The correct method for determining the vastus lateralis site for I.M. injection is to:

Correct Answer: D

Rationale: The correct answer is D because the vastus lateralis muscle is located in the anterior thigh, and the described method ensures proper localization for a safe intramuscular (I.M.) injection. The vastus lateralis is part of the quadriceps muscle group and is a common site for I.M. injections, particularly in infants and adults when other sites are contraindicated. To locate it, the clinician divides the thigh between the greater trochanter (the bony prominence at the top of the femur) and the lateral femoral condyle (the bony protrusion on the outer side of the knee) into thirds. The middle third on the anterior aspect of the thigh is the correct injection site, as it avoids major nerves and blood vessels while ensuring the medication is delivered into the muscle mass. This method is widely accepted in clinical practice and supported by anatomical studies. Choice A is incorrect because it describes the dorsogluteal site (upper outer quadrant of the buttock), which is not the vastus lateralis. The dorsogluteal site is associated with the gluteus maximus muscle and carries a higher risk of injuring the sciatic nerve or superior gluteal artery if not properly located. While it is a valid I.M. injection site, it is not the correct answer for targeting the vastus lateralis. Choice B is incorrect because it refers to the deltoid muscle site, located on the lateral aspect of the arm. The deltoid is another common I.M. injection site, particularly for vaccines, but it is not the vastus lateralis. The described landmark (acromion process) is specific to the deltoid and irrelevant to locating the vastus lateralis in the thigh. Choice C is incorrect because it describes an area on the abdomen (anterior to the umbilicus), which is not used for I.M. injections. The abdominal area is typically associated with subcutaneous injections (e.g., insulin) due to the presence of adipose tissue, not muscle mass. There is no valid anatomical basis for administering an I.M. injection in this location, making it entirely unrelated to the vastus lateralis. The correct method (D) ensures accurate placement in the vastus lateralis, minimizing complications such as nerve injury, injection into subcutaneous tissue, or accidental entry into blood vessels. The other choices either describe alternative injection sites or irrelevant anatomical locations, demonstrating a misunderstanding of the vastus lateralis's position and function. Proper identification of anatomical landmarks is critical for safe and effective I.M. injections, and the vastus lateralis is particularly advantageous due to its accessibility and reduced risk of complications compared to other sites.

Correct Answer: D

Rationale: The correct answer is **D: 26G** because intradermal injections require a fine, short needle to deposit medication or vaccines just below the epidermis without penetrating deeper tissues. A 26G needle is typically 26-gauge with a short bevel (usually ⅜ to ½ inch in length), which allows precise delivery into the dermal layer while minimizing trauma and leakage. The thin diameter reduces discomfort for the patient and ensures proper absorption, as intradermal injections rely on slow diffusion from the dermis into the local capillaries. This gauge is standard for procedures like tuberculin (TB) skin tests or allergy testing, where accuracy in placement is critical. **A: 20G** is incorrect because it is far too large for intradermal injections. A 20-gauge needle is thick and long, typically used for procedures requiring rapid fluid delivery (e.g., IV infusions or blood draws). Using such a large needle for intradermal injection would cause unnecessary pain, increase the risk of bleeding, and likely deposit the medication too deeply into subcutaneous or muscular tissue, compromising the intended immune response or diagnostic accuracy. **B: 22G** is incorrect because, while smaller than 20G, it is still too large for intradermal administration. A 22-gauge needle is commonly used for IM (intramuscular) injections or subcutaneous injections in adults, where deeper tissue penetration is needed. The diameter is too wide to reliably stay within the thin dermal layer, increasing the chance of misplaced medication and patient discomfort. **C: 25G** is incorrect because, although it is closer to the correct size, it is still less ideal than 26G for most intradermal procedures. While a 25-gauge needle can be used in some cases, it may not provide the same precision as a 26G needle, particularly for delicate applications like allergy testing where slight variations in depth can affect results. The marginally larger diameter may also cause more tissue disruption or leakage compared to the finer 26G needle. The choice of needle gauge balances precision, patient comfort, and clinical efficacy, and 26G is the optimal selection for intradermal injections due to its fine diameter and shallow penetration capability.

Correct Answer: A

Rationale: Parenteral administration refers to delivering medications via routes other than the digestive tract, typically involving injections. Penicillin, a widely used antibiotic, can be administered through specific parenteral routes to ensure optimal absorption, efficacy, and safety. The correct answer is **A (IM injection or an IV solution)** because penicillin formulations are specifically designed for intramuscular (IM) or intravenous (IV) administration. IM injections allow for slower absorption into the bloodstream, suitable for drugs like penicillin G benzathine, which provides prolonged action. IV administration delivers the drug directly into the bloodstream, ensuring rapid onset, which is critical in severe infections. Both methods are well-supported by pharmacokinetic studies and clinical practice guidelines. **Why other options are incorrect:** - **B (IV or intradermal injection):** Intradermal injections are used primarily for diagnostic tests (e.g., tuberculin skin tests) or vaccines, not for antibiotics like penicillin. The intradermal route lacks the capacity to deliver the volume or achieve the systemic drug levels required for antibiotic efficacy. - **C (Intradermal or subcutaneous injection):** Subcutaneous injections are unsuitable for penicillin because they can cause significant local irritation and inadequate absorption. Penicillin’s molecular properties and irritation potential make this route impractical, unlike drugs like insulin or heparin, which are designed for subcutaneous delivery. - **D (IM or subcutaneous injection):** While IM is correct, subcutaneous administration is inappropriate for penicillin due to the risk of tissue damage and inconsistent absorption. The subcutaneous layer lacks the vascularity needed for efficient drug distribution, leading to subtherapeutic levels and potential adverse reactions. The distinction between these routes hinges on the drug’s physicochemical properties, therapeutic goals, and anatomical considerations. Penicillin’s stability, solubility, and irritation profile limit its administration to IM or IV routes, ensuring both safety and clinical effectiveness. Misapplication via incorrect routes (e.g., intradermal or subcutaneous) could compromise treatment outcomes or cause harm, underscoring the importance of adhering to evidence-based administration practices.

Correct Answer: D

Rationale: The correct answer is D (600 mg) because 1 grain (gr) is equivalent to approximately 64.8 milligrams (mg). For practical clinical purposes, this is often rounded to 60 mg per grain for ease of calculation. Multiplying 10 gr by 60 mg/gr yields 600 mg. This conversion is standard in pharmacology, ensuring accurate dosing for medications like aspirin, where precision is critical. Choice A (0.6 mg) is incorrect because it represents a drastic underdose, likely resulting from a miscalculation where 10 gr was divided by 60 mg/gr instead of multiplied. This would be a 1000-fold error, rendering the dose therapeutically ineffective. Choice B (10 mg) is incorrect because it assumes a 1:1 conversion between grains and milligrams, which is not accurate. Grains are a much larger unit than milligrams, and this answer would also lead to a severe underdose, failing to achieve the intended therapeutic effect. Choice C (60 mg) is incorrect because it represents the conversion for 1 grain, not 10 grains. This error occurs if the physician's order is misinterpreted as a per-grain dose rather than the total required dose. While 60 mg might be a standard dose for certain aspirin formulations, it does not meet the 10 gr requirement specified in the question. Understanding unit conversions between grains and milligrams is crucial in medical practice to avoid dosing errors. Grains are an older unit still used in some prescriptions, whereas milligrams are the modern standard. Proper conversion ensures patient safety and therapeutic efficacy, particularly with medications like aspirin, where incorrect dosing can lead to treatment failure or toxicity. Always verify calculations and reference conversion tables when in doubt.

Correct Answer: C

Rationale: To determine the flow rate in drops per minute, multiply the ordered volume per hour by the drop factor (100 ml/hour x 15 gtt/ml = 1500 gtt/hour). Then, divide the result by 60 minutes to convert it to drops per minute (1500 gtt/hour · 60 minutes = 25 gtt/minute). Therefore, the correct answer is 25 gtt/minute.