P-Drug Concept

  • Medical students will learn about more than a thousand drugs.
  • The Essential drug list consists of about 200-300 drugs
  • More than 40000 different formulations are marketed
  • Most doctors will prescribe only 40-60 drugs in their lifetime.
  • Patients vary in age, gender, size and sociocultural characteristics,(  which may affect treatment choices.)
  • Patients also have their own perception of appropriate treatment, and should be fully informed partners in therapy.
  • Pharmacology reference works and formularies are drug-centred,
  • Clinical textbooks and treatment guidelines are disease-centred and provide treatment recommendatIions.
  • Different sources may give contradictory advice

Process of Rational Prescribing

Step I: define the patient’s problem and the diagnosis.

Step II: specify the therapeutic objective.

Step III:  choose a drug.

Step IV: Start the treatment.

Step V: Give information, instructions and warnings.

Step VI: Monitor and stop the treatment

P-Drug Concept

  • P-drugs are the drugs you have chosen to prescribe regularly, and with whom you have become familiar.
  • They are your drugs of choice for given indications.
  • The P-drug concept is more than just the name of a pharmacological substance, it also includes the dosage form, dosage schedule and duration of treatment.
  • P-drugs enable you to avoid repeated searches for a good drug in daily practice.
  • As you use your P‑drugs regularly, you will get to know their benefits and side effects thoroughly.
  • P-drugs are your drugs of first choice for a common condition.
  • P drug is selected for a disease and not for a particular patient
  • The activity of P drug selection can reduce the chances of irrational prescribing that is common problem
  • P drug can vary from doctor to doctor, country to country because of variation of cost, national formularies, essential drug list of the country, personal elucidation of information.

Choice of P-drug (STEP Criteria)

  • A P-drug is selected depending upon the following criteria:
  • Safety:                possible adverse effects.
  • Tolerability:       suitability for a patient.
  • Efficacy:              drug profile.
  • Price:                    always look at the total cost of treatment rather than the cost per unit.

Process of Choosing a P Drug

  • Define the Diagnosis
  • Set Therapeutic Objective
  • Make inventory of effective groups of drugs
  • Choose an Effective Group of drug
  • Choose a P drug

Define the Diagnosis

  • Remember that you are choosing a drug of first choice for a common condition.
  • You are not choosing a drug for an individual patient (when actually treating a patient you will verify whether your P-drug is suitable for that particular case.
  • To be able to select the best drug for a given condition, you should study the pathophysiology of the disease. The more you know about this, the easier it is to choose a P-drug.
  • When treating an individual patient you should start by carefully defining the patient’s problem 

Set Therapeutic Objective

Think of the therapeutic objective in terms of the patient and the benefit afforded to him.

Hypertension: Preventing end organ damage by regular treatment for lowering blood pressure to normotensive levels.

Diabetes: Delaying or preventing complications by normalising the blood sugar and Hba1c levels to acceptable normal limits by drug therapy.

Acute tonsilitis: Providing symptomatic relief for the self-limiting disease by giving a short course of antibiotics and supportive therapy.

Make inventory of effective groups of drugs

  • Based on: Efficacy, Safety, Suitability, Cost of treatment
    • Look at formularies or guidelines that exist in your hospital or health system, or at international guidelines,  WHO treatment guidelines for certain common disease groups.
    • Check the index of a good pharmacology reference book and determine EFFECTIVE groups  for your diagnosis
    • In most cases you will find only 2-4 groups of effective drugs .

A score between 0-1 is given for 4 criterias of Efficacy, Safety, Cost & Convenience/Suitibility. The score depends on the significance of the criteria for a disease. Eg. For Amoebic Dysentery- efficacy (0.4), safety (0.3), cost (0.1) and convenience (0.2). This 0.4, 0.3, 0.2 and 0.1 is also called as the weight.

The total score should add up to 1. (0.4+0.3+0.1+0.2=1).

Each group a score between 1-10 is given on all the 4 criterias after comparing with all the groups of drugs (higher score indicates a better value).

The drug which is choosen as a P drug whether it is effective and safe in this case?

patient is pregnant the drugs which are not given (contraindicated)

a. Sulfonamide and Cotrimoxazole: Teratogenic risk and causes neonatal hemolysis

b. Fluroquinolones: Cartilage damage and arthropathy

c. Aminolycosides: Ototoxicity

d. Tetracyclines: Brownish discolouration of teeth , temporary suppression of bone growth

e. Chloramphenicol: Gray baby syndrome, bone marrow suppression

f. Nitrofurantoin: Hemolytic anaemia in 3RD Trimester of pregnancy

Choose a P drug

  • Choose active drug and its dosage form
  • Choose a standard dose schedule
  • Choose a standard duration of treatment
  • Rather than reviewing all possible drugs for the treatment of dry cough every time you need one, you should decide, in advance, your first-choice treatment.
  •  The general approach in doing that is to specify your therapeutic objective, to make an inventory of possible treatments, and to choose your ‘P(ersonal) treatment’, on the basis of a comparison of their efficacy, safety, suitability and cost.
  • In certain diseases we can give more weight on efficacy rather than other criterias. Example AIDS, Carcinomas etc.where the prognosis of disease is very poor. So we have to prescribe the highly efficacious drugs so that the patient can live in a better way. As in case of acute and severe form of disease like myocardial infarction we require highly efficacious drugs so we can give more weight on the efficacy rather than other 3 criterias.
  • Conditions where we can give more weight on safety than efficacy for example efficacy (0.3), and safety (0.4): Diseases where we use drugs with narrow therapeutic index like in mania (Lithium), in Congestive cardiac failure (digoxin), Arrhythmias.
  • In certain circumstances we can give more weight on Cost (0.3), where the drugs are used for long time or life time. Eg Diabetes Mellitus, Rheumatic fever, Hypertension, Congestive heart failure, Parkinsonism.
  • In some diseases we can give more weight on convenience (0.3). Eg. Peptic ulcer where we are giving Anti H.Pylori treatment as more drugs are given in one day it will be less convenient.

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