Veterinary Anesthesia & Analgesia Support Group
Practical Information for the Compassionate Veterinary Practitioner
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    G Drugs
    Alphabetical Drug Summaries
     
    Dr. Bob Stein
   
   

1)   GABAPENTIN

a)      Classification

i)        A calcium channel blocker felt to have similar affects and applications as does its' brother, pregabalin

b)      General Information

i)        An oral prescription medication capable of helping reduce neuropathic and other chronic pain states

(1)   Gabapentin suppresses central sensitization[1],[2]

ii)     Gabapentin possesses nonlinear pharmacokinetics; bioavailability decreases with increasing dose; plasma levels plateau[3]

(1)   This is an absortion driven dynamic; at a point, excess drug simply passes down the alimentary canal without absorption, harm, or benefit

(2)   For linear, "what you give is what you get", calcium channel blocker effect see pregabalin

c)      Advantages/Recommended use

i)        Chronic pain management

ii)      Preoperative analgesic adjunct

iii)    Preoperative anxiolytic[4]

iv)    Generally free from adverse effects or drug interaction

(1)   Unlike NSAIDs, gabapentin is NOT associated with any expected gastrointestinal, renal, or hepatic adverse affects what-so-ever

d)      Cautionary Information

i)       Chronic use may cause a transient drowsiness usually lasting no more than a few days

ii)       Excreted unchanged in the urine

(1)   Reduce dose in patients with substantial renal impairment

iii)     Withdraw this drug gradually to avoid rebound pain

iv)     Use of the liquid form of gabapentin, which contains xylitol, is not recommended for dogs or cats

e)      Dosage Information

i)        Dogs

(1)   2.0 to 40 mg/kg (1.0 to 20.0 mg/lb) BID to TID PO

ii)       Cats

(1)   2.0 to 30.0 mg/kg (1.0 to 15 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 for dogs or cats

 

f)       Cost

            i)    Branded product is expensive - generics are bringing the price down to a moderate level

1 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 Central sensitization and Ca(V)α₂δ ligands in chronic pain syndromes: pathologic processes and pharmacologic effect. Tuchman M, Barrett JA, Donevan S, Hedberg TG, Taylor CP. J Pain. 2010 Dec;11(12):1241-9

3A comparison of the pharmacokinetics and pharmacodynamics of pregabalin and gabapentin. Bockbrader HN, Wesche D, Miller R, Chapel S, Janiczek N, Burger P. Clin Pharmacokinet. 2010 Oct 1;49(10):661-9

4 Pregabalin--profile of efficacy and tolerability in neuropathic pain. Stump P. Drugs Today (Barc). 2009 Oct;45 Suppl C:19-27

 

 

 

 

 

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
     
     
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Last modified: February 17, 2012 .