Pharmokinetics Flashcards
Routes of administration for opiates
Oral
IV
SC
IM
Transdermal patch (fentanyl)
Epidural
Intrathecal
Patient-controlled analgesia (PCA)
Opioids get distributed throughout all tissues
Exert their principle analgesic effects after they reach the CNS
Where does biotransformation primarily take place?
Liver
Where and how does excretion occur?
Excretion of drug metabolite and to a lesser extent the intact drug in the urine via the kidneys
Morphine
Morphine-6-Glucuronide (more potent than morphine)
Meperidine
Has an active metabolite (normeperidine), which may cause seizures at thigh plasma levels (particularly in elderly patients and pts with impaired renal/hepatic function)
Not for chronic pain
Methadone
Very long duration of action
Time for peak efficacy
- Morphine
20 minutes
Time of the duration of action
- Morphine
4 hours
Time for peak efficacy
- Meperidine
15 mins
Time of duration of action
- Meperidine
2-4 hours
Time of peak efficacy
- Fentanyl
5 mins
Time of duration of action
- Fentanyl
15-30 mins
Intrathecal and epidural
Use significantly lower doses and provide regional analgesia while decreasing systemic side effects
Patient controlled analgesia (PCA pumps)
Allow patients to control opiate injections using a parenteral (I.V.) injection devise
Analgesia
They relieve pain both by raising the pain threshold at the SC level and by altering the brain’s perception of pain
Induce sleep in clinical situation when pain is present and sleep is neccessary
Opiate analgesics
Represent the mainstay of therapy for the treatment of pts with acute (postoperative) and chronic pain
Less drug is need to prevent what?
Recurrence of pain than to relieve it
Cough suppression
Dextromethorphan
Acute pulmonary edema
- morphine only
Morphine used to decrease anxiety and decrease the perception of shortness of breath
Adjunct in anesthesia
Morphine
Fentanyl
Treatment of diarrhea
Diphenoxylate and loperamide (OTC)
Adverse effects of opiates
Sedation, drowsiness, mental clouding and coma (at toxic doses)
Mitosis (pinpoint pupil)
Euphoria
Constipation (severe)
Urinary retention
Respiratory depression
Nausea
Itching
Addiction liability
Adverse effects of opiates
- Miosis (pinpoint pupil)
Important diagnostically bc other causes of coma and respiratory depression produce dilation of pupil
Adverse effects of opiates
- Euphoria
D/t DA release in the nucleus accumbens
Adverse effects of opiates
- Constipation (severe)
Stool softeners and laxatives should be initiated early
Adverse effects of opiates
- Urinary retention
Increase antidiuretic hormone
Adverse effects of opiates
- Respiratory depression (cardinal toxic effect)
D/t a reduction in the responsiveness of the respiratory center to increase CO2 tension
Averse effects of opiates
- Itching
D/t opiate
Induced histamine release
Opiates contraindications
Head trauma
Neonates
Opiate-induced miosis
Respiratory depression
Opiates contraindications
- Head trauma
Increase intracranial pressure (ICP) from vasodilation and increase CSF volume
Opiates contraindications
- Neonates
Should not receive morphine bc of their low conjugating capabilities and immaturity of BBB
Opiates contraindications
- Opiate-induced miosis
Masks the pupillary response used to diagnose concussion
Opiates contraindications
- Risk of respiratory depression
From heroin is related to its active metabolites (6- acetlymorphine and morphine)
Tolerance
Repeated administration of therapeutic doses of the opiates causes gradual loss of effectiveness
In order to reproduce the original response
Larger dose is needed
Cross-tolerance
Pt tolerant to one opiate drug will also show some degree of tolerance to other opiate agonists
Tolerance does not develop to
Mitosis and constipation
