Opioid analgesics oral analgesic dosing

Opioid analgesic Approximate equivalent dose Oral conversion ratio... 

The combination of an opioid and nonopioid oral analgesic often results in analgesia superior to monotherapy and may allow for lower doses of each agent. An NSAID with a scheduled opioid dose is often effective for painful bone metastases. 

IR tablets - For the management of moderate to severe pain in patients who require treatment with an oral opioid analgesic. Individually adjust the dose according to severity of pain, patient response, and patient size. If the pain increases in severity, analgesia is not adequate, or tolerance occurs, a gradual increase in dosage may be required. 

Codeine, one of the principal alkaloids of opium, has an analgesic efficacy much lower than other opioids, due to an extremely low affinity for opioid receptors. It is approximately one-sixth as potent as morphine. It has a low abuse potential. In contrast to other opioids, with the exception of oxycodone, codeine is relatively more effective when administered orally than parenterally. This is due to methylation at the C3 site on the phenyl ring (Figure 7.3), which may protect it from conjugating enzymes. It is used in the management of mild-to-moderate pain, often in combination with non-opioid analgesics, such as aspirin or paracetamol. It is valuable as an antitussive and for the treatment of diarrhoea. Side effects are uncommon and respiratory depression, even with large doses, is seldom a problem. 

Diclofenac, a derivative of phenylacetic acid, is equipotent as an inhibitor of COX-1 and COX-2. In addition to prostaglandin inhibition a central analgesic action of diclofenac mediated by endogenous opioid peptides has been demonstrated. It can be administered orally, intramuscularly or intravenously, and is effective as a postoperative analgesic in a dose of 75-150 mg. The risks of adverse gastrointestinal effects is moderate and diclofenac does not appear to increase blood loss during or after surgery. 

Most opioid analgesics are well absorbed when given by subcutaneous, intramuscular, and oral routes. However, because of the first-pass effect, the oral dose of the opioid (eg, morphine) may need to be much higher than the parenteral dose to elicit a therapeutic effect. Considerable interpatient variability exists in first-pass opioid metabolism, making prediction of an effective oral dose difficult. Certain analgesics such as codeine and oxycodone are effective orally because they have... 

The following section describes the most important and widely used opioid analgesics, along with features peculiar to specific agents. Data about doses approximately equivalent to 10 mg of intramuscular morphine, oral versus parenteral efficacy, duration of analgesia, and intrinsic activity (maximum efficacy) are presented in Table 31-2. 

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