diffrent analgesic in im vs iv routes

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Analgesics: IM vs IV Routes

Here is a structured comparison covering opioids, NSAIDs, and acetaminophen across the two parenteral routes, drawn from Goodman & Gilman's Pharmacological Basis of Therapeutics, Miller's Anesthesia (10e), and Barash's Clinical Anesthesia (9e).

Why Route Matters

IV administration provides immediate, predictable onset and precise titratability. IM administration has variable absorption - serum drug concentrations show wider variability IM than IV. For this reason, IV is the preferred parenteral route when possible, and IM is generally a fallback or field route.

Miller's Anesthesia, 10e: "Serum drug concentrations may exhibit wider variability with certain routes of administration (e.g., intramuscular) than with others (e.g., intravenous)."

Opioid Analgesics - IM vs IV Comparison

Morphine

Parameter	IM	IV
Onset	10-30 min	2-5 min
Peak effect	30-60 min	15-20 min
Duration	3-5 h	3-4 h
Standard dose	10 mg/3-4 h	2-4 mg bolus; titrate
Remarks	Erratic absorption; historically common	Preferred for titration; PCA gold standard

Morphine (Equianalgesic Doses - Goodman & Gilman Table 23-2)

Oral equianalgesic: 30 mg
Parenteral equianalgesic (IM/IV/SC): 10 mg
Adult starting dose parenteral: 5 mg/3-4 h
Pediatric parenteral: 0.1 mg/kg/3-4 h

Fentanyl

Parameter	IM	IV
Onset	7-8 min	Immediate
Duration	1-2 h	0.5-1 h
Remarks	Used in pre-hospital/field settings	Standard intraoperative/ICU agent

Fentanyl is highly lipophilic - IM absorption is reasonably reliable compared to morphine.

Hydromorphone (Dilaudid)

Parameter	IM/SC	IV
Onset	~15 min	5 min
Peak effect	30-60 min	15-30 min
Duration	4-5 h (IR)	3-4 h
Equianalgesic parenteral dose	1.5 mg/3-4 h	1.5 mg/3-4 h
Adult starting dose	0.5 mg/3-4 h	0.2-0.5 mg bolus

Barash Table 55-11: Hydromorphone IM/SC onset ~15 min; duration IR 4-5 h, IM noted up to 45 h in some formulations.

Meperidine (Pethidine)

Parameter	IM	IV
Equianalgesic parenteral	100 mg/3 h	100 mg/3 h
Starting dose IM	50-100 mg/3-4 h	Not recommended as standard due to toxic metabolite
Special note	Historically common IM; now discouraged	Normeperidine accumulation risk; avoid in renal impairment

Both IM and IV routes are now largely discouraged for meperidine due to its toxic metabolite normeperidine (seizure risk). It is not recommended as a first-line analgesic in either adults or pediatric patients. - Miller's Anesthesia, 10e

Codeine

Parameter	IM	IV
Equianalgesic parenteral	75 mg/3-4 h	75 mg/3-4 h
Notes	IM use still practiced; absorbed erratically	IV not recommended due to histamine release risk

Codeine IV is generally avoided because of significant histamine release and cardiovascular instability.

Tramadol

Parameter	IM	IV
Equianalgesic dose	100 mg	100 mg
Adult dose	50-100 mg/6 h	50-100 mg slow IV over 15-20 min (to reduce seizure/nausea risk)
Notes	Moderate-pain use; available in many settings	IV must be given slowly; not recommended in pediatric patients

Buprenorphine

Parameter	IM	IV
Onset	~15 min	Faster
Duration	6 h (IM)	~6 h
Mean t½	~2.2 h following IV 0.3 mg	Same
Notes	Partial mu-agonist; ceiling for respiratory depression	Used for opioid use disorder management perioperatively

Multiple formulations exist: IV, IM, SC, buccal, intranasal.

Morphine Equivalence Summary (Goodman & Gilman Table 23-2)

Drug	Equianalgesic Parenteral Dose	IM Available?	IV Available?
Morphine	10 mg	Yes	Yes
Hydromorphone	1.5 mg	Yes	Yes
Oxymorphone	1 mg	Yes	Yes
Fentanyl	~0.1 mg (100 mcg)	Yes	Yes
Meperidine	100 mg	Yes (discouraged)	Yes (discouraged)
Codeine	75 mg	Yes	Avoid
Tramadol	100 mg	Yes	Yes (slow)
Methadone	10 mg	Yes	Yes
Levorphanol	2 mg	Yes	Yes
Hydrocodone	Not available	No	No
Oxycodone	Not available	No	No

NSAIDs - IM vs IV

NSAIDs can be given orally, rectally, IM, and IV.

Drug	IM	IV
Ketorolac	30-60 mg IM; widely used post-op	15-30 mg IV; good pain relief per meta-analyses
Diclofenac	Available IM	Available IV; good analgesic effect in acute post-op pain
Ibuprofen	Not standard IM	IV ibuprofen exists but insufficient data to fully support
Parecoxib (COX-2)	IM formulation available	IV formulation available

Miller's Anesthesia, 10e: "Diclofenac and ketorolac were found to give good pain relief [IV]. Not enough data was found to support or refute the use of IV ibuprofen."
All NSAIDs require caution in peptic ulcer disease, renal impairment, bleeding risk, and cardiovascular disease.

Acetaminophen (Paracetamol) - Routes

Route	Notes
Oral	Preferred when patient can tolerate PO
Rectal	Alternative when oral not feasible
IV	Available as IV formulation; used perioperatively; onset faster than oral
IM	Not a standard route - acetaminophen is not available as an IM formulation

IV acetaminophen is commonly used as part of multimodal analgesia. Evidence for opioid-sparing effect is inconsistent across studies.

Key Clinical Points

IV is preferred over IM in the hospital setting for opioids - more predictable pharmacokinetics, titratable, allows PCA.
IM is discouraged in pediatrics - painful, causes injection fear, variable absorption. IV or regional analgesia is preferred for moderate-severe pain. - Miller's Anesthesia, 10e
IM is acceptable in pre-hospital/field settings where IV access is unavailable (especially fentanyl, morphine, tramadol, ketorolac).
Meperidine IM/IV is now broadly discouraged in both adults and children due to normeperidine toxicity.
Codeine IV should be avoided due to histamine release.
Opioids administered parenterally provide more rapid and reliable onset than oral for moderate-severe pain.

Sources

Goodman & Gilman's The Pharmacological Basis of Therapeutics - Tables 23-2, 23-3, Chapter 23
Miller's Anesthesia, 10e - Chapters 77 (Postoperative Analgesia), Ch. 27 (Ambulatory Analgesia)
Barash's Clinical Anesthesia, 9e - Table 55-11 (Opioid Analgesic Pharmacokinetics)

diffrent analgesic in im vs iv routes with dilution and dosage

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Analgesics: IM vs IV Routes - Dosage, Dilution & Administration

All doses are for adult patients unless otherwise specified. Always titrate to effect and adjust for age, renal/hepatic function, and opioid tolerance.

OPIOID ANALGESICS

1. Morphine

Feature	IM	IV
Standard dose	5-10 mg q3-4 h	2-4 mg bolus; titrate q5-15 min
Pediatric dose	0.1 mg/kg/3-4 h	0.05-0.1 mg/kg bolus
Equianalgesic parenteral	10 mg	10 mg
Onset	10-30 min	2-5 min
Duration	3-5 h	3-4 h
Dilution (IV)	N/A	Dilute to 1 mg/mL in NS or D5W; give slow IV push over 4-5 min
PCA demand dose	-	1 mg/bolus; lockout 5-10 min
Infusion (IV)	-	1-5 mg/h (opioid-tolerant); not routinely recommended for opioid-naïve adults

IM absorption is erratic and produces wider serum concentration variability than IV. IV PCA optimal demand dose is 1 mg morphine in opioid-naïve adults. - Miller's Anesthesia, 10e

2. Fentanyl

Feature	IM	IV
Standard dose	50-100 mcg (1-2 mcg/kg)	25-100 mcg bolus (0.5-1 mcg/kg)
Onset	7-8 min	Immediate
Duration	1-2 h	30-60 min
Dilution (IV bolus)	N/A	May give undiluted (50 mcg/mL); slow IV push over 1-2 min
Infusion (IV)	-	25-200 mcg/h; dilute in NS (typically 10 mcg/mL)
PCA demand dose	-	10-20 mcg/bolus; lockout 5-10 min (Optimal: 40 mcg per Miller's, but 10-20 mcg used in practice)
Intraoperative	-	1-2 mcg/kg bolus for induction adjunct

Fentanyl's high lipophilicity makes IM absorption more reliable than morphine IM. IV duration is short (30-60 min) due to rapid redistribution. - Barash Table 55-11

3. Hydromorphone (Dilaudid)

Feature	IM	IV
Standard dose	1-2 mg q3-4 h	0.2-1 mg q2-4 h
Pediatric dose	0.015-0.02 mg/kg	0.01-0.015 mg/kg
Equianalgesic parenteral	1.5 mg (= 10 mg morphine)	1.5 mg
Onset	~15 min	5 min
Duration	4-5 h	3-4 h
Dilution (IV)	N/A	Dilute to 0.1-1 mg/mL in NS; slow IV push over 2-3 min
PCA demand dose	-	0.2-0.4 mg/bolus; lockout 5-10 min

Approximately 5-7x more potent than morphine mg-for-mg. Good choice in renal impairment (unlike morphine, active metabolite does not significantly accumulate).

4. Pethidine / Meperidine

Feature	IM	IV
Standard dose	50-100 mg q3-4 h	25-50 mg slow IV; not recommended as primary analgesic
Pediatric	0.75 mg/kg (not recommended)	Not recommended
Equianalgesic parenteral	100 mg (= 10 mg morphine)	100 mg
Onset	10-15 min	2-5 min
Duration	2-4 h	2-3 h
Dilution (IV)	N/A	Dilute to 10 mg/mL; give over 2-5 min

Both IM and IV routes are broadly discouraged in current practice due to accumulation of normeperidine (active toxic metabolite) causing CNS excitation, tremors, and seizures - especially in renal impairment or repeated dosing. Meperidine should not be used as a first-line analgesic in adults or children. - Miller's Anesthesia, 10e

5. Tramadol

Feature	IM	IV
Standard dose	50-100 mg q6 h	50-100 mg q6 h
Max daily dose	400 mg/day	400 mg/day
Onset	15-30 min	5-10 min
Duration	4-6 h	4-6 h
Dilution (IV)	N/A	Dilute 100 mg in 100 mL NS; infuse over 15-20 min (slow infusion mandatory to reduce seizure and nausea risk)
Pediatric	Not recommended	Not recommended

IV tramadol must be given as a slow infusion, never rapid bolus - risk of seizures, nausea, and cardiovascular instability with fast administration.

6. Codeine

Feature	IM	IV
Dose	30-60 mg q4-6 h	Avoid IV route
Equianalgesic parenteral	75 mg (= 10 mg morphine)	-
Onset IM	15-30 min	-
Duration	4-6 h	-

IV codeine is contraindicated due to significant histamine release causing bronchospasm, hypotension, and cardiovascular instability. IM is used but codeine is increasingly avoided entirely given its prodrug status (requires CYP2D6 conversion to morphine - poor metabolizers get no analgesia; ultra-rapid metabolizers risk toxicity). - Barash Table 55-11

7. Buprenorphine

Feature	IM	IV
Standard dose	0.3 mg q6-8 h	0.3 mg q6-8 h
Onset	~15 min	Faster onset
Duration	6 h	6 h
Dilution (IV)	N/A	May dilute in NS; give slow IV over 2 min
t½	2.2 h (after IV 0.3 mg)	Same

Partial mu-agonist with ceiling for respiratory depression. Multiple formulations: IV, IM, SC, buccal, intranasal, transdermal. - Barash Table 55-11

8. Oxymorphone

Feature	IM	IV
Equianalgesic dose	1 mg (= 10 mg morphine)	1 mg
Starting dose adult	1 mg q3-4 h	0.5 mg slow IV

9. Methadone

Feature	IM	IV
Equianalgesic dose	10 mg	10 mg
Starting dose adult	2.5-5 mg q8-12 h	Use with extreme caution; specialist supervision only
Duration	Variable (long: 24-36 h)	Same

Long and unpredictable half-life. QTc prolongation risk. IV use requires specialist supervision. - Goodman & Gilman Table 23-2

OPIOID EQUIANALGESIC SUMMARY (Parenteral Doses vs Oral)

(Goodman & Gilman Table 23-2)

Drug	Equianalgesic Oral	Equianalgesic Parenteral (IM=IV=SC)
Morphine	30 mg	10 mg
Hydromorphone	6 mg	1.5 mg
Oxymorphone	10 mg	1 mg
Oxycodone	20 mg	Not available parenterally
Meperidine	300 mg	100 mg
Codeine	130 mg	75 mg
Tramadol	100 mg	100 mg
Methadone	100 mg	10 mg
Levorphanol	4 mg	2 mg
Fentanyl (transdermal 72h patch 25 mcg/h)	= morphine 50 mg/24 h	~0.1 mg (100 mcg) IV/IM

NON-OPIOID ANALGESICS

10. Ketorolac (NSAID)

Feature	IM	IV
Adult loading dose	60 mg (single dose)	30 mg
Adult maintenance	30 mg q6 h	15-30 mg q6 h
Elderly / <50 kg	30 mg	15 mg
Pediatric (2-16 yr)	1 mg/kg (max 30 mg) single dose	0.5 mg/kg (max 15 mg) single dose
Duration of therapy	Max 5 days combined IM+IV+oral	Same
Onset	~30-45 min	15-30 min
Dilution (IV)	N/A	Give undiluted or dilute in NS; slow IV push over ≥15 sec (or infuse over 15 min for comfort)

IM loading dose is 60 mg because IM bioavailability is lower than IV. The total course must not exceed 5 days (all routes combined) due to risk of GI ulceration and renal toxicity. - Morgan & Mikhail's Clinical Anesthesiology, 7e; Goodman & Gilman

11. Diclofenac (NSAID)

Feature	IM	IV
Dose	75 mg IM once (deep IM, gluteal)	75 mg in 250-500 mL NS over 30-120 min
Frequency	Once daily (or 75 mg q12h max)	Once or twice; short-term only
Duration	Short-term post-op	Same

12. Parecoxib (COX-2 Selective NSAID)

Feature	IM	IV
Dose	40 mg loading, then 20-40 mg q6-12 h	Same dose; max 80 mg/day
Onset	7-14 min	Faster
Dilution (IV)	N/A	Reconstitute with NS; give as IV bolus

COX-2 selective - spares gastric mucosa and platelet function, but carries cardiovascular risk. - Miller's Anesthesia, 10e

13. IV Acetaminophen (Paracetamol IV)

Feature	IM	IV
Route	Not available as IM	Standard 100 mL vial (10 mg/mL = 1000 mg in 100 mL)
Adult dose (>50 kg)	-	1 g q6-8 h; max 4 g/day
Adult dose (≤50 kg or <10 yr)	-	15 mg/kg/dose q6 h; max 75 mg/kg/day
Infusion time	-	15 min IV infusion (do not give as bolus)
Onset	-	5-15 min

IV acetaminophen (Ofirmev/Paracetamol IV) is infused over 15 minutes. It is not given IM. Oral/rectal acetaminophen is equally effective and far less expensive. - Morgan & Mikhail's Clinical Anesthesiology, 7e

14. Ketamine (NMDA antagonist - adjuvant analgesic)

Feature	IM	IV
Sub-anesthetic analgesic dose	0.5-1 mg/kg IM	0.1-0.35 mg/kg bolus or 5-10 mg IVP once or q2h PRN refractory pain
Infusion	-	0.05-0.35 mg/kg/h (0.83-5.83 mcg/kg/min)
Onset	3-5 min	1-2 min
Dilution (IV bolus)	N/A	Dilute to 1 mg/mL or 2 mg/mL in NS or D5W

At sub-anesthetic doses, ketamine is a powerful opioid-sparing analgesic with no respiratory depression. Infusion should be on a monitored floor per institution protocol. - Barash Table 55-8

KEY CLINICAL PRINCIPLES

Principle	Detail
IV preferred over IM in hospital	More predictable, titratable, faster onset. IM serum levels vary widely
IM discouraged in pediatrics	Painful, fear of needles, variable absorption. IV or regional preferred
Never rapid IV bolus	Morphine, fentanyl, tramadol, hydromorphone must be given slowly to avoid respiratory depression, hypotension
Ketorolac IM dose > IV	IM 60 mg load vs IV 30 mg load due to bioavailability difference
Acetaminophen IV = 15 min infusion	Not a bolus; not available IM
Tramadol IV = slow infusion	100 mg in 100 mL over 15-20 min; rapid IV causes seizures
Meperidine/pethidine - avoid	Normeperidine toxicity; not first-line by either route
Codeine IV - avoid	Histamine release; cardiovascular instability

Sources

Goodman & Gilman's Pharmacological Basis of Therapeutics - Table 23-2, Ch. 23, Ch. 42
Miller's Anesthesia, 10e - Table 77.1, Ch. 77
Barash's Clinical Anesthesia, 9e - Tables 55-8 and 55-11
Morgan & Mikhail's Clinical Anesthesiology, 7e - Ketorolac Dosage section, IV Acetaminophen section

Needle gauge according to age for im

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IM injection needle gauge size by age WHO CDC recommendations

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IM injection needle gauge length by age

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IM Injection: Needle Gauge & Length by Age

(Based on CDC/ACIP General Best Practice Guidelines for Immunization & clinical pharmacology standards)

Needle selection for IM injection must be based on: age, sex, weight, injection site, and viscosity of the drug.

Complete Table: IM Needle Gauge & Length by Age

Age Group	Gauge	Needle Length	Preferred Site	Alternate Site
Neonate (0-28 days)	22-25 G	5/8 inch (16 mm)	Vastus lateralis (anterolateral thigh)	-
Infant (1-12 months)	22-25 G	1 inch (25 mm)	Vastus lateralis (anterolateral thigh)	-
Toddler (1-2 years)	22-25 G	1-1.25 inches (25-32 mm)	Vastus lateralis (anterolateral thigh)	Deltoid: 5/8-1 inch (16-25 mm)
Child (3-10 years)	22-25 G	5/8-1 inch (16-25 mm) deltoid	Deltoid muscle of arm (preferred)	Vastus lateralis: 1-1.25 inches
Older child / Adolescent (11-18 years)	22-25 G	5/8-1 inch (16-25 mm)	Deltoid muscle of arm (preferred)	Vastus lateralis: 1-1.5 inches

Adults (19 years and older) - Weight-Based

Weight	Gauge	Needle Length	Site
< 60 kg (< 130 lbs)	22-25 G	1 inch (25 mm) (some experts: 5/8 inch if skin stretched tightly)	Deltoid
60-70 kg (130-152 lbs)	22-25 G	1 inch (25 mm)	Deltoid
Men: 70-118 kg (152-260 lbs)	22-25 G	1-1.5 inches (25-38 mm)	Deltoid
Women: 70-90 kg (152-200 lbs)	22-25 G	1-1.5 inches (25-38 mm)	Deltoid
Men: > 118 kg (> 260 lbs)	22-25 G	1.5 inches (38 mm)	Deltoid
Women: > 90 kg (> 200 lbs)	22-25 G	1.5 inches (38 mm)	Deltoid

For any adult of any weight using the anterolateral thigh as alternate site: 1-1.5 inches.

Gauge Selection by Drug Viscosity (General Clinical Rule)

Drug Type	Recommended Gauge
Aqueous solutions (vaccines, heparin, most analgesics)	23-25 G
Standard IM drugs (opioids, antibiotics, hormones)	21-23 G
Viscous/oily preparations (depot injections, progesterone in oil, penicillin in oil)	19-21 G
Blood products	18-20 G

For analgesics (morphine, ketorolac, tramadol, etc.): 21-23 G is standard in adults; 23-25 G for children and thin patients.

IM Injection Sites Summary by Age

Neonate / Infant (0-12 months)
  → ONLY: Vastus lateralis (anterolateral thigh, middle third)
  → Deltoid NOT used (insufficient muscle mass)

Toddler (1-2 years)
  → Vastus lateralis (PREFERRED)
  → Deltoid acceptable if muscle mass adequate

Children (3-18 years)
  → Deltoid PREFERRED
  → Vastus lateralis as alternate

Adults
  → Deltoid PREFERRED (for most volumes ≤ 2 mL)
  → Ventrogluteal (preferred for volumes > 2 mL, viscous drugs)
  → Dorsogluteal (AVOID - risk of sciatic nerve injury)

Key Clinical Notes

Point	Detail
Aspiration	No longer routinely recommended at recommended IM sites (no large vessels present)
Injection angle	Always 90 degrees to the skin surface for IM
Dorsogluteal site	Avoid - higher risk of sciatic nerve damage, accidental subcutaneous injection (thick fat layer), and suboptimal drug absorption
Ventrogluteal site	Preferred for large-volume or viscous IM injections in adults (> 2 mL); free of major nerves and vessels
Max volume per site	Infant: 1 mL; Toddler/small child: 1-2 mL; Older child: 2 mL; Adult deltoid: 2-3 mL; Adult ventrogluteal: 3-5 mL
Neonates: 5/8" note	Only valid if skin stretched tightly and subcutaneous tissue NOT bunched
Obese patients	May require longer needle (up to 2 inches) to reach muscle through subcutaneous fat

Sources: CDC/ACIP General Best Practice Guidelines for Immunization (Vaccine Administration: Needle Gauge and Length); Immunization Action Coalition; clinical pharmacology standards

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