The first factor affecting the absorption of some medications is the amount of fat in a meal. The presence of fat will increase the absorption of some medications, such as Fortovase®, Viracept® and KaletraTM. It is recommended that these medications be taken with food so that the fat from the food will help maximize the absorption and therefore increase the bioavailability of the medication. Fat also increases the absorption of Sustiva® and may therefore increase its side effects; therefore, it is recommended that a person take Sustiva on an empty stomach or with a low-fat meal.
The second factor affecting the absorption of some medications is the acidity level in the stomach. Some medications are better absorbed in a more acidic (low pH) environment and others are better absorbed in a more basic (high pH) environment. Gastric pH levels decrease when eating; therefore, medications requiring low pH are best taken with food. This would include medications such as Reyataz®.
But food is not the only factor affecting gastric acidity. Over-the-counter antacids and prescription medications for gastrointestinal disorders affect acidity levels in the stomach which, in turn, may affect the absorption of certain medications. As a result, antacids and prescription acid-lowering medications should not be taken with certain HIV medications because they can lower the absorption of the HIV medication to noneffective levels.
Over-the-counter antacids, particularly those containing aluminum or magnesium carbonate as an active ingredient, can decrease the absorption of some HIV medications, including Rescriptor®, Lexiva® (and Agenerase®), and Reyataz. Maalox®, for example, when taken with Lexiva, decreases the maximum concentration (Cmax) of Lexiva by 35%.1 Antacids such as Maalox, Rolaids®, Mylanta® and Tums®, therefore, should be taken apart from these HIV medications. If these antacids must be taken, they should be taken at least two hours before or one hour after taking these HIV medications.
Prescription medications for Gastroesophageal Reflux Disease (GERD), or acid reflux, can also decrease the absorption of Reyataz and other medications. These medications generally fall into one of two categories, either Proton Pump Inhibitors (PPIs) or H2-Receptor Antagonists (or H2 Inhibitors/Blockers).
Proton Pump Inhibitors are long-acting medications for treating acid reflux and include such medications as Prilosec®, Prevacid®, Aciphex®, Nexium® and Protonix®. Prilosec, for example, when taken with Reyataz, decreases the absorption of Reyataz by 76%.2 Earlier this year, Bristol-Myers Squibb, the manufacturer of Reyataz, issued a "Dear Doctor" letter reminding physicians that Reyataz and Proton Pump Inhibitors should not be taken together, as recommended in the Reyataz package insert.3
H2 antagonists are short-acting medications for treating acid reflux and include such medications as Zantac®, Tagamet®, Pepcid® and Axid®. Zantac, for example, when taken with Lexiva, decreases the maximum concentration (Cmax) of Lexiva by 51%. H2 antagonists, when taken with Reyataz, also reduce plasma concentrations of Reyataz, and it is recommended that they be administered as far apart from Reyataz as possible, preferably 12 hours.4
This information demonstrates that there are clear reasons why certain HIV medications have food restrictions; however, most educational materials only tell us to take a certain medication with or without food. Rarely do they explain why. This is important information because there are other factors -- such as antacids -- that may also affect these medications. If any of your medications have food restrictions, it is important to understand why. Ask your doctor to explain why your medications have food restrictions and make sure that there are not other medications -- either prescription or over-the-counter medications -- which may interfere with their effectiveness.
Guy Pujol is the Executive Director of AIDS Treatment Initiatives.