Dr. Khawlah Dhamen. Assistant Professor Faculity of Medicine

Transcription

1 Dr. Khawlah Dhamen Assistant Professor Faculity of Medicine

2 1. Starts with prediction=an idea & hypothesis What helps? Awareness of the beneficial effects of plants and animal products (natural sources) Chemical identification of a wide variety of natural mediators and the possibility of modifying them chemically

3 e.g. epinephrine, norepinehrine acetylcholine histamine prostaglandins endogenous opioids hormones etc Avoid chemicals with highly reactive groups (toxic)

4 2. Design and synthesis of useful drugs or substances through simple techniques or with the help of advanced technology. Plant fractionation, chromatographic experiments identification of the active ingredients isolation purification good drug (recently most drugs of plant source could be synthesized)

5 Animal isolation of a substance (insulin) Simple peptides a.a sequencing machine Complex proteins recombinant DNA technology Receptology studies: Allowed synthesis of huge number of agonists and antagonists

6 However, as more would become known about detailed structure of receptors, rational drug design with aid of computers will become more feasible Rational drug design : This implies the ability to predict the chemical structure of drug molecule on basis of 3-dimensional structure of its receptor, employing at present suitable computer programs. Only few drugs in clinical use at present were developed in this rational way. Most drugs were in the past developed through random testing of chemicals, or modified molecules of known drugs that are known to have some other pharmacological effect.

7 Drug Nomenclature: - Chemical name e.g. acetyl salicylic acid - Generic name; nonproprietary; official; approved name... Aspirin (most widely used in pharmacology) - Official name... Aspirin BP; Aspirin USP - Trade name; Proprietary; brand name Remine ; Bufferin...etc

8 Preclinical testing In vitro studies Animal testing IND Clinical trials Long-term toxicity studies Phase 1 normal volunteers: safety, pharmacokinetics NDA Postmarketing surveillance (Phase 4) 1 to 5 years Phase 2 selected patients: therapeutic efficacy, dose range Phase 3 large populations of selected patients: therapeutic efficacy, safety in double blind studies 2 to 10 years Average years 1 year

9 3. Preclinical studies Studies on tissues and whole animals Determine efficacy Isolated tissue e.g. bronchi organ path testing drug etc Animal models drug BP drug blood sugar level

10 Determine pharmacokinetic parameters Absorption, distribution, metabolism etc Determine pharmacodynamics (MOA) Assessment of drug toxicity=safety Acute toxicity studies Determination of LD 50 ; Margin of safety etc Subacute and chronic toxicity studies. Repeated dose studies.

11 Daily observation of animals (wt., food and water intake..) Obtaining biological samples (blood; urine) Obtaining tissues (liver; spleen; stomach etc) for histopathological exam or studies

12 Special toxicology studies Mutagenicity (genotoxicity) tests Could delineate the induction of gene mutations (bacterial mutagenicity test or administration of drug to pregnant animals etc) Some mutations could result in the development of cancer

13 Carcinogenicity studies Not always required prior to early studies in man unless there is a high suspicion that the drug could be carcinogenic e.g. suspicion of mutagenicity; highly reactive groups on drug; histopathological abnormalities Required if the use of drug in man for more than one year or +ve mutagenic test

14 Phase 0 Phase 0 or first-in-human trials is a recent phase approved in accordance with the United States FDA s 2006 Guidelines Phase 0 trials are also known as human microdosing studies and are designed to speed up the development of promising drugs by establishing very early on whether the drug or agent behaves in human subjects as was expected from preclinical studies

15 Distinctive features of Phase 0 trials include the administration of single subtherapeutic doses of the study drug to a small number of subjects (10 to 15) to gather preliminary data on the agent's pharmacokinetics and pharmacodynamics. A Phase 0 study gives no data on safety or efficacy, being by definition a dose too low to cause any therapeutic effect. Drug development companies carry out Phase 0 studies to rank drug candidates in order to decide which has the best pharmacokinetic parameters in humans to take forward into further development.

16 Phase 0 studies enable go/no-go decisions to be based on relevant human models instead of relying on sometimes inconsistent animal data Questions have been raised by experts about whether Phase 0 trials are useful, ethically acceptable, feasible, speed up the drug development process or save money, and whether there is room for improvement.

17 Phase I Involves the use of a drug in humans for the first time It establishes dose level at which signs of toxicity first appear Conducted on healthy men with ages yrs

18 Usually a single dose is used initially and if no side effects exhibited, the dose is increased progressively until sufficient serum level is achieved (therapeutic level) or some toxic effects appear Such studies are conducted in hospital If no side effects result from single dose, multiple dose studies should be initiated =bioavailability-bioequivalence studies

19 Phase II If phase I studies prove that the drug is safe to continue, the new drug is administered to patients for the first time All patients should have only one problem (one disease) It assesses efficacy and establishes optimal dose range in patients (dose-response studies are important) Phase II studies are conducted on patients (certain countries ask for patients) Also patients are observed for toxicity to assess safety of the drug

20 Phase III Similar to phase II but conducted on large number of patients (several hundreds to thousands; reasonable) It also assesses safety and efficacy Could detect effects/side effects not observed in phase II

21 Phase IV Post-marketing studies Controlled and uncontrolled studies are often conducted after drug approval and marketing It further assesses safety & efficacy of drugs It allows for comparisons between different drugs used for the same disease

22 In addition, phase IV studies provide evidence of a new use to the drug e.g. aspirin-antiplatelet sildenafil citrate-ed Double-blind; single-blind placebo controlled studies are usually conducted

23 After all these clinical drug trials the drug is usually approved by national or International regulatory authorities and is licensed for General prescribing

24 Handout

25 Ethics of the use of drugs in humans Full detailed protocol has to be approved by the ethical committee, the institutional review board (IRB) All subjects should sign an informed agreement form All subjects should be insured for life and damage

26 Branches of pharmacology usually answer all of the following questions: - How much of a drug to give? Dose - How frequent a drug should be given? Related to the biological half-life (t 1/2 ) - When to give it? Before or after meals; at bed time, PRN... - How to give it? administration... etc

27 Factors affecting the dose Age Weight Route of administration Sex Factors affecting administration Physicochemical properties of drugs Site of action Status of patient Dosage interval

28 Schedule I Includes the drugs with high potential of Abuse Eg. LSD, Heroin.Marijuana, Flunitrazepam and Methaqualone Schedule II Includes morphine,codiene, pethidine, fentanyl, cocaine, amphetamine,methylphenidate, pentobarbital and secobarbital.these can be used under medical supervision only Schedule III Schedule IV Schedule V The drugs with moderate physical and psychological dependence eg. Stanzolol, ketamine,nalorphine,thiopental,suppository form of secobarbital and pentobarbital etc They have low potential for abuse and have limited physical and pshycological dependence eg. Long acting barbiturates,benzodiazapines, Propoxyphene,Pentazocine,Premolineolpidem and Zaleplon They have minimal use abuse potential and minimum dependence liability eg Lamotil and formulation containing Codiene while others are OTC drugs.,

29 DRUG PRESCRIBING AND DRUG COMPLIANCE

30 Therapeutic drug use could be for the following purposes: 1. Curative: seeking a cure for an existent disease or medical condition 2. Symptomatic: any medical therapy of a disease that only affects its symptoms, not its cause. 3. Replacement: Administration of a body substance to compensate for the loss, as from disease or surgery, of a gland or tissue that would normally produce the substance. 4. Supportive: is one that does not treat or improve the underlying condition, but instead increases the patient's comfort 5. Prophylactic or Preventive therapy: is a therapy that is intended to prevent a medical condition from occurring 6. Palliation: focuses on relieving and preventing the suffering of patients by addressing physical, emotional, spiritual and social concerns arising with illness. 30

31 Rational use of drugs: "patients receive medications appropriate to their clinical needs, in doses that meet their own individual requirements, for an adequate period of time, and at the lowest cost to them and their community". Choice of effective drugs should be based on : 1.Efficacy 2. Cost: affordable by patient and community 3. Chosen from Essential Drugs: These are effective drugs that are commonly used in community, and must always be available 31

32 Rational drug prescribing is based on a series of steps: 1. Making a specific diagnosis 2. Consider the pathophysiologic implications of the diagnosis 3. Select the specific therapeutic objective 4. Select a drug of choice: Consider patient criteria (age, other drugs also taken, other diseases, and nature of disease) as well as his clinical presentation 5. Design the appropriate dosing regimen, based on patient pharmacokinetics and if they are altered by his illness 6. Monitor for therapeutic effect(s), patient compliance, and adverse effects 32

33 1. Untreated indication 2. Improper drug selection 3. Subtherapeutic dosage 4. Overdosage/toxicity 5. Failure to receive drug 6. Adverse drug reactions/events 7. Interactions 8. Drug use without indication 33

34 These are of two major types: 1. Hospital prescription of drugs: This is written by the treating doctor on the Physician Order Sheet (POS) of the patient hospital chart. It is preceded by the date which is put on upper left hand of chart. The prescription includes the drug(s) and direction of use i.e. for each drug : the dose to be given to patient and its route, frequency of administration, and duration of use. This followed by signature of the treating doctor. A typical chart order might be as follows: 14/10/ :00 a.m. (1) Ampicillin 500 mg IV q6h x 5 days (2) Aspirin 0.6 g per rectum q6h prn temp over 38c Signiture 34

35 2. Office prescription: This is the physician request to the pharmacist aimed at dispensing drug(s) in proper amount to patient together with directions for effective therapeutic use. The prescription includes the following parts: 1. Identification : Doctor : Name, speciality, address, telephone(optional) Patient : Name, age, address( optional) Date 2. Superscription : which includes the suffix Rx : Recipe (Receive Thou) 3. Inscription ( Body of prescription ): This includes the drug(s), dose form and its strength in metric units, and directions for proper use by patient 35

36 4. Subscription: This includes directions for dispensing the correct amount of drug for the patient according to frequency of use and duration of treatment. 5. Re-fill directions: if needed; any special warning to be given to patient regarding drug storage or use, and if there is a need for child-proof container for drug(s) 6. Signature of prescribing doctor & his license number: usually at bottom of prescription The pharmacist puts a label on each drug container and it includes the followings : Drug name and its nature Directions of its use and storage Warnings Expiry date of drug 36

37 Dr Name Academic and professional degree Address Telephone No. Patient name : Date:. Age (years): Address : Dignosis:. Rx : Panadol tb 500mg 1x3 x4 p.c Panadol tablets (0.5 g ) Take one tablet p.c. tid for 4 days Signature Re-fill : once Warning : non License No. Childproof container : none 37

38 Label on bottle : Panadol. Analgesic or antipyretic - take one tablet 3 times daily before meals for 4 days Expiry date : July 2016 Note : Trade or proprietory name is used in office prescriptions, while generic name is used in hospital prescriptions 38

39 Some abbreviations, in latin or Greek, that may be needed in writing directions of drug use in prescriptions : ac : ante cibum (before meals) pc : post cibum (after meals) bid : twice daily tid or tds : three times daily qid : four times daily prn : when needed qd : every day qh : every hour qhs : every night at bedtime ss : one half stat : at once OD : right eye OL : left eye OU : both eyes 39

40 Some Measurements that may be used in directions of drug use in prescriptions : one tea spoonfull = 5 ml one table spoonfull = 15 ml one ounce (oz.) = 30 ml one quart = 1000 ml one drop = 0.05 ml one ml = 20 drops Common errors in prescription writing are due to : 1. Omission of information 2. poor prescription writing 3. inappropriate choice of drug(s) 40

41 Drug Compliance : means the extent to which the patient follows the instructions of proper drug(s) use, as given by his prescribing doctor on the prescription form. Causes of poor compliance : 1. Lack of patient teaching by his Dr on details of proper drug use or lack of understanding by patient of these instructions when taught to him 2. Failure of patient to obtain the drug due to problems of cost or handicap 3. Patient forgets to take drug, or loss of drug, or discontinues taking drug prematurely and thus may donate the medication to others 41

42 4. Polypharmacy (taking multiple drugs) : due to many diseases esp. in elderly ; this is esp. when multiple doses of each drug is needed daily 5. Frequent doses (> 3 / d) and long duration of treatment (months or years) 6. Age : neonates, infants, children, and elderly 7. Disabling adverse effects occur Consequences of poor compliance : 1. Reduced or loss of therapeutic effect, esp. with drugs having short half-life 2. Recurrence of disease 3. Withdrawal syndrome occur with some drugs 42

43 Pharmacodynamics is the study of the biochemical and physiological effects of drugs, in certain period. In brief, it can be described as what the drug does to the body. Drug receptors Effects of drug Responses to drugs Toxicity and adverse effects of drugs