为什么青霉素G不可口服，只能注射给药

青霉素是一种用于治疗细菌感染的广泛使用的抗生素。然而，对于许多人来说，他们可能会想知道为什么青霉素G不能通过口服的方式给药，而只能通过注射。在这篇文章中，我们将深入探讨这个问题，并理解为什么口服给药并不适合青霉素G。

首先，让我们了解一下青霉素G的性质。青霉素G属于β-内酰胺类抗生素，是由链霉菌（Penicillium chrysogenum）产生的天然抗生素。它通过抑制细菌细胞壁的合成而发挥作用。然而，青霉素G的特殊性质使得它不易通过口服途径给药。

青霉素G是一种大分子化合物，其分子量较大。当我们通过口服给药时，药物需要通过消化系统进行吸收。然而，口服给药后，许多因素会影响药物的吸收和利用，其中包括胃酸的分解、胃肠蠕动、肠道黏膜的屏障等。由于青霉素G的大分子量和化学性质，它很难通过肠黏膜进入血液循环。因此，青霉素G通过口服给药途径的吸收率非常低，并且不可靠。相比之下，注射给药通过直接将药物引入血液中，绕过了消化系统，从而提高了药物的吸收和利用率。

此外，青霉素G在胃酸的存在下会迅速分解。胃酸是一种强酸，可以破坏和降解许多分子。虽然胃酸对于杀灭细菌起到重要作用，但对于青霉素G来说，胃酸可能会破坏其化学结构，使其失去药效。这就是为什么青霉素G需要通过注射给药，绕过胃酸的影响。

总结起来，青霉素G不可口服的原因有两个主要的因素：其大分子量和化学性质导致其难以通过肠黏膜吸收，以及胃酸的存在使其易于分解。通过注射给药可以绕过这些问题，更有效地传递药物到目标位置。

In English:

Why Penicillin G Cannot Be Administered Orally, Only through Injection

Penicillin is a widely used antibiotic for treating bacterial infections. However, many may wonder why Penicillin G cannot be administered orally and is only given through injections. In this article, we will delve into this question and understand why oral administration is not suitable for Penicillin G.

Firstly, let us understand the nature of Penicillin G. Penicillin G belongs to the β-lactam class of antibiotics and is a naturally occurring antibiotic produced by Penicillium chrysogenum. It acts by inhibiting the synthesis of bacterial cell walls. However, the specific characteristics of Penicillin G make it unsuitable for oral administration.

Penicillin G is a large molecule with a high molecular weight. When we administer a drug orally, it needs to be absorbed through the digestive system. However, several factors affect the absorption and utilization of drugs after oral administration, including the degradation by stomach acid, gastrointestinal peristalsis, and the barrier of intestinal mucosa. Due to the large molecular weight and chemical properties of Penicillin G, it is challenging for it to pass through the intestinal mucosa into the bloodstream. Therefore, the absorption rate of Penicillin G through oral administration is very low and unreliable. In contrast, injection bypasses the digestive system by directly introducing the drug into the bloodstream, thereby increasing the absorption and utilization of the drug.

Additionally, Penicillin G rapidly degrades in the presence of stomach acid. Stomach acid, being a strong acid, can break down and degrade many molecules. While stomach acid plays a crucial role in killing bacteria, it can also destroy the chemical structure of Penicillin G, rendering it ineffective. This is why Penicillin G needs to be administered through injection to bypass the effects of stomach acid.

In summary, there are two main reasons why Penicillin G cannot be administered orally: its large molecular weight and chemical properties make it difficult to be absorbed through the intestinal mucosa, and the presence of stomach acid leads to its rapid degradation. Injection bypasses these issues, allowing for more effective delivery of the drug to the desired site.