Pharmacology: drug interactions, side effects, dosage calculation for Nurses and Health Professionals
Pharmacology: drug interactions, side effects, dosage calculation for Nurses and Health Professionals
1. Drug Interactions
Drug interactions occur when one drug affects the action of another drug, leading to increased or decreased efficacy or increased risk of adverse effects. Drug interactions can be:
- Pharmacodynamic Interactions: When drugs with similar or opposite effects influence each other’s action.
- Pharmacokinetic Interactions: When one drug affects the absorption, distribution, metabolism, or excretion of another.
Types of Drug Interactions
- Synergistic Effect: Two drugs given together enhance each other’s effects (e.g., alcohol and sedatives both increase central nervous system depression).
- Antagonistic Effect: One drug reduces the effect of another (e.g., naloxone blocks opioid effects).
- Enzyme Inhibition: Some drugs inhibit liver enzymes (CYP450 system), leading to reduced metabolism and increased levels of another drug (e.g., erythromycin increases the level of warfarin).
- Enzyme Induction: Some drugs increase the activity of enzymes, leading to faster metabolism and reduced levels of another drug (e.g., rifampin induces CYP enzymes, lowering the effectiveness of oral contraceptives).
- Displacement from Plasma Proteins: One drug can displace another from plasma proteins, increasing the free concentration of the displaced drug (e.g., aspirin displaces warfarin, increasing the risk of bleeding).
2. Side Effects
Side effects are unintended effects of a drug at therapeutic doses. They range from mild (nausea, dizziness) to severe (organ damage, anaphylaxis).
Common Side Effects by Drug Class
- Analgesics (e.g., opioids): Constipation, respiratory depression, sedation, nausea.
- Antibiotics (e.g., penicillins): Allergic reactions, gastrointestinal upset, diarrhea.
- Antihypertensives (e.g., ACE inhibitors): Cough, hyperkalemia, hypotension, angioedema.
- Diuretics (e.g., furosemide): Dehydration, electrolyte imbalance (e.g., hypokalemia), hypotension.
- Antidepressants (e.g., SSRIs): Sexual dysfunction, weight gain, insomnia, serotonin syndrome.
- Antipsychotics (e.g., haloperidol): Extrapyramidal symptoms, weight gain, sedation, metabolic syndrome.
- Anticoagulants (e.g., warfarin): Bleeding, bruising, gastrointestinal upset, teratogenic effects.
3. Dosage Calculation
Dosage calculation is crucial in ensuring that patients receive the appropriate amount of medication based on their weight, age, condition, and renal or liver function.
Dosage Calculation Formula
Example of Dosage Calculation:
IV Drip Rate Calculation:
Summary:
- Drug interactions should be monitored closely to avoid adverse effects or decreased efficacy.
- Side effects vary by drug class, with some being mild while others can be life-threatening.
- Dosage calculations are essential to avoid underdosing or overdosing, especially in special populations like children or patients with renal impairment.
Proper understanding of these concepts helps ensure safe and effective patient care.