions
(1)
Most would argue against this use
v)
Prior to brachycephalic anesthesia
(1)
Brachycephalics tend to have higher vagal tone making routine
anticholinergic use a consideration
(2)
To decrease salivary secretions
(a)
Most would argue against this use
d)
Cautionary Information
i)
Glycopyrrolate is a definite second choice in emergency cases
ii)
Can cause an initial paradoxical bradycardia and AV block when
given IV
(1)
This effect is usually overcome as plasma levels become therapeutic
iii)
Hypothermia results in decreased depolarization of cardiac
pacemaker cells, causing bradycardia. Since this bradycardia is not
vagally mediated, it can be refractory to glycopyrrolate
iv)
C Sections
(1)
This large molecule does not cross the trans-placental barrier
(a)
Avoid glycopyrrolate when fetal effect is desired as it will not
reach the fetus
v)
Use with caution in tachycardic patients
(1)
Tachyarrhythmia can be an undesirable effect
vi)
Increased heart rate can increase myocardial oxygen demand
vii)
Pupilary dilation may be undesirable for certain ophthalmic
procedure
viii)
Be especially cautious when used with patients on
amitriptyline as that behavioral medication possesses anticholinergic
properties
e)
Dosage Information
(1)
Dogs – 0.010 to 0.015 mg/kg (0.005 to 0.007 mg/lb) IV, IM, SC
(2)
Cats – 0.010 to 0.015 mg/kg (0.005 to 0.007 mg/lb) IV, IM, SC
f)
Cost
i)
Very low
H
1)
HALOTHANE
a)
Classification
i)
A halogenated hydrocarbon
b)
General Information
i)
A relatively fast acting inhalant anesthetic agent
ii)
MAC
(1)
Dogs - 0.76%
(2)
Cats - 0.82%
c)
Advantages/Recommended use
i)
A good choice for general anesthetic use
ii)
May facilitate bronchodilator for respiratory disease patients
d)
Cautionary Information
i)
Undergoes significant hepatic metabolism
(1)
Less well suited to patients with hepatic disease
(2)
Approximately 12% of absorbed drug is metabolized by liver
ii)
More arrhythmogenic than isoflurane
(1)
Avoid if cardiac trauma is suspected
iii)
More likely to trigger malignant hyperthermia than isoflurane
iv)
Vasodilation can create increased intracranial pressure
v)
Preservatives in the product create residue within the vaporizers
(1)
Yearly vaporizer maintenance is recommended
e)
Dosage Information
i)
Mask Induction
(1)
Not recommended
ii)
Induction following injectable agent
(1)
Initiate flow rates of 1.0 to 1.5 liter per minute at 2.5 % - 4.0 %
(a)
Reduce percentage as indicated by patients response
iii)
Maintenance – Moderately low flow use
(1)
Once stable, reduce oxygen flow to 500 ml to 1 liter
(a)
The reservoir bag must remain reasonably full
(i)
If not, the flow rate must be increased and the machine must be
examined for leaks at the earliest possible convenience
(2)
Remember that prior to surgical stimulation, a patient may appear
adequately anesthetized only to show a dramatic response to stimulation
(a)
An experienced anesthetist should be able to anticipate and
minimize this event
(3)
Effective analgesic & sedative premeds will significantly
reduce the level of inhalant agent necessary for maintenance of a surgical
plane of anesthesia
f)
Cost
i)
Low
2)
HEPARIN
a)
Classification
i)
Anticoagulant affecting both intrinsic and extrinsic pathways
b)
General Information
i)
Does not cross placenta
ii)
Protamine is the direct reversal agent
c)
Advantages/Recommended use
i)
To produce heparinized saline solutions
ii)
Treatment of DIC
iii)
Treatment of thromboembolic disease
d)
Cautionary Information
i)
Do not give IM
(1)
Can cause hematoma formation
(2)
Should be given IV or SC only
e)
Dosage Information
i)
Heparinized saline - 1 ml heparin per liter of 0.9% NaCl
(1)
Clearly identify bag contents and dating using a fluorescent orange
label
f)
Cost
i)
Low
3)
HYDROMORPHONE
a)
Classification
i)
Pure mu agonist
(1)
Class II
b)
General Information
i)
Duration of effect is 4 to 6 hours
ii)
Considered to have similar overall properties when compared to
oxymorphone although less potent
c)
Advantages/Recommended use
i)
General premed for anesthetic candidates in all categories
ii)
Generally less panting than oxymorphone
iii)
Unlike Morphine, should not cause transient hypotension
(1)
IV use is not associated
with histamine release
d)
Cautionary Information
i)
Bradycardia is common
ii)
Vomiting is common after IM administration
iii)
There is moderate sedative synergism between hydromorphone and
acepromazine in the dog
(1)
Acepromazine doses should be kept at the lower end of the dose
range
iv)
There is a tendency for cats to be agitated unless higher
Acepromazine doses are used
e)
Dosage Information
i)
Dog – 0.01 to 0.4 mg/kg (0.05 - 0.20 mg/lb) IV, IM
(1)
Generally 0.1 to 0.2 mg/kg (0.05 to 0.10 mg/lb)
ii)
Cats – 0.05 to 0.2 mg/kg (0.025 - 0.10 mg/lb) IV, IM
(1)
Generally 0.05 to 0.1 mg/kg (0.025 to 0.05 mg/lb)
iii)
Induction
(1)
IV induction #2 - combined with fentanyl, hydromorphone, or
oxymorphone – most useful for dogs
(a)
See Diazepam & an Opioid section under Induction Protocols for
details
iv)
Maintenance
(2)
IV maintenance – most useful for dogs
(a)
See Diazepam & an Opioid section under Maintenance Protocols
for details
v)
Epidural dose
(1)
0.03 to 0.10 mg/kg (0.015 to 0.05 mg/lb)
f)
Cost
i)
Low
I
1)
ISOFLURANE
a)
Classification
i)
Fluorinated hydrocarbon
b)
General Information
i)
Considered one of the safest common inhalant agent for patients and
staff
ii)
Its low solubility provided for quick inductions, level
adjustments, and recoveries
iii)
MAC
(1)
Dog - 1.2%
(2)
Cats - 1.5%
c)
Advantages/Recommended use
i)
2nd most rapid inductions and recoveries of common
inhalants
ii)
Does not sensitize the heart to epinephrine induced arrhythmia
iii)
Along with sevoflurane, an inhalant anesthetic of choice for
patients with:
(1)
Liver disease
(a)
Minimal hepatic metabolism
(2)
Intracranial disease
(a)
Less effect on CSF pressure when compared to Halothane
(b)
Maintain ETCO2 at 20 - 30 mm Hg to minimize increases in
CSF pressure
d)
Cautionary Information
i)
Commonly causes respiratory depression
ii)
At higher levels (esp. > 2 x MAC) can be potent cardiac
depressant and vasodilator
iii)
Can cause some increased CSF pressure
e)
Dosage Information
i)
Routine use
(1)
Mask Induction (not recommended for routine use)
(a)
Start with 100% oxygen @ 3 liters/min for 3 - 5 minutes
(b)
Do not cover patients eyes
(c)
After 3 - 5 minutes of O2, start isoflurane @ 0.5 %
(d)
Increase by 0.5 % every 30 - 60 seconds until 2 % is reached
(e)
Then increase to 3.5 % - 5 % to complete induction
(2)
Induction following injectable agent
(a)
Initiate flow rates of 1.0 to 1.5 liter per minute at 3.0 % - 5.0 %
(i)
Reduce percentage as indicated by patients response
(3)
Maintenance – Moderately low flow use
(a)
Once stable, reduce oxygen flow to 500 ml to 1 liter
(i)
The reservoir bag must remain reasonably full
1.
If not, the flow rate must be increased and the machine must be
examined for leaks at the earliest possible convenience
(b)
Remember that prior to surgical stimulation, a patient may appear
adequately anesthetized only to show a dramatic response to stimulation
(i)
An experienced anesthetist should be able to anticipate and
minimize this event
(ii)
Effective analgesic & sedative premeds will significantly
reduce the level of inhalant agent necessary for maintenance of a surgical
plane of anesthesia
f)
Cost
i)
Moderately low |
