Jeffrey L. Segar, MD
Peer Review Status: Internally Peer Reviewed

Drug Dosage Toxicity
Furosemide
 
(Lasix)
 
Inhibits chloride reabsorption in the ascending limb of the loop of Henle, inhibits tubular sodium transport
Initial dose: 1 mg/kg dose
 
IV slow push, IM, or PO.
 
May increase dose as required to a maximum of 2 mg/kg/dose IV or
 
IM and 6 mg/kg/dose PO.
 
For oliguria, repeat max. effective dose as required, but no more often than every 12 hr (fullterm) or 24 hr (premature) 1
Causes major urinary loss of sodium and chloride; also potassium and calcium. Increases prostaglandin secretion and renal blood flow.

Peak effect 1 - 3 hr after IV dose; duration 6 hr. Monitor for dehydration and electrolyte (Na, Cl, K) imbalances, ototoxicity, metabolic alkalosis, renal nephrocalcinosis.
Spironolactone
 
(Aldactone) antagonist of aldosterone
Oral: 1 to 3 mg/kg/d
 
÷ q 12 - 24 hr
increased Urine Ca++, Mg++, Na+, Cl-; decreased Urine K+; clinical effect usu. seen 2 -3 days after start therapy. Monitor for hyperkalemia, drowsiness, GI upset, masculinization, rash
Chlorothiazide
 
(Diuril, Diurigen)
 
decreased sodium reabsorption in the distal nephron
PO or IV: 10 - 20 mg/kg
 
÷ q 12 hr. 2
increased Urine Na+, K+, Mg++, Cl-, HCO3-, phosphorus; Urine Ca++ . Monitor for dehydration and electrolyte imbalances, metabolic alkalosis, hypercalcemia ,hyperglycemia, hyperuricemia; Donít use in pts w/ sig. liver / renal disease
Metolazone
 
decreased Na+ reabsortion in distal nephron
Oral: 0.2 - 0.4 mg/kg /day
 
divided q 12 - 24 hr.
Same as chlorothiazide; hypokalemia is major electrolyte imbalance

Footnotes

  1. The plasma clearance of furosemide varies considerably in the neonate (Aranda et al 1980, Chemtob et al 1987). Since the diuretic effect occurs subsequent to renal tubular secretion, the excessive plasma concentration is more likely to result in displacement of bilirubin or ototoxicity than enhanced diuretic effect. Avoiding an excessive plasma concentration of drug by appropriate dose and dosing intervals is prudent. Attention to the duration of diuretic response along with frequent assessment of diuretic needs (particularly when initiating therapy) will assist in determining the appropriate dose and dosing interval (as opposed to an arbitrary every 12 or 24 hour routine) (Vert et al 1982).
  2. The thiazides have a relatively flat dose response curve indicting that significant increases in dose are not associated with comparable increases in diuretic or antihypertensive effects. Because of the dependence of diuretic effect on renal elimination, an increase in dosing interval is recommended with renal failure (give every 24 hours with 50 percent or less of normal creatinine clearance).