NEET MDS Lessons
Pharmacology
Pharmacodynamics
Pharmacodynamics is the study of what drugs do to the body and how they do it.
Dose-Response Relationships
- Basic Features of the Dose-Response Relationship: The dose-response relationship is graded instead of all-or-nothing (as dose increases, response becomes progressively larger).
- Maximal Efficacy and Relative Potency
- Maximal Efficacy: the largest effects that a drug can produce
- Relative Potency: Potency refers to the amount of drug that must be given to elicit an effect.
- Potency is rarely an important characteristic of a drug.
- Potency of a drug implies nothing about its maximal efficacy.
Meperidine (Demerol)
Meperidine is a phenylpiperidine and has a number of congeners. It is mostly effective in the CNS and bowel
- Produces analgesia, sedation, euphoria and respiratory depression.
- Less potent than morphine, 80-100 mg meperidine equals 10 mg morphine.
- Shorter duration of action than morphine (2-4 hrs).
- Meperidine has greater excitatory activity than does morphine and toxicity may lead to convulsions.
- Meperidine appears to have some atropine-like activity.
- Does not constrict the pupils to the same extent as morphine.
- Does not cause as much constipation as morphine.
- Spasmogenic effect on GI and biliary tract smooth muscle is less pronounced than that produced by morphine.
- Not an effective antitussive agent.
- In contrast to morphine, meperidine increases the force of oxytocin-induced contractions of the uterus.
- Often the drug of choice during delivery due to its lack of inhibitory effect on uterine contractions and its relatively short duration of action.
- It has serotonergic activity when combined with monoamine oxidase inhibitors, which can produce serotonin toxicity (clonus, hyperreflexia, hyperthermia, and agitation)