Drug-Receptor Interactions

Drug Receptor:  any functional macromolecule in a cell to which a drug binds to produce its effects.  at receptors, drugs mimic or block the action of the body's own regulatory molecules.  

Receptors and Selectivity of Drug Action : If a drug interacts with only one kind of receptor, and if that receptor regulates just a few processes, then the effects of the drug will be limited.

Even though a drug is selective for one type of receptor, it can still produce a variety of effects.

Selectivity does not guarantee safety.

Theories of Drug-Receptor Interaction

- Simple Occupancy Theory:  Two factors - The intensity of the response to a drug is proportional to the number of receptors occupied by that drug, and the maximal response will occur when all available receptors have been occupied.

- Modified Occupancy Theory:  Assumes that all drugs acting at a particular receptor are identical with respect to the ability to bind to the receptor and the ability to influence receptor function once binding has taken place.

•    Affinity:  The strength of the attraction between a drug and its receptor.  Affinity is reflected in potency.  (Drugs with high affinity are very potent).

•    Intrinsic Activity:  The ability of a drug to activate a receptor following binding.  Reflected in the maximal efficacy (drugs with high intrinsic activity have high maximal efficacy).

Balanced Anesthesia
A barbiturate, narcotic analgesic agent, neuromuscular blocking agent, nitrous oxide and one of the more potent inhalation anesthetic.

Griseofulvin

• Griseofulvin is an antifungal drug. It is used both in animals and in humans, to treat ringworm infections of the skin and nails. It is derived from the mold Penicillium griseofulvum.
• It is administered orally.

Prostaglandines:

Every cell in the body is capable of synthesizing one or more types of PGS. The four major group of PGs are E, F, A, and B.

Pharmacological actions:

stimulation of cyclicAMP production and calcium use by various cells

CVS
PGE2 acts as vasodilator; it is more potent hypotensive than Ach and histamine

Uterous
PGE2 and PGF2α Contract human uterus

Bronchial muscle

PGF2α and thromboxan A2 cause bronchial muscle contraction.

PGE2 & PGI2 cause bronchial muscle dilatation

GIT: PGE2 and PGF2α cause colic and watery diarrhoea

Platelets

Thromboxan A2 is potent induce of platelets aggregation

Kidney

PGE2 and PGI2 increase water, Na ion and K ion excretion (act as diuresis) that cause renal vasodilatation and inhibit
tubular reabsorption

USE
PGI2: Epoprostenol (inhibits platelets aggregation)
PGE1: Alprostadil (used to maintain the potency of arterioles in neonates with congenital heart defects).
PGE2: Dinoproste (used as pessaries to induce labor)
Synthetic analogue of PGE1: Misoprostol (inhibit the secretion of HCl).

Erythromycin

used for people who have an allergy to penicillins. For respiratory tract infections, it has better coverage of atypical organisms, including  mycoplasma. It is also used to treat outbreaks of chlamydia, syphilis, and gonorrhea.

Erythromycin is produced from a strain of the actinomyces Saccaropolyspora erythraea, formerly known as Streptomyces erythraeus.

Propoxyphene

• A methadone analog.Used orally to relieve mild to moderate pain.
• A typical opiate, it does not possess anti-inflammatory or antipyretic actions, but has little or no antitussive activity.
• Cannot be used parenterally because of irritant properties.
• Has a low addiction potential primarily due to its lack of potency as an opiate.
• The most common adverse side effects are:• dizziness, drowsiness, and nausea and vomiting. • these effects are more prominent in ambulatory patients.
• Withdrawal symptoms have occurred in both adults and in neonates following use of the drug by the mother during pregnancy.
• CNS depression is additive with other CNS depressants.