Health, disease and the development of medicines revision notes

Discovery and Early Development

The process of developing new medicines starts with identifying potential drug candidates. This can involve screening natural compounds, synthesising new chemicals, or using computational models. Once a promising compound is found, the development stage optimises its chemical structure, formulation, and delivery method for best effect and stability.

Preclinical Testing

Before any new medicine can be tested in humans, it undergoes preclinical testing. This phase involves laboratory studies (in vitro) using cells and tissues, and animal studies (in vivo) to evaluate the drug's basic efficacy, toxicity, and potential side effects. The goal is to determine if the drug is safe enough to proceed to human trials and to gather data on dosage.

Clinical Testing (Human Trials)

Clinical testing is a multi-phase process with increasing numbers of human volunteers and patients:

• Phase 1: Small group of healthy volunteers (20-100) to assess safety, dosage, and side effects.
• Phase 2: Larger group of patients (100-300) with the target condition to confirm effectiveness and further evaluate safety.
• Phase 3: Even larger patient groups (hundreds to thousands) in randomised controlled trials to compare the new medicine with existing treatments or placebo, monitoring long-term effects and overall efficacy.
• Phase 4: Post-market surveillance after regulatory approval, continuously monitoring long-term effects and safety in the general population.

Regulatory Approval and Monitoring

After successful clinical trials, the extensive data is submitted to regulatory bodies (e.g., Medicines and Healthcare products Regulatory Agency in the UK) for review. If approved, the medicine can be marketed, but ongoing monitoring (Phase 4) is crucial for detecting rare or long-term side effects that may not have appeared during earlier trials.

Chlamydia: A Bacterial STI

Chlamydia is a bacterial infection spread through unprotected sexual contact (vaginal, anal, oral). Many infected individuals show no symptoms, especially in the early stages, making it easy to unwittingly transmit the infection. Symptoms, if present, can include unusual discharge, pain during urination, or abdominal pain. Left untreated, Chlamydia can lead to serious health issues such as pelvic inflammatory disease (PID) in women, which can cause infertility, or epididymitis in men. It is treatable with antibiotics.

HIV: A Viral STI

HIV (Human Immunodeficiency Virus) is a viral infection that primarily spreads through specific bodily fluids during sexual activity, sharing needles, or from mother to child. HIV attacks CD4+ T cells, which are crucial components of the immune system. This weakens the body's ability to fight off other infections and diseases. While there is no cure for HIV, antiretroviral therapy (ART) can effectively manage the viral load, allowing individuals with HIV to live long, healthy lives and significantly reducing the risk of transmission. Without treatment, HIV can progress to AIDS (Acquired Immunodeficiency Syndrome).

Preventing STI Spread

Prevention of STIs like Chlamydia and HIV largely relies on stopping the transmission routes. Key strategies include: consistent and correct use of barrier methods such as condoms during all types of sexual activity; regular STI testing, especially between partners or after unprotected encounters; reducing the number of sexual partners; and avoiding the sharing of needles or injection equipment. Education on sexual health and access to testing and treatment services are vital in controlling the spread of these infections in wider populations.

Pregnancy Testing and Diagnosis

Monoclonal antibodies are laboratory-produced antibodies that bind to specific antigens. In pregnancy tests, they detect human chorionic gonadotropin (hCG) in urine. For diagnostic imaging, they can be labelled with a radioactive or fluorescent marker and bind to specific antigens on cancer cells or blood clot components, allowing for precise localisation within the body through medical scans.

Treatment of Diseases and Advantages

Monoclonal antibodies are used in cancer treatment to deliver drugs or toxins directly to cancer cells, reducing damage to healthy cells. They can also block growth signals or trigger immune responses against cancer cells. A key advantage over traditional treatments like chemotherapy and radiotherapy is their high specificity, leading to fewer side effects because they target only diseased cells, unlike non-specific treatments that harm healthy cells too.

The Lytic Cycle

The lytic cycle is a rapid viral replication pathway resulting in host cell destruction. It begins with the virus attaching to a host cell and injecting its genetic material. The viral genes then hijack the host cell's metabolic machinery to synthesise viral proteins and nucleic acids. These components self-assemble into new virus particles. Finally, the host cell lyses (bursts), releasing the newly formed viruses to infect other cells.

The Lysogenic Cycle

In the lysogenic cycle, the viral genetic material integrates into the host cell's genome, forming a prophage (in bacteria) or a provirus (in eukaryotes). The host cell continues to live and reproduce, passing on the dormant viral genetic material to its daughter cells. The virus remains latent. Environmental stressors (like UV radiation or certain chemicals) can trigger the prophage to excise from the host genome, initiating the lytic cycle and leading to viral replication and cell lysis.

Key Differences and Similarities

Both cycles begin with viral attachment and injection of genetic material. The key difference is the fate of the host cell. The lytic cycle immediately leads to host cell death and the release of new virions, while the lysogenic cycle allows the host cell to survive and replicate with the viral DNA integrated. The lysogenic cycle can eventually transition to the lytic cycle, enabling the virus to spread after a period of dormancy, showcasing a survival strategy for the virus.