Small Animal Dermatology, 3rd edition

APPENDIX B DRUG FORMULARY 785

Levothyroxine sodium(Soloxine, Thyro-Tabs,Synthroid)

Replacement therapy fortreating patients withhypothyroidism.Levothyroxine is T

,which 4

is converted in mostpatients to the active T

. 3

High doses may producethyrotoxicosis, which isuncommon (compared topeople).

Drug

interactions

: Patients

receiving corticosteroidsmay have decreasedability to convert T

4

to T

. 3

Thyroid supplementationshould be guided bytesting to confirmdiagnosis andpostmedicationmonitoring to adjust dose.

0.1–0.8 mg tablets(in 0.1 mgincrements).

Dog: 18–22

μ
g/kg q12h

po (adjust dose viamonitoring).Cat: 10–20

μg/kg/day po

(adjust dose viamonitoring).

Lidocaine (Xylocaineand generic brands)

Local anesthetic.Lidocaine is alsocommonly used for acutetreatment of cardiacarrhythmias. Class 1antiarrhythmic. Decreasesphase 0 depolarizationwithout affectingconduction.

High doses cause CNSeffects (tremors, twitches,and seizures). Lidocainecan produce cardiacarrhythmias but hasgreater effect onabnormal cardiac tissuethan normal tissue. Catare more susceptible toadverse effects, and lowerdoses should be used.

When used for localinfiltration, manyformulations containepinephrine to prolongactivity at injection site.Avoid epinephrine inpatients with cardiacarrhythmias. Note thathuman formulations maycontain epinephrine, butno veterinary formulationscontain epinephrine. Toincrease pH, increaseonset of action, anddecrease pain frominjection, one may add1 mEq sodiumbicarbonate to 10 mLlidocaine (use immediatelyafter mixing).

5, 10, 15, 20 mg/mLinjection.

Dog (antiarrhythmic):2–4 mg/kg IV (to amaximum dose of8 mg/kg over 10 minperiod); 25–75

μg/kg/min

IV infusion; 6 mg/kg q1.5hIM.Cat (antiarrhythmic):0.25–0.75 mg/kg IVslowly, or10–40

μg/kg/min infusion.

For epidural (dog and cat):4.4 mg/kg of 2% solution.

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