Pharmacology Drug Absorption and Interactions

Definition: The process by which a drug enters the bloodstream from its site of administration.
Factors Affecting Absorption:
- Route of Administration:
  - Oral: affected by gastrointestinal motility, pH, and presence of food.
  - IV: direct entry into circulation; highest bioavailability.
  - Transdermal: influenced by skin permeability.
- Physicochemical Properties:
  - Solubility: drugs must be soluble to be absorbed.
  - Lipophilicity: lipophilic drugs pass through cell membranes more easily.
- Formulation:
  - Dosage forms (tablets, capsules, injections, etc.) impact absorption rate.
Bioavailability:
- The fraction of administered drug that reaches systemic circulation.
- Influences dosing regimens.

Definition: Occur when one drug affects the pharmacokinetics or pharmacodynamics of another drug.
Types:
- Pharmacokinetic Interactions:
  - Absorption: presence of one drug can affect the absorption of another.
  - Distribution: changes in protein binding can alter drug availability.
  - Metabolism: induction or inhibition of metabolic enzymes (e.g., CYP450).
  - Excretion: changes in renal function can affect drug clearance.
- Pharmacodynamic Interactions:
  - Synergistic Effects: combined effects are greater than individual effects.
  - Antagonistic Effects: one drug diminishes the effect of another.
Clinical Implications:
- Careful monitoring required to avoid adverse effects or therapeutic failures.

Definition: The specific conditions or diseases for which a drug is prescribed.
Categories:
- Analgesics: pain relief (e.g., NSAIDs, opioids).
- Antibiotics: treat infections (e.g., penicillin, tetracycline).
- Antihypertensives: reduce blood pressure (e.g., ACE inhibitors, beta-blockers).
- Antidepressants: treat mood disorders (e.g., SSRIs, SNRIs).
- Chemotherapy Agents: target cancer cells (e.g., cisplatin, doxorubicin).
Patient Considerations:
- Individual response variability based on genetics, age, and comorbid conditions.

Definition: The specific biochemical interaction through which a drug produces its effect.
Common Mechanisms:
- Receptor Binding:
  - Agonists activate receptors; antagonists block receptors.
- Enzyme Inhibition: Drugs may inhibit enzymes involved in biochemical pathways (e.g., ACE inhibitors).
- Ion Channel Modulation: Drugs may open or close ion channels affecting cell excitability (e.g., calcium channel blockers).
- Nucleic Acid Interaction: Some drugs interact with DNA/RNA to inhibit replication or transcription (e.g., certain chemotherapeutics).
Importance in Drug Development: Understanding mechanisms helps in designing more effective and targeted therapies.

Drug absorption is the entry of a drug into the bloodstream from its administration site.
Route of administration impacts absorption:
- Oral absorption is influenced by gastrointestinal motility, pH, and food presence.
- Intravenous (IV) administration provides direct circulation access and maximizes bioavailability.
- Transdermal absorption is determined by skin permeability.
Physicochemical properties play a crucial role:
- Solubility is essential; drugs must be soluble to be absorbed.
- Lipophilicity facilitates passage through cell membranes for lipophilic drugs.
Formulation type affects absorption rates, with different dosage forms (tablets, injections) having varying impacts.
Bioavailability refers to the fraction of an administered drug reaching systemic circulation, influencing dosing strategies.

Drug interactions occur when one drug alters the pharmacokinetics or pharmacodynamics of another.
Pharmacokinetic interactions include:
- Absorption changes, where one drug can affect another's uptake.
- Distribution changes due to variations in protein binding affecting drug availability.
- Metabolism alterations through enzyme induction or inhibition, notably with CYP450 enzymes.
- Excretion changes linked to renal function, impacting drug clearance rates.
Pharmacodynamic interactions encompass:
- Synergistic effects, where combined drugs lead to greater impact than individual drugs alone.
- Antagonistic effects, where one drug reduces the effectiveness of another.
Clinical implications require careful monitoring of drug combinations to prevent adverse effects and therapeutic failures.

Therapeutic uses define specific conditions or diseases for which drugs are prescribed.
Main categories of therapeutic drugs include:
- Analgesics for pain relief, such as NSAIDs and opioids.
- Antibiotics used to treat infections, like penicillin and tetracycline.
- Antihypertensives aimed at lowering blood pressure (e.g., ACE inhibitors, beta-blockers).
- Antidepressants for mood disorders, covering SSRIs and SNRIs.
- Chemotherapy agents designed to target cancer cells, including cisplatin and doxorubicin.
Patient considerations highlight variability in responses due to factors like genetics, age, and existing health conditions.

Mechanisms of action detail biochemical interactions through which drugs exert effects.
Common mechanisms include:
- Receptor binding where agonists activate and antagonists block specific receptors.
- Enzyme inhibition, exemplified by ACE inhibitors blocking critical pathways.
- Ion channel modulation alters excitability by opening or closing channels, like calcium channel blockers.
- Nucleic acid interaction involves drugs targeting DNA/RNA to inhibit replication/transcription, particularly in chemotherapy.
Understanding these mechanisms is vital for developing more effective and targeted therapies.