Correlation between withdrawal symptoms and medication pump residual volume in patients with implantable SynchroMed pumps.

OBJECTIVE

To investigate whether patients with implantable SynchroMed pumps (Medtronic, Inc., Minneapolis, MN) develop symptoms of drug withdrawal at residual medication volumes that exceed 2 ml (the alarm residual volume recommended by the manufacturer).

METHODS

The data sheets of 88 patients with implantable SynchroMed pumps were retrospectively reviewed. The following parameters were analyzed: development of symptoms of drug withdrawal; drugs used in the pump; disease state; drug residual volume in the pump; intake of orally administered medications; time of development of withdrawal symptoms; drug flow volume through the pump; daily intrathecally administered drug dose; and drug concentration in the pump.

RESULTS

Of 88 patients, 21 (24%) consistently developed symptoms of drug withdrawal 1 to 7 days before the drug residual volume reached a mean of 2.7 ml (range, 2.1-3.8 ml; median, 2.6 ml). Symptoms first developed 1 to 18 months after surgery. In all patients, symptoms of drug withdrawal subsided after pump refill and did not recur after the alarm volume was increased to 4 ml. Symptom development did not correlate with intake of orally administered medication, drug flow volume through the pump, intrathecally administered drug dose, drug concentration in the pump, drugs used in the pump, or disease state.

CONCLUSION

Some patients develop symptoms of drug withdrawal at residual volumes that exceed 2 ml. We could not identify factors that predict this occurrence. Withdrawal symptoms did not recur when the alarm volume was increased to 4 ml.