What is a drug

chemistry of drugs

1. WHAT IS A DRUG?? PHARMACOKINETICS & PHARMACODYNAMICS… PREPARED BY TAKEEN KHURSHID

2. DRUG AN IDEAL DRUG PHARMACOKINETICS PHARMACODYNAMICS SUMMARY CONTENTS…

3. DRUG Drug (French: Drogue-a dry herb) It is the single active chemical entity present in a medicine that is used for diagnosis , prevention , treatment/cure of a disease . This disease oriented definition of drug does not include contraceptives or use of drugs for improvement of health. The WHO (1966) has given a more comprehensive definition- "Drug is any substance or product that is used or is intended to be used to modify or explore physiological systems or pathological states for the benefit of the recipient."

4. AN IDEAL DRUG (There are No Perfect Drugs) Three most important properties: Effectiveness Safety Selectivity A DRUG SHOULD HAVE MAXIMUM BENEFIT AND MINIMUM HARM

5. Other important properties : Reversible action Ease of Administration Predictability Freedom from drug interactions Low cost Generic Name ease

6. Pharmacokinetics Pharmacokinetics is the study of Movement of drugs in the body and it describes the drug absorption, distribution within body, and drug elimination over time. It involves Four Processes Absorption Drug distribution Metabolism Drug elimination

7. 1.Absorption It is the process of entry of drug from site of administration into systemic circulation. The bioavailability of the drug depends on the extent of the absorption. Bioavailability is the percentage of drug that reaches the systemic circulation in an unchanged form and becomes available for biological effect following administration by any route .

8. Factors Influencing Absorption 1. Factors Related To Drug Physicochemical properties Degree of ionization, Degree of solubility, Chemical nature b ) Pharmaceutical form of drug For example Absorption of solutions is better than suspensions or tablets.

9. Factors Influencing Absorption 2. Factors Related To The Patient a) Route of administration b) Area and vascularity of absorbing surface c) Presence of other drugs and other specific factors

10. Route of A dministration: Absorption i.v. > inhaled > i.m . > oral > dermal

11. Distribution of Drugs Distribution is the movement of drug from the central compartment (blood) to peripheral compartments. Here the concentration gradient is the driving force for the movement from plasma to tissues. It depends on, Ionization, Molecular size, Binding to plasma proteins, Differences in regional blood flow P resence of tissue-specific transporters

12. Volume of distribution It is defined as the volume of fluid required to contain the total amount of drug Q in the body at the same concentration as that present in the plasma C p V d = Q/C p Importance of V d : 1.It helps in estimating the total amount of drug in body at any time. Amount of drug = V d x plasma concentration of drug at certain time. 2.Vd is important to determine the loading dose Loading dose = V d x desired concentration

13. Metabolism (Biotransformation ) Biotransformation means chemical alteration of the drug in the body. It is needed to render non polar (lipid-soluble) compounds to polar (lipid insoluble) so that they are not reabsorbed in the renal tubules and are excreted. The primary site for drug metabolism is liver; others are-kidney, intestine, lungs and plasma.

14. Elimination Or Excretion Elimination- Termination of Drug Action by which a drug or metabolite is eliminated from the body. Drugs and their metabolites are excreted in Urine, Faeces, Exhaled air, Saliva and sweat. Two-stage kidney process (filter, absorption) Metabolites that are poorly reabsorbed by kidney are excreted in urine. Some drugs have active (lipid soluble) metabolites that are reabsorbed into circulation (e.g., pro-drugs) Other routes of elimination: lungs, bile, skin

15. Pharmacodynamics

16. Pharmacodynamics Pharmacodynamics refers to the relationship between drug concentration at the site of action and the resulting effect , including the time course and intensity of therapeutic and adverse effects. The effect of a drug present at the site of action is determined by that drug’s binding with a receptor . The concentration at the site of the receptor determines the intensity of a drug’s effect

17. Drug Action Four major types of bio-macromolecular targets of drug action are there Enzyme Transmembrane ion channel (C) Membrane bound transporter ( D) Receptor

18. Factors Affecting Drug Response Density of receptors on the cell surface T he mechanism by which a signal is transmitted into the cell by second messengers. Regulatory factors that control gene translation and protein production may influence drug effect

19. Dose-response Curves for Therapeutic Effect And Adverse Effect Of The Same Drug

20. Dose-Response Functions Efficacy ED 50 = median effective dose Lethality LD 50 = median lethal dose Therapeutic Index = LD 50 /ED 50 = toxic dose/effective dose This is a measure of a drug’s safety A large number = a wide margin of safety A small number = a small margin of safety

21. Tolerance The effectiveness can decrease with continued use is referred to as tolerance. Tolerance may be caused by The pharmacokinetic factors, such as increased drug metabolism, that decrease the concentrations achieved with a given dose. The pharmacodynamic factors like when the same concentration at the receptor site results in a reduced effect with repeated exposure.

22. SUMMARY In  pharmacology, a  pharmaceutical drug, also called a medication or medicine, is a chemical substance used to treat, cure, prevent, or diagnose a disease or to promote  well-being. No drug is ideal but a drug should be effective, safe, selective.

23. Pharmacokinetics is what the Body Does To The Drug like how the drug is Absorbed, Distributed, Metabolized, and Excreted by the body – Drug disposition . Pharmacodynamics is what the Drug Does To The Body which may be the therapeutic effects or the adverse side effects - Drug action .

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