Nevertheless, theoretically, patients previously dependent upon the inotropic effects of digoxin could develop heart failure and hypokalaemia could result within 1–5 hours, owing to intracellular shifts of potassium, as the effects of digoxin are reversed. Patients who require redigitalization must wait for the complexes to be eliminated from the body by the kidneys, this taking 2–3 days with normal renal function. Unfortunately, fab fragments interfere with both fluorescence excitation transfer immunoassays and radioimmunoassays for digoxin. This means that serum drug levels cannot be monitored until the drug-antibody complexes are cleared from the circulation.