Page 410 - Feline Cardiology

434 Section Q: Which Drug for Which Disease?

regular formulation (administered q 8 hours) may be Severe LV hypertrophy
considered in asthmatic cats who are intolerant to
atenolol due to exacerbation of bronchoconstriction • Acceptable treatments: atenolol, ACE inhibitor, both,
and have marked hypertrophy and/or moderate to or none. No proven benefit to treatment even with
severe systolic anterior motion of the mitral valve. massive LV hypertrophy, but beta blockade and/or
• Calcium-channel blocker, sustained release (diltia- ACE inhibition likely beneficial if easily administered.
zem: Cardizem-CD or Dilacor-XL). Not recom-
mended due to adverse effects and variable absorption Congestive heart failure: see below
of this human formulation in the cat. Aortic thromboembolism: see below
• ACE inhibitor (benazepril 0.25 mg/kg PO q 24h, enal- Syncope: see “Arrhythmias,” below
april 0.25–0.5 mg/kg PO q 24h, ramipril 0.25–0.5 mg/
kg PO q24 h). Disparate results of two studies, showing DILATED CARDIOMYOPATHY (DCM)
either no improvement in hypertrophy or mild antihy- Early, compensated disease, where impostors (chamber
pertrophic effect in the compensated state (Taillefer dilation from alpha-antagonist sedatives, pathologic
and Di Fruscia 2006 et al.; MacDonald et al. 2006); bradycardias), valvular regurgitation, and left-to-right
long-term benefit unproven. shunting have been ruled out:

• Taurine (250 mg PO q 8–12h). Taurine status (whole
Clinical States (Patient Status Based blood +/- plasma) must be assessed in all cats with
on History and Physical Examination) echocardiographic findings consistent with DCM,
Early, compensated HCM (mild LV hypertrophy, no left since supplementation can be curative for taurine-
atrial enlargement) deficiency–induced myocardial failure (Pion et al.
1987). Despite safety and low cost of taurine, long-
• Acceptable treatments: atenolol, or diltiazem HCl (q term empiric supplementation should be preceded by
8h), or no treatment. confirmation of low blood levels because the tablet is
large and the act of pill administration may be signifi-
Systolic anterior motion of the mitral valve (docu- cantly onerous to patient or owner (and not of benefit
mented echocardiographically) when blood/plasma levels are within normal limits).
No known benefit to supplementation when taurine
• If congestive heart failure is absent: atenolol, or no levels are within normal limits.
treatment. • Digoxin (0.01875–0.03125 mg/cat PO q 48h). No
• If congestive heart failure is present: furosemide conclusive benefit shown in feline DCM from digoxin
and an ACE inhibitor (enalapril or benazepril); alone. Nevertheless, digoxin is justifiably part of most
atenolol if clinical signs of congestive heart failure treatment protocols when DCM has progressed to
are well-controlled and patient is overtly normal (con- cause CHF, not before. Monitor for clinical signs of
troversial; some use a lower dosage of atenolol, if toxicosis (vomiting, diarrhea, lethargy, inappetence).
any). May assess serum levels, though no known correla-
tion to benefit or outcome in the cat (used mainly to
Left atrial enlargement (moderate or severe) rule in/out toxicosis).
• Pimobendan (1.25 mg/cat PO q 12h). Dosage extrapo-
• Acceptable treatments (none has been shown to be lated from canine studies (4–10 times higher than
superior to any other, nor superior to no, treatment): human dosage). Informally described in 11 cases of
• Aspirin, regular dose (81 mg/cat PO q 3d); or feline RCM (Sturgess et al. 2007). Risks associated
with long-term treatment are unknown in the cat, but
• Aspirin, low-dose (5 or 20 mg/cat PO q 3d); or
Which Rx? • Warfarin (0.25–0.6 mg/cat PO q 24h, adjusted to early clinical experience is encouraging. Off-label,
maintain prothrombin time between 1.5 and 2.5
and considered investigational use.
times highest normal value); or
• Low molecular weight heparin (dalteparin: 150 IU/ • ACE inhibitor: no known benefit prior to congestive
heart failure, but coupled with furosemide it is part of
kg SC q 4h; enoxaparin 1.5 mg/kg SC q 6–8 h); phar- the standard of care for treatment of heart failure.
macokinetics in the cat require short dosage inter- • Beta blocker: contraindicated, due to decreased ino-
vals, which may be impractical for many owners as tropic function and heart rate (risk of inadequate
well as very expensive; or cardiac output) induced by beta blockade at recom-
• Clopidogrel (18.75 mg/cat PO q 24h with food). mended dosages. Microdose (e.g., <2 mg/cat PO q