Pharmacology Parenteral Routes

Questions and Answers

What does bioavailability measure in pharmacology?

The effectiveness of a drug at the receptor site.

The rate at which a drug is excreted from the body.

The amount of drug absorbed by the body.

The fraction of the drug dose reaching systemic circulation. (correct)

Which of the following routes of administration typically has the fastest onset of action?

Intravenous (correct)

Subcutaneous

Intramuscular

Oral

Which factor does NOT affect the distribution of a drug in the body?

Rate of metabolism (correct)

Molecular weight of the drug

Plasma protein binding

Blood flow to tissues

What is one disadvantage of subcutaneous administration?

Painful and may cause atrophy. Signup and view all the answers

Which method of drug delivery achieves systemic effects through the skin?

Transdermal patches Signup and view all the answers

In Experiment 2, what effect does intraperitoneal MgSO4 have on the body?

Sedation by blocking Calcium channels. Signup and view all the answers

When comparing two drugs with the same bioavailability but different pharmacological effects, these drugs are referred to as what?

Therapeutic equivalents Signup and view all the answers

How does inhalation as a route of administration benefit drug absorption?

It provides a large surface area for absorption. Signup and view all the answers

Which drug administration route has a bioavailability of 1?

Intravenous route Signup and view all the answers

What is a disadvantage of the oral drug administration route?

Degradation in the stomach Signup and view all the answers

Which factor does NOT affect the absorption of a drug?

Color of the tablet Signup and view all the answers

Which method is suitable for drugs that require no first pass metabolism?

Intramuscular route Signup and view all the answers

Which of the following is a major advantage of the rectal route of drug administration?

Lower risk of first pass metabolism Signup and view all the answers

What is the primary benefit of using intravenous (IV) administration in emergencies?

It provides immediate drug action Signup and view all the answers

Which characteristic of the intramuscular route is considered a disadvantage?

Painful administration Signup and view all the answers

What aspect of drug administration does 'onset of action' refer to?

Time from administration until therapeutic effect is noted Signup and view all the answers

What process primarily converts lipophilic drugs into more water-soluble metabolites for easier excretion?

Phase I metabolism Signup and view all the answers

Which enzyme system is mainly involved in the Phase I metabolism of drugs?

CYP450 Signup and view all the answers

What effect does malnutrition have on drug metabolism?

Inhibits liver microsomal enzymes Signup and view all the answers

Which of the following is a metabolic consequence for individuals with genetic polymorphisms regarding the drug isoniazid (INH)?

Slow acetylators risk accumulation and toxicity Signup and view all the answers

What is the main site of metabolism for most drugs in the body?

Liver Signup and view all the answers

Which of the following influences the metabolism of a drug?

All of the above Signup and view all the answers

What is the effect of grapefruit juice on drug metabolism?

Inhibits liver microsomal enzymes Signup and view all the answers

Study Notes

Routes of Drug Administration

High Blood Flow Characteristics
- Parenteral routes provide rapid absorption but have a high risk of infection.
- Commonly administered via subcutaneous (S.C), intrathecal, intra-articular, and intradermal routes.
Subcutaneous (S.C) Injection
- Administered at a 45° angle into adipose tissue.
- Common examples include heparin and insulin.
- Advantages: Can offer sustained effects.
- Disadvantages: May cause pain and tissue atrophy.
Intrathecal Injection
- Direct injection into cerebrospinal fluid (CSF).
- Example: nalbuphine (opioid analgesic).
Other Injection Methods
- Intra-articular: Injected into joint spaces.
- Intradermal: Injected in the dermis, typically at a 15° angle. Commonly used for vaccines.
Inhalation Administration
- Provides large surface area for absorption, leading to fewer systemic side effects.
- Example: aerosol treatments for asthma.
Topical Administration
- Includes creams, ointments, and eye drops for local effect.
- Rarely results in systemic circulation.
Transdermal Administration
- Achieves systemic effects via skin applications, often using patches.
- Examples include contraceptives and anti-anginal medications.

Experimental Observations

Experiment 1: Different administration routes to three mice (I.V, I.M, S.C)
- Results: Onset of action identified as I.V first, followed by I.M, and S.C last.
Experiment 2: Administration of MgSO4 orally vs. intraperitoneally (I.P)
- Oral MgSO4 causes diarrhea via non-absorption.
- I.P MgSO4 blocks calcium channels, resulting in sedation (loss of righting reflex).

Absorption and Distribution

Bioavailability (F)
- Defined as the fraction of a dose that reaches systemic circulation. Calculated as a percentage.
- Intravenous administration has 100% bioavailability, while oral routes often face first-pass metabolism issues.
Distribution Factors
- Movement of drugs from circulation to action sites is influenced by plasma protein binding (PPB), primarily albumin for acidic drugs.

Pharmacokinetics Overview

Absorption
- Movement of the drug from the administration site to systemic circulation affected by:
  - Drug's physical properties.
  - Drug concentration.
  - Surface area of absorption.
  - Blood flow at the site.
Onset and Duration of Action
- Onset: Time from drug administration to effect appearance.
- Duration: Time from first effect to its disappearance.

Enteral Routes of Administration

Oral
- Advantages: Convenient and cost-effective.
- Disadvantages: First-pass metabolism, gastrointestinal degradation, unsuitable for emergencies or nausea/vomiting.
Sublingual and Buccal
- Advantages: Bypass first-pass metabolism, rapid absorption.
- Disadvantages: Unpleasant taste, food/drink can affect absorption.
- Examples: Dinitrate (sublingual), Fentora (buccal).
Rectal
- Advantages: Useful for infants and when oral route is unavailable.
- Disadvantages: Inconvenient, can cause irritation, dependent on user for administration.

Parenteral Routes

Intravenous (I.V)
- Direct delivery to systemic circulation ensures rapid action with 100% bioavailability.
- Ideal for large volume dosing or during emergencies, despite safety concerns.
Intramuscular (I.M)
- Avoids first-pass metabolism and supports oily preparations.
- Rapid absorption but may cause pain and requires patient assistance.
Intraperitoneal (I.P)
- Also avoids first-pass metabolism and is useful for specific therapeutic applications.

Metabolism

Biotransformation
- Conversion of lipophilic drugs into hydrophilic metabolites for excretion.
- Can convert active drugs to inactive forms or vice versa.
- Key metabolic site: Liver (via CYP450 enzymes), also occurs in kidneys, lungs, GIT, and skin.
Metabolism Phases
- Phase I: Non-synthetic reactions that introduce polar groups to enhance hydrophilicity (CYP450 involvement).
- Phase II: Synthetic reactions (conjugation) with modifications like methylation or acetylation.
Factors Affecting Metabolism
- Genetic Variability: Differences in enzyme function can lead to dosing challenges (e.g., rapid vs. slow acetylators).
- Disease States: Conditions like liver disease can alter metabolic capacity.
- Dietary Influences: Malnutrition and substances like grapefruit juice can inhibit or induce liver microsomal enzymes.

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Description

This quiz covers various parenteral routes of drug administration, including subcutaneous, intrathecal, intra-articular, and intradermal methods. Analyze the advantages and disadvantages of each route along with examples. Perfect for students studying pharmacology and drug delivery systems.