Ivabradine can cause phosphenes, an enhanced brightness in a portion of the visual field; this side effect was reported in 3% of patients taking the drug in the SHIFT trial.167 Table 6. Acute Drug Therapy for SVT, Intravenous Administration* Drug Initial Dose Subsequent or Maintenance Dose Potential Adverse Effects Precautions (Exclude or Use With Caution) and Interactions Nucleoside Adenosine 6-mg rapid IV bolus (injected into IV as proximal or as close to the heart as possible), administered over 1 2 s, followed by rapid saline flush If no result within 1 2 min, 12-mg rapid IV bolus; can repeat 12-mg dose 1 time. The safe use of 18-mg bolus doses has been Transient AV block, flushing, chest pain, hypotension, or dyspnea, AF can be initiated or cause decompensation in the presence of pre-excitation, PVCs/ventricular tachycardia, bronchospasm (rare), or coronary steal. Minor side effects are usually transient because of adenosine s very short half-life. 