Retrovir

• Myalgia: Muscle pain or weakness.
• Dizziness: A sensation of spinning or lightheadedness.
• Dyspepsia: Indigestion or upper abdominal pain.
• Skin Pigmentation: Changes in the color of nails or skin (melanonychia), particularly in darker-skinned individuals.
• Fever: Unexplained elevation in body temperature.

• Pancreatitis: Inflammation of the pancreas, characterized by severe abdominal pain radiating to the back.
• Seizures: Though rare, neurological excitability can occur.
• Gynecomastia: Enlargement of breast tissue in males.
• Pure Red Cell Aplasia: A rare condition where the bone marrow stops producing red blood cells entirely.

> Warning: Stop taking Zidovudine and call your doctor immediately if you experience any of these serious reactions.

• Severe Anemia: Symptoms include extreme paleness, shortness of breath, and profound exhaustion. This is due to bone marrow suppression.
• Neutropenia: A dangerously low white blood cell count, which increases the risk of life-threatening infections. Symptoms include fever, chills, and sore throat.
• Lactic Acidosis: A buildup of lactic acid in the blood. Symptoms include deep and rapid breathing, drowsiness, nausea, vomiting, and stomach pain. This is a medical emergency.
• Hepatotoxicity (Liver Toxicity): Symptoms include yellowing of the skin or eyes (jaundice), dark urine, and pain in the upper right side of the stomach.
• Myopathy and Myositis: Severe muscle weakness and wasting, often associated with long-term use. This is linked to mitochondrial toxicity.

• Lipoatrophy: Long-term use of Zidovudine has been linked to the loss of subcutaneous fat, particularly in the face, arms, and legs. This can result in a 'sunken' appearance.
• Mitochondrial Toxicity: Because Zidovudine can interfere with human mitochondrial DNA polymerase, long-term use may lead to organ dysfunction, particularly in the muscles and liver.
• Insulin Resistance: Some patients may develop changes in how their body processes sugar, potentially leading to increased blood glucose levels.

Zidovudine carries several FDA Black Box Warnings, the most serious level of warning for a medication:

1. 1Hematologic Toxicity: Zidovudine has been associated with severe anemia (low red blood cells) and neutropenia (low white blood cells), particularly in patients with advanced HIV disease.
2. 2Myopathy: Prolonged use of Zidovudine has been linked to symptomatic myopathy (muscle disease) and myositis (muscle inflammation).
3. 3Lactic Acidosis and Severe Hepatomegaly with Steatosis: Fatal cases of lactic acidosis and severe liver enlargement with fatty deposits have been reported with the use of nucleoside analogs alone or in combination.

Report any unusual symptoms to your healthcare provider immediately. Regular blood tests are required to monitor for these side effects.

• Allergic Reactions: Though rare, hypersensitivity reactions can occur. If you develop a rash, hives, or swelling of the face/tongue, seek emergency care.
• Hepatotoxicity: Caution should be exercised in patients with known risk factors for liver disease. Treatment should be suspended in any patient who develops clinical or laboratory findings suggestive of lactic acidosis or pronounced hepatotoxicity.
• Immune Reconstitution Inflammatory Syndrome (IRIS): When starting Zidovudine, the immune system may get stronger and begin to fight infections that have been hidden in the body for a long time. This can cause an inflammatory response. Tell your doctor if you develop new symptoms after starting treatment.
• Fat Loss (Lipoatrophy): Patients should be monitored for signs of fat loss in the face and limbs, as this may be irreversible.

Patients taking Zidovudine require frequent laboratory monitoring to ensure safety:

• Complete Blood Count (CBC): Initially, CBCs should be performed every two weeks to monitor for anemia and neutropenia. Once the patient is stable, the frequency may be reduced to once a month or as directed by the physician.
• Liver Function Tests (LFTs): Regular monitoring of transaminases (AST, ALT) and bilirubin is necessary to detect early signs of liver damage.
• Renal Function: Periodic checks of serum creatinine and BUN levels.
• Viral Load and CD4+ Count: To assess the effectiveness of the HIV treatment regimen.

Zidovudine may cause dizziness, fatigue, or headaches in some patients. You should not drive or operate heavy machinery until you know how the medication affects you. If you feel drowsy or dizzy, avoid these activities.

Alcohol should be avoided or strictly limited while taking Zidovudine. Alcohol can increase the risk of liver toxicity and may exacerbate the risk of developing lactic acidosis. Furthermore, alcohol can interfere with the adherence to a strict medication schedule.

Do not stop taking Zidovudine without consulting your doctor. Sudden discontinuation can lead to a 'rebound' in viral load, increasing the risk of the virus becoming resistant to Zidovudine and other similar medications. If the drug must be stopped due to toxicity, your healthcare provider will transition you to an alternative antiretroviral agent.

> Important: Discuss all your medical conditions, especially liver disease, kidney disease, or blood disorders, with your healthcare provider before starting Zidovudine.

• Phenytoin: Zidovudine may alter the blood levels of phenytoin (an anti-seizure medication), and phenytoin may decrease Zidovudine levels. Blood level monitoring for phenytoin is recommended.
• Valproic Acid: May increase Zidovudine levels by inhibiting glucuronidation.
• Atovaquone: May increase Zidovudine levels, though the clinical significance is often minor.
• Methadone: May increase Zidovudine levels, potentially leading to increased side effects. Patients should be monitored for Zidovudine toxicity.

• High-Fat Meals: While Zidovudine can be taken with food, very high-fat meals may slightly decrease the peak concentration (Cmax) of the drug, though the total absorption (AUC) remains largely unchanged.
• Alcohol: As noted previously, alcohol increases the metabolic burden on the liver and increases the risk of lactic acidosis.

• St. John's Wort: This herbal supplement induces various metabolic pathways and may potentially decrease the effectiveness of antiretroviral therapy. It is generally recommended to avoid St. John's Wort while on HIV medications.
• Bone Marrow Suppressive Herbs: Any supplement that may affect blood counts should be avoided unless cleared by a hematologist.

Zidovudine can cause a significant increase in the Mean Corpuscular Volume (MCV) of red blood cells. While this is a common side effect and often used as a marker of medication adherence, it can mask the diagnosis of other types of anemia, such as Vitamin B12 or folate deficiency.

For each major interaction, the primary management strategy is either avoiding the combination or increasing the frequency of blood count monitoring.

> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking, including over-the-counter pain relievers and vitamins.

While Zidovudine is a unique chemical structure, patients who have experienced severe lactic acidosis or hepatic steatosis on other nucleoside analogs (like Didanosine or Stavudine) are at an increased risk of experiencing the same reaction with Zidovudine. This is considered a class-wide precaution for NRTIs.

> Important: Your healthcare provider will evaluate your complete medical history, including your current blood counts and liver status, before prescribing Zidovudine.

Zidovudine is FDA-approved for use in pediatric patients from birth onwards. It is used both for the treatment of HIV-1 infection and for the prevention of transmission in infants born to HIV-positive mothers. Dosing must be carefully adjusted as the child grows to avoid toxicity and ensure efficacy. Growth parameters should be monitored regularly.

Elderly patients (65+) may be more susceptible to Zidovudine-induced anemia and renal toxicity. Because renal function naturally declines with age, many elderly patients require lower doses (e.g., 100 mg three times daily) to avoid accumulation of the drug's glucuronide metabolite.

For patients with a GFR (Glomerular Filtration Rate) below 15 mL/min, the dose should be reduced. For those on hemodialysis, the recommended dose is 100 mg every 6 to 8 hours. Zidovudine is not efficiently removed by dialysis, so supplemental doses after dialysis are not typically required.

In patients with mild to moderate hepatic impairment, Zidovudine should be used with caution. In severe hepatic impairment (cirrhosis), the drug's half-life can be significantly prolonged, increasing the risk of lactic acidosis and bone marrow suppression. Close clinical monitoring is mandatory.

> Important: Special populations require individualized medical assessment and frequent laboratory follow-up to ensure the safest possible outcome.

Pharmacodynamics

The relationship between Zidovudine concentration and its antiviral effect is complex. While the plasma half-life is short, the intracellular half-life of the active triphosphate form is much longer (approximately 3 to 7 hours), which allows for twice-daily dosing. Viral resistance can develop through mutations in the reverse transcriptase gene (specifically 'Thymidine Analog Mutations' or TAMs).

| Parameter | Value |

|---|---|

| Bioavailability | 60% - 70% |

| Protein Binding | 25% - 38% |

| Half-life (Plasma) | 0.5 - 3.0 hours |

| Tmax | 0.5 - 1.5 hours |

| Metabolism | Hepatic Glucuronidation (GZDV) |

| Excretion | Renal (72% as metabolite, 14% unchanged) |

• Molecular Formula: C10H13N5O4
• Molecular Weight: 267.24 g/mol
• Solubility: Soluble in water (25 mg/mL at 25°C).
• Structure: It is a thymidine derivative where the 3'-hydroxy (-OH) group is replaced by an azido (-N3) group.

Zidovudine is classified as a Nucleoside Reverse Transcriptase Inhibitor (NRTI). Other drugs in this class include Lamivudine (3TC), Abacavir (ABC), and Emtricitabine (FTC). It is often the 'backbone' of older antiretroviral regimens.