๐Ÿ“– Pharmacodynamics

-

By Dr. Sk Sabir Rahaman, MBBS, MD (Pharmacology), DFM(Family Medicine), FCFM, CCEBDM, CCLSD 

๐Ÿ“ Specialist Family Physician | Consultant Pharmacologist | Lifestyle & Diabetes Expert


Definition:

Pharmacodynamics (Greek pharmacon = drug, dynamis = power) is the study of what the drug does to the body.

It covers:

  • Mechanism of action (MOA) at molecular, cellular, and systemic levels

  • Intensity and nature of pharmacological effects

  • Adverse drug reactions and therapeutic index

  • Dose–response relationships

๐Ÿ”น Core Concepts

1. Mechanism of Action (MOA)

Drugs act by binding to specific targets:

  • Receptors → ฮฒ-adrenergic receptors (adrenaline)

  • Ion channels → Ca²⁺ blockers (verapamil)

  • Enzymes → Acetylcholinesterase inhibitors (neostigmine)

  • Transporters → SSRIs (fluoxetine, blocks serotonin reuptake)

๐Ÿ‘‰ Interaction may stimulate, inhibit, or modulate physiological functions.

๐Ÿ”น Types of Drug Effects

1. Stimulation

  • ↑ Activity of cells/tissues.

  • Example: Adrenaline stimulates ฮฒ₁ receptors in the heart → ↑ heart rate (chronotropy), ↑ contractility (inotropy).

  • Clinical use: cardiac arrest, anaphylaxis.

2. Depression

  • ↓ Activity, often via neurotransmission suppression.

  • Examples:

    • Benzodiazepines, barbiturates, anesthetics → CNS depression via GABA.

    • ฮฒ-blockers → ↓ cardiac workload.

  • Uses: seizures, hypertension, angina, arrhythmias.

3. Irritation

  • Local inflammatory/sensory response (sometimes therapeutic).

  • Example: Methyl salicylate, capsaicin creams → cause vasodilation, sensory stimulation → pain relief.

  • Uses: myalgia, arthritis, sprains.

4. Cytotoxic Action

  • Selective destruction of microbes or cancer cells.

  • Examples:

    • Penicillin → inhibits bacterial cell wall.

    • Cisplatin, doxorubicin → damage DNA in cancer cells.

  • Uses: infections, cancer.

5. Replacement Therapy

  • Supplying deficient essential substances.

  • Examples:

    • Insulin → Type 1 diabetes

    • Levothyroxine → Hypothyroidism

    • Vit B12 → Pernicious anemia

    • Iron → Iron-deficiency anemia

  • Often lifelong therapies.

๐Ÿ”น Dose–Response Relationship (DRR)

  • Graded response: Continuous increase with dose (seen in individuals).

  • Quantal response: All-or-none, measured in populations (e.g., % achieving sleep).

Key terms:

  • Potency: Dose needed to achieve effect (fentanyl > morphine).

  • Efficacy: Max effect achievable → clinically more important.

  • Therapeutic index (TI): Safety margin = LD₅₀ / ED₅₀.

๐Ÿงญ Summary – Types of Drug Effects

  • Stimulation: Adrenaline, salbutamol → anaphylaxis, asthma

  • Depression: Diazepam, propofol → seizures, anesthesia

  • Irritation: Capsaicin, methyl salicylate → pain relief

  • Cytotoxic: Penicillin, doxorubicin → infection, cancer

  • Replacement: Insulin, levothyroxine → diabetes, hypothyroidism

Comments

Post a Comment

Popular posts from this blog

๐Ÿฅ Insulin Storage: Myths vs. Facts Every Diabetic Should Know

-
By Dr. Sk Sabir Rahaman, MBBS , MD (Pharmacology), DFM(Family Medicine), FCFM, CCEBDM, CCLSD   For millions living with diabetes, insulin is more than a medication — it’s a lifeline . However, widespread misconceptions about insulin storage often lead to avoidable panic, especially during heatwaves, power outages, or while traveling . ๐Ÿšซ The Myth: "Insulin must always stay refrigerated" Many believe that insulin instantly loses effectiveness once it’s out of the fridge. This is not true — and can cause undue stress, particularly in hot climates like India or during journeys where refrigeration isn’t available. ✅ The Fact: Most insulin types tolerate room temperature According to World Health Organization (WHO) and insulin manufacturer guidelines : ๐Ÿ”น Opened insulin vials or pens can be safely kept at room temperature (15–25°C / 59–77°F) for up to 28 days. That means: You don’t need to return it to the fridge every time after injection. It's safe fo...
Read more

๐Ÿงด TREATMENT OF POISONING – A COMPREHENSIVE OVERVIEW

-
By Dr. Sk Sabir Rahaman, MBBS , MD (Pharmacology), DFM(Family Medicine), FCFM, CCEBDM, CCLSD   ๐Ÿงช Definition & Scope Toxicology : Branch of pharmacology dealing with harmful effects of chemicals on living organisms. Poisoning : Harmful effects caused by ingestion, inhalation, dermal exposure, or injection of toxic substances (drugs, pesticides, household chemicals, industrial agents, venoms). Medico-legal importance : All poisoning cases are medical emergencies. Must be reported to police/authorities (especially suicidal, homicidal, or accidental cases) under Indian law. ๐Ÿ›‘ General Principles of Management (ABCDE of Toxicological Emergencies) A – Airway Ensure patency (tongue fall, aspiration common in comatose patients). Place in left lateral position to reduce aspiration. Intubate with cuffed endotracheal tube if airway compromised. Regular suction of secretions. B – Breathing Monitor with pulse oximetry and ABG. Give humidified oxy...
Read more

๐ŸŒฟ Rational Use of Medicines (RUM): A Guide for Safer and Smarter Prescribing

-
By Dr. Sk Sabir Rahaman, MBBS , MD (Pharmacology), DFM(Family Medicine), FCFM, CCEBDM, CCLSD   ๐Ÿ“ Specialist Family Physician | Consultant Pharmacologist | Lifestyle & Diabetes Expert Medicines save lives, ease suffering, and improve health outcomes. But when they are used irrationally , they can cause more harm than good. The World Health Organization (WHO) emphasizes the importance of the Rational Use of Medicines (RUM) to ensure patient safety, treatment effectiveness, and cost efficiency. In this blog, we’ll explore what RUM means, why it matters, and how healthcare professionals can practice it effectively. ๐Ÿ“Œ What is Rational Use of Medicines? According to WHO: “Rational use of medicines requires that patients receive medications appropriate to their clinical needs, in doses that meet their individual requirements, for an adequate period of time, and at the lowest cost to them and their community.” In simple words: it’s about prescribing the right medicine, in t...
Read more