Factors Influencing Drug Bioavailability and Pharmacology Principles
Factors Influencing Drug Bioavailability
Definition and Measurement
Bioavailability refers to the rate and extent to which a drug is absorbed from its dosage form and becomes available at the site of action. It is typically measured by analyzing the drug’s concentration-time curve in the blood or by assessing its excretion in urine.
Factors Affecting Bioavailability
- Physicochemical Properties: The drug’s solubility, lipophilicity, and molecular size influence its ability to cross biological membranes. Nonpolar drugs tend to be absorbed more readily through passive diffusion.
- Formulation: The dosage form (e.g., solution, tablet, capsule) and its composition can significantly impact absorption speed. Liquids and syrups are generally absorbed faster than solid forms.
- Co-administration: The presence of other substances, such as antacids, can affect drug absorption by altering gastric pH or forming complexes.
- Administration Routes: Different routes of administration (e.g., oral, intravenous, intramuscular) have varying degrees of first-pass metabolism and vascularity, influencing bioavailability.
- Physiological Factors: Gastrointestinal conditions, food intake, and malabsorption syndromes can also impact drug absorption.
Pharmacology Principles
Anticholinergic Drugs in Preanesthetic Medication
Anticholinergic drugs like atropine and hyoscine are used to reduce salivary and respiratory secretions, preventing complications during anesthesia. They also help prevent laryngospasm and vasovagal attacks.
Beta Blockers
Beta blockers have various uses, including managing hypertension, angina pectoris, arrhythmias, heart failure, and migraine prophylaxis.
Aspirin Adverse Effects
Aspirin can cause side effects such as gastrointestinal distress, bleeding, hypersensitivity reactions, and salicylism. In children, Reye’s syndrome is a serious concern.
Insulin in Diabetes Management
Insulin is essential for type 1 diabetes and may be required for type 2 diabetes when other treatments are ineffective. It helps regulate blood glucose levels.
Third-Generation Cephalosporins
These antibiotics have a broad spectrum of activity, are stable against beta-lactamases, and have a longer half-life and better tissue penetration compared to earlier generations.
Heparin
Heparin is an anticoagulant that acts by inhibiting thrombin and factor Xa, preventing blood clot formation. Adverse effects include bleeding and thrombocytopenia.
Sulfonylureas
Sulfonylureas stimulate insulin release from the pancreas and are used to treat type 2 diabetes. Hypoglycemia is a common adverse effect.
First-Choice Drugs for Hypertension
Diuretics, calcium channel blockers, ACE inhibitors, angiotensin II receptor blockers, and beta blockers are commonly used as first-line treatments for hypertension.
Systemic Routes of Drug Administration
Common routes include oral, sublingual, rectal, cutaneous, inhalation, nasal, and parenteral (e.g., subcutaneous, intramuscular, intravenous).
Drug Safety Evaluation
Therapeutic index and therapeutic range are used to assess drug safety. The therapeutic index is the ratio of the median lethal dose to the median effective dose, while the therapeutic range is the range of doses that produce therapeutic effects without unacceptable adverse effects.
Preventing Adverse Drug Effects
Strategies include avoiding inappropriate drug use, using appropriate doses and administration routes, considering patient history, monitoring for drug interactions, and using correct administration techniques.
Sulfonamides and Cotrimoxazole
Sulfonamides inhibit folic acid synthesis in bacteria. Cotrimoxazole, a combination of trimethoprim and sulfamethoxazole, is effective due to its synergistic action and reduced risk of resistance.
Antimicrobial Mechanisms of Action
Antimicrobials can target various bacterial processes, including cell wall synthesis, cell membrane permeability, protein synthesis, nucleic acid synthesis, and folic acid metabolism.