An equianalgesic chart is a conversion chart that lists equivalent doses of
analgesic

Analgesic

An analgesic is any member of the group of drugs used to relieve pain . The word analgesic derives from Greek an- and algos ....

s (drugs used to relieve pain). Equianalgesic charts are used for calculation of an equivalent dose (a dose which would offer an equal amount of analgesia) between different analgesics.

Format

Equianalgesic tables are available in different formats, such as pocket-sized cards for ease of reference. A frequently-seen format has the drug names in the left column, the route of administration in the center columns and any notes in the right column.

Purpose

There are several reasons for switching a patient to a different pain medication. These include practical considerations such as lower cost or unavailability of a drug at the patient's preferred pharmacy, or medical reasons such as lack of effectiveness of the current drug or to minimize adverse effects. Some patients request to be switched to a different narcotic due to stigma associated with a particular drug (i.e. a patient refusing methadone

Methadone

Methadone is a synthetic opioid, used medically as an analgesic and a maintenance anti-addictive for use in patients with opioid dependency. It was developed in Germany in 1937...

 due to its association with opioid

Opioid

An opioid is a psychoactive chemical that works by binding to opioid receptors, which are found principally in the central and peripheral nervous system and the gastrointestinal tract...

 addiction treatment

Methadone maintenance

Methadone maintenance is the use of methadone over a prolonged time as treatment for someone who is addicted to opioids or has severe pain problems that are resistant to other drugs.-Modality:...

). Equianalgesic charts are also used when calculating an equivalent dosage of the same drug, but with a different route of administration

Route of administration

A route of administration in pharmacology and toxicology is the path by which a drug, fluid, poison, or other substance is taken into the body.-Classification:Routes of administration are usually classified by application location...

.

Precautions

Equianalgesic chart are a useful tool, but the user must take care to correct for all relevant variables such as route of administration, cross tolerance, half-life

Half-life

Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...

 and the bioavailability

Bioavailability

In pharmacology, bioavailability is a subcategory of absorption and is used to describe the fraction of an administered dose of unchanged drug that reaches the systemic circulation, one of the principal pharmacokinetic properties of drugs. By definition, when a medication is administered...

 of a drug. For example, the narcotic levorphanol

Levorphanol

Levorphanol is an opioid medication used to treat severe pain. It is the levorotatory stereoisomer of the synthetic morphinan and a pure opioid agonist, first described in Germany in 1948 as an orally active morphine-like analgesic...

 is 4–8 times stronger

Potency (pharmacology)

In the field of pharmacology, potency is a measure of drug activity expressed in terms of the amount required to produce an effect of given intensity. A highly potent drug evokes a larger response at low concentrations, while a drug of lower potency evokes a small response at low concentrations...

 than morphine

Morphine

Morphine is a potent opiate analgesic medication and is considered to be the prototypical opioid. It was first isolated in 1804 by Friedrich Sertürner, first distributed by same in 1817, and first commercially sold by Merck in 1827, which at the time was a single small chemists' shop. It was more...

, but also has a much longer half-life. Simply switching the patient from 40 mg of morphine to 10 mg of levorphanol would be dangerous due to dose accumulation, and hence frequency of administration should also be taken into account.

There are other concerns about equianalgesic charts. Many charts derive their data from studies conducted on opioid-naïve patients. Patients with chronic

Chronic pain

Chronic pain has several different meanings in medicine. Traditionally, the distinction between acute and chronic pain has relied upon an arbitrary interval of time from onset; the two most commonly used markers being 3 months and 6 months since the initiation of pain, though some theorists and...

(rather than acute) pain may respond differently to analgesia. Repeated administration of a medication is also different from single dosing, as many drugs have active metabolites that can build up in the body. Patient variables such as sex, age, and organ function may also influence the effect of the drug on the system. These variables are rarely included in equianalgesic charts.