OTHER OPIOID ANALGESICS: DEXTROPROPOXYPHENE AND FENTANYL

Jun
20
2011

Posted by: admin in Categories: Pain Relief-Muscle Relaxers.

Dextropropoxyphene is a synthetic opioid agonist structurally related to methadone. Dextropropoxyphene is indicated for mild to moderate pain. It should be used with caution in patients with significant hepatic or renal impairment and in the elderly, in whom accumulation of the drug or its metabolite, norpropoxyphene, may predispose to toxicity. The side effects are similar to other opioid drugs. A small proportion of patients develop light-headedness, dysphoria and confusion at standard doses, necessitating changing to a different drug. Dextropropoxyphene is commercially available as napsylate alone or as hydrochloride with paracetamol.

Fentanyl-Fentanyl is a synthetic opioid agonist used for perioperative pain. It can be given by the IV, IM, SC, ED or transdermal routes. It has a short duration of action (0.5-lh) and can be used for painful procedures or to prevent incident pain. Fentanyl 0.1 mg is equivalent to morphine 10 mg IM. Patients intolerant of morphine and requiring parenteral therapy can be treated by continuous IV or SC infusion, although the latter is limited to lower doses because of the volumes required.

Fentanyl is the first opioid drug to be marketed for transdermal use. Fentanyl is absorbed from a Transdermal Therapeutic System’, each patch providing analgesia for 72 hours. After application of the first patch the plasma concentration of fentanyl rises slowly and does not peak for 12-24 hours; other analgesia will be required during this time. The amount of fentanyl absorbed varies between patients. There will be continued release of drug from the ‘reservoir’ in the subcutaneous tissues for about 24 hours after the patch is removed. The starting dose, as described in the product information and package insert, is calculated from the previous 24 hour requirement of oral morphine or equivalent. Transdermal fentanyl is effective in patients intolerant of oral morphine or unable to take it because of dysphagia or drowsiness. It is particularly useful in renal failure.