Currently, no published guidelines address the administration of adenosine by central venous access [1]. We describe three patients who received 3 or 6 mg (0.035 to 0.097 mg/kg) of adenosine and experienced heart block or ventricular asystole lasting from 3 to 21 seconds (see Table 1 below). A fourth exhibited no adverse effects after 3 mg (0.033 mg/kg) of adenosine. All were patients in intensive care who received adenosine diagnostically. None had known conduction abnormalities. Two were heart transplant recipients experiencing severe rejection.

Potential drug interactions with adenosine may have contributed to these adverse reactions [2, 3]. Dipyridamole was chronically administered to Patient 3, who experienced the most profound heart block. This patient received 0.035 mg/kg of adenosine, well below the usual dose of 0.085 mg/kg. However, one group of investigators found the mean effective adenosine dose to be 1 mg in patients receiving dipyridamole compared with 8.8 mg in patients not receiving dipyridamole [3]. Although patients undergoing heart transplantation may be more sensitive to adenosine [4], Patient 4 received the same 3-mg dose (0.033 mg/kg) without adverse effects.

At least one dose of a benzodiazepine, which may enhance the effects of adenosine, was given to three patients [2]. Clinicians should be aware of this potential interaction in settings where benzodiazepines are frequently administered.

The effect of adenosine may be potentiated when administered by central venous access [5]; its cumulative effective dose for supraventricular tachycardia was 67% of that required when the drug was given by peripheral routes [5]. Yet, Patient 4, who received 3 mg centrally (0.033 mg/kg), exhibited no adverse effects.

On the basis of our experience and that of others [5], an initial adenosine dose of 0.030 to 0.040 mg/kg (usually 3 mg) appears appropriate when administered by central access in the absence of other interacting drugs. Our patient receiving no known interacting drugs exhibited an appropriate response with a dose of 0.033 mg/kg, substantially less than the typical dose of 0.080 to 0.090 mg/kg [2]. Increasing the dose incrementally would appear preferable to waiting for prolonged heart block or asystole to dissipate. In patients receiving interacting drugs such as dipyridamole, further lowering of the dose may be warranted. Controlled studies are needed to determine the necessary adenosine dosage adjustments.