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Pharmacology - NEETMDS- courses
NEET MDS Lessons
Pharmacology

Fentanyl (Sublimaze)

  • Related chemically to meperidine.
  • Approximately 80 times more potent than morphine.
  • Duration of action very short (t1/2 20 min).
  • Used mainly following general anesthesia.
  • Neurolept analgesia: Fentanyl & Droperidol (Innovar)
  • fentanyl in analgesic (2-10 µg/kg), or anaesthetic (30-100 µg/kg) doses seldom causes significant decreases in blood pressure when given alone, even in patients with poor LV function
  • hypotension following fentanyl is mostly due to bradycardia and can be prevented by the use of anticholinergics, sympathomimetics or agents such as pancuronium this is more likely to occur in patients with high pre-existing sympathetic tone
  • hypertension is the commonest disturbance with high dose fentanyl anaesthesia, usually accompanying intubation, sternotomy, or aortic root dissection

Ketoprofen

It acts by inhibiting the body's production of prostaglandin.

Ketoconazole

synthetic antifungal drug

used for infections such as  athlete's foot, ringworm, candidiasis (yeast infection or thrush), jock itch.

Ketoconazole is used to treat eumycetoma, the fungal form of mycetoma.

MOA: Ketoconazole is imidazole structured, and interferes with the fungal synthesis of  ergosterol, the main constituent of cell membranes, as well as certain enzymes. It is specific for fungi, as mammalian cell membranes contain no ergosterol.

Sensitive fungi Ketoconazole inhibits growth of  dermatophytes and  yeast species (such as Candida albicans).

Examples of calculations of doses of vasoconstrictors

Ratio concentrations represent grams per millilitre

1:100,000 = 0.01 mg/mL or 10 µg/mL

1:200,000 = 0.005 mg/mL or 5 µg/mL

1:50,000 = 0.02 mg/mL or 20 µg/mL

1 cartridge of epinephrine 1:200,000 = 9 µg

1 cartridge of epinephrine 1:100,000 = 18 µg

1 cartridge of epinephrine 1:50,000 = 36 µg

1 cartridge of levonordefrin 1:20,000 = 90 µg

Stimulants: 

Amphetamines: amphetamine is a substrate of serotonin and NE uptake transporters so in cytoplasm, it competes for transport into storage vesicles → ↑ [ ] in cytoplasm then excess amines bind to membrane transporter and are transported out of cell

Drugs: 
a.    Dextroamphetamine: psychomotor stimulant (↓ fatigue), short-term weight loss, prevents narcolepsy
b.    Methylphenidate (Ritalin): prevents narcolepsy, treatment for ADD and ADHD
c.    Methamphetamine: psychomotor stimulant, abused widely (cheap, easy to make)

Side effects: 
a.    CNS: euphoria, anxiety, agitation, delirium, paranoia, panic, suicidal/homicidal impulses, psychoses, tolerance (develops rapidly to most CNS effects), physical dependence (not clinically relevant)
b.    CV: headache, chills, arrhythmias and HTN (may be fatal)

Routes of Drug Administration

Intravenous

  • No barriers to absorption since drug is put directly into the blood.
  • There is a very rapid onset for drugs administered intravenously.  This can be advantagous in emergency situations, but can also be very dangerous.
  • This route offers a great deal of control in respect to drug levels in the blood.
  • Irritant drugs can be administer by the IV route without risking tissue injury.
  • IV drug administration is expensive, inconvenient and more difficult than administration by other routes.
  • Other disadvantages include the risk of fluid overload, infection, and embolism.  Some drug formulations are completely unsafe for use intravenously.

Intramuscular:

  • Only the capillary wall separates the drug from the blood, so there is not a significant barrier to the drug's absorption.
  • The rate of absorption varies with the drug's solubility and the blood flow at the site of injection.
  • The IM route is uncomfortable and inconvenient for the patient, and if administered improperly, can lead to tissue or nerve damage.

Subcutaneous

Same characteristics as the IM route.

Oral

  • Two barriers to cross: epithelial cells and capillary wall.  To cross the epithelium, drugs have to pass through the cells.
  • Highly variable drug absorption influenced by many factors:  pH, drug solubility and stability, food intake, other drugs, etc.
  • Easy, convenient, and inexpensive.  Safer than parenteral injection, so that oral administration is generally the preferred route.
  • Some drugs would be inactivated by this route
  • Inappropriate route for some patients.
  • May have some GI discomfort, nausea and vomiting.
  • Types of oral meds = tablets, enteric-coated, sustained-release, etc.
  • Topical, Inhalational agents, Suppositories

Treatment modifications to consider if there are concerns regarding vasoconstrictors

- Monitor blood pressure and heart rate preoperatively

- Minimize administration of epinephrine or levonordefrin

- Monitor blood pressure and heart rate 5 min after injection

- May re-administer epinephrine or levonordefrin if blood pressure and heart rate are stable

- Continue to monitor as required

- Consider limiting epinephrine to 0.04 mg, levonordefrin to 0.2 mg

- Avoid epinephrine 1:50,000

- Never use epinephrine-impregnated retraction cord

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