[4] Equianalgesic charts are also used when calculating an equivalent dosage of the same drug, but with a different route of administration.
[citation needed] An equianalgesic chart can be a useful tool, but the user must take care to correct for all relevant variables such as route of administration, cross tolerance, half-life and the bioavailability of a drug.
Repeated administration of a medication is also different from single dosing, as many drugs have active metabolites that can build up in the body.
[6] Patient variables such as sex, age, and organ function may also influence the effect of the drug on the system.
Opioids are a class of compounds that elicit analgesic (pain killing) effects in humans and animals by binding to the μ-opioid receptor within the central nervous system.
[citation needed] This chart measures pain relief versus mass of medication.