Low doses of epidural ketamine or neostigmine, but not midazolam, improve morphine analgesia in epidural terminal cancer pain therapy.

STUDY OBJECTIVE

To examine analgesia and adverse effects of combination epidural pain therapy consisting of administration of morphine with either low dose of ketamine, neostigmine, or midazolam in terminal cancer pain patients.

DESIGN

Randomized double-blind study.

SETTING

Teaching hospital.

PATIENTS

48 terminal cancer patients suffering from chronic pain.

INTERVENTIONS

Patients were randomized to one of four groups (n = 12). The concept of visual analog scale (VAS), which consisted of a 10-cm line with 0 equaling "no pain at all" and 10 equaling "the worst possible pain" was introduced. All patients were taking oral amitriptyline 50 mg at bedtime. Pain was initially treated with epidural morphine 2 mg twice daily (12-hr intervals) to maintain the VAS below 4/10. Afterwards, VAS scores > or = 4/10 at any time were treated by adding the epidural study drug (2 ml), which was administered each morning, just after the 2-mg epidural morphine administration. The control group (CG) received 2 mg of epidural morphine (2 ml). The ketamine group (KG) received 0.2 mg/kg epidural ketamine (2 ml). The neostigmine group (NG) received 100 micrograms epidural neostigmine (2 ml). The midazolam group (MG) received 500 micrograms epidural midazolam (2 ml). Patients received the study drugs on a daily basis.

MEASUREMENTS AND MAIN RESULTS

Duration of effective analgesia was measured as time from the study drug administration to the first patient's VAS score > or = 4/10 recorded in days. The groups were demographically the same. The VAS pain scores prior to the treatment were also similar among groups. Only the patients in the KG demonstrated lower VAS scores compared to the MG (p = 0.018). Time since the epidural study drug administration until patient complaint of pain VAS > or = 4/10 was higher for both the KG and NG compared to the CG (KG > CG, p = 0.049; NG > CG; p = 0.0163). Only the KG used less epidural morphine compared to the CG during the period of study (25 days) (p = 0.003).

CONCLUSION

The association of either low-dose epidural ketamine or neostigmine (but not midazolam) to epidural morphine increased the duration of analgesia in the population studied (gt;20 days) compared to the CG and MG (8 to 10 days) when administered in the early stages of terminal cancer pain therapy, without increasing the incidence of adverse effects.