Equianalgesic

An equianalgesic chart is a conversion chart that lists equivalent doses of analgesics (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.^[1] Tables of this general type are also available for NSAIDs, benzodiazepines, depressants, stimulants, anticholinergics and others.

Format

Equianalgesic tables are available in different formats, such as pocket-sized cards for ease of reference.^[1] 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.^[2][3]

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 (e.g. a patient refusing methadone due to its association with opioid addiction treatment).^[4] Equianalgesic charts are also used when calculating an equivalent dosage of the same drug, but with a different route of administration.^{[citation needed]}

Precautions

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.^[5] For example, the narcotic levorphanol is 4–8 times stronger than morphine, 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-naive patients. Patients with chronic (rather than acute) pain may respond to analgesia differently. 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. These variables are rarely included in equianalgesic charts.^[7][3][8]

Opioid equivalency table

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. The following table lists opioid and non-opioid analgesic drugs and their relative potencies. Values for the potencies represent opioids taken orally unless another route of administration is provided. As such, their bioavailabilities differ, and they may be more potent when taken intravenously.^[9]

Nonlinearities

This chart measures pain relief versus mass of medication. Not all medications have a fixed relationship on this scale. Methadone is different from most opioids because its potency can vary depending on how long it is taken. Acute use (1–3 days) yields a potency about 1.5× stronger than that of morphine and chronic use (7 days+) yields a potency about 2.5 to 5× that of morphine.^[10][11] Similarly, the effect of tramadol increases after consecutive dosing due to the accumulation of its active metabolite and an increase of the oral bioavailability in chronic use.^[12][13]

Comparison to oral morphine^[a]

Analgesic	Strength (relative)	Equivalent dose (10 mg oral morphine)[b]	Bioavailability	Half-life of active metabolites (hours)	Oral-to-parenteral ratio	Speed of onset	Duration
Paracetamol[15] (non-opioid)	1⁄360	3600 mg	63–89%	1–4		37 min (PO); 8 min (IV)	5–6 hours
Aspirin[15] (NSAID, non-opioid)	1⁄360	3600 mg	80–100%	3.1–9
Ibuprofen[15] (NSAID, non-opioid)	1⁄222	2220 mg	87–100%	1.3–3
Diflunisal[15] (NSAID, non-opioid)	1⁄160	1600 mg	80–90%	8–12
Naproxen[15] (NSAID, non-opioid)	1⁄138	1380 mg	95%	12–24
Indomethacin[16][17] (NSAID non-opioid)	1⁄64
Diclofenac[15][18] (NSAID, non-opioid)	1⁄10	100 mg (est.)	50–60%	1–4
Ketorolac[19][20] (NSAID, non-opioid)	1⁄3	30 mg IM (est.)[21]	80–100%	5–7
Nefopam[22] (Centrally-acting non-opioid)	5⁄8	16 mg IM (est.)		Nefopam: 3–8, Desmethylnefopam 10–15
Piroxicam[23][24][25] (NSAID non-opioid)	3	6.66 mg				2–4 hours	40 hours
Dextropropoxyphene[26]	1⁄20	130–200 mg
Codeine[27]	3⁄20[10]	100–120 mg (PO)	~90%	2.5–3 (C6G 1.94;[28] morphine 2–3)		15–30 min (PO)	4–6 hours
Tramadol[27]	1⁄10	~100 mg	75% (IR), 85–90% (ER)	6.0–8.8[13] (M1)
Opium[29] (oral)	1⁄10	~100 mg	~25% (morphine)	2.5–3.0 (morphine, codeine)
Tilidine[30]	1⁄10	100 mg	6% (parent drug), 99% (active metabolite)[31]	nortilidine 3.3 (PO) & 4.9 IV, bisnortilidine 5 (PO) & 6.9 (IV)[31]	2.2:1	10–15 minutes (oral) 25–50 minutes (peak analgesic effect)	3–4 hours
Dihydrocodeine[32][33]	1⁄10[10]	100 mg	20%	4
Anileridine[34]	1⁄4	40 mg
Alphaprodine[35]	1⁄5	40–60 mg
Tapentadol[36]	3⁄10[10]	32 mg	32% (fasting)
Pethidine (meperidine)[37]	1⁄3[10]	30 mg SC/IV/IM 300 mg (PO)	50–60% Orally, 100% SC/IV/IM	3–5		5–15 sec if IV, 15–25 min if orally
Dipipanone[38][39]	2⁄5	25 mg (PO)		3.2–3.8 hours			±4 hours
Benzylfentanyl[40][41]	1⁄2
AH-7921[42]	4⁄5
SR-17018[43]	4⁄5	10–12 mg	100% IV (Presumably) Unknown (researches are still being made)			5–10 seconds if used IV and 15-25 min Orally (PO)
Nalbuphine[44]	9⁄10	10–11 mg	~33% (PO), 76% (SC), 81% (IM)[45]	3-6		3 minutes, 10 minutes (peak effect)	3–6 hours[46]
Hydrocodone[47]	1[10]	10 mg	70%[48]	3.8–6 (Instant Release; PO)		10–30 min (Instant Release; PO)	4–6
Pentazocine lactate (IV)[49]	1	10 mg SC/IV/IM, 150 mg (PO)
Morphine (oral)	1	10 mg	~25%	2–4	3:1	30 min (PO)	3–6 hours
Oxycodone (oral)[50]	1.5[10]	6.67 mg	(60–87 / ±75% PO) / 78.2%[51] (IN) / 100% (IV/IM) or other parenteral administrations apart from spinal administration	2–3 hours (Instant Release)(PO); 4.5 hours (Controlled Release)(PO)		10–30 min (Instant Release)(PO); 1 hour (Controlled Release)(PO)	3–6 hours (Instant Release)(PO); 10–12 hours (Controlled Release)(PO)[52]
Spiradoline[53]	1.5-7.0[54]
Nicomorphine[55]	2–3[56]	3.33–5 mg	20%	4
Butorphanol[57]	2.3	4.3 mg	~12% (PO), 25%-35% (SL), 70% (NAS)[58]	3 (IM/IV) 4.5-5.5 (NAS)	5.8:1	15 minutes	3–4 hours
Metopon[59]	3	3.5 mg
Oxycodone (IV/IM) or other parenteral administrations apart from spinal administration[60]	3–4	2.5–3.33 mg	(60–87 / ±75% PO) / 78.2%[51] (IN) / 100% (IV/IM) or other parenteral administrations apart from spinal administration	1.5–3 (IV/IM)		5 min (IV)[60]	2–4 hours
Morphine[27][61] (IV/IM) or other parenteral administrations apart from spinal administration	3–4	2.5–3.33 mg	100%	3–4	3:1/4:1	Instantaneously (from 5 to 15 sec; IV); 5–15 min (IM)	3–7 hours
Clonitazene[62]	2-3[63]	3.33 mg
Methadone (acute)[64][65]	3–4	2.5–3.33 mg	40–90%	15–60	2:1
Methadone (chronic)[65]	2.5–5[10]	2–4 mg	40–90%	15–60	2:1
Phenazocine[66]	3.2-4.3[67]	~2.5 mg				15 min (IV); 30 minutes (IM); 30–60 minutes (oral)[68]	3–5 hours[69]
Diamorphine (Heroin; IV/IM) or other parenteral administrations apart from spinal administration[70]	4–5 (IV,IM) 2–2.5 (insufflated)[71]	2–2.5 mg	100%	<0.6 (morphine prodrug)[72]		Instantaneously (from 5 to 15 sec; IV); 2 to 5 min (IM)	3 to 7 hours (morphine prodrug)[72]
6-MAM[73]	6–7 (IV,IM)	1.25–1.6	100% (IV,IM)	<0.6 (morphine prodrug)[72]	presumably 2:1	Instantaneously (from 5 to 15 sec; IV); 2 to 5 min (IM)	3 to 7 hours (morphine prodrug)[72]
Dezocine[74]	7.7-13	0.76-1.29 mg	97% (IM)	2.2	4–6 hours[75]	5 min (IV); 5-15 min (IM/BUC); 6–8 hours (TD)[76]
Hydromorphone[77][78][36]	10 (SC, IV, IM) 3–3.75 (PO)	0.5–0.75 mg (SC, IV, IM) 2.5 mg (PO)[10]	Orally: 30–35%, Intranasal: 52–58%, IV/IM: 100% 62%	2–3	5:1
Oxymorphone[50]	10 (SC, IV, IM) 3–4(PO)	3.33 mg (PO), 0.333 mg (IV,IM & Interlaminar)	PO: 10% Buccal: 28% Sublingual: 37.5% Intranasal: 43% IV, IM & IT: 100%	7.25–9.43		35 min (PO), Instantaneously (from 5 to 15 sec)(IV)	6–8 hours orally 2–6 hours parenteral
U-47700[79]	7.5	1.5 mg		1.5–3
Levorphanol[80]	8	1.25 mg	70%	11–16	1:1
Desomorphine[81]	8–10[82]	1–1.25 mg	~100% (IV)	2–3		Instantaneously (from 5 to 15 sec)(IV); 2–5 min (IM)	3–4 hours
N-Phenethylnormorphine[83]	8–14
Alfentanyl[84]	10–25	0.1-0.4 mg		1.5 (90–111 minutes)		Instantaneously (from 5 to 15 sec); 4× more rapid than fentanyl	0.25 hr (15 min); up to 54 minutes until offset of effects
Trefentanil[85]	10
Brifentanil[85]	10-25
Acetylfentanyl[85]	15[86]
7-Hydroxymitragynine[87]	17	~0.6 mg
Butyrfentanyl[88]	25
Enadoline[89]	25	15 μg (threshold) and 0.160 mg/kg (dissociative effects)
Buprenorphine (SL)[26]	40-80[10]	0.25 mg	30% (SL);[90] ~100% (TD); 65% (BUC);[91][92] 48% (INS)[93]	20–70, mean 37	3:1	45 min	12–24 hours
N-Phenethyl-14-ethoxymetopon[83]	60	160 μg
Furanylfentanyl[94]	50-100
Phenomorphan[95]	60–80	0.13–0.16 mg
N-Phenethylnordesomorphine[96]	85
Phenaridine[97]	50-100
Fentanyl[27]	50–100[10]	0.1 mg (100 μg) IM/IV	33% (SL); 92% (TD); 89% (INS); 50% (BUC)	0.04 (IV); 7 (TD)		5 min (TD/IV)	30–60 minutes (IV)
Metonitazene[98]	100	0.1 mg/100 μg
Acrylfentanyl[85]	50-100+[99]
Remifentanil[100]	100	100 μg	100% (IM/IV)	0.05 (3–6 min context-sensitive half-life; 7–18 min elimination half-life)[101]		Instantaneously (from 5 to 15 sec)	15 minutes; rapid offset of effects necessitates continuous infusion for maintenance of anesthesia
Parafluorofentanyl (2-Fluorofentanyl)[102]	111
Buprenorphine (Transdermal)[103][104]	100–115[10]	0.1 mg (100 μg)	30% (SL);[90] ~100% (TD); 65% (BUC);[91][92] 48% (INS)[93]		3:1	45–60 minutes	12–24 hours
14-Cinnamoyloxycodeinone[105]	177 (median potency) 101-310 (varied potencies among test subjects)[106]	77 μg	2.8% (PO); 5.8% (SC)		250:7
Protonitazepyne[98]	190-200[107]	55–60 μg
Protonitazene[98]	200[108]	50 μg
Ocfentanil[109]	200	40–80 μg
Ro4-1539[110]	240–480	20–40 μg
14-Methoxymetopon[111]	500 (IV)	20 μg
Isotonitazene[98]	500[112][needs update]	20 μg
Sufentanil[27]	500–1,000[113]	10–20 μg	9% (PO); 52-59% (SL); 78% (BUC); 100% (IM/IV)[114]	4.4	2:1	1-3 min (IV); 5 min (IN); 10 min (EPD); 6-15 min (SL)[115]	30 min (IV); 40-50 min (SL)[116][117]
BDPC[118]	504	~20 μg
Orthofluorofentanyl[102]	564	~17 μg
C-8813[118]	591	~15 μg
4-Phenylfentanyl[119]	800
Etonitazene[120]	1,000–1,500[121]	6.6–10 μg
3-Methylfentanyl[122]	1,000 (3-methylfentanyl, (trans)-(+-)-isomer; 6,600 (3-methylfentanyl, (cis)-(-)-isomer)[123]
N-Desetylisotonitazene[124][98]	2,000[125]	5–10 μg
Etonitazepyne[107][98]	2,000[126]	5 μg
Etorphine[127][128]	500–2,000[129]	3.3–10 μg
Ohmefentanyl[130]	6,300[131]
Acetorphine[128]	8,700	1.33 μg
Dihydroetorphine[132]	12,000	0.83–10 μg (20–40 μg SL)
Carfentanil[133]	10,000	1.0 μg		7.7
Lofentanil[134][135]	10,000-11,000[136]
4-Carboethoxyohmefentanil[137]	30,000
Ohmecarfentanil[138][137]	30,000
R-30490[139]	10,000-100,000
14-Methoxymetopon[140]	1,000,000 (intrathecal & supraspinal)	0.1 μg
PO: oral • BUC: buccal • SL: sublingual • TD: transdermal • IV: intravenous injection • IM: intramuscular injection • SC: subcutaneous injection • EPD: epidural injection "Strength" is defined as analgesic potency relative to oral morphine. Tolerance, sensitization, cross-tolerance, metabolism, and hyperalgesia may be complex factors in some individuals. Interactions with other drugs, food and drink, and other factors may increase or decrease the effect of certain analgesics and alter their half-life. Because some listed analgesics are prodrugs or have active metabolites, individual variation in liver enzymes (e.g., CYP2D6 enzyme) may result in significantly altered effects.

See also

• Oripavine – for more on the comparative strength of oripavine derivatives