The Concept of P-Drugs in Rational Prescribing

Main Takeaway: A P-drug is a prescriber’s personal choice of first-line medicine for a specific indication, selected through a systematic and evidence-based process. Developing and maintaining a personal formulary of P-drugs streamlines decision-making, promotes rational therapeutics, and enhances patient safety.

1. Definition and Purpose of P-Drugs

A P-drug (“personal drug”) is not merely the generic name of a medicine but encompasses:

• The drug substance itself
• The dosage form (e.g., tablet, injection)
• The dosage schedule (e.g., once daily)
• The duration of treatment

P-drugs serve as a clinician’s priority choices for given indications, reducing repetitive searches in daily practice and ensuring familiarity with each drug’s effects and side effects.

2. Relation to Essential Medicines and Guidelines

• Essential Medicines Lists (EMLs): National or WHO EMLs often contain dozens to hundreds of options; clinicians typically use only 40–60 drugs regularly. By selecting P-drugs from these lists, practitioners effectively create a personal essential medicines list tailored to their practice context.
• Standard Treatment Guidelines (STGs): Evidence-based STGs for common conditions should inform P-drug selection. P-drugs should align with STG recommendations while accounting for local availability, cost, and patient factors.

3. The Six-Step Process for Rational Prescribing

The WHO Guide to Good Prescribing outlines a six-step model, with P-drug selection comprising Step 3:

1. Define the patient’s problem. Summarize diagnosis and relevant patient characteristics (e.g., comorbidities, allergies).
2. Specify the therapeutic objective. Establish clear, measurable goals (e.g., reduce blood pressure to <140/90 mmHg).
3. Choose and verify your P-drug:
   a. Select a P-drug for the indication (Step 3a).
   b. Verify its suitability for this patient (Step 3b)—check for contraindications, interactions, and patient-specific factors.
4. Write the prescription. Include drug name, dose, schedule, and duration.
5. Provide information to the patient: instructions and warnings.
6. Monitor effectiveness and adverse effects; adjust or stop treatment as needed.

4. Criteria for Selecting P-Drugs (The STEP Framework)

When comparing drug options, apply the STEP criteria:

• Safety: Evaluate adverse-effect profiles and contraindications.
• Therapeutic efficacy: Assess evidence of clinical benefit.
• Economy (cost): Consider affordability and cost-effectiveness.
• Propriety (suitability): Account for patient convenience, formulation, dosing schedule, and special conditions (e.g., pregnancy).

Example: Selecting a P-Drug for Acute Amoebic Dysentery

Among nitroimidazoles, tinidazole may be preferred over metronidazole due to similar efficacy and cost but greater suitability (shorter course, once- or twice-daily dosing).

5. Benefits of a P-Drug Formulary

• Efficiency: Reduces time spent reviewing alternatives for routine cases.
• Familiarity: Clinician expertise with P-drugs improves recognition of expected effects and adverse reactions.
• Consistency: Supports standardized prescribing practices within and across healthcare teams.
• Rationality: Mitigates impulsive or non-evidence-based choices influenced by marketing or habit.

By systematically selecting and regularly reviewing P-drugs according to these principles, prescribers establish a robust foundation for safe, effective, and cost-conscious patient care.