Following antimicrobials are termed as type I calcimimetics that mimic the stimulatory effect of calcium, on the calcium sensing receptor to inhibit PTH secretion by the parathyroid gland EXCEPT:
**Core Concept**
The **calcium-sensing receptor (CaSR)** plays a crucial role in regulating parathyroid hormone (PTH) secretion in response to serum calcium levels. **Type I calcimimetics** are compounds that mimic the stimulatory effect of calcium on the CaSR, thereby inhibiting PTH secretion. This mechanism is significant in managing conditions like hyperparathyroidism.
**Why the Correct Answer is Right**
The correct answer, **B. Hamycin**, is an antifungal agent and does not act as a calcimimetic. In contrast, **streptomycin**, **neomycin**, and **gentamicin** are aminoglycoside antibiotics that can act as type I calcimimetics by activating the CaSR, which leads to decreased PTH secretion. This effect is particularly relevant in patients with hyperparathyroidism, where reducing PTH levels is desirable.
**Why Each Wrong Option is Incorrect**
**Option A:** Streptomycin is an aminoglycoside antibiotic that can mimic the effect of calcium on the CaSR, making it a type I calcimimetic.
**Option C:** Neomycin, another aminoglycoside antibiotic, also acts as a type I calcimimetic by stimulating the CaSR.
**Option D:** Gentamicin, similar to streptomycin and neomycin, is an aminoglycoside that can inhibit PTH secretion by activating the CaSR, classifying it as a type I calcimimetic.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that while aminoglycosides like streptomycin, neomycin, and gentamicin have this calcimimetic effect, their primary use is as antimicrobials, and their impact on calcium and PTH levels is a secondary consideration. This distinction is crucial for managing patients with both infectious diseases and disorders of calcium homeostasis.
**✓ Correct Answer: B. Hamycin**