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Monday, February 7, 2011

digoxin

Posted by Sampil 5:22 PM, under | No comments

digoxin
(di jox' in)
Digitek, Lanoxicaps, Lanoxin, Novo-Digoxin (CAN)

Pregnancy Category C

Drug classes
Cardiac glycoside
Cardiotonic

Therapeutic actions
Increases intracellular calcium and allows more calcium to enter the myocardial cell during depolarization via a sodium–potassium pump mechanism; this increases force of contraction (positive inotropic effect), increases renal perfusion (seen as diuretic effect in patients with CHF), decreases heart rate (negative chronotropiceffect), and decreases AV node conduction velocity.

Indications
·        CHF
·        Atrial fibrillation

Contraindications and cautions
·        Contraindicated with allergy to digitalis preparations, ventricular tachycardia, ventricular fibrillation, heart block, sick sinus syndrome, IHSS, acute MI, renal insufficiency and electrolyte abnormalities (decreased K+, decreased Mg2+increased Ca2+).
·        Use cautiously with pregnancy and lactation.

Available forms
Lanoxicaps capsules—0.05, 0.1, 0.2 mg; tablets—0.125, 0.25, mg, elixir—0.05 mg/mL; injection—0.25 mg/mL; pediatric injection—0.1 mg/mL

Dosages
Patient response is quite variable. Evaluate patient carefully to determine the appropriate dose.
ADULTS
Loading dose, 0.75–1.25 mg PO or 0.125–0.25 mg IV. Maintenance dose, 0.125–0.25 mg/day PO.
Lanoxicaps capsules
0.4–0.6 mg PO. Maintenance dose, 0.1 –0.3 mg/day PO.
PEDIATRIC PATIENTS
·        Loading dose:

Oral (mcg/kg)
IV (mcg/kg)
Premature
20–30
15–25
Neonate
25–35
20–30
1–24 mo
35–60
30–50
2–5 yr
30–40
25–35
5–10 yr
20–35
15–30
> 10 yr
10–15
8–12
Maintenance dose, 20%–30% of loading dose in divided daily doses. Usually 0.125–0.5 mg/day PO; 20%–30% for premature babies.
GERIATRIC PATIENTS WITH IMPAIRED RENAL FUNCTION
Creatinine Clearance (mL/min)
Dose
10–25
0.125 mg/day
26–49
0.1875 mg/day
50–79
0.25 mg/day

Pharmacokinetics
Route
Onset
Peak
Duration
Oral
30–120 min
2–6 hr
6–8 days
IV
5–30 min
1–5 hr
4–5 days

Metabolism: Some hepatic; T1/2: 30–40 hr
Distribution: May cross placenta; enters breast milk
Excretion: Urine, unchanged

IV facts
Preparation: Give undiluted or diluted in fourfold or greater volume of sterile water for injection, 0.9% sodium chloride injection, or 5% dextrose injection. Use diluted product promptly. Do not use if solution contains precipitates.
Infusion: Inject slowly over 5 min or longer.
Incompatibility: Do not mix with dobutamine.

Adverse effects
·        CNS: Headache, weakness, drowsiness, visual disturbances, mental status change
·        CV: Arrhythmias
·        GI: GI upset, anorexia

Interactions
·        Increased therapeutic and toxic effects of digoxin with thioaminesverapamilamiodaronequinidine, quinine, erythromycin, cyclosporine (a decrease indigoxin dosage may be necessary to prevent toxicity; when the interacting drug is discontinued, an increase in the digoxin dosage may be necessary)
·        Increased incidence of cardiac arrhythmias with potassium-losing (loop and thiazide) diuretics
·        Increased absorption or increased bioavailability of oral digoxin, leading to increased effects with tetracyclines, erythromycin
·        Decreased therapeutic effects with thyroid hormones, metoclopramidepenicillamine
·        Decreased absorption of oral digoxin if taken with cholestyramine, charcoal, colestipolantineoplastics (bleomycincyclophosphamidemethotrexate)
·        Increased or decreased effects of oral digoxin (adjust the dose of digoxin during concomitant therapy) with oral aminoglycosides
·        Increased risk of digoxin toxicity if taken with ginseng, hawthorn, or licorice therapy
·        Decreased absorption with psyllium
·        Decreased serum levels with St. John's wort

Nursing considerations
Assessment
·        History: Allergy to digitalis preparations, ventricular tachycardia, ventricular fibrillation, heart block, sick sinus syndrome, IHSS, acute MI, renal insufficiency, decreased K+, decreased Mg2+ increased Ca2+, pregnancy, lactation
·        Physical: Weight; orientation, affect, reflexes, vision; P, BP, baseline ECG, cardiac auscultation, peripheral pulses, peripheral perfusion, edema; R, adventitious sounds; abdominal percussion, bowel sounds, liver evaluation; urinary output; electrolyte levels, LFTs, renal function tests

Interventions
·        WARNING: Monitor apical pulse for 1 min before administering; hold dose if pulse < 60 in adult or < 90 in infant; retake pulse in 1 hr. If adult pulse remains < 60 or infant < 90, hold drug and notify prescriber. Note any change from baseline rhythm or rate.
·        Take care to differentiate Lanoxicaps from Lanoxin; dosage is very different
·        Check dosage and preparation carefully.
·        Avoid IM injections, which may be very painful.
·        Follow diluting instructions carefully, and use diluted solution promptly.
·        Avoid giving with meals; this will delay absorption.
·        Have emergency equipment ready; have K+ salts, lidocainephenytoin, atropine, cardiac monitor readily available in case toxicity develops.
·        WARNING: Monitor for therapeutic drug levels: 0.5–2 ng/mL.

Teaching points
·        Do not stop taking this drug without notifying your health care provider.
·        Take pulse at the same time each day, and record it on a calendar (normal pulse for you is___); call your health care provider if your pulse rate falls below ____.
·        Weigh yourself every other day with the same clothing and at the same time. Record this on the calendar.
·        Do not start taking any prescription or over-the-counter products without talking to your health care provider. Some combinations may increase the risk of digoxin toxicity and may put you at risk of adverse reactions.
·        Wear or carry a medical alert tag stating that you are on this drug.
·        Have regular medical checkups, which may include blood tests, to evaluate the effects and dosage of this drug.
·        Report unusually slow pulse, irregular pulse, rapid weight gain, loss of appetite, nausea, vomiting, blurred or "yellow" vision, unusual tiredness and weakness, swelling of the ankles, legs or fingers, difficulty breathing.

Adverse effects in Italic are most common; those in Bold are life-threatening.

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