Amiloride differs from spironolactone in that:

Amiloride is a K+ sparing diuretic and like other diuretics, act from luminal membrane side. On the other hand, Spironolactone does not require access to tubular lumen for action. Diuretic action of both amiloride and spironolactone is quite feeble. Due to its aldosterone receptor blocking action, spironolactone is more effective in the presence of conditions with elevated levels of aldosterone (like CHF). Both of these diuretics can cause hyperkalemia when used with K+ supplements or ACE inhibitors.