Influence of Age on Pain Relief From Analgesics

Analgesic and Thermic Responses to Intravenously Administered Morphine in 8- and 24-Week-Old Rats

“…The analgesic responses to morphine in relation to rat age, obtained in the present studies, are consistent with the findings of Bellville et al [2] and Kaiko [10] in postop erative patients. A similar response was noted in rats injected intraperitoneally [17].…”

“…Using the radiant-heat tech nique, investigators observed that patients younger than 20 years of age had the greatest degree of hypersensitivity to pain, and that pain sensitivity decreased with age as mani fested by increased pain threshold in the older age group [16]. In 712 post-operative patients, Bellville et al [2] demonstrated that morphine or pentazocine produced more pain relief in older patients than in younger ones, and suggested that the doses of analgesics should be adjusted in accordance with age. More recently, Kaiko [10] under took studies to identify age-related differ ences in analgesia after intramuscular ad ministration of morphine in cancer patients with postoperative pain.…”

“…The other factor is pharmacokinetics. On the ba sis of a lack of association between age and incidence of side effects, a kinetic explana tion was dismissed [2], Initial serum mor phine concentrations correlated with age [3]To elucidate the role of pharmacokinetics in altered pharmacodynamics of morphine in rats of different ages, in the present stud ies the effect of intravenous administration of two doses of morphine on the time course of analgesic and hyperthermic responses and pharmacokinetic parameters has been deter mined in 8-and 24-week-old rats.…”

Time Course of the Distribution of Morphine in Brain Regions, Spinal Cord and Serum following Intravenous Injection to Rats of Differing Ages

“…Several studies have been undertaken to determine possible relationships between aging and pain, and the efficacy o f analgesic drugs in the aged subjects [2], Patients younger than 20 years o f age were found to have the greatest degree o f hypersensitivity to pain, and that pain sensitivity decreased with age as evi denced by increased pain threshold to radiant heat in the older age group [3], The effect o f opiates has been determined in rodents and humans o f different ages. A greater pain relief was provided by morphine or pentazocine in older postoperative patients than in younger ones [4], Similar results were obtained after intramuscular injection o f morphine to can cer patients with postoperative pain. Thus, morphine produced enhanced analgesic effect o f longer duration in older patients than in the younger ones [5], Morphine produces greater pharmacological effects in older rats than in younger ones [6,7], However, in mice this activity was found to be in the reverse order [8], Thus, most studies in rodents and hu mans indicate that morphine produces greater analgesia in older subjects in compari son to younger subjects.…”

“…Some o f them include the phar macokinetic differences in the serum, distri bution in spinal and supraspinal structures involved in the actions o f morphine and the activity o f the opiate receptor systems. Expla nations were offered for the lack o f role o f kinetics in the difference in the analgesic response to morphine between the adult and the older patients [4], On the other hand, Berkowitz et al [21] demonstrated a relationship between the initial serum levels o f morphine with age in surgical patients. Previous studies from this laboratory have shown that for a 10 mg/kg dose o f intravenous morphine in the rat, Cmax was lower but the M RT and Vss were significantly higher in 24-week-old than in 8-week-old rats.…”