📖 Pharmacology
Meperidine
PharmacologyMeperidine (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)
Adverse reactions to Meperidine
• Generally resemble a combination of opiate and atropine-like effects.
- respiratory depression, - tremors, - delirium and possible convulsions, - dry mouth
• The presentation of mixed symptoms (stupor and convulsions) is quite common in addicts taking large doses of meperidine.
ANTICHOLINERGIC DRUGS
PharmacologyANTICHOLINERGIC DRUGS
Blocks the action of Ach on autonomic effectors.
Classification
Natural Alkaloids - Atropine. Hyoscine
Semi-synthetic deriuvatives:- Homatropine, Homatropine methylbromide, Atropine methonitrate.
Synthetic compounds
(a) Mydriatics - Cyclopentolate. Tropicamide.
(b) Antisecretory - Antispasmodics - Propantha1ine. Oxy-phenonium, Pirenzipine.
c) Antiparkinsonism- Benzotopine, Ethopropazine, Trihexyphenidyl, Procyclidine, Biperiden
Other drugs with anticholinergic properties • Tricyclic Antidepressants • Phenothiazines • Antihistaminics • Disopyramide
MUSCARINIC RECEPTORS SUBTYPES & ANTAGONISTS
• M 1 Antagonists – Pirenzepine, Telenzepine, dicyclomine, trihexyphenidyl
• M 2 Antagonists – Gallamine, methoctramine
• M 3 Antagonists – Darifenacin, solifenacin, oxybutynin, tolterodine
Pharmacological Actions
CNS - stimulation of medullary centres like vagal. respiratory. vasomotor and inhibition of vestibular excitation and has anti-motion sickness properties.
CVS - tachycardia.
Eye - mydriasis
Smooth muscles - relaxation of the muscles receiving parnsympathetic motor innervation.
Glands - decreased secretion of sweat and salivary glands
Body Temperature - is increased as there is stimulation of temperature regulating centre.
Respiratory System- Bronchodilatation & decrease in secretions. For COPD or Asthma - antimuscarinic drugs are effective
GIT - Pirenzepine & Telenzepine - decrease gastric secretion with lesser side effects.
Specific Agents
PharmacologySpecific Agents
Hydralazine [orally effective]
MOA: Not completely understood. Seems to be partially dependent on the release of EDRF and perhaps partially due to K+-channel activation
- in clinical doses action is manifest primarily on vascular smooth muscle (non-vascular muscle is not much affected).
- Re: Metabolism & Excretion. In cases of renal failure the plasma half life may be substantially increased (4-5 fold). One mode of metabolism is
via N-Acetylation (problem of slow acetylators)
Side Effects
- those typical of vasodilation = headache, nasal congestion, tachycardia etc.
- chronic treatment with high doses > 200 mg/day may induce a rheumatoid-like state which may resemble lupus erythematosus.
Minoxidil (Loniten) [orally effective]
MOA: K+-channel agonist
- very effective antihypertensive. Used primarily to treat life-threatening hypertension or hypertension resistant to other agents.
Side effects - growth of hair
Diazoxide (Hyperstat) [used only IV]
MOA: K+-channel agonist
- Administered by rapid IV injection; action appearing after 3-5 min; action may last from 4 to 12 hours.
Nitroprusside (Nipride) [used only IV]
MOA: increase in cGMP
- unlike the other vasodilators, venous tone is substantially reduced by nitroprusside.
- rapid onset of action (.30 sec); administered as an IV-infusion.
- particularly useful for hypertension associated with left ventricular failure.
Different Systems of the CNS & their functions
PharmacologyDifferent Systems of the CNS & their functions
These systems are pathways formed of specific parts of the brain and the neurons connecting them.
They include:
1.The pyramidal system
2.The extrapyramidal system
3.The limbic system
4.The reticular formation
5.The tuberohypophyseal system
The pyramidal system:
It originates from the motor area of the cerebral cortex and passes through the spinal cord, therefore it is also known as the “corticospinaltract”.
It is responsible for the regulation of the fine voluntary movements.
The extrapyramidal system:
It also controls the motor functionbut involves areas other than the corticospinal tract.
It is involved in the regulation of gross voluntary movements, thus it complements the function of the pyramidal system.
The “basal ganglia” constitute an essential part of this system.
Degenerative changes in the pathway running from the “substantianigra”to the “corpus striatum”(or nigrostriatal pathway) may cause tremors and muscle rigidity characteristic of “Parkinson’s disease”.
The limbic system:
The major parts of this system are: the hypothalamus, the basal ganglia, the hippocampus(responsible for short term memory), and some cortical areas.
The limbic system is involved in the control of “behavior”& “emotions”.
The reticular formation:
It is composed of interlacing fibers and nerve cells that run in all directions beginning from the upper part of the spinal cord and extending upwards.
It is important in the control of “consciousness” and “wakefulness”.
The tuberohypophyseal system:
It is a group of short neurons running from the hypothalamusto the hypophysis(pituitary gland) regulating its secretions.