How to prolong or shorten drug action and effects

Question 1

Duration of drug action depends on:
(6)

Answer 1

The absolute amount of drug given

The pharmaceutical preparation.

The reversibility of drug action.

The slope of the concentration-response curve.

The activity of metabolites.

The influence of disease on drug elimination.

Question 2

Reasons for prolonging drug action

Answer 2

Reduction of administration frequency
Avoidance of large fluctuations in plasma concentration of the drug.
Maintaneance of drug effect overnight without disturbing sleep.
Improved patient compliance.

Question 3

Methods

Answer 3

1.Delaying of absorption:
2.Increasing plasma protein binding of drug.
3.Reducing rate of metabolism of the drug
4. Reducing renal excretion

Question 4

Delaying of absorption:

Answer 4

Addition of epinephrine to L.A prolong their duration of action and reduce systemic effects.

Use of a relatively insoluble form or slow release form for s/c or i/m admin e.g poorly soluble salt, ester, complex injected as aqueous or oily solution

Procaine penicillin is a poorly soluble salt of penicillin
Oily solution (depot progestins)
Pellet implantation (testosterone)
Alteration of the physical characteristics of a drug e.g zinc insulin. Addition of ethinyl group to estradiol prolongs its duration of action.
Use of silastic and biodegradable s/c implants e.g Norplant.
Coating of drugs with resins, plastic materials or other substances e.g sustained release tablets, spansules.
Impregnation of drug in adhesive patches for transdermal delivery e.g nitroglycerin.
Corneal inserts e.g pilocarpine for glaucoma.

Question 5

3.Reducing rate of metabolism of the drug which can be achieved by:

Answer 5

chemical modification or coadministration with another drug that inhibits the metabolising enzyme of the first drug.

Question 6

. Reducing renal excretion by?

Answer 6

e.g coadministration of penicillin or ampicillin with probenecid, cilastin protects imipenem from degradation by dehydropeptidase in the kidneys.

Question 7

Factors important in dosage

Answer 7

Age
Sex
Weight
Halflife
disease states -some drugs are metabolized by liver and excreted by kidney
Use of other drugs
Anti-retro viral drugs