Antiemetics Flashcards
How many patients experience PONV?
20-30%
Increased in pediatrics (children >3yo)
Patients w/ risk factors increases to 70-80%
PONV associated with
Delayed recovery
Patient dissatisfaction
Most common complication observed in PACU
Reason for hospitalization following ambulatory surgery
50% patients w/ emesis in PACU will continue to experience PONV when d/c home
How to prevent and treat PONV
Target various pathways associated w/ N/V (different receptors)
Peripherally & centrally acting
Combination therapies
Patient Risk Factors
Female (unknown genetic cause)
History PONV or motion sickness
Non-smoker
Age (risk decreases by 10% per decade in adults >50yo)
Pediatrics 3-12yo highest age risk
Apprehension = swallowing air → abdominal distension & ↑ catecholamines
Gastroparesis & recent food ingestion r/t stomach contents
Surgical Risk Factors
Increased anesthetic or surgery duration
Each 30min increases PONV risk by 60% from initial score
Surgery type - laparoscopic, ophthalmic, ENT, T&A, breast, GU, & GYN
Anesthesia Risk Factors
Pre-op opioid analgesics administration - receptor site stimulation & serotonin release
Inhalational induction - PPV causes gastric distension
Volatile anesthetic agents (dose dependent & exposure time w/ surgery duration)
Nitrous oxide causes ↑ middle ear pressure, GI distension, & sympathetic nerve activation
*Maintenance - longer anesthesia time, general, opioid admin → highest risk
Consider Propofol as maintenance anesthetic rather than volatile gas for high risk patients
Propofol found to result in less PONV than other hypnotic agents
Post-op Risk Factors
Ambulation
Postural hypotension
Uncontrolled pain ↑ catecholamines & endogenous nociceptor activators such as serotonin
Post-op opioid administration (regardless if opioid-free anesthesia)
Early PO intake
Lower FiO2 concentration
Reversal agents such as Neostigmine >2.5mg
How to treat at-risk patients?
MULTI-MODAL APPROACH
Benefit from one or more prophylactic measures
Target different receptors & pathways
SAMBA
Society of Ambulatory Anesthesia
Identify at-risk patients for PONV
Employ management strategies to reduce risk
1-2 prophylactic measures in moderate risk adults
Multiple interventions in patients at high risk
Failed prophylaxis treatment
Try another antiemetic to target different receptor
Different pharmacological class
Apfel Score
Female gender
Nonsmoker
PONV history
Post-op opioids
Combination Therapy
Targets multiple receptors
Rapid onset & longer duration to cover post-op period
High risk patients will benefit from combo therapy
Utilize for certain surgical procedures including gastric, esophageal, plastics, ↑ ICP, mandibular jaw wiring, & eye
Direct Triggers
Noxious stimuli, toxins, drugs, or irritants
Indirect Triggers
Vomiting center in medulla oblongata stimulation
- Cerebral cortex/thalamus
- Vestibular apparatus
- Vagal afferent GI tracts
- Chemoreceptor trigger zone (CTZ)
Pathway
Efferent motor nerves travel through cranial nerves V, VII, IX, X, XII, sympathetic, & spinal nerves to stimulate various areas
Receptors
5-hydroxytryptamine (serotonin) - Ondansetron, Palonosetron, Dolasetron Dopamine (D2) - Droperidol, Prochlorperazine, Metoclopramide Histamine - Dimenhydrinate, Promethazine Muscarinic - Promethazine, Scopolamine Opioid
Serotonin Receptor Antagonists
Most common in practice
5-HT3 receptor subtype mediates vomiting
Ion channel found in the GI tract (abdominal vagal afferents) & brain (CTZ area postrema & NTS)
- Outside the blood-brain barrier
- Trigger zone activated by anesthetics & opioids
- Signals nucleus tractus solitarius resulting in PONV
- GI emetogenic stimuli
Antagonists inhibit central & peripheral stimulation
Effective, well-tolerated, & no sedation
Administer near end surgery
Ondansetron (Zofran)
Selective serotonin type 3 receptor antagonist
Most common antiemetic
Effective prophylactic & post-op antiemetic to prevent & treat PONV
Most effective when administered toward end surgical procedure
Ondansetron PK
Onset 30min
Peak plasma almost immediate
60% bioavailability
70% protein binding
Metabolism: CYP450 (liver) hydroxylation & conjugation
Decrease dose in liver failure patients - severe hepatic impairment will decrease clearance d/t ↑ plasma half-life (do not exceed 8mg/day)
No renal dose adjustment <5% metabolized by kidneys
Half-life 4hrs
Excreted via urine/feces
Ondansetron Dose
PO 4-8mg pre-op prophylaxis 16mg 1x prior to induction IV 4mg Do not administer > 16mg IV FDA warning based on 32mg QT prolongation risk
Ondansetron SE
Headache (mild to moderate) Dizziness Diarrhea Constipation QTc prolongation
Palonosetron
Selective serotonin type 3 receptor antagonist
Newest & most selective agent
Effective treatment for chemotherapy induced N/V
No safety/efficacy data in patients <18yo
NOT safe for pediatric patients
Palonosetron PK
Increased serotonin receptor affinity 100x
Half-life 40hrs
Therapeutic effects for 72hrs (long-acting)
80% excreted in urine over 6 days
Palonosetron Dose
0.75mg PONV
0.25mg chemo-induced N/V
No dosage adjustments for elderly, renal, or hepatic patients
Dolasetron (Anzemet)
Selective serotonin type 3 receptor antagonist
Dolasetron MOA
Reduce vagus nerve activity to limit vomiting center activation in the medulla oblongata
Dolasetron PK
Immediate onset (fast-acting) 75% protein binding Peak plasma ≈ 40min Duration 4-9hrs Elimination half-life 8hrs Metabolism: CYP450 & kidneys Active metabolite - hydrodolasetron Excreted in urine/feces
Dolasetron SE
Headache
Dizziness
Constipation
Potential QT prolongation
